1. 生态适应性：低能耗生存模式的进化基础
1.1 食性特化与资源独占
考拉（Phascolarctos cinereus）的生存策略核心在于其对桉树叶的高度特化性食性。桉树（Eucalyptus）作为其几乎唯一的食物来源，赋予了考拉在竞争激烈的植食动物界中独特的生态位 1。这种食性特化主要体现在以下几个方面：
首先，桉树叶虽然普遍存在，但其营养价值相对较低，且富含多种植物次生代谢产物（PSMs），如缩合单宁、萜烯和甲酰基间苯三酚化合物（formylated phloroglucinol compounds, FPCs）等，这些物质对大多数动物而言具有毒性或难以消化 23。考拉通过其独特的生理机制和行为选择，发展出对这些毒素的代谢能力。例如，考拉的肠道微生物群在桉树叶的消化和解毒过程中发挥着至关重要的作用 14。这些微生物能够帮助考拉分解桉树叶中的纤维素，并代谢其中的有毒化合物，从而使其能够从这种低质量食物中获取能量和营养。有研究表明，考拉肠道微生物群的组成和多样性与其对桉树叶的选择以及代谢能力密切相关 4。不同个体和区域考拉的肠道微生物存在差异，这可能导致它们在桉树叶选择和代谢能力上的个体差异 4。
其次，考拉在桉树叶选择上表现出高度的精准性。它们并非盲目取食所有桉树叶，而是会根据叶片的营养含量和毒素水平进行选择 56。考拉倾向于选择可用氮浓度较高但次生代谢产物（如sideroxylonals）浓度较低的桉树叶 5。这种选择性的摄食行为，使得考拉能够在有限的资源中优化营养摄入，并最大程度地规避毒素的危害。这种对特定桉树种和特定叶片类型的偏好，进一步巩固了其在资源利用上的独占性。例如，有研究发现，考拉在野生环境中主要食用某些桉树种类（如Eucalyptus viminalis 或 Eucalyptus obliqua），并且这种偏好可能源于个体间对特定食物的根本性偏好或消化能力差异 6。
最后，这种食性特化也使得考拉能够有效规避与其他植食动物的竞争。由于大多数其他植食动物无法忍受桉树叶的毒性和低营养价值，考拉得以独自享用这一广泛分布的食物资源。这降低了它们在食物获取上的竞争压力，为其生存创造了相对稳定的环境。尽管桉树叶的营养限制导致了考拉整体较低的能量需求和慢节奏生活，但其特化的食性策略在进化上成功地为其提供了可靠的食物来源，并有效规避了种间竞争 7。
1.2 行为模式的能量优化
考拉的生存策略与传统意义上活跃的捕食者或被捕食者大相径庭，其核心在于一种极致的“低能耗”行为模式，这种模式贯穿于其日常活动的方方面面，以适应其低营养的桉树叶食性。
首先，低活动量是考拉最显著的行为特征之一。它们每天大部分时间都处于静止状态，活动范围小，移动缓慢。这种行为模式是直接对桉树叶低营养价值的生理适应。桉树叶的纤维含量高，蛋白质和可消化碳水化合物含量低，且含有毒素，这意味着考拉从单位食物中获取的能量非常有限。为了最大化能量的利用效率，考拉通过减少运动来降低能量支出。研究发现，考拉在热应激期间，会紧贴树干以利用树干较低的温度进行热量传导散失，这是一种新颖的体温调节策略，可以显著减少蒸发散热所需消耗的能量，从而提高其在极端高温事件中的生存率8。这种行为不仅节省了能量，也进一步强调了其静态生活方式的生态学意义。
其次，长时间睡眠是考拉另一项重要的能量优化策略。长时间的休息和睡眠有助于降低基础代谢率，让消化系统有足够的时间处理难以消化的桉树叶。在睡眠期间，考拉的生理活动降至最低，心率和体温都会有所下降，从而显著减少能量消耗。有研究指出，考拉的心率在夜间会大幅下降，进入副交感神经系统主导的状态，相较于白天较低的心率进一步体现了其夜间低代谢的特点9。这种深度且长时间的休息，使其能够在能量摄入有限的情况下维持基本的生命活动。
再者，树栖习性不仅是考拉获取食物的途径，也是其重要的天敌防御机制。考拉大部分时间生活在桉树的树冠层，很少下地。这种垂直空间上的优势使其能够有效避开地面的捕食者，如澳洲野狗（dingoes）和各种体型的掠食性哺乳动物。虽然考拉在地面移动笨拙，但在树冠上，其强壮的爪子和抓握能力使其能稳固地附着在树枝上。此外，考拉的皮毛颜色与桉树皮相似，提供了良好的伪装，进一步增加了其在树冠上的隐蔽性。幼年考拉在母兽育儿袋和背上的依偎，也使其在生长初期获得了极大的保护，确保了低繁殖率下幼崽的存活率。综合来看，考拉的低活动量、长时间睡眠以及树栖生活方式，共同构成了一套高效的能量优化和天敌防御体系，使其能够在这种看似不利的生态位中持续生存。
1.3 栖息地选择的精准性
考拉对其栖息地的选择展现出高度的精准性，这种精准性主要体现在其对特定桉树种类分布的依赖上。考拉并非随意栖息于任何桉树林，而是优先选择那些能够提供其偏好食物种类和满足其营养需求的桉树群落6。这种选择性栖息策略是考拉生存的关键，因为它必须在食物资源的可获得性与环境稳定性之间取得微妙的平衡。
首先，考拉栖息地选择的首要标准是食物桉树的种类和质量。尽管桉树种类繁多，但只有少数几种桉树被考拉作为主要食物来源，例如某些地区的考拉主要以Eucalyptus viminalis或Eucalyptus obliqua为食6。这些偏好的桉树种类可能具有较低的有毒化合物含量，或含有考拉更易消化的营养成分1011。考拉能够通过嗅觉和味觉受体感应并选择这些特定的桉树叶，这得益于其味觉和犁鼻器受体的扩张进化，使其能够更好地闻出、品尝并调节对植物次生代谢产物的摄入12。因此，考拉的分布与这些特定桉树种的地理分布高度重合。高光谱航空影像技术已被证明能够以96%的准确率识别考拉的栖息桉树种类（基于像素级训练，但最终模型准确率为74%），这为评估和预测考拉的栖息地质量提供了有力工具，强调了特定桉树种类在栖息地选择中的重要性13。
其次，考拉的栖息地选择也反映了其对环境稳定性的需求。考拉依赖成熟的桉树林提供食物、庇护和繁殖场所。这些森林通常具有较为稳定的微气候，能够提供遮荫以避免极端高温，并减少风雨侵袭。考拉的低代谢率和长时间静止行为使其对环境变化较为敏感，因此稳定的栖息环境对其能量节约型生活方式至关重要。例如，在高温环境下，考拉会紧贴凉爽的树干以散热，这种行为进一步强调了栖息地微气候的重要性。
然而，这种高度特化的栖息地选择也带来了潜在的脆弱性。当栖息地因人类活动（如砍伐、城市扩张）或自然灾害（如森林火灾、干旱）而发生变化时，考拉的生存会受到严重威胁。栖息地的丧失和破碎化直接减少了考拉可利用的食物来源和安全的庇护所，限制了种群间的基因交流，并增加了其面临捕食者、车辆碰撞和疾病的风险1415。因此，精准的栖息地选择在保证考拉特定生态位的同时，也使其对环境扰动表现出较低的弹性。为了缓解这些威胁，保护和恢复含有考拉偏好桉树种类的栖息地，并建立生态廊道，是维持考拉种群健康和遗传多样性的关键措施12。
2. 遗传多样性与种群韧性：历史与现代的基因支撑
2.1 历史种群波动与遗传瓶颈
考拉的种群历史经历了几次剧烈的波动，特别是19世纪末至20世纪初，由于大规模的捕猎活动，其数量急剧下降，给考拉的遗传多样性带来了严重的瓶颈效应1617。这一时期，考拉因其皮毛而遭到大量捕杀，导致一些地区种群的局部灭绝，并使得整个物种的种群规模骤减16。
历史基因组学研究为我们理解这些事件对考拉遗传多样性的影响提供了宝贵的数据。通过分析19世纪和20世纪早期采集的博物馆标本的基因组（历史基因组）与现代考拉种群的基因组（现代基因组），研究人员能够追踪遗传多样性随时间的变化16。例如，有研究利用37个历史基因组和25个现代基因组，分析了考拉在历史和现有地理范围内的种群结构和遗传多样性演变16。结果显示，考拉的全基因组杂合度（genome-wide heterozygosity）随时间推移而降低16。在历史数据集中发现了一些现代考拉种群中已不存在的线粒体单倍型和核基因型，这表明历史上的捕猎和栖息地丧失导致了部分遗传变异的永久性丢失16。
然而，也有研究指出，线粒体DNA（mtDNA）多样性的低水平可能在考拉种群遭遇近期衰退之前就已存在17。通过对19世纪和20世纪博物馆标本中mtDNA超变区的测序，研究人员发现历史样本中的mtDNA单倍型与现代考拉种群中的单倍型是相同的，并且没有检测到新的单倍型17。稀疏分析（rarefaction analyses）也表明，博物馆样本中mtDNA的遗传多样性与现代考拉的相似17。这提示我们，低mtDNA多样性可能反映了考拉更古老的历史模式，而非仅仅是近期近亲繁殖或奠基者效应的结果17。
尽管存在一些复杂性，但总体而言，历史上的种群衰退确实对考拉的遗传多样性造成了负面影响，特别是在核基因组层面，导致了杂合度的降低和一些特有基因型的丢失16。这种遗传瓶颈效应使得幸存的考拉种群更容易受到疾病、环境变化和近亲繁殖的威胁，从而降低了其对未来挑战的适应能力。例如，南部考拉种群由于过去的瓶颈事件和奠基者效应，其杂合度远低于北部种群18。了解这些历史波动及其对遗传多样性的影响，对于制定有效的保护策略至关重要。
2.2 现代种群的遗传现状
考拉现代种群的遗传现状复杂多样，表现出显著的地理差异，这主要与历史上的种群波动、瓶颈效应以及人类干预下的重新安置有关 192021。当前考拉种群的遗传结构、近交水平和遗传负荷在澳大利亚北部（昆士兰州和新南威尔士州）和南部（维多利亚州和袋鼠岛）之间存在明显差异，这些差异直接影响了考拉种群的韧性和对环境变化的适应能力。
地理差异与遗传多样性：
北部考拉种群（昆士兰州和新南威尔士州）通常表现出更高的遗传多样性，包括更丰富的MHC II类基因变异 19。MHC基因在免疫应答中扮演关键角色，高多样性意味着种群对病原体具有更强的抵抗潜力 1922。例如，对MHC II类基因（DAB和DBB）的分析发现，北部考拉种群（昆士兰州和新南威尔士州）比南部考拉种群（维多利亚州）拥有更多的MHC II类变体和更高的多样性 19。这种差异可能归因于北部种群未经历如同南部种群那样的严重奠基者效应，或是在北方存在更强的病原体驱动的平衡选择压力 19。
相比之下，南部考拉种群（特别是维多利亚州和袋鼠岛）的遗传多样性显著较低 202123。这主要是由于19世纪末至20世纪初的严重瓶颈事件和随后的种群重建计划。例如，袋鼠岛的考拉种群起源于20世纪20年代从少数个体迁入，目前虽然种群数量庞大，但个体和种群层面的多样性极低，存在严重的奠基者效应和近交现象 20。维多利亚州的考拉也经历了类似的瓶颈效应，导致其线粒体DNA变异性很低，甚至在整个南部地区，线粒体DNA限制性片段长度多态性（mtDNA-RFLP）的变异性都非常有限 2123。
近交水平与遗传负荷：
遗传多样性的缺失往往伴随着高水平的近交。南部考拉种群，尤其是那些经历过严重瓶颈和再安置的种群，表现出更高的近交水平和更长的纯合片段（Runs of Homozygosity, RoH） 2024。例如，袋鼠岛考拉的基因组分析显示，其具有更长且数量更多的纯合片段，以及更高比例的纯合遗传负荷，这表明严重的瓶颈效应导致了近交和适应不良的风险增加 20。高水平的近交会降低种群的适应性，增加对疾病的易感性，并可能导致近交衰退，即种群健康和繁殖力下降。
遗传负荷是指种群中积累的有害突变。在遗传多样性较低和近交程度较高的种群中，有害隐性等位基因表达的机会增加，从而增加了遗传负荷的风险 20。虽然考拉的染色体组相对稳定，但某些疾病如衣原体感染和考拉逆转录病毒（KoRV）感染，与宿主的遗传背景密切相关。北部考拉的KoRV内源化程度更高，病毒载量通常也更高，而南部考拉则KoRV流行率较低或无KoRV 2526。这种差异可能与南北种群在遗传上的不同韧性以及免疫系统对病毒的响应能力有关。
对种群韧性的影响：
- 适应性潜力下降： 南部考拉种群的低遗传多样性限制了其适应未来环境变化和新型病原体的能力 1920。例如，MHC多样性的降低可能导致对某些疾病的抵抗力减弱 19。
- 疾病易感性增加： 衣原体感染具有可遗传的易感性，这可能影响考拉的生存和繁殖成功率 27。
- 保护管理挑战： 现代基因组学研究强调，对于高度隔离且遗传多样性低的考拉种群，主动管理措施（如遗传救援和建立生态廊道）对于提高其遗传多样性至关重要 2024。新南威尔士州的考拉种群管理分区并未完全反映遗传多样性的分布，需要谨慎的遗传管理以避免进一步限制基因流 28。
总而言之，考拉现代种群的遗传现状是一个地理上两极分化的图景：北部种群相对健康，拥有较高的遗传多样性，而南部种群则受到历史瓶颈和近交的严重影响，面临着遗传多样性丧失和适应性潜力下降的风险。深入理解这些遗传特征对于制定精确的保护策略，以确保考拉在未来能够维持其种群韧性至关重要。
2.3 适应性遗传变异的保留
尽管考拉种群在历史上经历了显著的遗传瓶颈，且现代种群的遗传多样性存在地理差异，但其在关键功能基因，尤其是与免疫应答和疾病抗性相关的基因上，依然保留了一定程度的适应性遗传变异。这些多态性对于考拉应对不断变化的病原体和环境压力至关重要，是其能够持续生存的重要基因支撑。
MHC基因的多态性及其维持机制：
主要组织相容性复合体（MHC）基因是脊椎动物免疫系统中最具多态性的基因之一，它们编码的蛋白负责结合并呈递抗原肽给T淋巴细胞，从而启动适应性免疫应答 29。在考拉中，MHC基因的多态性被认为是其抵御病原体（如衣原体和考拉逆转录病毒KoRV）的关键因素。
- MHC II类基因： 对考拉MHC II类DA和DB基因的研究发现，其β1结构域变异程度高于α1结构域，且有证据表明存在正选择作用 29。在对澳大利亚东部12个考拉种群的MHC II类DA β1 (DAB) 和DB β1 (DBB) 变体进行的广泛地理研究中，共发现了13种DAB和7种DBB变体 19。值得注意的是，北部考拉种群（昆士兰州和新南威尔士州）的MHC II类多样性明显高于南部种群（维多利亚州），这可能与北部地区更强的病原体驱动的平衡选择或南部品种的奠基者效应有关 19。尽管南部种群的整体MHC多样性较低，但其发现的三种DAB变体之间存在显著的序列分化，表明即使在多样性受限的情况下，也存在对抗原识别重要的功能性变异 19。平衡选择（Balancing Selection）是维持MHC多态性的主要机制之一，它通过赋予杂合子对多种病原体的抗性优势，从而在种群中保留更多的等位基因。
- MHC I类基因： 考拉的MHC I类基因在清除细胞内病原体（如衣原体和KoRV）感染方面发挥核心作用 30。研究鉴定了考拉基因组中的11个MHC I类基因，其中Phci-UA、UB和UC三个基因表现出相对较高的遗传变异性，并在所有检测组织中表达，被认为是考拉的经典MHC基因 30。在Phci-UA和UC中检测到分化选择（Diversifying Selection）的证据，而在Phci-UB中可能存在基因转换（Gene Conversion）以产生新的等位基因 30。这些机制共同促进了MHC I类基因多样性的维持，以应对不断演变的病原体抗原。
抗病毒相关基因及抗菌肽的多样性：
除了MHC基因，考拉在其他免疫相关基因上也保留了适应性变异，这对其抵御病毒和细菌感染至关重要。
- KoRV内源化相关变异： 考拉逆转录病毒（KoRV）在考拉种群中处于活跃内源化的过程中，这为研究脊椎动物基因组演化中的基本过程提供了独特的机会 3132。北部考拉普遍存在内源性和外源性KoRV，且病毒诱导疾病的发生率很高，而南部考拉则KoRV流行率较低或仅存在缺陷型的“RecKoRV”变体 32。对KoRV全基因组的分析显示，在约130年的演化过程中，考拉逆转录病毒的序列、蛋白质结构和转录结合位点整体上是保守的，但也检测到138个多态性位点，其中72个在多个个体中发现 31。在非同义多态性中，env基因中涉及氨基酸之间大的理化差异的激进取代有所增加，这可能反映了抗病毒免疫压力或对受体干扰的规避 31。这种宿主-病毒共同演化过程中产生的遗传变异可能有助于考拉种群适应KoRV的存在。
- 抗菌肽（AMPs）的多样性： 抗菌肽是真核生物先天免疫系统的重要组成部分，其中猫抗菌肽（cathelicidins）和防御素（defensins）是哺乳动物主要的两种类型，并且猫抗菌肽在有袋类动物中经历了物种特异性扩增 33。对418个考拉全基因组的分析显示，虽然抗菌肽的等位基因多样性低于MHC等其他免疫基因家族，表明其相对保守，但在PhciDEFB12中观察到平衡选择 33。在活性肽中也发现了一些非同义单核苷酸多态性（SNPs），这些SNP可能通过终止密码子的产生、结构改变和肽电荷增加来改变AMP的功能 33。值得注意的是，考拉抗菌肽PhciCATH5（一种对衣原体具有活性的猫抗菌肽）的复制数变异（CNVs）在南部考拉中比北部更常见 33。由于AMP复制数与表达水平相关，这提示可能存在衣原体选择压力导致PhciCATH5的重复，从而增强考拉对衣原体感染的抵抗力 33。
这些在MHC基因、抗病毒相关基因和抗菌肽中保留的适应性遗传变异，共同构成了考拉面对复杂病原体环境时的“基因武器库”。它们通过维持多态性来确保种群能够识别和响应各种病原体，通过平衡选择机制在种群中保留有益的等位基因，并通过基因重复等方式增强对特定疾病的抵抗力。理解并保护这些适应性遗传变异，对于提升考拉种群对疾病的韧性，进而保障其长期的生存至关重要。
3. 疾病应对：宿主-病原体动态平衡的生存智慧
3.1 主要病原的威胁与限制
考拉的生存受到多种威胁，其中疾病，尤其是衣原体（Chlamydia pecorum）感染和考拉逆转录病毒（Koala Retrovirus, KoRV）感染，是导致种群数量下降的主要因素之一 14。这两种病原体以不同的机制影响考拉的健康、繁殖和生存，对考拉种群构成了严重的限制。
衣原体（Chlamydia pecorum）
- 致病机制： 鹦鹉热衣原体（Chlamydia pecorum）是一种革兰氏阴性、专性细胞内细菌，是引起考拉衣原体病的主要病原体。这种感染会导致考拉的眼部、泌尿生殖道和呼吸道出现炎症和纤维化。在眼部，感染可导致结膜炎、角膜炎，严重时甚至引起失明。在泌尿生殖道，衣原体感染是导致雌性考拉不育症和膀胱炎的关键原因，可通过引起卵管炎症和阻塞导致不孕，这直接影响了考拉的繁殖成功率。在雄性考拉中，感染可导致睾丸炎和附睾炎。严重的衣原体感染可导致个体消瘦、免疫力下降，最终引发死亡 1434。
- 传播途径： 衣原体主要通过性接触传播，母婴垂直传播也可能发生。此外，考拉在社交互动或共享栖息地时也可能通过分泌物间接传播。野外研究表明，雌性考拉似乎无法主动避免与感染衣原体的雄性交配，这使得衣原体在种群中持续传播 35。
- 对种群的影响范围： 衣原体感染在考拉种群中普遍存在，尤其是在澳大利亚北部（昆士兰州和新南威尔士州）的考拉种群中。例如，在昆士兰州东南部进行的一项大规模管理项目中，86.3%的受治疗考拉成功被释放，其中标准治疗方案的成功率达到94.8%，这表明衣原体感染在这些地区普遍且需要积极干预 34。而在南澳大利亚的袋鼠岛（Kangaroo Island）考拉种群中，则被发现完全没有衣原体感染，这使得该种群成为一个重要的无病原体保护区 36。衣原体疾病对个体生存和繁殖率有重大影响，并导致种群数量下降 27。通过数学模型预测，针对1-2岁雌性考拉进行5年的衣原体疫苗接种项目，在疫苗有效性达到75%且每年覆盖10%的种群时，有望在5-6年内逆转由衣原体引起的种群下降趋势 37。
考拉逆转录病毒（Koala Retrovirus, KoRV）
- 致病机制： KoRV是一种伽马逆转录病毒，存在外源性（通过水平传播感染）和内源性（整合到宿主基因组并垂直遗传）两种形式。KoRV-A是原型内源性形式，所有考拉都感染了KoRV-A 383940。然而，非KoRV-A亚型（如KoRV-B、C、D、F、G、H、I、K、M等）与更严重的疾病相关联 38394142。特别是KoRV-B，它最初在美国一家动物园的少数考拉中发现，并与白血病发病率增加、其他癌症以及衣原体疾病加重有关 3839。高病毒载量（viral loads, VLs）的KoRV感染被认为是衣原体病高发的一个主要因素 43。多亚型共感染（如KoRV-A、B和C）可能导致更严重的疾病表现，例如白细胞计数升高、淋巴瘤和最终死亡 39。
- 传播途径： KoRV可以通过母婴垂直传播，也可能通过成年个体间的接触发生水平传播 3842。在圈养考拉种群中，KoRV-A、B、D、I和K亚型的外源性传播主要发生在母兽与其幼崽之间，甚至存在子宫内传播KoRV-D的可能性 42。KoRV的这种双重传播模式使得其在种群中的扩散复杂且难以控制。
- 对种群的影响范围： KoRV在澳大利亚考拉种群中的分布存在显著的地理差异。北部考拉种群几乎所有个体都感染了多种KoRV亚型，病毒载量较高，疾病发生率也高。而袋鼠岛的考拉种群则无KoRV 3638。KoRV的存在与高病毒载量使得考拉对其他感染（如衣原体）的易感性增加，从而加速了种群的衰退 43。然而，最近的研究发现，一些考拉已经进化出了“适应性基因组免疫”机制，能够主动抑制内源性KoRV的转录，这为减少考拉疾病负担和未来的保护管理提供了新的希望 43。例如，在MAP4K4基因的3'非翻译区内，一个KoRV-A前病毒插入能够触发piRNA的产生，进而导致前病毒基因组整合量减少20%并使KoRV转录水平降低10倍，这可能有助于考拉抵抗KoRV感染 43。
综上所述，衣原体和KoRV是考拉面临的两大主要病原体威胁。衣原体直接导致繁殖障碍和个体死亡，而KoRV则通过免疫抑制间接加剧了其他疾病的严重性，并直接导致癌症。这两种病原体的广泛流行和复杂的传播机制，对考拉种群的健康和可持续性构成了持续的挑战。
3.2 免疫系统的适应性进化
考拉在面对衣原体和考拉逆转录病毒（KoRV）等病原体的持续威胁时，其免疫系统展现出了一系列特殊的适应性进化，这些机制在维持种群生存中扮演着关键角色。
抗菌肽（AMPs）的抗菌活性与黏膜免疫：
抗菌肽是先天免疫系统的重要组成部分，能够提供广谱的抗菌、抗病毒和抗真菌活性。在有袋类动物中，尤其是考拉，猫抗菌肽（cathelicidins）家族经历了物种特异性扩增，这表明它们在抵抗病原体方面具有重要作用 3344。
- PhciCath5 的抗菌活性： 研究发现考拉体内存在多种猫抗菌肽，其中一个名为PhciCath5的抗菌肽展现出显著的抗菌活性，尤其对导致考拉疾病的鹦鹉热衣原体（Chlamydia pecorum）具有灭活作用 44。PhciCath5能够有效灭活两种衣原体分离株（MarsBar和IPTaLE）的初级体，并显著减少细胞内衣原体包涵体的数量 44。此外，PhciCath5还对多种真菌以及革兰氏阴性、革兰氏阳性细菌（包括耐甲氧西林金黄色葡萄球菌MRSA）具有抗菌活性 44。其作用机制可能是通过静电相互作用附着在病原体细胞膜上，随后破坏膜的完整性，导致细胞死亡 44。
- 在黏膜免疫中的作用： 抗菌肽广泛表达于考拉全身组织中，包括易受衣原体感染的黏膜组织 44。由于衣原体主要通过黏膜途径感染，PhciCath5在黏膜表面的表达可能为其提供了抵御感染的第一道防线。虽然自然状态下PhciCath5的浓度可能不足以完全阻止或控制衣原体感染，但其存在无疑是考拉抵御病原体的重要先天免疫机制 44。未来对PhciCath5进行修饰以增强其活性，有望为治疗考拉衣原体感染提供新的解决方案 44。
- 复制数变异与衣原体选择压力： 值得注意的是，PhciCath5的复制数变异（CNVs）在考拉种群中普遍存在，并且在南部考拉中比北部更常见 33。由于AMP的复制数与表达水平相关，研究人员推测，衣原体对考拉可能存在选择压力，导致PhciCATH5基因的重复以增强其对衣原体感染的抵抗力 33。这表明考拉的免疫系统正在通过遗传适应来应对衣原体的威胁。
Toll样受体（TLRs）与细胞因子对KoRV的应答机制：
Toll样受体（TLRs）是进化上保守的模式识别受体，在先天免疫中识别病原体相关分子模式（PAMPs）并启动免疫应答 45。细胞因子则是免疫细胞间通讯的关键分子，调控免疫反应的强度和类型。
- TLRs对KoRV感染的响应： 考拉体内表达多种TLRs（TLR2-10和TLR13），这些受体在KoRV感染中发挥着重要作用 45。对感染不同KoRV亚型（KoRV-A、KoRV-B和/或KoRV-C）的考拉外周血单核细胞（PBMCs）进行分析，发现TLRs的表达模式存在差异 45。特别是在多重KoRV亚型共感染的考拉中，TLR5、TLR7、TLR9、TLR10和TLR13的mRNA表达呈现显著差异 46。TLR7和TLR9通常识别病毒核酸，TLR5识别细菌鞭毛蛋白，而TLR10和TLR13的病毒识别功能仍在研究中。这些差异表达表明TLRs在识别KoRV并启动先天免疫应答中具有重要意义，可能影响宿主对KoRV感染的易感性和疾病进展 4546。
- 细胞因子应答： KoRV感染也诱导了考拉体内细胞因子的变化。例如，在接种KoRV疫苗的考拉中，疫苗接种后4-8周内，干扰素-γ（IFN-γ）的表达水平显著上调，而IL-8（一种趋化因子）的表达则在8周后下调 47。IFN-γ是T辅助1型（Th1）免疫反应的关键细胞因子，对清除病毒感染至关重要。这表明考拉的适应性免疫系统能够对KoRV产生有效的细胞免疫应答 47。
此外，感染外源性KoRV亚型（KoRV-B和KoRV-C）的考拉，其IL-6表达水平高于仅感染内源性KoRV-A的考拉 48。IL-6是一种促炎细胞因子，其升高可能反映了机体对病毒感染的炎症反应。而在淋巴瘤并伴有KoRV-A和KoRV-B共感染的考拉中，IL-10（一种免疫抑制细胞因子）的表达显著增加，并伴随CD4:CD8b比值的降低，这提示KoRV可能导致免疫抑制 48。对多种KoRV亚型共感染的考拉PBMCs研究显示，尽管 IFN-γ、IL-6和IL-10的表达在不同KoRV亚型感染之间差异不显著，但IFN-γ的表达趋势接近显著差异（p=0.0534），暗示着KoRV亚型可能对宿主的先天免疫反应，包括IFN-γ和TLRs反应，产生影响 46。
综上所述，考拉的免疫系统通过抗菌肽（如PhciCath5）的进化扩增和多样化，增强了对衣原体等细菌病原体的先天防御能力，特别是在黏膜表面。同时，其TLRs和细胞因子在识别KoRV并调控抗病毒免疫应答方面也发挥着关键作用。这些适应性遗传变异和免疫应答机制共同构成了考拉在严峻疾病威胁下得以生存的重要生物学保障。
3.3 疾病易感性的遗传与环境因素
考拉对疾病的易感性并非单一因素决定，而是由宿主遗传背景和环境因素共同作用的结果，尤其是针对衣原体感染和考拉逆转录病毒（KoRV）的影响。理解这些复杂关联对于精准评估种群健康和制定有效保护策略至关重要。
MHC基因多态性与衣原体感染结局的关联：
主要组织相容性复合体（MHC）基因在宿主免疫应答中扮演核心角色，其高度多态性使得物种能够识别和抵御多种病原体。在考拉中，MHC基因变异已被证实与衣原体感染的易感性和疾病进展密切相关。
- 特定MHC等位基因与疾病易感性/保护性： 研究发现，考拉的MHC等位基因与衣原体病的进展存在显著关联。例如，对昆士兰州东南部两个考拉种群的研究揭示，特定的MHC等位基因与衣原体病进展相关，并鉴定了两个推定的易感变异（DCb 03, DBb 04）和两个保护性变异（DAb 10, UC 01:01）49。这意味着携带某些MHC等位基因的考拉可能更容易发展为严重的衣原体病，而携带另一些等位基因的考拉则可能具有更强的抵抗力。
