Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
BMC Evol Biol. 2011 Jun 21;11:174. doi: 10.1186/1471-2148-11-174.
Pleistocene climate fluctuations have shaped the patterns of genetic diversity observed in many extant species. In montane habitats, species' ranges may have expanded and contracted along an altitudinal gradient in response to environmental fluctuations leading to alternating periods of genetic isolation and connectivity. Because species' responses to climate change are influenced by interactions between species-specific characteristics and local topography, diversification pattern differs between species and locations. The eastern Himalayas is one of the world's most prominent mountain ranges. Its complex topography and environmental heterogeneity present an ideal system in which to study how climatic changes during Pleistocene have influenced species distributions, genetic diversification, and demography. The Elliot's laughing thrush (Garrulax elliotii) is largely restricted to high-elevation shrublands in eastern Himalayas. We used mitochondrial DNA and microsatellites to investigate how genetic diversity in this species was affected by Pleistocene glaciations.
Mitochondrial data detected two partially sympatric north-eastern and southern lineages. Microsatellite data, however, identified three distinct lineages congruent with the geographically separated southern, northern and eastern eco-subregions of the eastern Himalayas. Geographic breaks occur in steep mountains and deep valleys of the Kangding-Muli-Baoxin Divide. Divergence time estimates and coalescent simulations indicate that lineage diversification occurred on two different geographic and temporal scales; recent divergence, associated with geographic isolation into individual subregions, and historical divergence, associated with displacement into multiple refugia. Despite long-term isolation, genetic admixture among these subregional populations was observed, indicating historic periods of connectivity. The demographic history of Garrulax elliotii shows continuous population growth since late Pleistocene (about 0.125 mya).
While altitude-associated isolation is typical of many species in other montane regions, our results suggest that eco-subregions in the eastern Himalayas exhibiting island-like characteristics appear to have determined the diversification of Garrulax elliotii. During the Pleistocene, these populations became isolated on subregions during interglacial periods but were connected when these expanded to low altitude during cooler periods. The resultant genetic admixture of lineages might obscure pattern of genetic variation. Our results provide new insights into sky island diversification in a previously unstudied region, and further demonstrate that Pleistocene climatic changes can have profound effects on lineage diversification and demography in montane species.
更新世气候波动塑造了许多现存物种遗传多样性的模式。在高山生境中，物种的分布范围可能会沿着海拔梯度扩张和收缩，以响应导致遗传隔离和连通性交替的环境波动。由于物种对气候变化的反应受到物种特有特征和局部地形之间相互作用的影响，因此不同物种和地点的多样化模式也不同。喜马拉雅东部是世界上最突出的山脉之一。其复杂的地形和环境异质性为研究更新世期间气候变化如何影响物种分布、遗传多样化和种群动态提供了理想的系统。笑翠鸟（Garrulax elliotii）主要局限于喜马拉雅东部的高海拔灌丛中。我们使用线粒体 DNA 和微卫星来研究这种物种的遗传多样性如何受到更新世冰川作用的影响。
线粒体数据检测到两个部分共生的东北和南部谱系。然而，微卫星数据鉴定出三个不同的谱系，与喜马拉雅东部地理上分离的南部、北部和东部生态亚区一致。地理断裂发生在康定-木里-宝兴分水岭的陡峭山脉和深谷中。分歧时间估计和合并模拟表明，谱系多样化发生在两个不同的地理和时间尺度上；最近的分化与个体亚区的地理隔离有关，而历史分化与向多个避难所的迁移有关。尽管长期隔离，但这些亚区种群之间存在遗传混合，表明存在历史连通时期。笑翠鸟的种群历史显示自更新世晚期（约 0.125 百万年前）以来持续的种群增长。
虽然与海拔相关的隔离是许多其他高山地区物种的典型特征，但我们的结果表明，表现出岛屿特征的喜马拉雅东部生态亚区似乎决定了笑翠鸟的多样化。在更新世期间，这些种群在间冰期期间在亚区隔离，但在较冷时期扩展到低海拔时连接。谱系的遗传混合可能掩盖了遗传变异的模式。我们的研究结果为以前未被研究的地区的天岛多样化提供了新的见解，并进一步表明更新世气候变化对高山物种的谱系多样化和种群动态有深远的影响。
