Peter Benjamin M, Slatkin Montgomery
Department of Integrative Biology, University of California, Berkeley, California, 94720; Current address: Department of Human Genetics, University of Chicago, Chicago, Illinois, 60637.
Evolution. 2015 Mar;69(3):721-34. doi: 10.1111/evo.12609. Epub 2015 Mar 10.
The gradual loss of diversity and the establishment of clines in allele frequencies associated with range expansions are patterns observed in many species, including humans. These patterns can result from a series of founder events occurring as populations colonize previously unoccupied areas. We develop a model of an expanding population and, using a branching process approximation, show that spatial gradients reflect different amounts of genetic drift experienced by different subpopulations. We then use this model to measure the net average strength of the founder effect, and we demonstrate that the predictions from the branching process model fit simulation results well. We further show that estimates of the effective founder size are robust to potential confounding factors such as migration between subpopulations. We apply our method to data from Arabidopsis thaliana. We find that the average founder effect is approximately three times larger in the Americas than in Europe, possibly indicating that a more recent, rapid expansion occurred.
在包括人类在内的许多物种中，都观察到了与范围扩张相关的多样性逐渐丧失以及等位基因频率渐变群的建立。这些模式可能源于种群在殖民以前未被占据的区域时发生的一系列奠基者事件。我们构建了一个扩张种群的模型，并使用分支过程近似法表明，空间梯度反映了不同亚种群经历的不同程度的遗传漂变。然后，我们使用这个模型来测量奠基者效应的净平均强度，并证明分支过程模型的预测与模拟结果拟合良好。我们进一步表明，有效奠基者大小的估计对于潜在的混杂因素（如亚种群之间的迁移）具有稳健性。我们将我们的方法应用于拟南芥的数据。我们发现，美洲的平均奠基者效应大约是欧洲的三倍，这可能表明发生了更近、更快的扩张。