- MHC II类基因与衣原体抗体水平： MHC II类基因在启动抗体介导的免疫应答中至关重要。对考拉MHC II类DAB和DBB基因的研究发现，特定MHC II类变异与衣原体热休克蛋白60（c-hsp60）抗体水平升高之间存在关联50。高水平的c-hsp60抗体常常与衣原体感染导致的纤维化和不孕症相关。这种关联进一步支持了MHC基因在衣原体病病理生理学中的功能作用50。
- 种群MHC多样性的重要性： 考拉种群MHC基因多样性的高低直接影响其对衣原体感染的整体抵抗力。Toll样受体（TLR）基因多样性在考拉种群间存在空间差异，这些差异与MHC多样性模式一致51。这种多样性上的差异可能导致考拉在面对病原体感染时表现出不同程度的抵抗力或易感性。
外源性/内源性KoRV亚型对免疫抑制的差异化影响：
考拉逆转录病毒（KoRV）以其内源性（KoRV-A）和多种外源性（KoRV-B至M）亚型存在，它们对考拉免疫系统的影响存在显著差异，进而影响考拉对其他疾病（如衣原体感染）的易感性。
- KoRV-A作为内源性病毒： KoRV-A普遍存在于所有考拉的基因组中，通常被认为是内源性病毒，其对宿主健康的直接影响相对较小。然而，KoRV-A的转录水平仍可能影响免疫应答。
- 外源性KoRV亚型的致病性： 与KoRV-A不同，外源性KoRV亚型，特别是KoRV-B和KoRV-C，被认为与更严重的疾病表型相关，包括淋巴瘤、其他癌症和免疫抑制5253。当考拉感染这些外源性KoRV亚型时，病毒载量通常会升高，这与免疫系统的显著变化相关。
- 免疫抑制机制： KoRV导致免疫抑制的机制复杂，可能涉及以下方面：
- CD4:CD8b比例降低： 在感染KoRV-A和KoRV-B并伴有淋巴瘤的考拉中，观察到IL-10（一种免疫抑制细胞因子）表达的显著增加，并伴随CD4:CD8b淋巴细胞比例的降低48。CD4细胞（辅助T细胞）在协调免疫应答中至关重要，其数量下降或功能受损会削弱考拉对抗感染的能力。
- 促炎细胞因子上调： 感染外源性KoRV（如KoRV-B和/或KoRV-C）的考拉，其IL-6（一种促炎细胞因子）表达水平高于仅感染内源性KoRV-A的考拉48。持续的高水平炎症可能导致免疫耗竭，并为机会性感染创造条件。
- 肺炎与KoRV： 对患有肺炎的死亡考拉进行检查发现，KoRV在脾脏中呈现显著更高的总KoRV和KoRV-A载量，这提示KoRV可能通过免疫抑制作用导致肺炎和机会性感染54。
- KoRV与其他疾病的协同作用： KoRV诱导的免疫抑制被认为是加重其他疾病严重性的重要因素。例如，KoRV感染与南澳大利亚考拉的牙周病发病率增加有关，提示KoRV可能通过调节免疫应答来促进牙周病的发生55。KoRV和其他感染之间的协同作用形成了一个恶性循环，即KoRV削弱考拉的免疫系统，使其更容易感染并发展为严重疾病，而感染本身也进一步加剧了考拉的健康问题。
因此，考拉对疾病的易感性是一个多层面的问题，MHC基因的多态性决定了其对衣原体感染的固有抵抗力，而KoRV，特别是外源性亚型，通过诱导免疫抑制，显著增加了考拉对包括衣原体在内的多种病原体的脆弱性。深入研究这些遗传和环境因素的相互作用，是开发针对考拉疾病的综合管理和保护策略的关键。
4. 繁殖与种群补充：数量维持的生物学保障
4.1 繁殖策略的权衡
考拉的繁殖策略呈现出一种独特的权衡，即以低繁殖率（通常每胎一崽，哺乳期长）来换取相对较高的幼崽存活率。这种策略与考拉低营养、低能量的桉树叶食性及其特殊的生理生态环境紧密相关，并严重依赖于母系细致入微的照料。
考拉的繁殖率在哺乳动物中属于较低水平。雌性考拉每次仅产一崽。幼崽在出生时非常小且未发育完全，会在母亲的育儿袋中度过约6-7个月的袋内发育期。随后，它们会继续依赖母亲进行哺乳和照顾，直到大约1岁左右才能完全独立。这意味着考拉的育儿周期非常长，从出生到幼崽完全独立，可能需要一整年的时间。这种长期的母婴依赖显著限制了雌性考拉的繁殖频率。例如，有研究指出，考拉的哺乳期比其他有袋类和真兽类动物长58% 7。尽管产奶量在泌乳高峰期是哺乳动物中按体重计算最低的，但由于哺乳时间极长，考拉在繁殖上的总能量投入与其他哺乳动物相似 7。
然而，这种低繁殖率策略与考拉高幼崽存活率之间存在着精妙的平衡。延长幼崽的发育时间和母乳喂养期，确保了幼崽在离开育儿袋并开始尝试食用桉树叶之前，能够获得足够的营养支持和免疫保护。考拉母乳的营养成分会随着幼崽发育阶段而变化，以满足其不同时期的生长需求。此外，母兽还会通过提供一种特殊的、半消化的粪便（称为“pap”），将关键的肠道微生物群垂直传递给幼崽，这对幼崽消化有毒桉树叶和建立自身消化系统至关重要。
母系照料行为在幼崽的存活中发挥着决定性作用。考拉幼崽在早期完全依赖母兽获取食物、保暖和保护。母兽会将幼崽长时间抱在腹部或背部，为其提供庇护。这种密切的母婴关系不仅提供了物理上的保护，也传授了生存所需的技能，例如如何选择合适的桉树叶以及如何识别和躲避捕食者。在圈养条件下，雄性年龄、日照长度和母兽年龄是影响交配成功率的重要因素 56。而雌性考拉的配偶选择不仅受行为因素影响，也受到基因因素的影响，例如雄性MHC II类基因的杂合度与雌性在交配前后选择雄性有关 57。这表明，雌性考拉在繁殖中的选择可能进一步优化了后代的生存潜力。
总而言之，考拉的低繁殖率并非其生存劣势，而是一种经过长期进化的适应性策略。通过投入大量的时间和能量进行母系照料，并确保幼崽在生理和行为上都具备独立生存的能力后才将其放手，考拉有效提高了每一只幼崽的存活机会。这种“少而精”的繁殖模式，结合其对桉树生态位的独特适应，是其在自然界中得以持续繁衍的关键生物学保障。
4.2 生殖生理的特殊性
考拉的生殖生理具有一些独特之处，这些特征不仅支持了其在自然状态下的繁殖成功率，也为在保护工作中应用辅助生殖技术（Assisted Reproductive Technologies, ARTs）提供了潜在的机遇。ARTs在管理破碎种群的遗传多样性和降低圈养繁殖成本方面具有重要潜力，并可以为野外考拉种群的恢复提供遗传上更具韧性的个体 5859。
精子抗冻性与精液保存稳定性：
考拉的精子在长期冷却和冷冻保存后仍能保持一定的活力，这为其精液的收集、运输和长期储存提供了可能性。
- 冷冻保存可行性： 早在1996年，研究就发现考拉精子在冷冻保存后能重新恢复活力，特别是在含有6%和/或8%甘油的稀释剂中，精子的活力评分和活精子百分比变化不大 60。这意味着考拉精子对冷冻损伤具有一定的耐受性。
- 精液稀释与抗生素： 为了有效保存精液，需控制细菌污染。研究已确定考拉射出精液和包皮的正常微生物菌群，并筛选出适宜的抗生素（如青霉素G和庆大霉素）。在PBS稀释剂中加入这些抗生素，在24小时孵育期内对精子活力没有不利影响，并能有效抑制细菌生长，从而延长精子在16°C下储存的时间，并减少人工授精过程中疾病传播的可能性 61。
- DNA稳定性： 尽管冷冻保存可能导致精子DNA碎片化（SDF），考拉精子在冷冻解冻后的DNA完整性表现出“显著的稳定性”，即使在4°C冷藏16天后，其SDF值仍低于16% 62。这表明考拉精子的染色质结构对冷冻损伤具有较强的抵抗力。然而，精子核蛋白（protamine）的组成可能会影响DNA稳定性。考拉精子的DNA稳定性高于袋熊（wombat），这可能与它们精子中精蛋白的精氨酸残基数量差异有关 63。
- 线粒体功能与渗透压敏感性： 冷冻保存对考拉精子线粒体功能和质膜完整性有一定影响。研究表明，解冻后精子的线粒体膜电位（MMP）显著下降，特别是在复温至35°C时 64。考拉精子也对高渗环境较为敏感，但细胞松弛素D（F-actin解聚剂）对其质膜的柔韧性没有显著改善 65。这提示，虽然考拉精子具有一定的抗冻性，但优化冷冻方案以最小化渗透压应激和线粒体损伤仍是提升冷冻效果的关键。
辅助生殖技术（ARTs）在保护中的应用潜力：
ARTs，特别是人工授精（AI），已被证明在考拉保护中具有可行性和前景，为遗传管理和种群恢复提供了新的工具。
- 人工授精的成功实践： 考拉是首批通过人工授精成功繁育出后代的有袋类动物之一 666768。研究表明，使用稀释、稀释冷藏或未稀释的电射精精液进行人工授精，可以获得与自然交配相似的受孕率，并成功产下育儿袋幼崽 69。冷藏保存72小时的精液进行人工授精也成功产下幼崽，这为精液的远程运输提供了可能性 69。
- 精子库的建立： 鉴于考拉精子较好的冷冻保存特性，建立考拉精子库（genome resource bank）成为可能 5870。精子库可以储存来自不同地理区域和遗传背景的雄性考拉精子，从而保留遗传多样性，防止基因丢失，并在必要时用于遗传救援，为野外考拉种群补充遗传多样性 5859。
- 遗传管理： 通过ARTs引入外部遗传物质，可以降低圈养种群的近交水平，提高其遗传多样性和适应性，同时可能减少圈养繁殖项目的成本 59。例如，遗传和经济模型预测，通过人工授精或胞浆内单精子注射（ICSI）补充冷冻保存的创始人精子，可以显著减少近交，降低所需圈养种群规模，并在成本可控的范围内实现雄心勃勃的遗传保留目标（如维持90%、95%或99%的起始种群杂合度达100年），从而产出适合野外放归的考拉 59。
- 克服季节性繁殖： 虽然雄性考拉的繁殖功能存在季节性变化，冬季是采集精液的最佳季节 70，但ARTs可以克服这种季节性限制，允许在全年任何时候利用保存的精液进行繁殖。
综上所述，考拉独特的精子生理特性（如较好的抗冻性和DNA稳定性）为精液的保存和人工授精提供了坚实的基础。辅助生殖技术作为一种有效的保护工具，在提高考拉种群遗传多样性、降低近交风险以及应对栖息地丧失等威胁方面，展现出巨大的应用潜力。
4.3 肠道微生物的垂直传递
考拉幼崽能够消化有毒且营养贫乏的桉树叶，其关键在于肠道微生物群的建立与功能发挥。这一至关重要的过程并非独立发生，而是高度依赖于母系微生物群的垂直传递。这种传递机制对于幼崽建立健康的消化系统、代谢桉树叶中的毒素以及高效利用营养是不可或缺的。
母系微生物群的代际传递机制：
考拉幼崽在出生后的头几个月，完全依赖母乳获取营养。在幼崽离开育儿袋、开始尝试食用桉树叶之前，母兽会产生一种特殊的、软糊状的排泄物，被称为“pap”（也称作“special faeces”）。幼崽会通过食用这种“pap”来接种母体肠道中的微生物群。
- “Pap”的重要性： “Pap”是一种富含母体肠道微生物的半消化物质，它包含了成年考拉消化桉树叶所需的关键细菌。通过摄食“pap”，幼崽得以接收母体的细菌群落，这些细菌群落在幼崽的肠道中定植，并逐渐形成能够分解桉树叶纤维和代谢毒素的微生物生态系统。
- 垂直传递的实证： 研究明确指出，考拉肠道微生物群的成熟和继承在野外与圈养环境中是相似的，幼崽的微生物组在6到12个月大时逐渐向成年考拉的组成转变 71。9个月大的幼崽肠道微生物与成年考拉更为相似，但仍有区别 71。在门水平上，幼崽与成年考拉的差异与圈养考拉一致，例如厚壁菌门（Firmicutes）的相对丰度随着幼崽发育而增加，而变形菌门（Proteobacteria）则减少 71。这种现象在其他食草动物（如大熊猫和兔子）中也有类似体现，即肠道微生物中的某些内生菌（endophytes）可以直接来源于植物，并在消化道中定植，甚至成为稳定的常驻菌群 72。
- 母系遗传与微生物群： 近期研究进一步揭示了考拉肠道微生物群的组成和多样性存在个体和区域差异，并且这些差异与母系线粒体遗传起源密切相关 4。与母系线粒体起源相关的肠道细菌家族，如Rikenellaceae和Synergistaceae，被认为参与纤维消化和次生代谢产物的降解 4。这表明，母系遗传不仅影响幼崽的生理特征，也可能通过某种机制影响其微生物群的垂直传递和构成。
对幼崽消化桉树叶毒素的必要性：
桉树叶不仅营养价值低，还含有对大多数动物有毒的次生代谢产物。考拉的肠道微生物群在解毒和营养利用方面发挥着不可替代的作用。
- 毒素代谢： 肠道微生物，特别是某些细菌类群，能够分解桉树叶中的单宁、萜烯和甲酰基间苯三酚化合物（FPCs）等有毒物质，从而降低其对考拉的毒性，并使其能够安全摄食桉树叶。如果幼崽未能成功接种这些关键的微生物，它们将无法有效处理桉树叶中的毒素，这将直接威胁其生存。
- 纤维素降解： 桉树叶富含纤维素和半纤维素，而考拉自身不具备完全降解这些复杂碳水化合物的能力。肠道微生物中的纤维素降解菌（如Clostridium，其具有高效的纤维素酶体）能够将这些纤维转化为可被考拉吸收利用的短链脂肪酸等能量物质 72。研究表明，在圈养幼崽发育过程中，涉及半纤维素和纤维素降解的基因丰度逐渐增加，成年野外考拉中也普遍存在这些基因，这强调了纤维素降解微生物在成年考拉肠道中的重要性 71。
- 营养利用效率： 肠道微生物不仅帮助解毒和降解纤维，还能促进多种营养物质的吸收和合成，从而提高考拉从桉树叶中获取能量和营养的效率。
- 与觅食行为的关联： 肠道微生物群的多样性和组成差异，也被发现与考拉的觅食多样性相关 4。这提示，健康的肠道微生物群可能使得考拉能够消化更广泛的桉树叶种类，从而增加其食物选择的灵活性。
总之，考拉肠道微生物的垂直传递是其生存策略中的一个关键环节。通过母体向幼崽传递功能性微生物群，考拉幼崽才能顺利过渡到以桉树叶为食的阶段，并有效应对桉树叶的毒性和营养挑战。这一复杂的生物学过程，凸显了母系照料在考拉种群补充和数量维持中的深远意义。
5. 人类干预与保护：现代生存的外部驱动
5.1 栖息地保护的有效性
考拉种群的生存与发展日益受到人类活动的深刻影响，因此，有效的栖息地保护措施成为考拉现代生存的外部驱动力。栖息地丧失和退化是考拉种群面临的主要威胁之一，而林业管理实践，尤其是选择性砍伐和再生林的质量，直接关系到考拉栖息地的有效性和种群密度。
林业管理（如选择性砍伐）对考拉密度的实际影响：
传统的观念认为，林业砍伐活动，即使是选择性砍伐，也会对考拉的栖息地造成负面影响，导致其种群密度下降。然而，一些近期研究对这一假设提出了挑战，并强调了在规范化管理下的林业活动与考拉保护的兼容性。
- 选择性砍伐的影响： 新南威尔士州（NSW）东北部森林的一项研究评估了在有旨在保护环境价值的法规下，选择性砍伐对考拉密度的影响。该研究采用BACIPS（Before-After-Control-Impact Paired Series）设计，通过声学传感器和雄性叫声的空间计数模型，对3600公顷区域内的雄性考拉密度进行了估计。结果显示，在选择性砍伐后，考拉的密度并没有显著下降，年度变化也很小 73。令人惊讶的是，在某些之前经历了重度砍伐、现在以幼龄再生林为主的区域，5-10年后考拉的密度甚至与对照组（未砍伐的原始林）相当，其中一个被砍伐区域的考拉密度位居研究中第二高 73。这表明，如果林业法规能够提供足够的栖息地保障，考拉能够维持其种群密度，即使是在采伐区域内也是如此 73。
- 栖息地连通性与缓冲区： 为了减轻林业活动的影响，保留森林（retention forestry）策略旨在通过在采伐区域内保留一定数量的树木或建立景观缓冲区来缓解对生物多样性的影响 74。例如，在采伐区域内保留关键的取食树种和连通廊道，对于考拉的移动和资源获取至关重要。
再生林与原始林的栖息地质量对比：
再生林（或次生林）在提供考拉栖息地方面，其质量与原始林（或老龄林）之间存在复杂的动态关系，这取决于再生林的发展阶段、管理方式以及植被组成。
- 再生林的潜力： 如前所述，一些研究表明，即使是5-10年后的重度砍伐区域（现为幼龄再生林），其考拉密度也能达到与原始林相似的水平 73。这可能得益于再生林中新生的桉树叶可能具有更高的营养价值或更低的毒素含量，吸引考拉前来取食。此外，再生林在提供庇护和连接景观方面也可能发挥作用。
- 原始林的重要性： 原始林通常拥有更高大的树木、更复杂的树冠结构和更丰富的生物多样性，为考拉提供更稳定和多样化的食物来源、更佳的遮荫以及更安全的避难所。考拉对其栖息地的选择具有精准性，偏好含有特定桉树种类的区域 13。原始林中往往包含考拉偏好的成熟桉树种，这些树木的结构和生理特性可能更符合考拉的需求。
- 环境因素的影响： 栖息地质量不仅取决于林木的年龄和结构，还受到海拔、重要取食树种的覆盖度、景观NDVI（归一化植被指数）以及火灾等环境因素的影响 74。例如，高海拔地区（>1000米）的考拉出现概率较低，而重要取食树种和高景观NDVI则与考拉出现概率呈正相关 74。这意味着在评估再生林质量时，需要综合考虑这些环境因素。
- 长期影响与适应性： 长期来看，再生林能否完全替代原始林的功能，仍需更深入的研究。考拉需要一定年龄的桉树来提供足够的食物量和栖息空间。再生林在生长初期可能无法完全满足考拉的所有需求，但随着树木的成熟，其栖息地质量会逐渐提高。因此，可持续的林业管理应平衡木材生产与考拉栖息地保护的需求，确保原始林的核心区域得到有效保护，并促进再生林向高质量栖息地的演变。
综上所述，栖息地保护的有效性是一个多维度的议题。规范化的林业管理，包括选择性砍伐和保留森林策略，可以在一定程度上与考拉保护兼容。然而，为了确保考拉种群的长期生存，仍需关注栖息地的连通性、生物多样性以及再生林在不同发展阶段的质量，并将其纳入全面的保护规划之中。
5.2 威胁缓解措施的实施
考拉面临的人为威胁，尤其是道路致死和犬类攻击，对其种群的长期生存构成严重挑战。为了缓解这些威胁，人类实施了多种防控措施，其有效性评估对于指导未来的保护工作至关重要。
道路致死（如野生动物通道建设）
道路和车辆交通是生物多样性最普遍的威胁之一，它们导致栖息地破碎化、增加动物死亡率，并开辟新的区域供人类开发自然资源 75。随着车辆数量的迅速增长，考拉的道路致死率也随之上升。
- 野生动物通道建设： 为了降低考拉因车辆碰撞导致的死亡，建设野生动物通道（如高架桥或地下通道）被视为一种重要的缓解措施。这些通道旨在为考拉提供安全的跨越道路的路径，减少其与车辆直接接触的机会。然而，野生动物通道的有效性并非一概而论，其成功与否取决于多种因素，包括通道的设计、位置以及考拉对通道的接受程度 15。例如，在昆士兰州中部克拉克-康纳斯山脉的一条主要高速公路上，考拉车辆碰撞的发生地点分布呈随机模式，这暗示着考拉可能没有特定的穿越点 76。在这种情况下，野生动物通道的设置可能需要更广泛的覆盖或结合其他策略，以提高其有效性。
- 道路网络规划优化： 除了建设通道，优化道路网络规划也是一个重要的缓解策略。研究表明，在大多数情况下，通过增加现有道路的车流量来适应车辆数量的增长，相比于建设新道路，对野生动物（包括考拉）的死亡率影响更小 75。例外情况是现有道路密度非常低但车流量极高的区域。这提示，在城市化和交通发展过程中，应优先考虑现有道路的扩容而非盲目新建道路，以最小化对考拉栖息地的进一步破碎化和死亡风险 75。
- 驾驶员可见度： 对考拉车辆碰撞事件的分析发现，驾驶员的可见度是预测碰撞发生的重要因素之一 76。这意味着在考拉活动频繁的区域，改善道路设计以提高驾驶员对路边考拉的可见度（如清除路边障碍物），或设置警示标志，也能在一定程度上降低碰撞风险。
- 生境同质性： 景观同质性也可能影响考拉的道路穿越行为。如果景观和植被相对同质，考拉可能不会集中在特定的穿越点，这使得预测和缓解道路致死变得更加复杂 76。
犬类攻击（如养犬管理）
犬类攻击是考拉面临的另一主要人为威胁，尤其是在人类居住区边缘和栖息地碎片化区域。
- 养犬管理与社区参与： 缓解犬类攻击的关键在于有效的养犬管理和社区教育。这包括强制规定犬只在夜间拴养、在考拉栖息地附近区域对犬只进行严格监管（如要求在公共场所牵绳），以及对犬主进行宣传教育，提高他们对考拉保护的意识。
- 社会阻碍： 然而，养犬管理往往面临社会层面的阻碍。例如，犬主不愿在夜间拴养犬只的社会阻碍，被认为是影响考拉恢复行动成功的重要因素之一 15。这意味着单纯的法规制定可能不足以解决问题，还需要深入的社区工作和行为改变干预措施。
- 犬类攻击对考拉生理压力的影响： 犬类攻击不仅导致考拉直接死亡，幸存的考拉也会遭受严重的生理和心理压力。被犬只攻击的考拉在获救后，其粪便糖皮质激素代谢物（FCM）水平升高，表明其承受了巨大的生理应激 77。这种生理压力会影响考拉的康复和后续生存，因此预防犬类攻击不仅能减少死亡，也能改善受伤考拉的预后。
- 栖息地破碎化与犬类接触： 栖息地破碎化将考拉推向人类居住区的边缘，增加了它们与家犬和野犬接触的机会。因此，栖息地恢复和连接生态廊道，能够减少考拉暴露于犬类攻击的风险。
总而言之，道路致死和犬类攻击是复杂且多维度的问题，需要整合工程、规划、法规和社区参与等多方面的缓解措施。评估这些措施的有效性需要长期的数据监测和科学研究，并需持续调整策略以适应不断变化的环境和挑战。
5.3 保护策略的社会协同
考拉的保护不仅仅是科学问题，更是一个复杂的社会议题，涉及科学专家、公众、政策制定者等多个利益相关方的价值观、认知和意见。在考拉管理，特别是种群控制等敏感问题上，专家与公众之间常常存在显著的意见差异。理解这些差异并在此基础上实现社会协同，是优化考拉保护政策、确保其有效性和可持续性的关键 78。
专家与公众对考拉管理（如种群控制）的意见差异：
- 对致死性管理的接受度： 专家和公众在考拉种群管理选项的社会可接受性上存在显著差异 78。几十年来，关于如何最好地管理考拉过剩种群的争论一直困扰着澳大利亚，专家们多次建议对过剩考拉进行扑杀，但管理者很少实施 78。文献指出，这可归因于人们认为公众反对扑杀考拉，但缺乏实证证据评估这一判断 78。例如，在对澳大利亚专家和公众进行的一项全国性调查中，发现在管理选项的可接受性方面存在显著差异，尽管可接受性的两极分化大致相同 78。然而，扑杀和土著狩猎等致死性管理选项引发了截然相反的意见 78。公众对致死性控制的接受度往往较低，这可能与他们对考拉作为“标志性物种”的情感投入，以及对动物福利的普遍关注有关。在评估野火中不同资产的社会价值时，一项针对澳大利亚成年人的调查显示，受访者压倒性地优先考虑保护考拉种群（最佳-最差得分1913），甚至高于防止蜗牛或植物物种灭绝 79。这表明考拉在公众心目中具有极高的情感和象征价值。
- 环境价值观与人-野生动物关系信念： 专家和公众的意见差异还可由其潜在的环境价值观和对人-野生动物关系的基本信念来解释 78。公众对致死性控制的接受度可以通过他们对人-野生动物关系的信念来解释，但这在专家中不适用 78。专家可能更多地基于生物学的承载力、种群健康和生态系统平衡等科学考量来做出判断，而公众则可能更侧重于个体动物的福利和“不伤害”的伦理原则。生物圈价值观以及更丰富的经验和知识可能在专家的可接受性判断中发挥更大的作用 78。
- 种群过剩问题： 在某些地区，如南澳大利亚州和维多利亚州，考拉种群数量在过去曾因成功引入和栖息地管理而变得非常庞大，甚至超出了当地桉树林的承载能力，导致栖息地退化和考拉健康状况下降。在这种情况下，科学家和野生动物管理者可能会建议通过种群控制措施（如异地搬迁、绝育或在极端情况下扑杀）来维持生态平衡和考拉种群的长期健康。然而，公众对这些措施的理解和接受度往往存在挑战。
基于科学与社会价值的保护政策优化路径：
为了弥合专家与公众之间的分歧，并制定出更有效、更具社会支持的考拉保护政策，需要采取多管齐下的方法：
加强公众参与和教育：
- 透明的信息沟通： 保护机构应向公众透明地解释考拉种群管理决策背后的科学依据，包括种群过剩对考拉自身健康和栖息地的负面影响。例如，通过清晰的数据和案例展示，让公众了解在缺乏干预的情况下，种群过剩如何导致考拉饥饿和栖息地破坏。
- 多元化的解决方案讨论： 在讨论敏感的种群控制措施时，应提供多种非致死性替代方案的信息，如绝育、异地搬迁等，并解释每种方案的优缺点、成本和可行性。同时，要指出这些替代方案在处理大规模过剩种群时的局限性。
- 价值观念的理解与尊重： 认识到公众对考拉的深厚情感是保护工作的重要动力，而非障碍。在沟通中尊重公众的价值观，并寻求将科学目标与社会伦理关切相结合的策略。
整合多学科视角制定政策：
灵活的、基于证据的管理策略：
- 区域性差异管理： 考拉种群的遗传多样性、密度和面临的威胁在不同地区存在显著差异。例如，昆士兰州和新南威尔士州的考拉种群正面临衰退，而维多利亚州和南澳大利亚州的部分种群则可能存在过剩问题。因此，保护政策应具有区域特异性，避免“一刀切”的方案。
- 长期监测与适应性管理： 实施管理措施后，应持续监测其对考拉种群、栖息地和社区反应的影响，并根据监测结果适时调整策略。
- 遗传多样性的维护： 基因组测序等工具在管理受威胁物种方面具有强大作用 80。通过基因组调查等开放数据资源，可以加速对考拉基因组多样性的研究，为保护规划提供信息 80。例如，确定哪些种群具有高遗传多样性，哪些种群需要遗传救援（如通过异地搬迁或ARTs引入新的基因）。
资金与资源投入：
通过这些策略，可以在科学指导下，平衡考拉保护的生态需求与社会伦理期待，从而构建一个更加全面、可持续的考拉保护框架。
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参考文献
1Variation in koala microbiomes within and between individuals: effect of body region and captivity status.PubMed
Niccoló Alfano, Alexandre Courtiol, Hanna Vielgrader, et al.
Sci Rep. 2015 May 11;5:10189. doi: 10.1038/srep10189.
