Phylogeography and systematics of the Peromyscus eremicus species group and the historical biogeography of North American warm regional deserts

Phylogeographic relationships among 26 populations from throughout the geog raphic range of the Peromyscus eremicus species group are described based o n sequence data for a 699-bp fragment of the mitochondrial DNA COIII gene. Distance, maximum-likelihood, and maximum-parsimony analyses of phylogeneti c trees generated under four separate character-weighting strategies and re presenting five alternative biogeographic hypotheses revealed the existence of a cryptic species (Peromyscus fraterculus, previously included under P. eremicus) on the Baja California Peninsula and adjacent southwestern Calif ornia and two distinct forms of P. eremicus, one from the Mojave, Sonoran, and northwestern Chihuahuan regional deserts (West) and one from the remain der of the Chihuahuan Desert (East). Distinctiveness of P. fraterculus is s upported by previous morphometric and allozyme analyses, including comparis ons with neighboring P. eremicus and parapatric P. eva, with which P. frate rculus shares a sister taxon relationship. Divergence of the eva + fratercu lus, West + East eremicus, and P. merriami haplotype lineages likely occurr ed in the late Neogene (3 Ma), in response to northern extension of the Sea of Cortez and elevation of the Sierra Madre Occidental; divergence of eva from fraterculus is concordant with the existence of a trans-Peninsular sea way during the Pleistocene (1 Ma); and divergence of West from East eremicu s occurred during the Pleistocene pluvial-interpluvial cycles, but well bef ore the Wisconsinan glacial interval. The sequence of divergence within the eremicus species group and causal association of geological events of the Neogene and Holocene provide a working hypothesis against which phylogeogra phic patterns among other arid-adapted species of the warm regional deserts of North America may be compared. (C) 2000 Academic Press.