Yang Yuchen, Li Jianfang, Yang Shuhuan, Li Xinnian, Fang Lu, Zhong Cairong, Duke Norman C, Zhou Renchao, Shi Suhua
State Key Laboratory of Biocontrol and Guangdong Provincial Key Laboratory of Plant Resources, Sun Yat-sen University, Guangzhou, 510275, China.
Hainan Dongzhai Harbor National Nature Reserve, Haikou, 571129, China.
BMC Evol Biol. 2017 Jan 18;17(1):22. doi: 10.1186/s12862-016-0849-z.
A large-scale systematical investigation of the influence of Pleistocene climate oscillation on mangrove population dynamics could enrich our knowledge about the evolutionary history during times of historical climate change, which in turn may provide important information for their conservation.
In this study, phylogeography of a mangrove tree Sonneratia alba was studied by sequencing three chloroplast fragments and seven nuclear genes. A low level of genetic diversity at the population level was detected across its range, especially at the range margins, which was mainly attributed to the steep sea-level drop and associated climate fluctuations during the Pleistocene glacial periods. Extremely small effective population size (Ne) was inferred in populations from both eastern and western Malay Peninsula (44 and 396, respectively), mirroring the fragility of mangrove plants and their paucity of robustness against future climate perturbations and human activity. Two major genetic lineages of high divergence were identified in the two mangrove biodiversity centres: the Indo-Malesia and Australasia regions. The estimated splitting time between these two lineages was 3.153 million year ago (MYA), suggesting a role for pre-Pleistocene events in shaping the major diversity patterns of mangrove species. Within the Indo-Malesia region, a subdivision was implicated between the South China Sea (SCS) and the remaining area with a divergence time of 1.874 MYA, corresponding to glacial vicariance when the emerged Sunda Shelf halted genetic exchange between the western and eastern coasts of the Malay Peninsula during Pleistocene sea-level drops. Notably, genetic admixture was observed in populations at the boundary regions, especially in the two populations near the Malacca Strait, indicating secondary contact between divergent lineages during interglacial periods. These interregional genetic exchanges provided ample opportunity for the re-use of standing genetic variation, which could facilitate mangrove establishment and adaptation in new habitats, especially in the context of global climate changes.
Phylogeogrpahic analysis in this study reveal that Pleistocene sea-level fluctuations had profound influence on population differentiation of the mangrove tree S. alba. Our study highlights the fragility of mangrove plants and offers a guide for the conservation of coastal mangrove communities experiencing ongoing changes in sea-level.
对更新世气候振荡对红树林种群动态影响的大规模系统研究，可以丰富我们对历史气候变化时期进化历史的认识，进而为红树林的保护提供重要信息。
在本研究中，通过对三个叶绿体片段和七个核基因进行测序，研究了红树植物海桑的系统地理学。在其分布范围内，尤其是在分布边缘，检测到种群水平的遗传多样性较低，这主要归因于更新世冰期期间海平面的急剧下降和相关的气候波动。在马来半岛东部和西部的种群中推断出极小的有效种群大小（Ne）（分别为44和396），这反映了红树林植物的脆弱性以及它们对未来气候扰动和人类活动缺乏抵抗力。在两个红树林生物多样性中心：印度-马来西亚和澳大拉西亚地区，鉴定出两个高度分化的主要遗传谱系。这两个谱系之间的估计分裂时间为315.3万年前（百万年前），表明更新世前事件在塑造红树林物种的主要多样性模式中发挥了作用。在印度-马来西亚地区内，南海（SCS）和其余地区之间存在细分，分歧时间为187.4万年前，这与冰期隔离相对应，当时露出的巽他陆架在更新世海平面下降期间阻止了马来半岛东西海岸之间的基因交流。值得注意的是，在边界地区的种群中观察到了遗传混合，特别是在马六甲海峡附近的两个种群中，这表明在间冰期不同谱系之间发生了二次接触。这些区域间的基因交流为现存遗传变异的重新利用提供了充足的机会，这有助于红树林在新栖息地的建立和适应，特别是在全球气候变化的背景下。
本研究中的系统地理学分析表明，更新世海平面波动对红树植物海桑的种群分化有深远影响。我们的研究突出了红树林植物的脆弱性，并为保护正在经历海平面持续变化的沿海红树林群落提供了指导。