Metagenomic analysis of 16S ribosomal RNA has been used to profile microbial communities at high resolution, and to examine their association with host diet or diseases. We examined the oral and gut microbiome composition of two captive koalas to determine whether bacterial communities are unusual in this species, given that their diet consists almost exclusively of Eucalyptus leaves. Despite a highly specialized diet, koala oral and gut microbiomes were similar in composition to the microbiomes from the same body regions of other mammals. Rectal swabs contained all of the diversity present in faecal samples, along with additional taxa, suggesting that faecal bacterial communities may merely subsample the gut bacterial diversity. Furthermore, the faecal microbiomes of the captive koalas were similar to those reported for wild koalas, suggesting that captivity may not compromise koala microbial health. Since koalas frequently suffer from ocular diseases caused by Chlamydia infection, we also examined the eye microbiome composition of two captive koalas, establishing the healthy baseline for this body part. The eye microbial community was very diverse, similar to other mammalian ocular microbiomes but with an unusually high representation of bacteria from the family Phyllobacteriaceae.
2Four species of arboreal folivore show differential tolerance to a secondary metabolite.PubMed
Lora M Jensen, Ian R Wallis, Karen J Marsh, et al.
Oecologia. 2014 Sep;176(1):251-8. doi: 10.1007/s00442-014-2997-4. Epub 2014 Jun 29.
The marsupials that eat Eucalyptus in south-eastern Australia provide an example of animals with similar niche requirements occurring sympatrically. They certainly differ in size, ranging from about 1 kg in the greater glider (Petauroides volans) and the closely related common ringtail possum (Pseudocheirus peregrinus), to 4 kg (common brushtail possum, Trichosurus vulpecula) and up to 15 kg in the koala (Phascolarctos cinereus). All species, however, may eat considerable amounts of eucalypt foliage, often favouring the same species, and thus appear to compete for food. In order to better understand the degree of competition for food, we measured feeding by the greater glider in response to increasing concentrations of a specific group of eucalypt plant secondary metabolites (PSM), the sideroxylonals, and then compared it to results published for the other species. The greater glider was more resilient than the other species to increasing concentrations of sideroxylonals. We suggest this allows gliders to feed on leaves from the eucalypt subgenus, Symphyomyrtus, while its small size and gliding ability allow it to feed where koalas cannot, on the young leaves on top of the canopy. In contrast, the common ringtail possum is well adapted to feeding from species of the subgenus Eucalyptus, which do not produce sideroxylonals but contain less available nitrogen (AvailN) than do the symphyomyrtles. These 'nutritional niches' segregate the forest and along with other factors, such as generalist and specialist feeding strategies and differences in body size and requirements for shelter, presumably minimise competition between the marsupial species.
3Tree use by koalas in a chemically complex landscape.PubMed
Ben D Moore, William J Foley
Nature. 2005 May 26;435(7041):488-90. doi: 10.1038/nature03551.
Although defence against herbivores is often argued to be the main action of plant secondary metabolites (PSMs), very few examples have demonstrated that intraspecific variation in PSM concentrations influences foraging by wild vertebrate herbivores. Experiments with captive animals often indicate that PSM concentrations influence how much herbivores eat from individual plants, but these experiments do not replicate the subtle trade-offs in diet selection faced by wild animals, which must avoid predators and extremes of weather, interact with conspecifics, and achieve a balanced, nutritious diet, while avoiding intoxication by PSMs. We characterized the foliar chemistry of every tree from two Eucalyptus species available to a population of koalas (Phascolarctos cinereus) and considered rates of tree visitation over a ten-year period. We show that visitation rate was most strongly influenced by tree size, but that koalas also visited trees less frequently if the foliage contained either high concentrations of deterrent PSMs known as formylated phloroglucinol compounds, or low concentrations of nitrogen. Consequently, plant chemistry restricts the use of trees by this herbivore, and thus limits the food available to koalas and potentially influences koala populations.
4Association of maternal genetics with the gut microbiome and eucalypt diet selection in captive koalas.PubMed
Kotaro Kondo, Mirei Suzuki, Mana Amadaira, et al.
PeerJ. 2024 May 27;12:e17385. doi: 10.7717/peerj.17385. eCollection 2024.
BACKGROUND: Koalas, an Australian arboreal marsupial, depend on eucalypt tree leaves for their diet. They selectively consume only a few of the hundreds of available eucalypt species. Since the koala gut microbiome is essential for the digestion and detoxification of eucalypts, their individual differences in the gut microbiome may lead to variations in their eucalypt selection and eucalypt metabolic capacity. However, research focusing on the relationship between the gut microbiome and differences in food preferences is very limited. We aimed to determine whether individual and regional differences exist in the gut microbiome of koalas as well as the mechanism by which these differences influence eucalypt selection. METHODS: Foraging data were collected from six koalas and a total of 62 feces were collected from 15 koalas of two zoos in Japan. The mitochondrial phylogenetic analysis was conducted to estimate the mitochondrial maternal origin of each koala. In addition, the 16S-based gut microbiome of 15 koalas was analyzed to determine the composition and diversity of each koala's gut microbiome. We used these data to investigate the relationship among mitochondrial maternal origin, gut microbiome and eucalypt diet selection. RESULTS AND DISCUSSION: This research revealed that diversity and composition of the gut microbiome and that eucalypt diet selection of koalas differs among regions. We also revealed that the gut microbiome alpha diversity was correlated with foraging diversity in koalas. These individual and regional differences would result from vertical (maternal) transmission of the gut microbiome and represent an intraspecific variation in koala foraging strategies. Further, we demonstrated that certain gut bacteria were strongly correlated with both mitochondrial maternal origin and eucalypt foraging patterns. Bacteria found to be associated with mitochondrial maternal origin included bacteria involved in fiber digestion and degradation of secondary metabolites, such as the families Rikenellaceae and Synergistaceae. These bacteria may cause differences in metabolic capacity between individual and regional koalas and influence their eucalypt selection. CONCLUSION: We showed that the characteristics (composition and diversity) of the gut microbiome and eucalypt diet selection of koalas differ by individuals and regional origins as we expected. In addition, some gut bacteria that could influence eucalypt foraging of koalas showed the relationships with both mitochondrial maternal origin and eucalypt foraging pattern. These differences in the gut microbiome between regional origins may make a difference in eucalypt selection. Given the importance of the gut microbiome to koalas foraging on eucalypts and their strong symbiotic relationship, future studies should focus on the symbiotic relationship and coevolution between koalas and the gut microbiome to understand individual and regional differences in eucalypt diet selection by koalas.
5Nutritional correlates of koala persistence in a low-density population.PubMed
Eleanor Stalenberg, Ian R Wallis, Ross B Cunningham, et al.
PLoS One. 2014 Dec 3;9(12):e113930. doi: 10.1371/journal.pone.0113930. eCollection 2014.
It is widely postulated that nutritional factors drive bottom-up, resource-based patterns in herbivore ecology and distribution. There is, however, much controversy over the roles of different plant constituents and how these influence individual herbivores and herbivore populations. The density of koala (Phascolarctos cinereus) populations varies widely and many attribute population trends to variation in the nutritional quality of the eucalypt leaves of their diet, but there is little evidence to support this hypothesis. We used a nested design that involved sampling of trees at two spatial scales to investigate how leaf chemistry influences free-living koalas from a low-density population in south east New South Wales, Australia. Using koala faecal pellets as a proxy for koala visitation to trees, we found an interaction between toxins and nutrients in leaves at a small spatial scale, whereby koalas preferred trees with leaves of higher concentrations of available nitrogen but lower concentrations of sideroxylonals (secondary metabolites found exclusively in eucalypts) compared to neighbouring trees of the same species. We argue that taxonomic and phenotypic diversity is likely to be important when foraging in habitats of low nutritional quality in providing diet choice to tradeoff nutrients and toxins and minimise movement costs. Our findings suggest that immediate nutritional concerns are an important priority of folivores in low-quality habitats and imply that nutritional limitations play an important role in constraining folivore populations. We show that, with a careful experimental design, it is possible to make inferences about populations of herbivores that exist at extremely low densities and thus achieve a better understanding about how plant composition influences herbivore ecology and persistence.
6Fundamental dietary specialisation explains differential use of resources within a koala population.PubMed
Karen J Marsh, Michaela D J Blyton, William J Foley, et al.
Oecologia. 2021 Jul;196(3):795-803. doi: 10.1007/s00442-021-04962-3. Epub 2021 Jun 17.
The diets of individual animals within populations can differ, but few studies determine whether this is due to fundamental differences in preferences or capacities to eat specific foods, or to external influences such as dominance hierarchies or spatial variation in food availability. The distinction is important because different drivers of dietary specialisation are likely to have different impacts on the way in which animal populations respond to, for example, habitat modification. We used a captive feeding study to investigate the mechanisms driving individual dietary specialisation in a population of wild koalas (Phascolarctos cinereus) in which individuals predominantly ate either Eucalyptus viminalis or Eucalyptus obliqua foliage. All six koalas that primarily ate E. viminalis in the wild avoided eating E. obliqua for more than 1 month in captivity. In contrast, all seven koalas that primarily ate E. obliqua could be maintained exclusively on this species in captivity, although they ate less from individual trees with higher foliar concentrations of unsubstituted B-ring flavanones (UBFs). Our results show that fundamental differences between individual animals allow some to exploit food resources that are less suitable for others. This could reduce competition for food, increase habitat carrying capacity, and is also likely to buffer the population against extinction in the face of habitat modification. The occurrence of fundamental individual specialisation within animal populations could also affect the perceived conservation value of different habitats, translocation or reintroduction success, and population dynamics. It should therefore be further investigated in other mammalian herbivore species.
7Production of milk and nutrition of the dependent young of free-ranging koalas (Phascolarctos cinereus).PubMed
A K Krockenberger, I D Hume, S J Cork
Physiol Zool. 1998 Jan-Feb;71(1):45-56. doi: 10.1086/515891.
