The dynamics of natural selection and vicariance in the Dominican anole: Patterns of within-island molecular and morphological divergence

The larger islands of the Lesser Antilles are ecologically and geologically complex and are inhabited by single, but morphologically variable, Anolis species. Although earlier work has indicated that a large part of the morph ological variation in Anolis oculatus from Dominica can be attributed to se lection, a history of recurrent volcanic activity over the last few million years suggests that vicariance may have also played a significant role. We report a study of variation in the cytochrome b gene of mitochondrial DNA across the island to address this issue. We uncovered a very high degree of polymorphism, with an overall gene diversity of 0.97 and a nucleotide dive rsity of 0.04. Sequences, on average, differ by 3.82% and the maximum pairw ise divergence (corrected for multiple hits) is 9.29%. Most haplotypes are restricted to single localities (a pattern not changed by increasing the sa mple size). Phylogenetic analysis revealed the presence of two distinct lin eages on the island with strong phylogeographic structure. One of these is geographically restricted to a relatively small part of the central Caribbe an coast. Sublineages were also discernible within the other more widely di stributed lineage, but resolution within and support for these sublineages was poor. The phylogeographic pattern is not congruent with generalized bod y shape and scalation, but is significantly correlated with color pattern. Even when correcting for this lineage effect with partial Matrix correspond ence tests, the relationship between color pattern and vegetation is reaffi rmed, suggesting that although both vicariance and selection have played a role in the morphological differentiation of this species, selection for cu rrent environmental conditions has been more important. We discuss the caus es of the phylogeographic structure in light of the volcanic history of the island and highlight the exceptional instance of congruence between all mo rphological character systems and lineage boundaries, which occurs at the t ransition between the northern and southern Caribbean ecotypes.