Gene flow, refugia, and evolution of geographic variation in the song sparrow (Melospiza melodia)

Despite marked geographic variation in size and plumage color, mtDNA variation was not geographically structured. Subspecies were not identifiable by mtDNA analysis. Postglaciation dispersal may have scattered mtDNA haplotypes across the continent. Evolution of size and plumage coloration has probably proceeded faster than mtDNA evolution, leading to the well-structure continental pattern of morphological variation. The nonordered geographic distribution of haplotypes may reflect the recency of population establishment following completion of range expansion. Dispersal distance was estimated from the mtDNA data at 6.1km per generation, an order of magnitude greater than that (0.3km) estimated from demographic data. Rooting the haplotype cladogram with a putative primitive haplotype identified Newfoundland and the Queen Charlotte Islands as potential sites of recent refugia. -from Authors