Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University, Townsville, QLD, 4811, Australia.
Department of Regional Development, Manufacturing and Water, Bundaberg, QLD, Australia.
BMC Ecol Evol. 2022 May 2;22(1):57. doi: 10.1186/s12862-022-02009-6.
Approximately 50% of freshwater turtles worldwide are currently threatened by habitat loss, rural development and altered stream flows. Paradoxically, reptiles are understudied organisms, with many species lacking basic geographic distribution and abundance data. The iconic Irwin's turtle, Elseya irwini, belongs to a unique group of Australian endemic freshwater turtles capable of cloacal respiration. Water resource development, increased presence of saltwater crocodiles and its cryptic behaviour, have made sampling for Irwin's turtle in parts of its range problematic, resulting in no confirmed detections across much of its known range for > 25 years. Here, we used environmental DNA (eDNA) analysis for E. irwini detection along its historical and contemporary distribution in the Burdekin, Bowen and Broken River catchments and tributaries. Five replicate water samples were collected at 37 sites across those three river catchments. Environmental DNA was extracted using a glycogen-aided precipitation method and screened for the presence of E. irwini through an eDNA assay targeting a 127 base pair-long fragment of the NADH dehydrogenase 4 (ND4) mitochondrial gene.
Elseya irwini eDNA was detected at sites within its historic distribution in the lower Burdekin River, where the species had not been formally recorded for > 25 years, indicating the species still inhabits the lower Burdekin area. We also found higher levels of E. iriwni eDNA within its contemporary distribution in the Bowen and Broken Rivers, matching the prevailing scientific view that these areas host larger populations of E. irwini.
This study constitutes the first scientific evidence of E. irwini presence in the lower Burdekin since the original type specimens were collected as part of its formal description, shortly after the construction of the Burdekin Falls Dam. From the higher percentage of positive detections in the upper reaches of the Broken River (Urannah Creek), we conclude that this area constitutes the core habitat area for the species. Our field protocol comprises a user-friendly, time-effective sampling method. Finally, due to safety risks associated with traditional turtle sampling methods in the Burdekin River (e.g., estuarine crocodiles) we propose eDNA sampling as the most pragmatic detection method available for E. irwini.
目前，全球约有 50%的淡水龟类受到栖息地丧失、农村发展和溪流流量改变的威胁。具有讽刺意味的是，爬行动物是研究不足的生物，许多物种缺乏基本的地理分布和丰度数据。标志性的欧文龟（Elseya irwini）属于澳大利亚特有淡水龟类的独特群体，能够进行泄殖腔呼吸。水资源开发、咸水鳄的增加以及其隐蔽的行为，使得在欧文龟的部分分布区域进行采样变得困难，导致在其已知分布区域的大部分地区已经超过 25 年没有确认的发现。在这里，我们使用环境 DNA（eDNA）分析来检测欧文龟在其历史和当代分布的伯德金、鲍文和破碎河流域及其支流中的存在。在这三个河流流域的 37 个地点采集了 5 个重复水样。使用糖原辅助沉淀法提取环境 DNA，并通过针对 NADH 脱氢酶 4（ND4）线粒体基因 127 个碱基长片段的 eDNA 检测来筛选欧文龟的存在。
在伯德金河下游欧文龟的历史分布区域内的一些地点检测到了欧文龟的 eDNA，在那里已经超过 25 年没有正式记录到该物种，表明该物种仍然栖息在伯德金河下游地区。我们还在欧文龟当代分布的鲍文和破碎河流域内发现了更高水平的欧文龟 eDNA，这与普遍的科学观点一致，即这些地区拥有更大的欧文龟种群。
这项研究是自伯德金瀑布大坝建成后不久，为正式描述欧文龟而采集原始模式标本以来，首次在伯德金河下游发现欧文龟存在的科学证据。从破碎河上游（厄拉纳克里克）的阳性检测百分比更高，我们得出结论，该地区是该物种的核心栖息地。我们的实地工作方案包括一种用户友好、高效的采样方法。最后，由于在伯德金河进行传统龟类采样方法存在安全风险（例如，河口鳄），我们建议使用 eDNA 采样作为欧文龟最实用的检测方法。
