HISTORICAL BIOGEOGRAPHY OF THE BANANAQUIT (COEREBA-FLAVEOLA) IN THE CARIBBEAN REGION - A MITOCHONDRIAL-DNA ASSESSMENT

We analyzed mitochondrial DNA (mtDNA) restriction-site variation in ba nanaquit (Coereba flaveola; Aves, Coerebinae) populations sampled on 1 2 Caribbean islands and at 5 continental localities in Central America and northern South America. Multiple fixed restriction-site differenc es genetically defined several regional bananaquit populations. An mtD NA clade representing all Jamaican bananaquits was the most divergent; the estimated average sequence divergence (d(xy)) between Jamaican an d all other mtDNA haplotypes surveyed was 0.027. Three groups of popul ations, representing Central America, northern South America, and the eastern Antilles (Puerto Rico to Grenada) were nearly equally differen tiated among themselves (average d(xy) = 0.014), and may represent a s ingle, recent range expansion. Within the eastern Antilles, three geog raphically restricted haplotype groups were identified: Puerto Rico, n orth-central Lesser Antilles (U.S. Virgin Islands to St. Lucia), and G renada-St. Vincent. The evolutionary relationships of these groups wer e not clear. Genetic homogeneity of the island populations from the U. S. Virgin Islands to St. Lucia suggested a recent spread of a specific north-central Lesser Antillean haplotype through most of those island s. Haplotype variation across this region indicated that this spread m ay have occurred in two waves, first through the southernmost islands of St. Lucia, Martinique, and Dominica, and more recently from Guadelo upe to the north. The geographic distribution of mtDNA haplotypes, and of bananaquit populations, suggests periods of invasiveness followed by relative geographic quiescence. Although most genetic studies of bi rd populations have revealed homogeneity over large geographic areas, our findings provide a remarkable counterexample of strong geographic structuring of mtDNA variation over relatively small distances. Furthe rmore, although the mtDNA data were consistent with several subspecifi c distinctions, it was clear that named subspecies do not define equal ly differentiated evolutionary entities.