The production of milk by lactating females, and energy expenditure and foliage intake of their dependent young, were investigated in free-ranging koalas. Koalas had the lowest mass-specific daily milk-energy production at peak lactation so far recorded in a mammal, but the duration of reproduction was 58% longer than the combined marsupial and eutherian average. As a consequence, the total energy input to reproduction in koalas was similar to that in other mammals. We propose that the prolonged lactation and low daily rate of energy transfer to the young by female koalas is an adaptation to the low energy availability from their diet of Eucalyptus foliage. Energy requirements (field metabolic rates) of young koalas were lower than those expected for typical marsupials (only 60% at permanent pouch exit), which may be a necessary preadaptation that allows the low rate of maternal energy transfer. However, the energy requirements of the adult females were no lower than expected for marsupials. This pattern of energy requirements and age resulted in a linear relationship between field metabolic rate and mass for the koalas in this population. Differences in milk production between the years of the study coincided with fluctuations in the availability of preferred young foliage, which suggests that lactational output by koalas may be flexible and affected by diet quality. Despite the interannual differences in milk production, growth of the young was similar in the two years.
8Tree-hugging koalas demonstrate a novel thermoregulatory mechanism for arboreal mammals.PubMed
Natalie J Briscoe, Kathrine A Handasyde, Stephen R Griffiths, et al.
Biol Lett. 2014 Jun;10(6). doi: 10.1098/rsbl.2014.0235.
How climate impacts organisms depends not only on their physiology, but also whether they can buffer themselves against climate variability via their behaviour. One of the way species can withstand hot temperatures is by seeking out cool microclimates, but only if their habitat provides such refugia. Here, we describe a novel thermoregulatory strategy in an arboreal mammal, the koala Phascolarctos cinereus. During hot weather, koalas enhanced conductive heat loss by seeking out and resting against tree trunks that were substantially cooler than ambient air temperature. Using a biophysical model of heat exchange, we show that this behaviour greatly reduces the amount of heat that must be lost via evaporative cooling, potentially increasing koala survival during extreme heat events. While it has long been known that internal temperatures of trees differ from ambient air temperatures, the relevance of this for arboreal and semi-arboreal mammals has not previously been explored. Our results highlight the important role of tree trunks as aboveground 'heat sinks', providing cool local microenvironments not only for koalas, but also for all tree-dwelling species.
9ECG response of koalas to tourists proximity: a preliminary study.PubMed
Yan Ropert-Coudert, Lisa Brooks, Maki Yamamoto, et al.
PLoS One. 2009 Oct 12;4(10):e7378. doi: 10.1371/journal.pone.0007378.
Koalas operate on a tight energy budget and, thus, may not always display behavioral avoidance reaction when placed in a stressful condition. We investigated the physiological response of captive koalas Phascolarctos cinereus in a conservation centre to the presence of tourists walking through their habitat. We compared, using animal-attached data-recorders, the electrocardiogram activity of female koalas in contact with tourists and in a human-free area. One of the koalas in the tourist zone presented elevated heart rate values and variability throughout the recording period. The remaining female in the exhibit area showed a higher field resting heart rates during the daytime than that in the isolated area. In the evening, heart rate profiles changed drastically and both the koalas in the exhibit and in the tourist-free zones displayed similar field resting heart rates, which were lower than those during the day. In parallel, the autonomic nervous systems of these two individuals evolved from sympathetic-dominant during the day to parasympathetic-dominant in the evening. Our results report ECG of free-living koalas for the first time. Although they are preliminary due to the difficulty of having sufficient samples of animals of the same sex and age, our results stress out the importance of studies investigating the physiological reaction of animals to tourists.
10Intraspecific variation in Eucalyptus secondary metabolites determines food intake by folivorous marsupials.PubMed
I R Lawler, W J Foley, B M Eschler, et al.
Oecologia. 1998 Aug;116(1-2):160-169. doi: 10.1007/s004420050575.
Traditional approaches to the question of the effects of plant secondary metabolites on the feeding choices of folivores of Eucalyptus have focused on the tree species level, although numerous field studies of foraging behaviour have identified selection at the level of the individual trees. Attempts to relate these decisions to deterrency resulting from secondary leaf chemistry have been inconclusive because assays used have focused on broad groups of compounds such as "total" phenolics. In this study we have conducted no-choice feeding trials with two arboreal mammalian folivores, the common ringtail possum (Pseudocheirus peregrinus) and the koala (Phascolarctos cinereus), to measure deterrency of individual trees of two species of Eucalyptus, E. ovata and E. viminalis. Average daily intakes of E. ovata foliage by common ringtail possums ranged from 2.5 to 50 g kg body mass. Koala intakes of foliage from the same individual trees ranged from 22.4 to 36.3 g kg body mass. When fed foliage from different individual E. viminalis trees, common ringtail possums ate between 1.26 and 6.28 g kg body mass while koalas ate from 14.3 to 45.9 g kg body mass. Correlative analyses showed no relationships between feeding and several measures of nutritional quality, nor with total phenolics or condensed tannins. They did, however, identify two groups of plant secondary metabolites that may cause deterrency: terpenes, and a defined group of phenolic compounds, the diformylphloroglucinols (DFPs). Further bioassay experiments with common ringtail possums showed that only the DFPs could cause the effects seen with the foliage experiments at concentrations similar to those found in the leaves. We argue that, when in sufficiently high concentrations, DFPs determine the level of food intake by these animals irrespective of other questions of nutritional quality of the leaves.
11Eucalyptus foliar chemistry explains selective feeding by koalas.PubMed
Ben D Moore, William J Foley, Ian R Wallis, et al.
Biol Lett. 2005 Mar 22;1(1):64-7. doi: 10.1098/rsbl.2004.0255.
The koala is the quintessential specialist herbivore, feeding almost exclusively on Eucalyptus foliage. Consequently, the limitations imposed on the koala's diet by plant defences indicate the extent to which evolutionary adaptations allow mammalian herbivores to circumvent such defences. We tested whether a recently discovered group of plant secondary metabolites, the formylated phloroglucinol compounds (FPCs), deters koalas from feeding on some eucalypt foliage. We found that captive koalas ate less foliage in a single night from trees with high FPC concentrations. Individual trees also differ in the types of FPC they possess, but for a given eucalypt species, most FPCs were similarly effective deterrents. Two closely related and sympatric eucalypt species could be clearly separated by the amounts that koalas ate from each; however, this difference could not be explained by total FPC concentrations alone. We suggest, that in this case, the presence of a distinct type of FPC deters koala herbivory on the less palatable species, and may have facilitated the evolutionary divergence of these species. We conclude that plant defences probably play an important role in determining the distribution and abundance of koalas.
12Adaptation and conservation insights from the koala genome.PubMed
Rebecca N Johnson, Denis O'Meally, Zhiliang Chen, et al.
Nat Genet. 2018 Aug;50(8):1102-1111. doi: 10.1038/s41588-018-0153-5. Epub 2018 Jul 2.
The koala, the only extant species of the marsupial family Phascolarctidae, is classified as 'vulnerable' due to habitat loss and widespread disease. We sequenced the koala genome, producing a complete and contiguous marsupial reference genome, including centromeres. We reveal that the koala's ability to detoxify eucalypt foliage may be due to expansions within a cytochrome P450 gene family, and its ability to smell, taste and moderate ingestion of plant secondary metabolites may be due to expansions in the vomeronasal and taste receptors. We characterized novel lactation proteins that protect young in the pouch and annotated immune genes important for response to chlamydial disease. Historical demography showed a substantial population crash coincident with the decline of Australian megafauna, while contemporary populations had biogeographic boundaries and increased inbreeding in populations affected by historic translocations. We identified genetically diverse populations that require habitat corridors and instituting of translocation programs to aid the koala's survival in the wild.
13A new approach improving koala habitat prediction using hyperspectral airborne imagery.PubMed
Cristian Gabriel Orlando, Floris Van Ogtrop, Thomas F A Bishop, et al.
Sci Total Environ. 2025 Dec 20;1009:181104. doi: 10.1016/j.scitotenv.2025.181104. Epub 2025 Dec 2.
Koala populations are declining primarily due to habitat loss, making large-scale habitat quality prediction essential for conservation. A first approach to defining koala habitat quality involves identifying the number of different 'koala' trees species present, and their individual chemical composition. Previous studies have used remote sensing, from drones to satellites, to measure these factors. While the trade-off between scale and resolution is evolving, airborne hyperspectral data currently offers a promising avenue for developing predictive models. In the past, koala studies predicting nitrogen content using airborne data achieved relatively high accuracies, but they did not explore the potential of classifying koala tree species and incorporate this explanatory variable into nitrogen models. Here, we test these ideas while testing a new approach: using individual canopy pixels, rather than canopy averages, to train models. We argue that pixel-level training exposes models to noisy pixels (different shading, angle or background), forcing them to still find patterns and improving robustness to new data. Furthermore, this approach increases training data by leveraging within-canopy variability, reducing the need for large sampling effort. We found that species classification using individual pixels achieved 96 % accuracy, but over iterations converged to the same accuracy (74 %) as using average canopy reflectance. Furthermore, we demonstrate that pixel-level training and explicit incorporation of tree species substantially improves the nitrogen prediction model (R = 0.61). Our findings support the use of this approach in future airborne data, allowing for improvements to models predicting koala habitat. Such models inform regional-scale habitat assessments and conservation decisions, helping prioritize high-value areas.
14Helping koalas battle disease - Recent advances in Chlamydia and koala retrovirus (KoRV) disease understanding and treatment in koalas.PubMed
Bonnie L Quigley, Peter Timms
FEMS Microbiol Rev. 2020 Sep 1;44(5):583-605. doi: 10.1093/femsre/fuaa024.
The iconic Australian marsupial, the koala (Phascolarctos cinereus), has suffered dramatic population declines as a result of habitat loss and fragmentation, disease, vehicle collision mortality, dog attacks, bushfires and climate change. In 2012, koalas were officially declared vulnerable by the Australian government and listed as a threatened species. In response, research into diseases affecting koalas has expanded rapidly. The two major pathogens affecting koalas are Chlamydia pecorum, leading to chlamydial disease and koala retrovirus (KoRV). In the last eight years, these pathogens and their diseases have received focused study regarding their sources, genetics, prevalence, disease presentation and transmission. This has led to vast improvements in pathogen detection and treatment, including the ongoing development of vaccines for each as a management and control strategy. This review will summarize and highlight the important advances made in understanding and combating C. pecorum and KoRV in koalas, since they were declared a threatened species. With complementary advances having also been made from the koala genome sequence and in our understanding of the koala immune system, we are primed to make a significant positive impact on koala health into the future.
15Impediments to the success of management actions for species recovery.PubMed
Chooi Fei Ng, Hugh P Possingham, Clive A McAlpine, et al.
PLoS One. 2014 Apr 3;9(4):e92430. doi: 10.1371/journal.pone.0092430. eCollection 2014.
Finding cost-effective management strategies to recover species declining due to multiple threats is challenging, especially when there are limited resources. Recent studies offer insights into how costs and threats can influence the best choice of management actions. However, when implementing management actions in the real-world, a range of impediments to management success often exist that can be driven by social, technological and land-use factors. These impediments may limit the extent to which we can achieve recovery objectives and influence the optimal choice of management actions. Nonetheless, the implications of these impediments are not well understood, especially for recovery planning involving multiple actions. We used decision theory to assess the impact of these types of impediments for allocating resources among recovery actions to mitigate multiple threats. We applied this to a declining koala (Phascolarctos cinereus) population threatened by habitat loss, vehicle collisions, dog attacks and disease. We found that the unwillingness of dog owners to restrain their dogs at night (a social impediment), the effectiveness of wildlife crossings to reduce vehicle collisions (a technological impediment) and the unavailability of areas for restoration (a land-use impediment) significantly reduced the effectiveness of our actions. In the presence of these impediments, achieving successful recovery may be unlikely. Further, these impediments influenced the optimal choice of recovery actions, but the extent to which this was true depended on the target koala population growth rate. Given that species recovery is an important strategy for preserving biodiversity, it is critical that we consider how impediments to the success of recovery actions modify our choice of actions. In some cases, it may also be worth considering whether investing in reducing or removing impediments may be a cost-effective course of action.
16Road to Extinction? Past and Present Population Structure and Genomic Diversity in the Koala.PubMed
Binia De Cahsan, Marcela Sandoval Velasco, Michael V Westbury, et al.
Mol Biol Evol. 2025 Apr 1;42(4). doi: 10.1093/molbev/msaf057.
Koalas are arboreal herbivorous marsupials, endemic to Australia. During the late 1800s and early 1900s, the number of koalas declined dramatically due to hunting for their furs. In addition, anthropogenic activities have further decimated their available habitat, and decreased population numbers. Here, we utilize 37 historic and 25 modern genomes sampled from across their historic and present geographic range, to gain insights into how their population structure and genetic diversity have changed across time; assess the genetic consequences of the period of intense hunting, and the current genetic status of this iconic Australian species. Our analyses reveal how genome-wide heterozygosity has decreased through time and unveil previously uncharacterized mitochondrial haplotypes and nuclear genotypes in the historic dataset, which are absent from today's koala populations.
17Historically low mitochondrial DNA diversity in koalas (Phascolarctos cinereus).PubMed
Kyriakos Tsangaras, María C Ávila-Arcos, Yasuko Ishida, et al.
BMC Genet. 2012 Oct 24;13:92. doi: 10.1186/1471-2156-13-92.
BACKGROUND: The koala (Phascolarctos cinereus) is an arboreal marsupial that was historically widespread across eastern Australia until the end of the 19th century when it suffered a steep population decline. Hunting for the fur trade, habitat conversion, and disease contributed to a precipitous reduction in koala population size during the late 1800s and early 1900s. To examine the effects of these reductions in population size on koala genetic diversity, we sequenced part of the hypervariable region of mitochondrial DNA (mtDNA) in koala museum specimens collected in the 19th and 20th centuries, hypothesizing that the historical samples would exhibit greater genetic diversity. RESULTS: The mtDNA haplotypes present in historical museum samples were identical to haplotypes found in modern koala populations, and no novel haplotypes were detected. Rarefaction analyses suggested that the mtDNA genetic diversity present in the museum samples was similar to that of modern koalas. CONCLUSIONS: Low mtDNA diversity may have been present in koala populations prior to recent population declines. When considering management strategies, low genetic diversity of the mtDNA hypervariable region may not indicate recent inbreeding or founder events but may reflect an older historical pattern for koalas.
18Koalas (Phascolarctos cinereus) From Queensland Are Genetically Distinct From 2 Populations in Victoria.PubMed
Christina T Ruiz-Rodriguez, Yasuko Ishida, Neil D Murray, et al.
J Hered. 2016;107(7):573-580. doi: 10.1093/jhered/esw049. Epub 2016 Aug 11.
The koala (Phascolarctos cinereus) suffered population declines and local extirpation due to hunting in the early 20th century, especially in southern Australia. Koalas were subsequently reintroduced to the Brisbane Ranges (BR) and Stony Rises (SR) by translocating individuals from a population on French Island descended from a small number of founders. To examine genetic diversity and north-south differentiation, we genotyped 13 microsatellite markers in 46 wild koalas from the BR and SR, and 27 Queensland koalas kept at the US zoos. The Queensland koalas displayed much higher heterozygosity (H = 0.73) than the 2 southern Australian koala populations examined: H = 0.49 in the BR, whereas H = 0.41 in the SR. This is consistent with the historical accounts of bottlenecks and founder events affecting the southern populations and contrasts with reports of high genetic diversity in some southern populations. The 2 southern Australian koala populations were genetically similar (F = 0.018, P = 0.052). By contrast, northern and southern Australian koalas were highly differentiated (F = 0.27, P < 0.001), thereby suggesting that geographic structuring should be considered in the conservation management of koalas. Sequencing of 648bp of the mtDNA control region in Queensland koalas found 8 distinct haplotypes, one of which had not been previously detected among koalas. Queensland koalas displayed high mitochondrial haplotype diversity (H = 0.753) and nucleotide diversity (π = 0.0072), indicating along with the microsatellite data that North American zoos have maintained high levels of genetic diversity among their Queensland koalas.
19MHC class II diversity of koala (Phascolarctos cinereus) populations across their range.PubMed
Q Lau, W Jaratlerdsiri, J E Griffith, et al.
Heredity (Edinb). 2014 Oct;113(4):287-96. doi: 10.1038/hdy.2014.30. Epub 2014 Apr 2.
Major histocompatibility complex class II (MHCII) genes code for proteins that bind and present antigenic peptides and trigger the adaptive immune response. We present a broad geographical study of MHCII DA β1 (DAB) and DB β1 (DBB) variants of the koala (Phascolarctos cinereus; n=191) from 12 populations across eastern Australia, with a total of 13 DAB and 7 DBB variants found. We identified greater MHCII variation and, possibly, additional gene copies in koala populations in the north (Queensland and New South Wales) relative to the south (Victoria), confirmed by STRUCTURE analyses and genetic differentiation using analysis of molecular variance. The higher MHCII diversity in the north relative to south could potentially be attributed to (i) significant founder effect in Victorian populations linked to historical translocation of bottlenecked koala populations and (ii) increased pathogen-driven balancing selection and/or local genetic drift in the north. Low MHCII genetic diversity in koalas from the south could reduce their potential response to disease, although the three DAB variants found in the south had substantial sequence divergence between variants. This study assessing MHCII diversity in the koala with historical translocations in some populations contributes to understanding the effects of population translocations on functional genetic diversity.
20Conservation Arks: Genomic Erosion and Inbreeding in an Abundant Island Population of Koalas.PubMed
Katie Gates, Jonathan Sandoval-Castillo, Julian E Beaman, et al.
Mol Ecol. 2025 Oct;34(20):e70097. doi: 10.1111/mec.70097. Epub 2025 Sep 13.
The persistence of many threatened species depends on isolated habitat patches such as conservation parks, fenced reserves, and islands. While these 'conservation arks' provide refuge from many contemporary threats, they can also pose risks of genetic diversity loss and inbreeding depression, further exacerbating extinction risk. A pertinent example is the Kangaroo Island koala population in South Australia that originated from a few translocated founding individuals in the 1920s but now sustains a large population with a low prevalence of infectious disease. We investigated the extent and consequences of founder effects on genomic diversity, inbreeding, and adaptive potential in Kangaroo Island koalas by comparing them with mainland Australian populations using high-coverage whole genomes. Our findings support sharp, recent declines in effective population sizes (N) in both mainland and Kangaroo Island populations. However, Kangaroo Island koalas had much lower individual and population-level diversity. Together with longer and more numerous runs of homozygosity and an increased proportion of homozygous genetic load, these results support the hypothesis that a severe bottleneck has contributed to inbreeding and maladaptation in Kangaroo Island koalas. While Kangaroo Island has the potential to conserve a viable population of koalas, we recommend genetic rescue to restore diversity and mitigate inbreeding depression in this isolated population. Our results emphasise the need for longitudinal genomic monitoring and genetic management to maintain long-term viability and resilience in potential conservation arks. Understanding the demographic history of such populations will help inform future conservation aimed at preventing genetic erosion and preserving biodiversity.
21Low genetic variability of the koala Phascolarctos cinereus in south-eastern Australia following a severe population bottleneck.PubMed
B A Houlden, P R England, A C Taylor, et al.
Mol Ecol. 1996 Apr;5(2):269-81.
Genotyping of koalas at CA-repeat microsatellite loci has revealed significant differences in the levels of allelic diversity (A) and expected heterozygosity (H(E)) between populations from north-eastern and south-eastern Australia. In the 10 populations studied, allelic diversity ranged from 8.0 in the Nowendoc population to 1.7 in the Kangaroo Is. population, and values of H(E) ranged from 0.831 in the Nowendoc population to 0.331 in the Kangaroo Is. population. Data from pooled populations revealed koalas from the north-eastern region had significantly higher levels of allelic diversity (A = 11.5 +/- 1.4) than those from south-eastern Australia (A = 5.3 +/- 1.0). Furthermore significantly higher heterozygosity levels were found in the north-eastern (H(E) = 0.851) vs. the south-eastern (H(E) = 0.436) regions of Australia. Following a near-extinction bottleneck in the 1920s, mainland Victorian and Kangaroo Is. koalas have been involved in an extensive program of relocations. The source populations of the relocated animals were islands in Westernport Bay, which were founded by very few individuals in the late 1800s and early 1900s. The significantly lower levels of variation between south-eastern Australian populations suggests that human intervention has had a severe effect on levels of genetic diversity in this region, and this may have long-term genetic consequences.
22High-throughput immunogenetic typing of koalas suggests possible link between MHC alleles and cancers.PubMed
Bonnie L Quigley, Galit Tzipori, Karen Nilsson, et al.
Immunogenetics. 2020 Dec;72(9-10):499-506. doi: 10.1007/s00251-020-01181-7. Epub 2020 Oct 20.
Characterizing the allelic diversity within major histocompatibility complex (MHC) genes is an important way of determining the potential genetic resilience of a population to infectious and ecological pressures. For the koala (Phascolarctos cinereus), endemic diseases, anthropogenic factors and climate change are all placing increased pressure on this vulnerable marsupial. To increase the ability of researchers to study MHC genetics in koalas, this study developed and tested a high-throughput immunogenetic profiling methodology for targeting MHC class I UA and UC genes and MHC class II DAB, DBB, DCB and DMB genes in a population of 82 captive koalas. This approach was validated by comparing the determined allelic profiles from 36 koala family units (18 dam-sire-joey units and 18 parent-joey pairs), finding 96% overall congruence within family profiles. Cancers are a significant cause of morbidity in koalas and the risk factors remain undetermined. Our analysis of this captive population revealed several novel MHC alleles, including a potential link between the DBB*03 allele and a risk of developing cancer. This method offers a reliable, high-throughput protocol for expanded study into koala immunogenetics.
23Conservation genetics of the koala (Phascolarctos cinereus): low mitochondrial DNA variation amongst southern Australian populations.PubMed
A C Taylor, J M Graves, N D Murray, et al.
Genet Res. 1997 Feb;69(1):25-33. doi: 10.1017/s0016672397002607.
Koala (Phascolarctos cinereus) populations in southern Australia have a history of bottlenecks-earlier this century the species became extinct in South Australia, and almost so in Victoria. Subsequently large numbers of animals from island populations (founded from very few animals) have been translocated back to mainland sites and to other islands in the region. As part of a larger study of the genetic structure of koala populations in southern Australia, we have undertaken a survey of mitochondrial DNA restriction fragment length polymorphism (mtDNA-RFLP) variability. Genomic DNA from 91 koalas from five populations was examined using 23 restriction enzymes, and mtDNA fragments were detected using a domestic cat full-length mtDNA clone. Only one of the enzymes, TaqI, revealed polymorphism-a relatively low amount of variation compared with other mammals, although low mtDNA-RFLP variation has also been reported in Queensland koalas. French Island and populations established predominantly from French Island immigrant koalas, either directly or via other island populations, were indistinguishable by haplotype frequencies. The mtDNA data are thus consistent with the interpretation that the koala translocation programme has homogenized gene frequencies amongst those populations involved. South Gippsland is not recorded as having received translocated koalas directly, and has significantly different mtDNA-RFLP haplotype frequencies from all other populations examined. The fact that this distinction was not previously observed in nuclear gene frequencies may reflect predominantly male-mediated dispersal in koalas.
