Distinguishing the effects of selection from demographic history in the genetic variation of two sister passerines based on mitochondrial-nuclear comparison

Determining the mechanisms responsible for the distribution of genetic diversity in natural populations has occupied a central role in molecular evolution. Our study was motivated by the unprecedented observation that a widespread Eurasian flycatcher, Ficedula albicilla, exhibited no variation at the mitochondrial DNA (mtDNA) ND2 gene in 75 individuals sampled over a 5000-km distance. In contrast, its sister species, F. parva, had low but considerably higher levels of mtDNA variation. We assessed whether natural selection or demographic factors could explain the absence of mtDNA variation in F. albicilla. Eighteen nuclear genes were sequenced to estimate the two species’ phylogeographic histories, and for comparison to the mtDNA data. Multilocus coalescence analyses suggested that F. albicilla experienced a population expansion perhaps following a population bottleneck. Simulations based on this demographic history, however, did not replicate the extremely low level of mtDNA variation. ...

解析自然种群遗传多样性分布的形成机制，长期以来都是分子进化领域的核心研究课题。本研究的出发点是一项前所未有的观测发现：在跨度5000公里的范围内采集的75只广布欧亚的红喉姬鹟（Ficedula albicilla）个体中，其线粒体DNA（mitochondrial DNA, mtDNA）的ND2基因未检测到任何遗传变异。与之形成鲜明对比的是，其姊妹物种F. parva的mtDNA变异水平虽低，却显著更高。我们旨在评估自然选择或种群历史动态因素能否解释红喉姬鹟中mtDNA变异缺失的现象。本研究对18个核基因（nuclear genes）进行了测序，以推断这两个物种的系统地理历史，并用于与mtDNA数据的对比分析。多位点溯祖分析（multilocus coalescence analysis）结果显示，红喉姬鹟可能在经历种群瓶颈（population bottleneck）后发生了种群扩张（population expansion）。然而，基于该种群历史动态所开展的模拟实验，未能复现红喉姬鹟mtDNA变异水平极低的现象……