Department of Plant Biology, University of Minnesota, Saint Paul, Minnesota 55108, USA.
Am Nat. 2011 Oct;178 Suppl 1:S44-57. doi: 10.1086/661783. Epub 2011 Sep 12.
Abstract Theoretical models of species' geographic range limits have identified both demographic and evolutionary mechanisms that prevent range expansion. Stable range limits have been paradoxical for evolutionary biologists because they represent locations where populations chronically fail to respond to selection. Distinguishing among the proposed causes of species' range limits requires insight into both current and historical population dynamics. The tools of molecular population genetics provide a window into the stability of range limits, historical demography, and rates of gene flow. Here we evaluate alternative range limit models using a multilocus data set based on DNA sequences and microsatellites along with field demographic data from the annual plant Clarkia xantiana ssp. xantiana. Our data suggest that central and peripheral populations have very large historical and current effective population sizes and that there is little evidence for population size changes or bottlenecks associated with colonization in peripheral populations. Whereas range limit populations appear to have been stable, central populations exhibit a signature of population expansion and have contributed asymmetrically to the genetic diversity of peripheral populations via migration. Overall, our results discount strictly demographic models of range limits and more strongly support evolutionary genetic models of range limits, where adaptation is prevented by a lack of genetic variation or maladaptive gene flow.
摘要 物种地理分布范围的理论模型确定了阻止其扩张的种群和进化机制。稳定的分布范围对于进化生物学家来说是一个悖论，因为它们代表了种群长期无法对选择做出反应的位置。要区分物种分布范围的各种原因，需要深入了解当前和历史的种群动态。分子群体遗传学的工具为研究范围极限的稳定性、历史人口动态和基因流动率提供了一个窗口。在这里，我们使用基于 DNA 序列和微卫星的多基因数据集以及一年生植物 Clarkia xantiana ssp. xantiana 的实地人口统计数据，评估了替代的范围极限模型。我们的数据表明，中心和外围种群具有非常大的历史和当前有效种群大小，并且几乎没有证据表明与外围种群的殖民化相关的种群大小变化或瓶颈。虽然范围极限种群似乎很稳定，但中心种群表现出种群扩张的特征，并且通过迁移不对称地为外围种群的遗传多样性做出了贡献。总体而言，我们的结果否定了严格的范围极限种群模型，而更有力地支持了范围极限的进化遗传模型，在这种模型中，由于缺乏遗传变异或适应不良的基因流，适应性受到阻碍。
