Mitochondrial DNA phylogeography of the new world flying squirrels (Glaucomys): Implications for pleistocene biogeography

Cytochrome-b sequence data of mitochondrial DNA (mtDNA) were used to infer evolutionary and biogeographic histories of the New World flying squirrels, Glaucomys sabrinus and G. volans. Two distinct mtDNA lineages were recover ed within G. sabrinus: a western lineage consisting of populations from wes tern California, Oregon, and Washington, and a much larger "eastern" Lineag e comprised of populations from the remainder of the species' range (North Carolina, West Virginia, Michigan, Utah, Alaska, eastern Washington, Britis h Columbia, and Alberta). In contrast, only one major mtDNA lineage was rec overed within G. volans. Little sequence variation was observed among popul ations of G. volans (less than or equal to 0.6%), but sequence variation wi thin G. sabrinus was much higher (2.3% and 2.6% within the eastern and west ern clades, respectively, and 4.3-7.2% between the two clades). The level o f sequence divergence observed between the eastern and western mtDNA clades of G. sabrinus (4.3-7.2%) was slightly greater than that observed between the two species, G. sabrinus and G. volans (4.0-6.1%), suggesting the possi bility of an unrecognized species within G. sabrinus. Minimum levels of seq uence divergence among the three mtDNA clades were nearly equal (ca. 4% in all pairwise comparisons), suggesting that Glaucomys underwent a relatively rapid diversification in the early-to-middle Pleistocene. The mtDNA discon tinuity in the Pacific Northwest within G. sabrinus is congruent with simil ar disjunctions in a variety of vertebrate taxa, suggesting that an ancestr al North American boreal ecosystem may have been divided into two distinct communities at this time.