Baker Allan J, Dennison Michael D, Lynch Alejandro, Le Grand Gerald
Department of Ornithology, Royal Ontario Museum, Toronto, Ontario, M5S 2C6, CANADA.
Department of Zoology, University of Toronto, Toronto, Ontario, M5S 1A1, CANADA.
Evolution. 1990 Jul;44(4):981-999. doi: 10.1111/j.1558-5646.1990.tb03819.x.
Peripherally isolated populations of common chaffinches (Fringilla coelebs) in the Canaries, Madeira, and Azores were compared genetically with their putative ancestral stock in Iberia and Morocco, and with a population of blue chaffinches (F. teydea) from Tenerife, using protein electrophoresis of 42 loci. The continental populations are only weakly differentiated genetically (F = 0.092), despite distinctive subspecific differences in plumage and morphometrics between Iberia and Morocco populations. Estimated levels of gene flow among continental populations are high enough to account for their relative genetic homogeneity, and it is unlikely that homogenizing selection is operating to mimic the effects of gene flow. In contrast, the Atlantic island populations are well differentiated genetically (F = 0.321), and have diverged considerably from their continental conspecifics. The development of significant genetic differentiation within the Canaries but not the Azores likely results from smaller population sizes, very restricted gene flow, and enhanced random drift in the former populations. There is no convincing evidence in support of stronger directional selection acting on genotypes or phenotypes to reduce within-population variability in Canaries populations as proposed by Grant (1979), although other tenets of his model of island evolution are supported by our analysis. Although genetic variability is reduced in four of the Canaries populations, only the Hierro population appears to have encountered a severe bottleneck. Yet it has not differentiated markedly from the La Palma population to which it is subspecifically allied. We conclude that gradual divergence in isolated populations of small to moderate size is the most plausible explanation for the evolution of intraspecific and interspecific diversity in Atlantic island chaffinches.
利用对42个基因座的蛋白质电泳技术，对加那利群岛、马德拉群岛和亚速尔群岛上普通苍头燕雀（Fringilla coelebs）的外围隔离种群，与其在伊比利亚半岛和摩洛哥的假定祖先种群，以及来自特内里费岛的蓝苍头燕雀（F. teydea）种群进行了基因比较。尽管伊比利亚半岛和摩洛哥种群在羽毛和形态测量上存在明显的亚种差异，但大陆种群在基因上的分化程度很弱（F = 0.092）。估计大陆种群之间的基因流动水平很高，足以解释它们相对的基因同质性，而且不太可能是同质化选择在模拟基因流动的效果。相比之下，大西洋岛屿种群在基因上有明显的分化（F = 0.321），并且与其大陆同种有很大差异。加那利群岛内而非亚速尔群岛内出现显著基因分化，可能是由于前者种群规模较小、基因流动非常有限以及随机漂变增强所致。没有令人信服的证据支持格兰特（1979年）提出的，对基因型或表型有更强的定向选择作用以降低加那利群岛种群内变异性的观点，尽管我们的分析支持了他岛屿进化模型的其他原则。虽然加那利群岛的四个种群的遗传变异性有所降低，但只有耶罗岛种群似乎经历了严重的瓶颈效应。然而，它与同属一个亚种的帕尔马岛种群并没有明显分化。我们得出结论，对于大西洋岛屿苍头燕雀种内和种间多样性的进化，最合理的解释是中小规模隔离种群的逐渐分化。
