Evolutionary history suggests rapid differentiation in the yellow-throated warbler Dendroica dominica

Molecular tools are reshaping many traditional paradigms concerning the timeframe of avian diversification in North America. Phylogeographic studies have become essential for guiding the emerging paradigms. However, the current pool of such studies tends not to be evenly dispersed across the landscape, which limits the generality of inferences. The southeastern United States is one region where the tempo and mode of recent avian diversification is poorly understood. One phylogeographic break in particular, the Tombigbee River discontinuity, divides eastern and western phylogroups in Alabama, and, though it is known to have influenced the phylogeographic patterns of some fish and reptiles, its role in promoting recent avian diversification is not well understood. Eastern and western morphological subspecies of the yellow-throated warbler Dendroica dominica divide along the phylogeographic break created by the Tombigbee River discontinuity suggesting that this bird was also affected by this vicariance. To determine whether the phylogeographic patterns of the yellow-throated warbler are consistent with this biogeographic barrier, I analyzed mitochondrial control region sequences of 109 yellow-throated warblers from across the species' range and, from a subset of these samples, sequences from a sex-linked nuclear gene. Considerable variation was uncovered, but most of this variation was found within rather than among populations or subspecies. A shallow phylogenetic tree, star-like haplotype network, and unimodal mismatch distribution all suggested a recent expansion. Coalescent modeling indicated that modern populations are derived from a single common ancestral population and that differences among subspecies in morphology, ecology, and migratory pathways are the result of recent and rapid evolution, possibly driven by selection.