24Genomics identifies koala populations at risk across eastern Australia.PubMed
Elspeth A McLennan, Toby G L Kovacs, Luke W Silver, et al.
Ecol Appl. 2025 Jan;35(1):e3062. doi: 10.1002/eap.3062. Epub 2024 Nov 29.
Koalas are an iconic, endangered, Australian marsupial. Disease, habitat destruction, and catastrophic mega-fires have reduced koalas to remnant patches of their former range. With increased likelihood of extreme weather events and ongoing habitat clearing across Australia, koala populations are vulnerable to further declines and isolation. Small, isolated populations are considered at risk when there is increased inbreeding, erosion of genomic diversity, and loss of adaptive potential, all of which reduce their ability to respond to prevailing threats. Here, we characterized the current genomic landscape of koalas using data from The Koala Genome Survey, a joint initiative between the Australian Federal and New South Wales Governments that aimed to provide a future-proofed baseline genomic dataset across the koala's range in eastern Australia. We identified several regions of the continent where koalas have low genomic diversity and high inbreeding, as measured by runs of homozygosity. These populations included coastal sites along southeast Queensland and northern and mid-coast New South Wales, as well as southern New South Wales and Victoria. Analysis of genomic vulnerability to future climates revealed that northern koala populations were more at risk due to the extreme expected changes in this region, but that the adaptation required was minimal compared with other species. Our genomic analyses indicate that continued development, particularly linear infrastructure along coastal sites, and resultant habitat destruction are causing isolation and subsequent genomic erosion across many koala populations. Habitat protection and the formation of corridors must be employed for all koala populations to maintain current levels of diversity. For highly isolated koala populations, active management may be the only way to improve genomic diversity in the short term. If koalas are to be conserved for future generations, reversing their genomic isolation must be a priority in conservation planning.
25Genome Reference Assembly for Bottlenecked Southern Australian Koalas.PubMed
Adam Mark Blanchard, Richard David Emes, Alex David Greenwood, et al.
Genome Biol Evol. 2023 Jan 4;15(1). doi: 10.1093/gbe/evac176.
Koala populations show marked differences in inbreeding levels and in the presence or absence of the endogenous Koala retrovirus (KoRV). These genetic differences among populations may lead to severe disease impacts threatening koala population viability. In addition, the recent colonization of the koala genome by KoRV provides a unique opportunity to study the process of retroviral adaptation to vertebrate genomes and the impact this has on speciation, genome structure, and function. The genome build described here is from an animal from the bottlenecked Southern population free of endogenous and exogenous KoRV. It provides a more contiguous genome build than the previous koala reference derived from an animal from a more outbred Northern population and is the first koala genome from a KoRV polymerase-free animal.
26Genetic diversity of Koala retrovirus gene subtypes: insights into northern and southern koala populations.PubMed
Nishat Sarker, Jessica Fabijan, Jennifer Seddon, et al.
J Gen Virol. 2019 Sep;100(9):1328-1339. doi: 10.1099/jgv.0.001304. Epub 2019 Jul 23.
Koala retrovirus (KoRV) is a recently endogenized retrovirus associated with neoplasia and immunosuppression in koala populations. The virus is known to display sequence variability and to be present at varying prevalence in different populations, with animals in southern Australia displaying lower prevalence and viral loads than northern animals. This study used a PCR and next-generation sequencing strategy to examine the diversity of the KoRV gene in both proviral DNA and viral RNA forms in two distinct populations representative of the 'northern' and 'southern' koala genotypes. The current study demonstrated that the full range of KoRV subtypes is present across both populations, and in both healthy and sick animals. KoRV-A was the predominant proviral subtype in both populations, but there was marked diversity of DNA and RNA subtypes within individuals. Many of the northern animals displayed a higher RNA viral diversity than evident in their proviral DNA, indicating relatively higher replication efficiency of non-KoRV-A subtypes. The southern animals displayed a lower absolute copy number of KoRV than the northern animals as reported previously and a higher preponderance of KoRV-A in individual animals. These discrepancies in viral replication and diversity remain unexplained but may indicate relative protection of the southern population from KoRV replication due to either viral or host factors and may represent an important protective effect for the host in KoRV's ongoing entry into the koala genome.
27Susceptibility to a sexually transmitted disease in a wild koala population shows heritable genetic variance but no inbreeding depression.PubMed
Romane H Cristescu, Kasha Strickland, Anthony J Schultz, et al.
Mol Ecol. 2022 Nov;31(21):5455-5467. doi: 10.1111/mec.16676. Epub 2022 Sep 12.
The koala, one of the most iconic Australian wildlife species, is facing several concomitant threats that are driving population declines. Some threats are well known and have clear methods of prevention (e.g., habitat loss can be reduced with stronger land-clearing control), whereas others are less easily addressed. One of the major current threats to koalas is chlamydial disease, which can have major impacts on individual survival and reproduction rates and can translate into population declines. Effective management strategies for the disease in the wild are currently lacking, and, to date, we know little about the determinants of individual susceptibility to disease. Here, we investigated the genetic basis of variation in susceptibility to chlamydia using one of the most intensively studied wild koala populations. We combined data from veterinary examinations, chlamydia testing, genetic sampling and movement monitoring. Out of our sample of 342 wild koalas, 60 were found to have chlamydia. Using genotype information on 5007 SNPs to investigate the role of genetic variation in determining disease status, we found no evidence of inbreeding depression, but a heritability of 0.11 (95% CI: 0.06-0.23) for the probability that koalas had chlamydia. Heritability of susceptibility to chlamydia could be relevant for future disease management, as it suggests adaptive potential for the population.
28Reversing the decline of threatened koala () populations in New South Wales: Using genomics to enhance conservation outcomes.PubMed
Matthew J Lott, Greta J Frankham, Mark D B Eldridge, et al.
Ecol Evol. 2024 Jul 31;14(8):e11700. doi: 10.1002/ece3.11700. eCollection 2024 Aug.
Genetic management is a critical component of threatened species conservation. Understanding spatial patterns of genetic diversity is essential for evaluating the resilience of fragmented populations to accelerating anthropogenic threats. Nowhere is this more relevant than on the Australian continent, which is experiencing an ongoing loss of biodiversity that exceeds any other developed nation. Using a proprietary genome complexity reduction-based method (DArTSeq), we generated a data set of 3239 high quality Single Nucleotide Polymorphisms (SNPs) to investigate spatial patterns and indices of genetic diversity in the koala (), a highly specialised folivorous marsupial that is experiencing rapid and widespread population declines across much of its former range. Our findings demonstrate that current management divisions across the state of New South Wales (NSW) do not fully represent the distribution of genetic diversity among extant koala populations, and that care must be taken to ensure that translocation paradigms based on these frameworks do not inadvertently restrict gene flow between populations and regions that were historically interconnected. We also recommend that koala populations should be prioritised for conservation action based on the scale and severity of the threatening processes that they are currently faced with, rather than placing too much emphasis on their perceived value (e.g., as reservoirs of potentially adaptive alleles), as our data indicate that existing genetic variation in koalas is primarily partitioned among individual animals. As such, the extirpation of koalas from any part of their range represents a potentially critical reduction of genetic diversity for this iconic Australian species.
29Characterisation of four major histocompatibility complex class II genes of the koala (Phascolarctos cinereus).PubMed
Quintin Lau, Sarah E Jobbins, Katherine Belov, et al.
Immunogenetics. 2013 Jan;65(1):37-46. doi: 10.1007/s00251-012-0658-5. Epub 2012 Oct 23.
Major histocompatibility complex (MHC) class II molecules have an integral role in the adaptive immune response, as they bind and present antigenic peptides to T helper lymphocytes. In this study of koalas, species-specific primers were designed to amplify exon 2 of the MHC class II DA and DB genes, which contain much of the peptide-binding regions of the α and β chains. A total of two DA α1 domain variants and eight DA β1 (DAB), three DB α1 and five DB β1 variants were amplified from 20 koalas from two free-living populations from South East Queensland and the Port Macquarie region in northern New South Wales. We detected greater variation in the β1 than in the α1 domains as well as evidence of positive selection in DAB. The present study provides a springboard to future investigation of the role of MHC in disease susceptibility in koalas.
30Characterisation of MHC class I genes in the koala.PubMed
Yuanyuan Cheng, Adam Polkinghorne, Amber Gillett, et al.
Immunogenetics. 2018 Feb;70(2):125-133. doi: 10.1007/s00251-017-1018-2. Epub 2017 Jul 1.
Koala (Phascolarctos cinereus) populations are on the decline across the majority of Australia's mainland. Two major diseases threatening the long-term survival of affected koala populations are caused by obligate intracellular pathogens: Chlamydia and koala retrovirus (KoRV). To improve our understanding of the koala immune system, we characterised their major histocompatibility complex (MHC) class I genes, which are centrally involved in presenting foreign peptides derived from intracellular pathogens to cytotoxic T cells. A total of 11 class I genes were identified in the koala genome. Three genes, Phci-UA, UB and UC, showed relatively high genetic variability and were expressed in all 12 examined tissues, whereas the other eight genes had tissue-specific expression and limited polymorphism. Evidence of diversifying selection was detected in Phci-UA and UC, while gene conversion may have played a role in creating new alleles at Phci-UB. We propose that Phci-UA, UB and UC are likely classical MHC genes of koalas, and further research is needed to understand their role in koala chlamydial and KoRV infections.
31Hybridization capture reveals evolution and conservation across the entire Koala retrovirus genome.PubMed
Kyriakos Tsangaras, Matthew C Siracusa, Nikolas Nikolaidis, et al.
PLoS One. 2014 Apr 21;9(4):e95633. doi: 10.1371/journal.pone.0095633. eCollection 2014.
The koala retrovirus (KoRV) is the only retrovirus known to be in the midst of invading the germ line of its host species. Hybridization capture and next generation sequencing were used on modern and museum DNA samples of koala (Phascolarctos cinereus) to examine ca. 130 years of evolution across the full KoRV genome. Overall, the entire proviral genome appeared to be conserved across time in sequence, protein structure and transcriptional binding sites. A total of 138 polymorphisms were detected, of which 72 were found in more than one individual. At every polymorphic site in the museum koalas, one of the character states matched that of modern KoRV. Among non-synonymous polymorphisms, radical substitutions involving large physiochemical differences between amino acids were elevated in env, potentially reflecting anti-viral immune pressure or avoidance of receptor interference. Polymorphisms were not detected within two functional regions believed to affect infectivity. Host sequences flanking proviral integration sites were also captured; with few proviral loci shared among koalas. Recently described variants of KoRV, designated KoRV-B and KoRV-J, were not detected in museum samples, suggesting that these variants may be of recent origin.
32Differential and defective transcription of koala retrovirus indicates the complexity of host and virus evolution.PubMed
R E Tarlinton, A R Legione, N Sarker, et al.
J Gen Virol. 2022 Jun;103(6). doi: 10.1099/jgv.0.001749.
Koala retrovirus (KoRV) is unique amongst endogenous (inherited) retroviruses in that its incorporation to the host genome is still active, providing an opportunity to study what drives this fundamental process in vertebrate genome evolution. Animals in the southern part of the natural range of koalas were previously thought to be either virus-free or to have only exogenous variants of KoRV with low rates of KoRV-induced disease. In contrast, animals in the northern part of their range universally have both endogenous and exogenous KoRV with very high rates of KoRV-induced disease such as lymphoma. In this study we use a combination of sequencing technologies, Illumina RNA sequencing of 'southern' (south Australian) and 'northern' (SE QLD) koalas and CRISPR enrichment and nanopore sequencing of DNA of 'southern' (South Australian and Victorian animals) to retrieve full-length loci and intregration sites of KoRV variants. We demonstrate that koalas that tested negative to the KoRV gene qPCR, used to detect replication-competent KoRV, are not in fact KoRV-free but harbour defective, presumably endogenous, 'RecKoRV' variants that are not fixed between animals. This indicates that these populations have historically been exposed to KoRV and raises questions as to whether these variants have arisen by chance or whether they provide a protective effect from the infectious forms of KoRV. This latter explanation would offer the intriguing prospect of being able to monitor and selectively breed for disease resistance to protect the wild koala population from KoRV-induced disease.
33AMPed up immunity: 418 whole genomes reveal intraspecific diversity of koala antimicrobial peptides.PubMed
Cleopatra Petrohilos, Emma Peel, Luke W Silver, et al.
Immunogenetics. 2025 Jan 8;77(1):11. doi: 10.1007/s00251-024-01368-2.
Characterising functional diversity is a vital element to understanding a species' immune function, yet many immunogenetic studies in non-model organisms tend to focus on only one or two gene families such as the major histocompatibility complex (MHC) or toll-like receptors (TLR). Another interesting component of the eukaryotic innate immune system is the antimicrobial peptides (AMPs). The two major groups of mammalian AMPs are cathelicidins and defensins, with the former having undergone species-specific expansions in marsupials. Here, we utilised data from 418 koala whole genomes to undertake the first comprehensive analysis of AMP diversity across a mammalian wildlife species' range. Overall, allelic diversity was lower than other immune gene families such as MHC, suggesting that AMPs are more conserved, although balancing selection was observed in PhciDEFB12. Some non-synonymous SNPs in the active peptide are predicted to change AMP function through stop gains, change in structure, and increase in peptide charge. Copy number variants (CNVs) were observed in two defensins and one cathelicidin. Interestingly, the most common CNV was the duplication of PhciCATH5, a cathelicidin with activity against chlamydia, which was more common in the southern part of the species range than the north. AMP copy number is correlated with expression levels, so we hypothesise that there is a selective pressure from chlamydia for duplications in PhciCATH5. Future studies should use phenotypic metadata to assess the functional impacts of this gene duplication.
34Optimising the short and long-term clinical outcomes for koalas (Phascolarctos cinereus) during treatment for chlamydial infection and disease.PubMed
Amy Robbins, Joanne Loader, Peter Timms, et al.
PLoS One. 2018 Dec 27;13(12):e0209679. doi: 10.1371/journal.pone.0209679. eCollection 2018.
Koalas (Phascolarctos cinereus) have suffered severe declines in the northern extent of their range due to a variety of threats, including habitat destruction, trauma from cars and dogs, climate change and importantly, disease. The most significant pathogen in koalas is Chlamydia pecorum, which causes inflammation and fibrosis at mucosal sites, resulting in blindness, infertility and death in severe cases. Chlamydia treatment can be problematic in koalas as the response to treatment is often poor in chronic cases and antimicrobial choice is limited. Thus, chlamydial disease is a severely threatening process for koala conservation. We investigated the short and long-term clinical outcomes for 167 koalas with Chlamydia that underwent capture, telemetric monitoring and intensive veterinary management as part of a large-scale population management program in South East Queensland. Chlamydia treatments included the standard regimen of daily subcutaneous chloramphenicol injections (60mg/kg) for 14 to 28-days, and a variety of non-standard regimens such as topical antimicrobials only (for ocular disease), surgical treatment only (for bilateral reproductive tract disease), and other antimicrobials/treatment lengths. To assess these regimens we analysed clinical records, field monitoring data and swab samples collected from the urogenital tract and ocular conjunctiva. Overall, in contrast to other studies, treatment was generally successful with 86.3% of treated koalas released back into the wild. The success of treatment rose to 94.8% however, when the standard treatment regimen was employed. Further, 100% of koalas that were also treated with surgical ovariohysterectomy (n = 12) remained healthy for a median of 466 days of post-treatment monitoring, demonstrating the benefits of surgical treatment. Previous studies reported 45-day chloramphenicol regimens, but the shorter standard regimen still achieved microbiological cure and reduces the risk of negative sequelae associated with treatment and/or captivity and treatment costs. Despite these positive clinical outcomes, alternatives to chloramphenicol are warranted due to its decreasing availability.
35Inbreeding and disease avoidance in a free-ranging koala population.PubMed
Anthony J Schultz, Romane H Cristescu, Jon Hanger, et al.
Mol Ecol. 2020 Jul;29(13):2416-2430. doi: 10.1111/mec.15488. Epub 2020 Jun 29.
Habitat destruction and fragmentation are increasing globally, forcing surviving species into small, isolated populations. Isolated populations typically experience heightened inbreeding risk and associated inbreeding depression and population decline; although individuals in these populations may mitigate these risks through inbreeding avoidance strategies. For koalas, as dietary specialists already under threat in the northern parts of their range, increased habitat fragmentation and associated inbreeding costs are of great conservation concern. Koalas are known to display passive inbreeding avoidance through sex-biased dispersal, although population isolation will reduce dispersal pathways. We tested whether free-ranging koalas display active inbreeding avoidance behaviours. We used VHF tracking data, parentage reconstruction, and veterinary examination results to test whether free-ranging female koalas avoid mating with (a) more closely related males; and (b) males infected with sexually transmitted Chlamydia pecorum. We found no evidence that female koalas avoid mating with relatively more related available mates. In fact, as the relatedness of potential mates increases, so did inbreeding events. We also found no evidence that female koalas can avoid mating with males infected with C. pecorum. The absence of active inbreeding avoidance mechanisms in koalas is concerning from a conservation perspective, as small, isolated populations may be at even higher risk of inbreeding depression than expected. At risk koala populations may require urgent conservation interventions to augment gene flow and reduce inbreeding risks. Similarly, if koalas are not avoiding mating with individuals with chlamydial disease, populations may be at higher risk from disease than anticipated, further impacting population viability.
36Chlamydia pecorum prevalence in South Australian koala (Phascolarctos cinereus) populations: Identification and modelling of a population free from infection.PubMed
Jessica Fabijan, Charles Caraguel, Martina Jelocnik, et al.
Sci Rep. 2019 Apr 18;9(1):6261. doi: 10.1038/s41598-019-42702-z.
Chlamydia pecorum is an established and prevalent infection that produces severe clinical disease in many koala populations, contributing to dramatic population declines. In wild South Australian koala populations, C. pecorum occurrence and distribution is unknown. Here, C. pecorum-specific real-time quantitative PCR (qPCR) was applied to ocular and urogenital swabs from targeted surveys of wild koalas from the mainland Mount Lofty Ranges (MLR) (n = 75) and Kangaroo Island (KI) (n = 170) populations. Historical data from 13,081 KI koalas (1997-2018) provided additional evidence for assessing the absence of C. pecorum infection. In the MLR population, 46.7% (CI: 35.1-58.6%) of koalas were C. pecorum positive by qPCR but only 4% had grade 3 clinical disease. MLR koala fertility was significantly reduced by C. pecorum infection; all reproductively active females (n = 16) were C. pecorum negative, whereas 85.2% of inactive females (n = 23) were positive (P < 0.001). KI koalas were C. pecorum negative and the population was demonstrated to be free of C. pecorum infection with 95% confidence. C. pecorum is a real threat for the sustainability of the koala and KI is possibly the last isolated, large C. pecorum-free population remaining in Australia. These koalas could provide a safeguard against this serious disease threat to an iconic Australian species.
37A 5-year Chlamydia vaccination programme could reverse disease-related koala population decline: predictions from a mathematical model using field data.PubMed
Andrew P Craig, Jon Hanger, Jo Loader, et al.
Vaccine. 2014 Jul 16;32(33):4163-70. doi: 10.1016/j.vaccine.2014.05.049. Epub 2014 May 28.
BACKGROUND: Many koala populations around Australia are in serious decline, with a substantial component of this decline in some Southeast Queensland populations attributed to the impact of Chlamydia. A Chlamydia vaccine for koalas is in development and has shown promise in early trials. This study contributes to implementation preparedness by simulating vaccination strategies designed to reverse population decline and by identifying which age and sex category it would be most effective to target. METHODS: We used field data to inform the development and parameterisation of an individual-based stochastic simulation model of a koala population endemic with Chlamydia. The model took into account transmission, morbidity and mortality caused by Chlamydia infections. We calibrated the model to characteristics of typical Southeast Queensland koala populations. As there is uncertainty about the effectiveness of the vaccine in real-world settings, a variety of potential vaccine efficacies, half-lives and dosing schedules were simulated. RESULTS: Assuming other threats remain constant, it is expected that current population declines could be reversed in around 5-6 years if female koalas aged 1-2 years are targeted, average vaccine protective efficacy is 75%, and vaccine coverage is around 10% per year. At lower vaccine efficacies the immunological effects of boosting become important: at 45% vaccine efficacy population decline is predicted to reverse in 6 years under optimistic boosting assumptions but in 9 years under pessimistic boosting assumptions. Terminating a successful vaccination programme at 5 years would lead to a rise in Chlamydia prevalence towards pre-vaccination levels. CONCLUSION: For a range of vaccine efficacy levels it is projected that population decline due to endemic Chlamydia can be reversed under realistic dosing schedules, potentially in just 5 years. However, a vaccination programme might need to continue indefinitely in order to maintain Chlamydia prevalence at a sufficiently low level for population growth to continue.
38Koala retrovirus diversity, transmissibility, and disease associations.PubMed
HaoQiang Zheng, Yi Pan, Shaohua Tang, et al.
Retrovirology. 2020 Oct 2;17(1):34. doi: 10.1186/s12977-020-00541-1.
BACKGROUND: Koalas are infected with the koala retrovirus (KoRV) that exists as exogenous or endogenous viruses. KoRV is genetically diverse with co-infection with up to ten envelope subtypes (A-J) possible; KoRV-A is the prototype endogenous form. KoRV-B, first found in a small number of koalas with an increased leukemia prevalence at one US zoo, has been associated with other cancers and increased chlamydial disease. To better understand the molecular epidemiology of KoRV variants and the effect of increased viral loads (VLs) on transmissibility and pathogenicity we developed subtype-specific quantitative PCR (qPCR) assays and tested blood and tissue samples from koalas at US zoos (n = 78), two Australian zoos (n = 27) and wild-caught (n = 21) in Australia. We analyzed PCR results with available clinical, demographic, and pedigree data. RESULTS: All koalas were KoRV-A-infected. A small number of koalas (10.3%) at one US zoo were also infected with non-A subtypes, while a higher non-A subtype prevalence (59.3%) was found in koalas at Australian zoos. Wild koalas from one location were only infected with KoRV-A. We observed a significant association of infection and plasma VLs of non-A subtypes in koalas that died of leukemia/lymphoma and other neoplasias and report cancer diagnoses in KoRV-A-positive animals. Infection and VLs of non-A subtypes was not associated with age or sex. Transmission of non-A subtypes occurred from dam-to-offspring and likely following adult-to-adult contact, but associations with contact type were not evaluated. Brief antiretroviral treatment of one leukemic koala infected with high plasma levels of KoRV-A, -B, and -F did not affect VL or disease progression. CONCLUSIONS: Our results show a significant association of non-A KoRV infection and plasma VLs with leukemia and other cancers. Although we confirm dam-to-offspring transmission of these variants, we also show other routes are possible. Our validated qPCR assays will be useful to further understand KoRV epidemiology and its zoonotic transmission potential for humans exposed to koalas because KoRV can infect human cells.
