National Institute of Advanced Studies, Indian Institute of Science Campus, Bangalore, India.
PLoS One. 2010 Oct 13;5(10):e13321. doi: 10.1371/journal.pone.0013321.
Sky islands, formed by the highest reaches of mountain tracts physically isolated from one another, represent one of the biodiversity-rich regions of the world. Comparative studies of geographically isolated populations on such islands can provide valuable insights into the biogeography and evolution of species on these islands. The Western Ghats mountains of southern India form a sky island system, where the relationship between the island structure and the evolution of its species remains virtually unknown despite a few population genetic studies.
We investigated how ancient geographic gaps and glacial cycles have partitioned genetic variation in modern populations of a threatened endemic bird, the White-bellied Shortwing Brachypteryx major, across the montane Shola forests on these islands and also inferred its evolutionary history. We used bayesian and maximum likelihood-based phylogenetic and population-genetic analyses on data from three mitochondrial markers and one nuclear marker (totally 2594 bp) obtained from 33 White-bellied Shortwing individuals across five islands. Genetic differentiation between populations of the species correlated with the locations of deep valleys in the Western Ghats but not with geographical distance between these populations. All populations revealed demographic histories consistent with population founding and expansion during the Last Glacial Maximum. Given the level of genetic differentiation north and south of the Palghat Gap, we suggest that these populations be considered two different taxonomic species.
Our results show that the physiography and paleo-climate of this region historically resulted in multiple glacial refugia that may have subsequently driven the evolutionary history and current population structure of this bird. The first avian genetic study from this biodiversity hotspot, our results provide insights into processes that may have impacted the speciation and evolution of the endemic fauna of this region.
由彼此物理隔离的山脉最高点形成的天空岛屿，是世界上生物多样性最丰富的地区之一。对这些岛屿上地理隔离种群的比较研究，可以为这些岛屿上物种的生物地理学和进化提供有价值的见解。印度南部的西高止山脉形成了一个天空岛屿系统，尽管有一些种群遗传研究，但这些岛屿的岛屿结构与物种进化之间的关系仍然知之甚少。
我们调查了古老的地理间隔和冰川周期如何在这些岛屿的山地 Shola 森林中，将受威胁的特有鸟类——白腹短翅 Brachypteryx major 的现代种群的遗传变异分割开来，并推断了其进化历史。我们使用贝叶斯和最大似然系统发育和种群遗传分析，对来自五个岛屿的 33 只白腹短翅个体的三个线粒体标记和一个核标记（共 2594bp）的数据进行了分析。物种种群之间的遗传分化与西高止山脉深谷的位置相关，而与这些种群之间的地理距离无关。所有种群的历史人口动态都与末次冰期最大值期间的种群建立和扩张一致。鉴于帕尔加特峡谷南北的遗传分化水平，我们建议将这些种群视为两个不同的分类物种。
我们的研究结果表明，该地区的地貌和古气候在历史上导致了多个冰川避难所，这可能随后推动了这种鸟类的进化历史和当前的种群结构。这是该生物多样性热点地区的第一个鸟类遗传研究，我们的研究结果为可能影响该地区特有动物的物种形成和进化的过程提供了新的认识。
