Colonization history of atlantic island common chaffinches (Fringilla coelebs) revealed by mitochondrial DNA.

Common chaffinches (Fringilla coelebs) are thought to have colonized the Atlantic island archipelagoes (the Azores, Madeira, and the Canaries) from neighboring continental populations (Iberia and north Africa) within the last million years. However, colonization may have occurred separately from north Africa to the Canaries and from Iberia to the Azores (as would be predicted geographically) or in one wave from Iberia to the Azores and then to Madeira and the Canaries. These alternatives have different implications for the evolution of morphometric and plumage differentiation in island chaffinches. To determine the most likely colonization route, we estimated the phylogenetic relationships among island and continental subspecies of common chaffinch using sequences from four mtDNA genes (cytochrome b, ATPase 6, NADH 5, and the control region). The most strongly supported mtDNA phylogeny places the continental subspecies together as the sister group to a monophyletic clade containing the island subspecies. This is consistent with a single wave of colonization, and suggests that patterns of similarity among Atlantic island common chaffinches, such as blue pigmentation, short wings, and long tarsi, are due to common colonization history rather than to convergent evolution in a common island environment. However, spectral analysis of phylogenetic splits showed that although monophyly of island haplotypes is favored, there is also substantial support for their polyphyletic origin. We attribute the latter to the confounding effect of homoplasy at multistate sites and to the relatively rapid sequence of colonization events which provided insufficient time for the accumulation of strong phylogenetic signal. These problems are likely to be significant impediments in attempts to test hypotheses of phylogenetic histories of recently evolved populations and taxa.