Evolutionary relationships of white-footed mice (Peromyscus) on islands inthe Sea of Cortez, Mexico

Sixteen populations of Peromyscus on islands in the Sea of Cortez (= Gulf o f California), Mexico, were compared with 9 mainland species of Peromyscus based on sequence data for a 699-base-pair fragment of the mitochondrial DN A (mtDNA) COIII gene. An unrooted neighbor-joining tree based on corrected pairwise estimates of sequence divergence among variable mtDNA haplotypes i ndicated a recent (late Pleistocene) origin from a source on the adjacent m ainland for 10 island forms representing P. boylii, P. crinitus, P. eremicu s, P. eva, P. fraterculus, and P. maniculatus. Five other populations did n ot seem to be derived from species currently on the nearest mainland, sugge sting overwater dispersal or distributional changes on the mainland after d rowning of land-bridge connections. One population, possibly of more ancien t origin, on Isla Cerralvo near the Baja California peninsula, probably ori ginated via trans-Gulf rafting from the Sonoran mainland. Based on these re sults, 4 insular species (P. stephani, P. interparietalis, P. caniceps, and P. dickeyi) should be considered subspecies of P. boylii, P. eremicus, P. fraterculus, and P. merriami, respectively. The emergent view of evolutiona ry relationships within the subgenus Haplomylomys in the region reflects pr e-Pleistocene phylogeographic events on the mainland surrounding the Gulf a nd a more recent origin of island populations.