39Koala retrovirus (KoRV) subtypes and their impact on captive koala (Phascolarctos cinereus) health.PubMed
Md Abul Hashem, Mohammad Enamul Hoque Kayesh, Fumie Maetani, et al.
Arch Virol. 2021 Jul;166(7):1893-1901. doi: 10.1007/s00705-021-05078-y. Epub 2021 Apr 26.
Koala retrovirus (KoRV), a major pathogen of koalas, exists in both endogenous (KoRV-A) and exogenous forms (KoRV-B to J). However, the impact of infection with multiple subtypes is not well understood. Accordingly, in this study, we surveyed a representative sample from a Japanese zoo population to determine the infection status for three KoRV subtypes (KoRV-A, B, and C) and to investigate the proviral and RNA load profiles in animals with single- and multiple-subtype infections, using peripheral blood mononuclear cells (PBMCs) and plasma. Six koalas were evaluated in the study; all were infected with KoRV-A, and two koalas were coinfected with non-A subtypes (KoRV-B and/or KoRV-C). The highest KoRV total RNA and viral loads in PBMCs and plasma were found in a koala infected with multiple subtypes (KoRV-A, -B and -C). The other koala infected with multiple subtypes (KoRV-A and B) showed the highest proviral PBMC load but the lowest RNA copy number in PBMC and plasma. PBMCs from this animal were cultured for further investigation, and KoRV RNA was detected in the cells and culture supernatant after 7 and/or 14 days. The koalas harboring multiple subtypes had a higher white blood cell count than those harboring only KoRV-A and were judged to be leukemic, and they subsequently died due to lymphoma. Accordingly, we conclude that coinfection with multiple KoRV subtypes may be linked to more-severe disease. In a sequence alignment, the detected KoRV-A env gene showed 100% sequence identity to the reference gene, whereas the KoRV-B and -C env genes varied from their reference sequences.
40Coinfection with koala retrovirus subtypes A and B and its impact on captive koalas in Japanese zoos.PubMed
Md Abul Hashem, Mohammad Enamul Hoque Kayesh, Osamu Yamato, et al.
Arch Virol. 2019 Nov;164(11):2735-2745. doi: 10.1007/s00705-019-04392-w. Epub 2019 Sep 5.
Koala retrovirus (KoRV) is unique among endogenous retroviruses because its endogenization is still active. Two major KoRV subtypes, KoRV-A and B, have been described, and KoRV-B is associated with disease and poses a health threat to koalas. Here, we investigated the co-prevalence of KoRV-A and KoRV-B, detected by type-specific PCR and sequencing, and their impact on the health of koalas in three Japanese zoos. We also investigated KoRV proviral loads and found varying amounts of genomic DNA (gDNA) in peripheral blood mononuclear cells (PBMCs). We found that 100% of the koalas examined were infected with KoRV-A and 60% (12/20) were coinfected with KoRV-B. The KoRV-A sequence was highly conserved, whereas the KoRV-B sequence varied among individuals. Interestingly, we observed possible vertical transmission of KoRV-B in one offspring in which the KoRV-B sequence was similar to that of the father but not the mother. Moreover, we characterized the KoRV growth patterns in concanavalin-A-stimulated PBMCs isolated from KoRV-B-coinfected or KoRV-B-uninfected koalas. We quantified the KoRV provirus in gDNA and the KoRV RNA copy numbers in cells and culture supernatants by real-time PCR at days 4, 7, and 14 post-seeding. As the study population is housed in captivity, a longitudinal study of these koalas may provide an opportunity to study the transmission mode of KoRV-B. In addition, we characterized KoRV isolates by infecting tupaia cells. The results suggested that tupaia may be used as an infection model for KoRV. Thus, this study may enhance our understanding of KoRV-B coinfection and transmission in the captive koalas.
41Phylogenetic Diversity of Koala Retrovirus within a Wild Koala Population.PubMed
K J Chappell, J C Brealey, A A Amarilla, et al.
J Virol. 2017 Jan 18;91(3). doi: 10.1128/JVI.01820-16. Print 2017 Feb 1.
UNLABELLED: Koala populations are in serious decline across many areas of mainland Australia, with infectious disease a contributing factor. Koala retrovirus (KoRV) is a gammaretrovirus present in most wild koala populations and captive colonies. Five subtypes of KoRV (A to E) have been identified based on amino acid sequence divergence in a hypervariable region of the receptor binding domain of the envelope protein. However, analysis of viral genetic diversity has been conducted primarily on KoRV in captive koalas housed in zoos in Japan, the United States, and Germany. Wild koalas within Australia have not been comparably assessed. Here we report a detailed analysis of KoRV genetic diversity in samples collected from 18 wild koalas from southeast Queensland. By employing deep sequencing we identified 108 novel KoRV envelope sequences and determined their phylogenetic diversity. Genetic diversity in KoRV was abundant and fell into three major groups; two comprised the previously identified subtypes A and B, while the third contained the remaining hypervariable region subtypes (C, D, and E) as well as four hypervariable region subtypes that we newly define here (F, G, H, and I). In addition to the ubiquitous presence of KoRV-A, which may represent an exclusively endogenous variant, subtypes B, D, and F were found to be at high prevalence, while subtypes G, H, and I were present in a smaller number of animals. IMPORTANCE: Koala retrovirus (KoRV) is thought to be a significant contributor to koala disease and population decline across mainland Australia. This study is the first to determine KoRV subtype prevalence among a wild koala population, and it significantly expands the total number of KoRV sequences available, providing a more precise picture of genetic diversity. This understanding of KoRV subtype prevalence and genetic diversity will be important for conservation efforts attempting to limit the spread of KoRV. Furthermore, KoRV is one of the only retroviruses shown to exist in both endogenous (transmitted vertically to offspring in the germ line DNA) and exogenous (horizontally transmitted between infected individuals) forms, a division of fundamental evolutionary importance.
42Diversity and transmission of koala retrovirus: a case study in three captive koala populations.PubMed
Briony A Joyce, Michaela D J Blyton, Stephen D Johnston, et al.
Sci Rep. 2022 Sep 22;12(1):15787. doi: 10.1038/s41598-022-18939-6.
Koala retrovirus is a recently endogenized retrovirus associated with the onset of neoplasia and infectious disease in koalas. There are currently twelve described KoRV subtypes (KoRV-A to I, K-M), most of which were identified through recently implemented deep sequencing methods which reveal an animals' overall KoRV profile. This approach has primarily been carried out on wild koala populations around Australia, with few investigations into the whole-population KoRV profile of captive koala colonies to date. This study conducted deep sequencing on 64 captive koalas of known pedigree, housed in three institutions from New South Wales and South-East Queensland, to provide a detailed analysis of KoRV genetic diversity and transmission. The final dataset included 93 unique KoRV sequences and the first detection of KoRV-E within Australian koala populations. Our analysis suggests that exogenous transmission of KoRV-A, B, D, I and K primarily occurs between dam and joey. Detection of KoRV-D in a neonate sample raises the possibility of this transmission occurring in utero. Overall, the prevalence and abundance of KoRV subtypes was found to vary considerably between captive populations, likely due to their different histories of animal acquisition. Together these findings highlight the importance of KoRV profiling for captive koalas, in particular females, who play a primary role in KoRV exogenous transmission.
43Adaptive evolution of koala retrovirus transcription silencing and what it means for conservation.PubMed
Keith J Chappell, Michaela B J Blyton, Zhiping Weng, et al.
Clin Transl Med. 2025 Jul;15(7):e70343. doi: 10.1002/ctm2.70343.
Koala populations in Australia face a barrage of threats, chiefly, habitat degradation and the effects of climate change including drought and bushfire. Further, high rates of chlamydiosis, linked to koala retrovirus (KoRV) viral load, is a major contributing factor to northern population decline. However, recent work by Yu et al., (Cell, 2024) has provided a glimmer of hope: some koalas have evolved 'adaptive genome immunity', which is able to actively suppress endogenous KoRV transcription. A single KoRV-A provirus insertion within MAP4K4 gene's 3' UTR is shown to be the trigger for production of sense and anti-sense piRNAs, and that MAP4K4 KoRV integration is linked to both a 20% reduction in proviral genome integrations and 10-fold reduction of KoRV transcription within male germline tissue. Here we discuss how this finding offers the potential to reduce koala disease burden and can be incorporated into conservation management to help save this iconic species.
44Koala cathelicidin PhciCath5 has antimicrobial activity, including against Chlamydia pecorum.PubMed
Emma Peel, Yuanyuan Cheng, Julianne T Djordjevic, et al.
PLoS One. 2021 Apr 14;16(4):e0249658. doi: 10.1371/journal.pone.0249658. eCollection 2021.
Devastating fires in Australia over 2019-20 decimated native fauna and flora, including koalas. The resulting population bottleneck, combined with significant loss of habitat, increases the vulnerability of remaining koala populations to threats which include disease. Chlamydia is one disease which causes significant morbidity and mortality in koalas. The predominant pathogenic species, Chlamydia pecorum, causes severe ocular, urogenital and reproductive tract disease. In marsupials, including the koala, gene expansions of an antimicrobial peptide family known as cathelicidins have enabled protection of immunologically naïve pouch young during early development. We propose that koala cathelicidins are active against Chlamydia and other bacteria and fungi. Here we describe ten koala cathelicidins, five of which contained full length coding sequences that were widely expressed in tissues throughout the body. Focusing on these five, we investigate their antimicrobial activity against two koala C. pecorum isolates from distinct serovars; MarsBar and IPTaLE, as well as other bacteria and fungi. One cathelicidin, PhciCath5, inactivated C. pecorum IPTaLE and MarsBar elementary bodies and significantly reduced the number of inclusions compared to the control (p<0.0001). Despite evidence of cathelicidin expression within tissues known to be infected by Chlamydia, natural PhciCath5 concentrations may be inadequate in vivo to prevent or control C. pecorum infections in koalas. PhciCath5 also displayed antimicrobial activity against fungi and Gram negative and positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Electrostatic interactions likely drive PhciCath5 adherence to the pathogen cell membrane, followed by membrane permeabilisation leading to cell death. Activity against E. coli was reduced in the presence of 10% serum and 20% whole blood. Future modification of the PhciCath5 peptide to enhance activity, including in the presence of serum/blood, may provide a novel solution to Chlamydia infection in koalas and other species.
45Toll-Like Receptor Expression Profiles in Koala () Peripheral Blood Mononuclear Cells Infected with Multiple KoRV Subtypes.PubMed
Mohammad Enamul Hoque Kayesh, Md Abul Hashem, Kyoko Tsukiyama-Kohara
Animals (Basel). 2021 Apr 1;11(4):983. doi: 10.3390/ani11040983.
Toll-like receptors (TLRs), evolutionarily conserved pattern recognition receptors, play an important role in innate immunity by recognizing microbial pathogen-associated molecular patterns. Koala retrovirus (KoRV), a major koala pathogen, exists in both endogenous (KoRV-A) and exogenous forms (KoRV-B to J). However, the expression profile of TLRs in koalas infected with KoRV-A and other subtypes is yet to characterize. Here, we investigated TLR expression profiles in koalas with a range of subtype infection profiles (KoRV-A only vs. KoRV-A with KoRV-B and/or -C). To this end, we cloned partial sequences for TLRs (TLR2-10 and TLR13), developed real-time PCR assays, and determined TLRs mRNA expression patterns in koala PBMCs and/or tissues. All the reported TLRs for koala were expressed in PBMCs, and variations in TLR expression were observed in koalas infected with exogenous subtypes (KoRV-B and KoRV-C) compared to the endogenous subtype (KoRV-A) only, which indicates the implications of TLRs in KoRV infection. TLRs were also found to be differentially expressed in koala tissues. This is the first report of TLR expression profiles in koala, which provides insights into koala's immune response to KoRV infection that could be utilized for the future exploitation of TLR modulators in the maintenance of koala health.
46Molecular Insights into Innate Immune Response in Captive Koala Peripheral Blood Mononuclear Cells Co-Infected with Multiple Koala Retrovirus Subtypes.PubMed
Mohammad Enamul Hoque Kayesh, Md Abul Hashem, Fumie Maetani, et al.
Pathogens. 2022 Aug 14;11(8):911. doi: 10.3390/pathogens11080911.
Koala retrovirus (KoRV) exists in both endogenous and exogenous forms and has appeared as a major threat to koala health and conservation. Currently, there are twelve identified KoRV subtypes: an endogenous subtype (KoRV-A) and eleven exogenous subtypes (KoRV-B to -I, KoRV-K, -L, and -M). However, information about subtype-related immune responses in koalas against multiple KoRV infections is limited. In this study, we investigated KoRV-subtype (A, B, C, D, and F)-related immunophenotypic changes, including CD4, CD8b, IFN-γ, IL-6, and IL-10 mRNA expression, in peripheral blood mononuclear cells (PBMCs) obtained from captive koalas (n = 37) infected with multiple KoRV subtypes (KoRV-A to F) reared in seven Japanese zoos. Based on KoRV subtype infection profiles, no significant difference in CD4 and CD8b mRNA expression was observed in the study populations. Based on the different KoRV subtype infections, we found that the IFN-γ mRNA expression in koala PMBCs differs insignificantly ( = 0.0534). In addition, IL-6 and IL-10 mRNA expression also did not vary significantly in koala PBMCs based on KoRV subtype differences. We also investigated the Toll-like receptors (TLRs) response, including TLR2-10, and TLR13 mRNA in koala PBMCs infected with multiple KoRV subtypes. Significant differential expression of TLR5, 7, 9, 10, and 13 mRNA was observed in the PBMCs from koalas infected with different KoRV subtypes. Therefore, based on the findings of this study, it is assumed that co-infection of multiple KoRV subtypes might modify the host innate immune response, including IFN-γ and TLRs responses. However, to have a more clear understanding regarding the effect of multiple KoRV subtypes on host cytokines and TLR response and pathogenesis, further large-scale studies including the koalas negative for KoRV and koalas infected with other KoRV subtypes (KoRV-A to -I, KoRV-K, -L and -M) are required.
47Koalas vaccinated against Koala retrovirus respond by producing increased levels of interferon-gamma.PubMed
Olusola Olagoke, Bonnie L Quigley, Peter Timms
Virol J. 2020 Oct 31;17(1):168. doi: 10.1186/s12985-020-01442-7.
Koala retrovirus (KoRV) is believed to be in an active state of endogenization into the koala genome. KoRV is present as both an endogenous and exogenous infection in all koalas in northern Australia. KoRV has been linked to koala pathologies including neoplasia and increased susceptibility to Chlamydia. A KoRV vaccine recently trialled in 10 northern koalas improved antibody response and reduced viral load. This communication reports the expression of key immune genes underlining the innate and adaptive immune response to vaccination in these northern koalas. The results showed that prior to vaccination, IL-8 was expressed at the highest levels, with at least 200-fold greater expression compared to other cytokines, while CD8 mRNA expression was significantly higher than CD4 mRNA expression level. Interferon-γ was up-regulated at both 4- and 8-weeks post-vaccination while IL-8 was down-regulated at 8-weeks post-vaccination.
48CD4, CD8b, and Cytokines Expression Profiles in Peripheral Blood Mononuclear Cells Infected with Different Subtypes of KoRV from Koalas () in a Japanese Zoo.PubMed
Mohammad Enamul Hoque Kayesh, Md Abul Hashem, Fumie Maetani, et al.
Viruses. 2020 Dec 9;12(12):1415. doi: 10.3390/v12121415.
Koala retrovirus (KoRV) poses a major threat to koala health and conservation, and currently has 10 identified subtypes: an endogenous subtype (KoRV-A) and nine exogenous subtypes (KoRV-B to KoRV-J). However, subtype-related variations in koala immune response to KoRV are uncharacterized. In this study, we investigated KoRV-related immunophenotypic changes in a captive koala population (Hirakawa zoo, Japan) with a range of subtype infection profiles (KoRV-A only vs. KoRV-A with KoRV-B and/or -C), based on qPCR measurements of CD4, CD8b, IL-6, IL-10 and IL-17A mRNA expression in unstimulated and concanavalin (Con)-A-stimulated peripheral blood mononuclear cells (PBMCs). Although CD4, CD8b, and IL-17A expression did not differ between KoRV subtype infection profiles, IL-6 expression was higher in koalas with exogenous infections (both KoRV-B and KoRV-C) than those with the endogenous subtype only. IL-10 expression did not significantly differ between subtype infection profiles but did show a marked increase-accompanying decreased CD4:CD8b ratio-in a koala with lymphoma and co-infected with KoRV-A and -B, thus suggesting immunosuppression. Taken together, the findings of this study provide insights into koala immune response to multiple KoRV subtypes, which can be exploited for the development of prophylactic and therapeutic interventions for this iconic marsupial species.
49Koala immunogenetics and chlamydial strain type are more directly involved in chlamydial disease progression in koalas from two south east Queensland koala populations than koala retrovirus subtypes.PubMed
Amy Robbins, Jonathan Hanger, Martina Jelocnik, et al.
Sci Rep. 2020 Sep 14;10(1):15013. doi: 10.1038/s41598-020-72050-2.
Chlamydial disease control is increasingly utilised as a management tool to stabilise declining koala populations, and yet we have a limited understanding of the factors that contribute to disease progression. To examine the impact of host and pathogen genetics, we selected two geographically separated south east Queensland koala populations, differentially affected by chlamydial disease, and analysed koala major histocompatibility complex (MHC) genes, circulating strains of Chlamydia pecorum and koala retrovirus (KoRV) subtypes in longitudinally sampled, well-defined clinical groups. We found that koala immunogenetics and chlamydial genotypes differed between the populations. Disease progression was associated with specific MHC alleles, and we identified two putative susceptibility (DCb 03, DBb 04) and protective (DAb 10, UC 01:01) variants. Chlamydial genotypes belonging to both Multi-Locus Sequence Typing sequence type (ST) 69 and ompA genotype F were associated with disease progression, whereas ST 281 was associated with the absence of disease. We also detected different ompA genotypes, but not different STs, when long-term infections were monitored over time. By comparison, KoRV profiles were not significantly associated with disease progression. These findings suggest that chlamydial genotypes vary in pathogenicity and that koala immunogenetics and chlamydial strains are more directly involved in disease progression than KoRV subtypes.
50Identification of MHCII variants associated with chlamydial disease in the koala (Phascolarctos cinereus).PubMed
Quintin Lau, Joanna E Griffith, Damien P Higgins
PeerJ. 2014 Jun 19;2:e443. doi: 10.7717/peerj.443. eCollection 2014.
Chlamydiosis, the most common infectious disease in koalas, can cause chronic urogenital tract fibrosis and infertility. High titres of serum immunoglobulin G against 10 kDa and 60 kDa chlamydial heat-shock proteins (c-hsp10 and c-hsp60) are associated with fibrous occlusion of the koala uterus and uterine tube. Murine and human studies have identified associations between specific major histocompatibility complex class II (MHCII) alleles or genotypes, and higher c-hsp 60 antibody levels or chlamydia-associated disease and infertility. In this study, we characterised partial MHCII DAB and DBB genes in female koalas (n = 94) from a single geographic population, and investigated associations among antibody responses to c-hsp60 quantified by ELISA, susceptibility to chlamydial infection, or age. The identification of three candidate MHCII variants provides additional support for the functional role of MHCII in the koala, and will inform more focused future studies. This is the first study to investigate an association between MHC genes with chlamydial pathogenesis in a non-model, free-ranging species.
51Spatial variation in toll-like receptor diversity in koala populations across their geographic distribution.PubMed
Jian Cui, Kimberley C Batley, Luke W Silver, et al.
Immunogenetics. 2024 Nov 30;77(1):5. doi: 10.1007/s00251-024-01365-5.
The koala (Phascolarctos cinereus) is an iconic Australian species that is listed as endangered in the northern parts of its range due to loss of habitat, disease, and road deaths. Diseases contribute significantly to the decline of koala populations, primarily Chlamydia and koala retrovirus. The distribution of these diseases across the species' range, however, is not even. Toll-like receptors (TLRs) play a crucial role in innate immunity by recognising and responding to various pathogens. Variations in TLR genes can influence an individual's susceptibility or resistance to infectious diseases. The aim of this study was to identify koala TLR diversity across the east coast of Australia using 413 re-sequenced genomes at 30 × coverage. We identified 45 single-nucleotide polymorphisms (SNP) leading to 51 alleles within ten TLR genes. Our results show that the diversity of TLR genes in the koala forms four distinct genetic groups, which are consistent with the diversity of the koala major histocompatibility complex (MHC), another key immune gene family. The bioinformatics approach presented here has broad applicability to other threatened species with existing genomic resources.
52A preliminary study of gene expression changes in Koalas Infected with Koala Retrovirus (KoRV) and identification of potential biomarkers for KoRV pathogenesis.PubMed
Lipi Akter, Md Abul Hashem, Mohammad Enamul Hoque Kayesh, et al.
BMC Vet Res. 2024 Oct 30;20(1):496. doi: 10.1186/s12917-024-04357-5.
BACKGROUND: Koala retrovirus (KoRV), a major pathogen of koalas, exists in both endogenous (KoRV-A) and exogenous forms (KoRV-A to I and K to M) and causes multiple disease phenotypes, including carcinomas and immunosuppression. However, the direct association between the different KoRV subtypes and carcinogenesis remains unknown. Differentially expressed gene (DEG) analysis of peripheral blood mononuclear cells (PBMCs) of koalas carrying both endogenous (KoRV-A) and exogenous (KoRV-A, B, and C) subtypes was performed using a high-throughput RNA-seq approach. PBMCs were obtained from three healthy koalas: one infected with endogenous (KoRV-A; Group I) and two infected with exogenous (KoRV-B and/or KoRV-C; Group II) subtypes. Additionally, spleen samples (n = 6) from six KoRV-infected deceased koalas (K1- K6) and blood samples (n = 1) from a live koala (K7) were collected and examined to validate the findings. RESULTS: All koalas were positive for the endogenous KoRV-A subtype, and eight koalas were positive for KoRV-B and/or KoRV-C. Transcription of KoRV gag, pol, and env genes was detected in all koalas. Upregulation of cytokine and immunosuppressive genes was observed in koalas infected with KoRV-B or KoRV-B and -C subtypes, compared to koalas infected with only KoRV-A. We found 550 DEG signatures with significant (absolute p < 0.05, and absolute log Fold Change (FC) > 1.5) dysregulation, out of which 77.6% and 22.4% DEGs were upregulated (logFC > 1.5) and downregulated (logFC < - 1.5), and downregulated (logFC < - 1), respectively. We identified 17 unique hub genes (82.3% upregulated and 17.7% down-regulated), with KIF23, CCNB2, POLR3F, and RSL24D1 detected as the potential hub genes modified with KoRV infection. Real-time RT-qPCR was performed on seven koalas to ascertain the expression levels of four potential hub genes, which were subsequently normalized to actin copies. Notably, all seven koalas exhibited distinct expression signatures for the hub genes, especially, KIF23 and CCNB2 show the highest expression in healthy koala PBMC, and POLR3F shows the highest expression in koala with lymphoma (K1). CONCLUSION: Thus, it can be concluded that multiple KoRV subtypes affect disease progression in koalas and that the predicted hub genes could be promising prognostic biomarkers for pathogenesis.
