Data from: Partial support for the central–marginal hypothesis within a population: reduced genetic diversity but not increased differentiation at the range edge of an island endemic bird

Large-scale population comparisons have contributed to our understanding of the evolution of geographic range limits and species boundaries, as well as the conservation value of populations at range margins. The central–marginal hypothesis (CMH) predicts a decline in genetic diversity and an increase in genetic differentiation toward the periphery of species’ ranges due to spatial variation in genetic drift and gene flow. Empirical studies on a diverse array of taxa have demonstrated support for the CMH. However, nearly all such studies come from widely distributed species, and have not considered if the same processes can be scaled down to single populations. Here, we test the CMH on a species composed of a single population: the Island Scrub-Jay (Aphelocoma insularis), endemic to a 250 km2 island. We examined microsatellite data from a quarter of the total population and found that homozygosity increased toward the island’s periphery. However, peripheral portions of the island did not exhibit higher genetic differentiation. Simulations revealed that highly localized dispersal and small total population size, but not spatial variation in population density, were critical for generating fine-scale variation in homozygosity. Collectively, these results demonstrate that microevolutionary processes driving spatial variation in genetic diversity among populations can also be important for generating spatial variation in genetic diversity within populations.

大尺度种群比较研究有助于我们深入理解地理分布范围边界与物种分界的演化进程，以及分布边缘种群的保护价值。中心-边缘假说（Central–Marginal Hypothesis, CMH）提出，受遗传漂变与基因流的空间变异影响，物种分布范围边缘区域的遗传多样性会出现下降，遗传分化程度则会升高。针对多个类群开展的实证研究均为该假说提供了支持证据。然而，此类研究几乎均基于广布物种，尚未探讨上述演化过程是否可推演至单一种群层面。本研究针对仅存单一种群的岛屿灌丛鸦（Aphelocoma insularis）展开中心-边缘假说验证，该物种为面积250平方千米的海岛特有种。我们分析了总种群四分之一个体的微卫星（microsatellite）数据，发现岛屿边缘区域的纯合度有所升高。但岛屿周边区域并未表现出更高的遗传分化水平。模拟实验结果表明，高度局域化的扩散模式与较小的种群总规模是驱动纯合度精细空间变异的关键因素，而种群密度的空间异质性则无此作用。综上，本研究结果表明，驱动种群间遗传多样性空间变异的微演化过程，同样对种群内部遗传多样性的空间变异具有重要作用。