Griswold Cortland K, Baker Allan J
Department of Zoology, University of Toronto, Ontario, Canada.
Evolution. 2002 Jan;56(1):143-53. doi: 10.1111/j.0014-3820.2002.tb00856.x.
We analyzed sequences from a 275-bp hypervariable region in the 5' end of the mitochondrial DNA control region in 190 common chaffinches (Fringilla coelebs) from 19 populations in Europe and North Africa, including new samples from Greece and Morocco. Coalescent techniques were applied to estimate the time to the most recent common ancestor (TMRCA) and divergence times of these populations. The first objective of this study was to infer the locations of refugia where chaffinches survived the last glacial episode, and this was achieved by estimating the TMRCA of populations in regions surrounding the Mediterranean that were unglaciated in the late Pleistocene. Although extant populations in Iberia, Corsica, Greece, and North Africa harbor haplotypes that are basal in a phylogenetic tree, this information alone cannot be used to infer that these localities served as refugia, because it is impossible to infer the ages of populations and their divergence times without also considering the population genetic processes of mutation, migration, and drift. Provided we assume the TMRCAs of populations are a reasonable estimate of a population's age, coalescent-based methods place resident populations in Iberia, Corsica, Greece, and North Africa during the time of the last glacial maximum, suggesting these regions served as refugia for the common chaffinch. The second objective was to determine when populations began diverging from each other and to use this as a baseline to estimate current levels of gene flow. Divergence time estimates suggest that European populations began diverging about 60,000 years before present. The relatively recent divergence of populations in North Africa, Italy, and Iberia may explain why classic migration estimates based on equilibrium assumptions are high for these populations. We compare these estimates with nonequilibrium-based estimates and show that the nonequilibrium estimates are consistently lower than the equilibrium estimates.
我们分析了来自欧洲和北非19个种群的190只苍头燕雀（Fringilla coelebs）线粒体DNA控制区5'端275 bp高变区的序列，包括来自希腊和摩洛哥的新样本。应用溯祖技术来估计这些种群最近共同祖先的时间（TMRCA）和分歧时间。本研究的首要目标是推断苍头燕雀在上次冰期事件中存活下来的避难所位置，这是通过估计地中海周围晚更新世未被冰川覆盖地区种群的TMRCA来实现的。尽管伊比利亚半岛、科西嘉岛、希腊和北非的现存种群拥有系统发育树中处于基部的单倍型，但仅这一信息不能用于推断这些地方曾是避难所，因为如果不考虑突变、迁移和漂变等种群遗传过程，就不可能推断种群的年龄及其分歧时间。假设种群的TMRCA是对种群年龄的合理估计，基于溯祖的方法表明，在上次末次盛冰期时，伊比利亚半岛、科西嘉岛、希腊和北非存在常驻种群，这表明这些地区是苍头燕雀的避难所。第二个目标是确定种群何时开始相互分化，并以此为基线来估计当前的基因流动水平。分歧时间估计表明，欧洲种群大约在距今60,000年前开始分化。北非、意大利和伊比利亚半岛种群相对较近的分化可能解释了为什么基于平衡假设的经典迁移估计对这些种群来说较高。我们将这些估计与基于非平衡的估计进行比较，结果表明非平衡估计始终低于平衡估计。