53Toll-Like Receptor and Cytokine Responses to Infection with Endogenous and Exogenous Koala Retrovirus, and Vaccination as a Control Strategy.PubMed
Mohammad Enamul Hoque Kayesh, Md Abul Hashem, Kyoko Tsukiyama-Kohara
Curr Issues Mol Biol. 2021 Apr 30;43(1):52-64. doi: 10.3390/cimb43010005.
Koala populations are currently declining and under threat from koala retrovirus (KoRV) infection both in the wild and in captivity. KoRV is assumed to cause immunosuppression and neoplastic diseases, favoring chlamydiosis in koalas. Currently, 10 KoRV subtypes have been identified, including an endogenous subtype (KoRV-A) and nine exogenous subtypes (KoRV-B to KoRV-J). The host's immune response acts as a safeguard against pathogens. Therefore, a proper understanding of the immune response mechanisms against infection is of great importance for the host's survival, as well as for the development of therapeutic and prophylactic interventions. A vaccine is an important protective as well as being a therapeutic tool against infectious disease, and several studies have shown promise for the development of an effective vaccine against KoRV. Moreover, CRISPR/Cas9-based genome editing has opened a new window for gene therapy, and it appears to be a potential therapeutic tool in many viral infections, which could also be investigated for the treatment of KoRV infection. Here, we discuss the recent advances made in the understanding of the immune response in KoRV infection, as well as the progress towards vaccine development against KoRV infection in koalas.
54Investigation of koala retrovirus in captive koalas with pneumonia and comparative analysis of subtype distribution.PubMed
Lipi Akter, Md Abul Hashem, Tofazzal Md Rakib, et al.
Arch Virol. 2023 Nov 27;168(12):298. doi: 10.1007/s00705-023-05928-x.
This study focused on the involvement of koala retrovirus (KoRV) in pneumonia in koalas. Three deceased pneumonic koalas from a Japanese zoo were examined in this study. Hematological and histopathological findings were assessed, and KoRV proviral DNA loads in the blood and tissues were compared with those of eight other KoRV-infected koalas from different zoos. Demographic data and routine blood profiles were collected, and blood and tissue samples were analyzed to rule out concurrent infections in pneumonic koalas. KoRV subtyping and measurement of the KoRV proviral DNA load were performed by polymerase chain reaction (PCR) using specific primers targeting the pol and env genes. The results showed that the koalas had histopathologically suppurative and fibrinous pneumonia. Chlamydiosis was not detected in any of the animals. PCR analysis revealed KoRV-A, -B, and -C infections in all koalas, except for animals K10-11, which lacked KoRV-B. Significant variations in the proviral DNA loads of these KoRV subtypes were observed in all tissues and disease groups. Most tissues showed reduced KoRV loads in koalas with pneumonia, except in the spleen, which had significantly higher loads of total KoRV (2.54 × 10/µg DNA) and KoRV-A (4.74 × 10/µg DNA), suggesting potential immunosuppression. This study revealed the intricate dynamics of KoRV in various tissues, indicating its potential role in koala pneumonia via immunosuppression and opportunistic infections. Analysis of the levels of KoRV proviral DNA in different tissues will shed light on viral replication and the resulting pathogenesis in future studies.
55Periodontal disease in free-ranging koalas (Phascolarctos cinereus) from the Mount Lofty Ranges, South Australia, and its association with koala retrovirus infection.PubMed
R G Butcher, L M Pettett, J Fabijan, et al.
Aust Vet J. 2020 May;98(5):200-206. doi: 10.1111/avj.12919. Epub 2020 Jan 23.
BACKGROUND: In northern Australian koala populations (Queensland and New South Wales), periodontal disease (gingivitis and periodontitis) is common while koala retrovirus subtype A is endogenous, with other subtypes transmitted exogenously. Koala retrovirus has been hypothesised to cause immune suppression and may predispose koalas to diseases caused by concurrent infections. In southern Australia populations (Victoria and South Australia) periodontal disease has not been investigated, and koala retrovirus is presumably exogenously transmitted. This study described oral health in South Australian koalas and investigated if an association between periodontal disease and koala retrovirus exists. METHODS: Oral health was examined for wild-caught koalas from the Mount Lofty Ranges (n = 75). Koala retrovirus provirus was detected in whole blood using nested PCR and proviral load determined with qPCR. Periodontal disease severity was recorded and used to calculate the Final Oral Health Index (0-normal, 24-severe).Results Periodontal disease was observed in 84% (63/75) of koalas; 77% had gingivitis (58/75) and 65% (49/75) had periodontitis. The average Final Oral Health Index was 5.47 (s.d 3.13). Most cases of periodontal disease were associated with the incisors. Koala retrovirus-infected koalas were more likely to present with periodontitis (p = 0.042) and the Final Oral Health Index was negatively correlated with proviral load (ρ = -0.353, p = 0.017). CONCLUSION: South Australian koalas had a high prevalence of gingivitis and periodontitis. Periodontal disease was more prevalent in the incisors. Exogenous koala retrovirus infection may also facilitate the development of periodontitis by modulation of the immune response to concurrent oral bacterial infections.
56Demographic, environmental and genetic determinants of mating success in captive koalas (Phascolarctos cinereus).PubMed
Kendra C Abts, Jamie A Ivy, J Andrew DeWoody
Zoo Biol. 2018 Nov;37(6):416-433. doi: 10.1002/zoo.21457. Epub 2018 Nov 29.
Many factors have been shown to affect mating behavior. For instance, genes of the major histocompatibility complex (MHC) are known to influence mate choice in a wide variety of vertebrate species. The genetic management of captive populations can be confounded if intrinsic mate choice reduces or eliminates reproductive success between carefully chosen breeding pairs. For example, the San Diego Zoo koala colony only has a 45% copulation rate for matched individuals. Herein, we investigated determinants of koala mating success using breeding records (1984-2010) and genotypes for 52 individuals at four MHC markers. We quantified MHC diversity according to functional amino acids, heterozygosity, and the probability of producing a heterozygous offspring. We then used categorical analysis and logistic regression to investigate both copulation and parturition success. In addition, we also examined age, day length, and average pairwise kinship. Our post-hoc power analysis indicates that at a power level of 1-β = 0.8, we should have been able to detect strong MHC preferences. However, we did not find a significant MHC effect on either copulation or parturition success with one exception: pairs with lower or no production of a joey had significantly lower MHC functional amino acid diversity in the categorical analysis. In contrast, day length and dam age (or age difference of the pair) consistently had an effect on mating success. These findings may be leveraged to improve the success of attempted pairs, conserve resources, and facilitate genetic management.
57Disentangling the mechanisms of mate choice in a captive koala population.PubMed
Parice A Brandies, Catherine E Grueber, Jamie A Ivy, et al.
PeerJ. 2018 Aug 21;6:e5438. doi: 10.7717/peerj.5438. eCollection 2018.
Successful captive breeding programs are crucial to the long-term survival of many threatened species. However, pair incompatibility (breeding failure) limits sustainability of many captive populations. Understanding whether the drivers of this incompatibility are behavioral, genetic, or a combination of both, is crucial to improving breeding programs. We used 28 years of pairing data from the San Diego Zoo koala colony, plus genetic analyses using both major histocompatibility complex (MHC)-linked and non-MHC-linked microsatellite markers, to show that both genetic and non-genetic factors can influence mating success. Male age was reconfirmed to be a contributing factor to the likelihood of a koala pair copulating. This trend could also be related to a pair's age difference, which was highly correlated with male age in our dataset. Familiarity was reconfirmed to increase the probability of a successful copulation. Our data provided evidence that females select mates based on MHC and genome-wide similarity. Male heterozygosity at MHC class II loci was associated with both pre- and post-copulatory female choice. Genome-wide similarity, and similarity at the MHC class II DAB locus, were also associated with female choice at the post-copulatory level. Finally, certain MHC-linked alleles were associated with either increased or decreased mating success. We predict that utilizing a variety of behavioral and MHC-dependent mate choice mechanisms improves female fitness through increased reproductive success. This study highlights the complexity of mate choice mechanisms in a species, and the importance of ascertaining mate choice mechanisms to improve the success of captive breeding programs.
58Emerging arguments for reproductive technologies in wildlife and their implications for assisted reproduction and conservation of threatened marsupials.PubMed
Lachlan G Howell, Ryan R Witt
Theriogenology. 2023 Mar 1;198:19-29. doi: 10.1016/j.theriogenology.2022.12.008. Epub 2022 Dec 7.
Assisted reproductive technologies (ARTs) have significant potential to make a meaningful contribution to the conservation of threatened wildlife. This is true of Australia's iconic, and endangered koala (Phascolarctos cinereus). If developed, ARTs could offer a solution to manage genetic diversity and costs in breeding programs and may provide frozen repositories for either insurance or the practical production of genetically resilient koalas for release and on-ground recovery. Holding back the wider use of ARTs for koalas and other wildlife is a lack of funding to close the remaining knowledge gaps in the marsupial reproductive sciences and develop the reproductive tools needed. This lack of funding is arguably driven by a poor understanding of the potential contribution ARTs could make to threatened species management. We present a review of our cross-disciplinary and accessible strategy to draw much needed public attention and funding for the development of ARTs in wildlife, using emerging cost and genetic modelling arguments and the koala as a case study.
59Modelling Genetic Benefits and Financial Costs of Integrating Biobanking into the Captive Management of Koalas.PubMed
Lachlan G Howell, Stephen D Johnston, Justine K O'Brien, et al.
Animals (Basel). 2022 Apr 12;12(8):990. doi: 10.3390/ani12080990.
Zoo and wildlife hospital networks are set to become a vital component of Australia's contemporary efforts to conserve the iconic and imperiled koala (). Managed breeding programs held across zoo-based networks typically face high economic costs and can be at risk of adverse genetic effects typical of unavoidably small captive colonies. Emerging evidence suggests that biobanking and associated assisted reproductive technologies could address these economic and genetic challenges. We present a modelled scenario, supported by detailed costings, where these technologies are optimized and could be integrated into conservation breeding programs of koalas across the established zoo and wildlife hospital network. Genetic and economic modelling comparing closed captive koala populations suggest that supplementing them with cryopreserved founder sperm using artificial insemination or intracytoplasmic sperm injection could substantially reduce inbreeding, lower the required colony sizes of conservation breeding programs, and greatly reduce program costs. Ambitious genetic retention targets (maintaining 90%, 95% and 99% of source population heterozygosity for 100 years) could be possible within realistic cost frameworks, with output koalas suited for wild release. Integrating biobanking into the zoo and wildlife hospital network presents a cost-effective and financially feasible model for the uptake of these tools due to the technical and research expertise, captive koala colonies, and facilities that already exist across these networks.
60Effect of cooling and cryopreservation on sperm motility and morphology of several species of marsupial.PubMed
D A Taggart, C M Leigh, V R Steele, et al.
Reprod Fertil Dev. 1996;8(4):673-9. doi: 10.1071/rd9960673.
The effects of long-term cooling and freezing on sperm motility are described for six marsupial species: the fat-tailed dunnart, koala, brushtail possum, long-footed potoroo, northern brown bandicoot and ring-tailed possum. The effects of up to eight days of cooling at 4 degrees C on the motility of dunnart spermatozoa and the effect of cryopreservation on spermatozoa of the other species were determined. The cryoprotectant used was a Tris-citrate-fructose-egg yolk-glycerol diluent. The percentage and rating of sperm motility, and sperm structure, as determined by light microscopy, were investigated. Sperm motility in the fat-tailed dunnart was retained for up to six days when cooled to 4 degrees C, suggesting that sperm from this species have some degree of tolerance to cold shock. After this time, however, the percentage of motile spermatozoa and their motility rating declined. In all species except the fat-tailed dunnart, reinitiation of motility following cryopreservation occurred across a range of glycerol concentrations (4-17%). Cryoprotectant containing 6% and/or 8% glycerol resulted in little change of motility rating or of the percentage of live sperm after thawing, although there was some decline in the percentage of motile sperm. The unusual structural and motility characteristics of dunnart spermatozoa may account for the lack of success of sperm cryopreservation in this species.
61Antibiotics for the preservation of koala (Phascolarctos cinereus) semen.PubMed
S D Johnston, D O'Boyle, A J Frost, et al.
Aust Vet J. 1998 May;76(5):335-8. doi: 10.1111/j.1751-0813.1998.tb12362.x.
AIM: To determine the normal microbial flora of the koala ejaculate and prepuce in order to select appropriate antibiotics for addition into diluents designed for the preservation of semen. PROCEDURE: Bacteriological samples of the koala prepuce (n = 12) and ejaculate (n = 20) were submitted for microbial culture and sensitivity testing. Microbial flora of ejaculates collected by electroejaculation and artificial vagina were compared. The effects of varying concentrations of penicillin G and gentamicin on sperm motility and on the growth of bacteria in diluted semen stored at room temperature and 16 degrees C over a 24 h period were investigated. RESULTS: A range of bacteria was isolated from the koala prepuce and ejaculate. The predominant organisms in semen collected by electroejaculation and artificial vagina were Corynebacterium spp, none of which could be assigned to any recognised species. The addition of penicillin G and gentamicin to a PBS-based diluent at dose rates of 1000 to 2000 IU/mL and 100 to 200 micrograms/mL respectively, resulted in no adverse effect on sperm motility over a 24 h incubation period. Penicillin G (1000 IU/mL) and gentamicin (100 micrograms/mL) prevented growth of bacterial contaminants in diluted koala semen. CONCLUSION: By controlling the growth of bacteria in extended koala semen, penicillin G and gentamicin are likely to lengthen the period by which spermatozoa can be stored at 16 degrees C and reduce the possibility of disease transmission during artificial insemination procedures.
62The effect of chilled storage and cryopreservation on the sperm DNA fragmentation dynamics of a captive population of koalas.PubMed
Stephen D Johnston, Yeng Peng Zee, Carmen López-Fernández, et al.
J Androl. 2012 Sep-Oct;33(5):1007-15. doi: 10.2164/jandrol.111.015248. Epub 2012 Jan 26.
This experiment documented the incidence and variability of sperm characteristics found in freshly collected and ex vivo-manipulated semen samples from a population of disease-free captive koalas with a special emphasis on the dynamic aspects of DNA fragmentation. These changes were analyzed in light of the putative negative effect of iatrogenic damage after chilled storage and cryopreservation with respect to different semen extender compositions to maximize sperm longevity. Sperm DNA fragmentation (SDF) dynamics (SDF assessment after a varying period of time) was investigated with the sperm chromatin dispersion assay after either dilution in tris-citrate media and chilled preservation at 4°C for upward of 16 days or cryopreservation in either glycerol or dimethylacetamide (DMA) tris-citrate-based cryoprotectant media; corresponding data on progressive sperm motility, plasma membrane integrity, and the proportion of koala sperm with relaxed chromatin were also recorded. SDF analysis of the captive koala population revealed a low mean (± SEM) basal level of only 6.7% ± 0.9%. The percentage of progressive sperm motility, percentage of intact sperm plasma membranes, and the percentage of relaxed chromatin did not correlate significantly with that of basal SDF. Moreover, despite the absence of cysteine residues in marsupial protamines, koala spermatozoa showed remarkable stability in terms of their DNA integrity after the incubation of either fresh, chilled, or frozen-thawed semen samples; observations of progressive motility (P < .05) and plasma membrane integrity (P < .05) revealed that chilled koala spermatozoa declined after 4 days, whereas the incidence of relaxed chromatin increased after 8 days. Although koala SDF increased significantly (P < .05) with the period of chilled storage, these values remained less than 16% after 16 days storage and subsequent incubation at 35°C for a further 48 hours. Survivorship of prefreeze sperm DNA damage was not different when compared with sperm frozen in DMA or between sperm frozen in DMA or glycerol; however, spermatozoa frozen in glycerol showed a higher (P = .042) rate of DNA fragmentation than prefreeze spermatozoa. This result differed from that of observations of progressive motility, plasma membrane integrity, and relaxed chromatin, which were all adversely affected (P < .05) after cryopreservation in either glycerol or DMA; however, the postthaw characteristics of sperm cryopreserved in either glycerol or DMA were not different. After thawing, koala sperm chromatin tended to decondense; however, the incidence of sperm DNA fragmentation was not correlated with the incidence of sperm chromatin relaxation after glycerol (R = .2) or DMA (R = -.04) cryopreservation.
63Protamine composition of koala and wombat spermatozoa provides new insights into DNA stability following cryopreservation.PubMed
S D Johnston, C López-Fernández, F Arroyo, et al.
Reprod Fertil Dev. 2019 Sep;31(10):1558-1566. doi: 10.1071/RD18512.
To investigate differences in the post-thaw DNA stability of koala and wombat spermatozoa, protamine amino acid sequences were compared and it was found that there were three more arginine residues for the wombat. Koala and wombat spermatozoa, cryopreserved using identical protocols, were examined for changes in sperm DNA fragmentation (SDF) dynamics over 24h of post-thaw incubation. Following validation of a wombat sperm chromatin dispersion test, wombat DNA showed a rate of SDF that was 6-fold higher than for koala spermatozoa (P=0.038). Finally, we examined whether expected differences in chromatin compactness, associated with protamine sequence, had an effect on restriction site accessibility of sperm DNA. Thawed spermatozoa were exposed to Alu I and EcoR1 endonuclease restriction enzymes and the SDF dynamics were observed. Koala spermatozoa exposed to Alu I showed a greater rate of SDF (P=0.01), whereas wombat spermatozoa exposed to EcoR1 showed a greater rate of SDF (P=0.032). We conclude that restriction sites in these species are differentially present or exposed and potentially account for differences in SDF dynamics. Although differences in the arginine composition of protamine may explain relative differences in SDF following cryopreservation, they do not support the hypothesis that increased arginine composition increases DNA stability; rather, increased arginine composition in the wombat may reduce post-thaw chromatin swelling.
64Effects of cryopreservation on mitochondrial function and heterogeneity, lipid raft stability and phosphatidylserine translocation in koala (Phascolarctos cinereus) spermatozoa.PubMed
Yeng Peng Zee, William V Holt, Camryn D Allen, et al.
Reprod Fertil Dev. 2007;19(7):850-60. doi: 10.1071/rd07084.
Koala sperm mitochondria were examined by cryomicroscopy using the fluorescent probe JC-1, which distinguishes high (red) and low (green) mitochondrial membrane potential (MMP). At normal body temperature, approximately 70% of live and untreated spermatozoa exhibited high MMP whereas <3% of live untreated spermatozoa exhibited low potential. A third class, in which single midpieces contained mixed mitochondrial populations, was also detected. Heterogeneity was noted in the level of MMP between individual koalas, individual spermatozoa and even between mitochondrial gyres within single midpieces. MMP of the live sperm population was not significantly affected by glycerol but was suppressed by freezing and thawing treatments. After thawing, MMP declined significantly during rewarming, especially as the temperature increased from 5 to 35 degrees C. The distribution of the ganglioside GM1 was examined using fluorescent-labelled cholera toxin B. In fresh, untreated koala spermatozoa GM1 was detected on the head and midpiece, but not on the principal piece. No significant redistribution of GM1 was observed after chilling and cryotreatment. Phosphatidylserine translocation across the plasma membrane was examined using fluorescent-labelled annexin V. Few fresh spermatozoa exhibited phosphatidylserine translocation (approximately 1%); this was not increased by chilling or cryopreservation, thus implying that cryotreatment had little effect on plasma membrane lipid asymmetry.
65An investigation into the similarities and differences governing the cryopreservation success of koala (Phascolarctos cinereus: goldfuss) and common wombat (Vombatus ursinus: shaw) spermatozoa.PubMed
S D Johnston, C MacCallum, D Blyde, et al.
Cryobiology. 2006 Oct;53(2):218-28. doi: 10.1016/j.cryobiol.2006.06.001. Epub 2006 Aug 2.
The aim of this study was to determine the relative cryopreservation success of koala and wombat spermatozoa and to investigate reasons for their respective post-thaw survival by examining the sperm's response to a range of osmotic media and determining the presence and distribution of F-actin. An hypothesis was proposed that F-actin may be imparting a degree of structural inflexibility to the koala sperm plasma membrane; hence, exposure of spermatozoa to cytochalasin D (5 microM), a F-actin depolymerisation agent, should result in increased plasticisation of the membrane and greater tolerance of cell volume changes that typically occur during cryopreservation. In experiment 1, koala (n = 4) and wombat (n = 4) spermatozoa packaged in 0.25 mL straws were cryopreserved using two freezing rates (fast-3 cm above liquid N2 interface; slow-6 degrees C/min in a freezing chamber) and two glycerol concentrations (8 and 14% v/v) in a tris-citrate glucose buffer with 15% (v/v) egg yolk. Wombat spermatozoa showed better (P < 0.01) post-thaw survival (% motile, % intact plasma membranes, % decondensed sperm heads) than koala spermatozoa. When exposed to media of varying osmolality, koala spermatozoa were less tolerant (% intact plasma membrane) of hyper-osmotic conditions (920 and 1410 mOsmol/kg) than wombat spermatozoa. F-actin was localised using a monoclonal antibody but only found in the wombat sperm head. When koala and wombat spermatozoa were exposed to media of varying osmolality, cytochalasin D had no beneficial effect on sperm survival (% intact plasma membranes). This study has demonstrated that wombat spermatozoa are highly tolerant of cryopreservation when compared to koala sperm but that spermatozoa from both species show greatest post-thaw survival when frozen slowly in 14% glycerol. Koala sperm are also particularly susceptible to hyper-osmotic environments but lack of detectable F-actin in the koala spermatozoan suggests that poor cryopreservation success in this species is unlikely to be associated with F-actin induced plasma membrane inflexibility.
66The koala (Phascolarctos cinereus): a case study in the development of reproductive technology in a marsupial.PubMed
Stephen D Johnston, William V Holt
Adv Exp Med Biol. 2014;753:171-203. doi: 10.1007/978-1-4939-0820-2_9.
