Historical processes and the evolution of geographic variation patterns in the yellow warbler (Dendroica petechia).

Abstract

The model of the role population differentiation plays in the allopatric speciation process predicts that phenotypic differentiation is correlated with genetic differentiation through the action of microevolutionary processes like genetic drift. In this dissertation I test the hypothesis that patterns of geographic variation in plumage color pattern of Yellow Warbler (Dendroica petechia) are concordant with patterns of genetic differentiation. Among different populations of this widespread avian species are varying degrees of phenotypic differentiation and varying levels of geographic isolation. Widely distributed migratory, continental populations vary little in plumage over their ranges. In contrast, widely distributed sedentary, continental populations show little plumage variation in some geographic areas and vary dramatically in others. Sedentary, insular populations in the Caribbean also exhibit a range in the degree of inter-population variation. A restriction endonuclease analysis of mitochondrial DNA (mtDNA) from populations sampled over a wide geographic range in this species revealed genetic population structure. Most mtDNA haplotypes were restricted in geographic distribution. The phylogenetic analysis of mtDNA suggested, however, that even though mtDNA haplotypes are distributed non-randomly with respect to geography, in some cases populations do not represent independent evolutionary units. Haplotypes sampled from the same populations do not always form monophyletic groups. Some island populations in the West Indies thus contain multiple haplotypes that cluster in different clades in the phylogenetic analysis, suggesting that islands have been colonized multiple times from different sources. Nevertheless, the hypothesis that phenotypic divergence is correlated with genetic divergence is supported. In areas where phenotype changes over short geographic distances, the distribution of mtDNA haplotypes suggests that the populations are also genetically divergent with divergence measured as the proportion of total genetic variance that is attributed to variation among populations (G$\sb{\rm st}$).