The successful development and application of an assisted breeding program in any animal relies primarily on a thorough understanding of the fundamental reproductive biology (anatomy, physiology and behaviour) of the species in question. Surely, the ultimate goal and greatest hallmark of such a program is the efficacious establishment of a series of reliable techniques that facilitate the reproductive and genetic management of fragmented populations, both in captivity and in the wild. Such an achievement is all the more challenging when the reproductive biology of that species is essentially rudimentary and without adequate reproductive models to compare to. Using the koala (Phascolarctos cinereus) as a case study, this chapter provides some personal insights into the evolution of a concept that began as a small undergraduate student project but that subsequently evolved into the first-ever successful artificial insemination of a marsupial. Apart from this historical perspective, we also provide a brief review of the current reproductive biology of the koala, discuss technical elements of current assisted breeding technology of this species, its potential application to the wombat, and the future role it might play in helping to conserve wild koala populations. There is little doubt that the unique reproductive biology and tractability of the koala has in this case been a benefit rather than a hindrance to the success of artificial breeding in this species.
67Using the Koala (Phascolarctos cinereus) as a Case Study to Illustrate the Development of Artificial Breeding Technology in Marsupials: an Update.PubMed
Stephen D Johnston, William V Holt
Adv Exp Med Biol. 2019;1200:327-362. doi: 10.1007/978-3-030-23633-5_12.
The successful development and application of an assisted breeding program in any animal relies primarily on a thorough understanding of the fundamental reproductive biology (anatomy, physiology and behaviour) of the species in question. Surely, the ultimate goal and greatest hallmark of such a program is the efficacious establishment of a series of reliable techniques that facilitate the reproductive and genetic management of fragmented populations, both in captivity and in the wild. Such an achievement is all that more challenging when knowledge of the reproductive biology of that species is essentially rudimentary and without adequate models to compare to. Using the koala (Phascolarctos cinereus) as a case study, this chapter provides insights into the development of a concept that began as small undergraduate student project but that subsequently evolved into the first-ever successful artificial insemination of a marsupial. Apart from this historical perspective, we shall also provide a brief review of the current reproductive biology of the koala, discuss technical elements of current assisted breeding technology of this species, its application to the closely related wombat, and the potential role it might play in helping to conserve wild koala populations in the form of a live koala genome bank. There is little doubt that the unique reproductive biology and tractability of the koala has been a benefit rather than a hindrance to the success of artificial breeding in this species.
68Artificial insemination in marsupials.PubMed
John C Rodger, Damien B B P Paris, Natasha A Czarny, et al.
Theriogenology. 2009 Jan 1;71(1):176-89. doi: 10.1016/j.theriogenology.2008.09.006. Epub 2008 Oct 23.
Assisted breeding technology (ART), including artificial insemination (AI), has the potential to advance the conservation and welfare of marsupials. Many of the challenges facing AI and ART for marsupials are shared with other wild species. However, the marsupial mode of reproduction and development also poses unique challenges and opportunities. For the vast majority of marsupials, there is a dearth of knowledge regarding basic reproductive biology to guide an AI strategy. For threatened or endangered species, only the most basic reproductive information is available in most cases, if at all. Artificial insemination has been used to produce viable young in two marsupial species, the koala and tammar wallaby. However, in these species the timing of ovulation can be predicted with considerably more confidence than in any other marsupial. In a limited number of other marsupials, such precise timing of ovulation has only been achieved using hormonal treatment leading to conception but not live young. A unique marsupial ART strategy which has been shown to have promise is cross-fostering; the transfer of pouch young of a threatened species to the pouches of foster mothers of a common related species as a means to increase productivity. For the foreseeable future, except for a few highly iconic or well studied species, there is unlikely to be sufficient reproductive information on which to base AI. However, if more generic approaches can be developed; such as ICSI (to generate embryos) and female synchronization (to provide oocyte donors or embryo recipients), then the prospects for broader application of AI/ART to marsupials are promising.
69Successful artificial insemination in the koala (Phascolarctos cinereus) using extended and extended-chilled semen collected by electroejaculation.PubMed
Camryn D Allen, Michelle Burridge, Sarah Mulhall, et al.
Biol Reprod. 2008 Apr;78(4):661-6. doi: 10.1095/biolreprod.107.064824. Epub 2007 Dec 19.
Artificial insemination in the koala using chilled, electroejaculated semen provides for a marked improvement in the reproductive and genetic management of captive koala colonies in Australia and internationally, and makes available the option of using semen collected from wild populations to expand restricted gene pools. Dilution of koala semen for artificial insemination is complicated because koalas are induced ovulators, and it is thought that ovulating factors are present in the semen, so that semen extension for preservation purposes might be anticipated to result in a failure to induce ovulation. The first two experiments of this study were designed to determine whether artificial insemination using undiluted, extended, and extended-chilled semen collected by electroejaculation was capable of inducing a luteal phase and/or the production of pouch young. In Experiment 1, 1 ml undiluted electroejaculated semen, 2 ml diluted (1:1) semen, and 1 ml diluted (1:1) semen resulted in seven of nine, six of nine, and six of nine koalas showing a luteal phase, respectively; four pouch young were produced in each treatment. A second artificial insemination experiment was conducted in which 2 ml diluted (1:1) semen was administered in three groups of nine koalas. The first group received semen that had been collected and diluted immediately without chilling, the second group was deposited with semen stored chilled for 24 h, and the final group received semen that had been chilled for 72 h. In the first group, five females had a luteal phase, but none became pregnant. In group 2, two of the five females that had a luteal phase gave birth, whereas in group 3, four of the six females that had a luteal phase produced pouch young. In addition, experiment 3 was conducted to determine whether it was possible to produce pouch young by naturally mating koalas that were in the latter stages of their behavioral estrus; this information is important to the logistics of transporting koala semen for artificial insemination by establishing the maximum time frame in which females might be expected to shed a fertile oocyte. Of the 12 females mated on Day 8 of estrus, 6 gave birth, whereas only 3 of the 10 females naturally mated on Day 10 of estrus produced pouch young. The majority of females (21 of 22) in experiment 3 showed evidence of a luteal phase. Together, these experiments have shown that it is possible to use undiluted, extended, or extended-chilled semen to produce koala offspring up to Day 8 of estrus at conception rates similar to those achieved following natural mating. These findings represent a significant advancement in the use of reproductive technology in marsupials and provide the basis for the shipment of koala semen over long distances. The pouch young produced in this study represent the first marsupials born following artificial insemination of extended-chilled semen and bring the total number of koalas produced by artificial insemination to 31.
70Seasonal reproduction in wild and captive male koala (Phascolarctos cinereus) populations in south-east Queensland.PubMed
Camryn D Allen, Deidré L de Villiers, Brett D Manning, et al.
Reprod Fertil Dev. 2010;22(4):695-709. doi: 10.1071/RD09113.
The effects of breeding season (late spring to early autumn) on south-east Queensland male koala fertility were examined to improve the efficacy of the AI procedure and to determine the practicality of using free-range animals as semen donors for a genome resource bank. Seasonal changes in male koala reproductive function were assessed in a wild free-range population (n = 14; obtained every 6 weeks from January to November 2005), a necropsied healthy wild population (n = 84; obtained monthly from September 2004 to August 2005) and a captive population (n = 7; obtained monthly from October 2005 to October 2006). Reproductive parameters investigated included bodyweight, coat score, sternal gland area and activity, testosterone secretion, reproductive anatomy volume and semen quality (before and after cryopreservation). Collectively, these findings show that reproduction in male koalas from south-east Queensland changes seasonally and that winter appears to be the optimal season in which to collect semen samples by electroejaculation. While it was possible to repeatedly collect semen from free-range koalas for future genetic management via potential storage in a genome resource bank, the survival of these spermatozoa after cryopreservation was poor and will require further improvement.
71Characterization of the juvenile koala gut microbiome across wild populations.PubMed
Michaela D J Blyton, Rochelle M Soo, Philip Hugenholtz, et al.
Environ Microbiol. 2022 Sep;24(9):4209-4219. doi: 10.1111/1462-2920.15884. Epub 2022 Jan 12.
In this study we compared the faecal microbiomes of wild joey koalas (Phascolarctos cinereus) to those of adults, including their mothers, to establish whether gut microbiome maturation and inheritance in the wild is comparable to that seen in captivity. Our findings suggest that joey koala microbiomes slowly shift towards an adult assemblage between 6 and 12 months of age, as the microbiomes of 9-month-old joeys were more similar to those of adults than those of 7-month-olds, but still distinct. At the phylum level, differences between joeys and adults were broadly consistent with those in captivity, with Firmicutes increasing in relative abundance over the joeys' development and Proteobacteria decreasing. Of the fibre-degrading genes that increased in abundance over the development of captive joeys, those involved in hemicellulose and cellulose degradation, but not pectin degradation, were also generally found in higher abundance in adult wild koalas compared to 7-month-olds. Greater maternal inheritance of the faecal microbiome was seen in wild than in captive koalas, presumably due to the more solitary nature of wild koalas. This strong maternal inheritance of the gut microbiome could contribute to the development of localized differences in microbiome composition, population health and diet through spatial clustering of relatives.
72We and herbivores eat endophytes.PubMed
Esperanza Martínez-Romero, José Luis Aguirre-Noyola, Rafael Bustamante-Brito, et al.
Microb Biotechnol. 2021 Jul;14(4):1282-1299. doi: 10.1111/1751-7915.13688. Epub 2020 Dec 15.
Health depends on the diet and a vegetal diet promotes health by providing fibres, vitamins and diverse metabolites. Remarkably, plants may also provide microbes. Fungi and bacteria that reside inside plant tissues (endophytes) seem better protected to survive digestion; thus, we investigated the reported evidence on the endophytic origin of some members of the gut microbiota in animals such as panda, koala, rabbits and tortoises and several herbivore insects. Data examined here showed that some members of the herbivore gut microbiota are common plant microbes, which derived to become stable microbiota in some cases. Endophytes may contribute to plant fibre or antimetabolite degradation and synthesis of metabolites with the plethora of enzymatic activities that they display; some may have practical applications, for example, Lactobacillus plantarum found in the intestinal tract, plants and in fermented food is used as a probiotic that may defend animals against bacterial and viral infections as other endophytic-enteric bacteria do. Clostridium that is an endophyte and a gut bacterium has remarkable capabilities to degrade cellulose by having cellulosomes that may be considered the most efficient nanomachines. Cellulose degradation is a challenge in animal digestion and for biofuel production. Other endophytic-enteric bacteria may have cellulases, pectinases, xylanases, tannases, proteases, nitrogenases and other enzymatic capabilities that may be attractive for biotechnological developments, indeed many endophytes are used to promote plant growth. Here, a cycle of endophytic-enteric-soil-endophytic microbes is proposed which has relevance for health and comprises the fate of animal faeces as natural microbial inoculants for plants that constitute bacterial sources for animal guts.
73Regulated timber harvesting does not reduce koala density in north-east forests of New South Wales.PubMed
Brad Law, Leroy Gonsalves, Joanna Burgar, et al.
Sci Rep. 2022 Mar 10;12(1):3968. doi: 10.1038/s41598-022-08013-6.
The compatibility of forestry and koala conservation is a controversial issue. We used a BACIPS design to assess change in koala density after selective harvesting with regulations to protect environmental values. We also assessed additional sites heavily harvested 5-10 years previously, now dominated by young regeneration. We used replicate arrays of acoustic sensors and spatial count modelling of male bellowing to estimate male koala density over 3600 ha. Paired sites in nearby National Parks served as controls. Naïve occupancy was close to 100% before and after harvesting, indicating koalas were widespread across all arrays. Average density was higher than expected for forests in NSW, varying between arrays from 0.03-0.08 males ha. There was no significant effect of selective harvesting on density and little change evident between years. Density 5-10 years after previous heavy harvesting was equivalent to controls, with one harvested array supporting the second highest density in the study. Within arrays, density was similar between areas mapped as selectively harvested or excluded from harvest. Density was also high in young regeneration 5-10 years after heavy harvesting. We conclude that native forestry regulations provided sufficient habitat for koalas to maintain their density, both immediately after selective harvesting and 5-10 years after heavy harvesting.
74Passive acoustics and sound recognition provide new insights on status and resilience of an iconic endangered marsupial (koala Phascolarctos cinereus) to timber harvesting.PubMed
Bradley S Law, Traecey Brassil, Leroy Gonsalves, et al.
PLoS One. 2018 Oct 31;13(10):e0205075. doi: 10.1371/journal.pone.0205075. eCollection 2018.
Retention forestry aims to mitigate impacts of native forestry on biodiversity, but data are limited on its effectiveness for threatened species. We used acoustics to investigate the resilience of a folivorous marsupial, the koala Phascolarctos cinereus, to timber harvesting where a key mitigation practice is landscape exclusion of harvesting. We deployed acoustic recorders at 171 sites to record male bellows (~14,640 hours) for use in occupancy modelling and for comparisons of bellow rate (bellows night-1). Surveys targeted modelled medium-high quality habitat, with sites stratified by time since logging and logging intensity, including old growth as a reference. After scanning recordings with software to identify koala bellows, we found a high probability of detection (~0.45 per night), but this varied with minimum temperature and recorder type. Naïve occupancy was ~ 64% across a broad range of forests, which was at least five times more than expected based on previous surveys using alternative methods. After accounting for imperfect detection, probability of occupancy was influenced by elevation (-ve), cover of important browse trees (+ve), landscape NDVI (+ve) and extent of recent wildfire (-ve, but minor effect). Elevation was the most influential variable, though the relationship was non-linear and low occupancy was most common at tableland elevations (> 1000 m). Neither occupancy nor bellow rate were influenced by timber harvesting intensity, time since harvesting or local landscape extent of harvesting or old growth. Extrapolation of occupancy across modelled habitat indicates that the hinterland forests of north-east NSW support a widespread, though likely low density koala population that is considerably larger than previously estimated. Retention forestry has a significant role to play in mitigating harvesting impacts on biodiversity, including for forest specialists, but localised studies are needed to optimise prescriptions for koalas.
75A few large roads or many small ones? How to accommodate growth in vehicle numbers to minimise impacts on wildlife.PubMed
Jonathan R Rhodes, Daniel Lunney, John Callaghan, et al.
PLoS One. 2014 Mar 19;9(3):e91093. doi: 10.1371/journal.pone.0091093. eCollection 2014.
Roads and vehicular traffic are among the most pervasive of threats to biodiversity because they fragmenting habitat, increasing mortality and opening up new areas for the exploitation of natural resources. However, the number of vehicles on roads is increasing rapidly and this is likely to continue into the future, putting increased pressure on wildlife populations. Consequently, a major challenge is the planning of road networks to accommodate increased numbers of vehicles, while minimising impacts on wildlife. Nonetheless, we currently have few principles for guiding decisions on road network planning to reduce impacts on wildlife in real landscapes. We addressed this issue by developing an approach for quantifying the impact on wildlife mortality of two alternative mechanisms for accommodating growth in vehicle numbers: (1) increasing the number of roads, and (2) increasing traffic volumes on existing roads. We applied this approach to a koala (Phascolarctos cinereus) population in eastern Australia and quantified the relative impact of each strategy on mortality. We show that, in most cases, accommodating growth in traffic through increases in volumes on existing roads has a lower impact than building new roads. An exception is where the existing road network has very low road density, but very high traffic volumes on each road. These findings have important implications for how we design road networks to reduce their impacts on biodiversity.
76Landscape Homogeneity May Drive the Distribution of Koala Vehicle Collisions on a Major Highway in the Clarke-Connors Range in Central Queensland, Australia.PubMed
Rolf Schlagloth, Flavia Santamaria, Michael Harte, et al.
Animals (Basel). 2024 Oct 8;14(19):2902. doi: 10.3390/ani14192902.
After the loss and fragmentation of habitat, vehicle collisions are one of the main threats to the long-term survival of wild koalas. Koala road strike data were analysed for a section of the Peak Downs Highway between Nebo and Spencer's Gap, west of Mackay, Queensland, Australia. The analysis was carried out on 345 records (October 2014 to November 2023), and results suggested the spatial distribution of koala road strike followed a random pattern along this section of the highway, assuming a Poisson point pattern on a linear network. An analysis of the candidate predictors of koala vehicle collisions, including habitat and road variables, found that the amount of high-quality koala habitat (as defined by the local koalas' tree species preference) present and the driver visibility were the only significant predictors. The relative homogeneity of landuse and vegetation across this landscape may mean that koalas do not concentrate at specific crossing points. More research, including detailed habitat mapping, is needed into this population, which currently lacks government and conservation attention, to inform mitigation efforts and reduce mortality rates for this potentially nationally significant population.
77Physiological Stress in Rescued Wild Koalas Are Influenced by Habitat Demographics, Environmental Stressors, and Clinical Intervention.PubMed
Edward Narayan, Tayla Vanderneut
Front Endocrinol (Lausanne). 2019 Jan 29;10:18. doi: 10.3389/fendo.2019.00018. eCollection 2019.
Koalas are rescued from the wild often with incidence of burns from bushfire, injury from animal attacks, vehicle collision, and diseases. Exposure to environmental stressors (trauma and disease) could generate physiological stress and potentially impact the outcomes of clinical management intervention and rehabilitation of rescued wild koalas. It is important to quantify the stress physiology of wild koalas upon registering into clinical care. This study demonstrates the first report of physiological stress assessment in rescued wild koalas ( = 22) to determine the potential influences of habitat-specific demographics, stressor category, and clinical diagnosis. Fecal samples were collected from the koalas at rescue and routinely during hospitalization to provide a longitudinal assessment of the koala's stress response throughout clinical care. Fecal glucocorticoid metabolites (FCM) enzyme-immunoassay was used to index physiological stress non-invasively. Koalas were admitted with exposure to various categories of environmental trauma such as vehicle collision, dog attack, burns from forest fire (this also related to conditions such as copious drinking and flat demeanor), and other injury. The main disease diagnosed was chlamydial infections. In terms of environmental interactions, it was found that habitat-specific demographics, location where the rescued koala was found, especially the rural-urban fringe, influenced FCM levels. Furthermore, there was significant interaction between location, stressor category, and clinical diagnosis for mean FCM levels. However, these factors were not predictive of the clinical outcome (euthanized or released). Overall, the results provide invaluable insights into how wild koalas respond physiologically to environmental trauma and disease and how methods of care, husbandry, and treatment can be used to further reduce the impacts of stress with the ultimate aim of increasing the rehabilitation and future release of rescued koalas to revive the declining mainland populations.
78Mind the gap: Comparing expert and public opinions on managing overabundant koalas.PubMed
Margreet Drijfhout, Dave Kendal, Pete Green
J Environ Manage. 2022 Apr 15;308:114621. doi: 10.1016/j.jenvman.2022.114621. Epub 2022 Feb 5.
Management decisions that do not adequately align with the values and opinions of the public-at-large can lead to controversy and conflict. In conservation and natural resource management, knowledge of the public's values and opinions are often assumed or based on the personal perceptions of experts, rather than on empirical evidence. Mismatches can occur, and in Australia, an ongoing debate about how to best manage overabundant koalas has divided experts and members of the public for decades. On several occasions, experts have recommended culling of overabundant koalas, and yet culls are rarely conducted by managers. Anecdotally this is due to perceived public opposition to the culling of koalas, but there is little empirical evidence to evaluate this assessment. Using a nationwide survey, we investigated the social acceptability of different options for koala management in a population of experts and the general public, and how underlying environmental values and basic beliefs about human-wildlife relationships can explain differences of opinion. We found significant differences in the acceptability of management options between experts and the general public, although the polarity of acceptability was mostly the same. However, the lethal management options of culling and indigenous hunting elicited opposing opinions. Consistent with previous research, beliefs about human-wildlife relationships and belief profiles were found to be useful in explaining differences in acceptability of lethal control among the public, but not among experts. Biospheric values and increased experience and knowledge could play a greater role in the formation of experts' acceptability judgements. Due consideration of evidence-based knowledge of people's opinions can avoid reactive decision-making based on the opinions of a vocal minority. Where differences of opinion exist between experts and the general public, reconciling these divergent views should lead to better conservation outcomes with reduced conflict over potentially controversial management actions.
79Social valuation of biodiversity relative to other types of assets at risk in wildfire.PubMed
John C Z Woinarski, Stephen T Garnett, Kerstin K Zander
Conserv Biol. 2024 Jun;38(3):e14230. doi: 10.1111/cobi.14230. Epub 2024 Feb 11.
Environmental crises, such as wildfires, can cause major losses of human life, infrastructure, biodiversity, and cultural values. In many such situations, incident controllers must make fateful choices about what to protect-and hence what to abandon. With an online representative survey of >2000 adult Australians, we investigated social attitudes to this dilemma. We used best-worst scaling to assess preferences across a set of 11 assets representing human life, infrastructure, biodiversity, and cultural values. Survey respondents overwhelmingly prioritized a single human life (best-worst score of 6647 out of possible score ranging from -10695 to 10695), even if that choice resulted in extinction of other species. Inanimate (replaceable) objects were accorded lowest priority (best-worst scores of -4655 for a shed and -3242 for a house). Among biodiversity assets, respondents prioritized protecting a population of the iconic koala (Phascolarctos cinereus) (best-worst score of 1913) ahead of preventing the extinction of a snail (score -329) and a plant species (-226). These results variably support current policy in that they emphasize the importance the community places on protection of human life, but results diverged from conventional practice in rating some biodiversity assets ahead of infrastructure. The preference for protecting a population of koalas ahead of action taken to prevent the extinction of an invertebrate and plant species corroborates previous research reporting biases in the way people value nature. If noncharismatic species are not to be treated as expendable, then the case for preventing their extinction needs to be better made to the community. Given the increasing global incidence of high-severity wildfires, further sampling of societal preferences among diverse asset types is needed to inform planning, policy, and practice relating to wildfire. Other preemptive targeted management actions (such as translocations) are needed to conserve biodiversity, especially noniconic species, likely to be imperiled by catastrophic events.
80Koala Genome Survey: An Open Data Resource to Improve Conservation Planning.PubMed
Carolyn J Hogg, Luke Silver, Elspeth A McLennan, et al.
Genes (Basel). 2023 Feb 22;14(3):546. doi: 10.3390/genes14030546.
Genome sequencing is a powerful tool that can inform the management of threatened species. Koalas () are a globally recognized species that captured the hearts and minds of the world during the 2019/2020 Australian megafires. In 2022, koalas were listed as 'Endangered' in Queensland, New South Wales, and the Australian Capital Territory. Populations have declined because of various threats such as land clearing, habitat fragmentation, and disease, all of which are exacerbated by climate change. Here, we present the Koala Genome Survey, an open data resource that was developed after the Australian megafires. A systematic review conducted in 2020 demonstrated that our understanding of genomic diversity within koala populations was scant, with only a handful of SNP studies conducted. Interrogating data showed that only 6 of 49 New South Wales areas of regional koala significance had meaningful genome-wide data, with only 7 locations in Queensland with SNP data and 4 locations in Victoria. In 2021, we launched the Koala Genome Survey to generate resequenced genomes across the Australian east coast. We have publicly released 430 koala genomes (average coverage: 32.25X, range: 11.3-66.8X) on the Amazon Web Services Open Data platform to accelerate research that can inform current and future conservation planning.