EVOLUTIONARY IMPLICATIONS OF GENIC VARIATION AMONG INSULAR POPULATIONS OF PEROMYSCUS-MANICULATUS AND PEROMYSCUS-OREAS

A survey of electrophoretic variation in proteins encoded by 24 gene loci revealed differences in allele frequencies (principally at ADH, ES-1, and GOT-1) between two karyotypically characterized species of deer mice (Peromyscus maniculatus and P. oreas) from Vancouver Island and smaller islands in the Queen Charlotte Strait and Strait of Georgia. The large number of alleles common to the two taxa and the absence of fixed allelic differences are consistent with a hypothesis of recent common ancestry. In addition, random variance in allele frequencies among small-island populations of both species is indicative of interspecific divergence accelerated by stochastic processes. Nevertheless, genetic consequences of geographic isolation (low genic variability and high interpopulational differentiation) are more pronounced in P. oreas than in P. maniculatus, and this is attributed to differences in potential for gene flow. Patterns of geographic variation evident in morphological analyses, summarized in the recognition of P. maniculatus austerus and three subspecies of P. oreas (P. o. oreas, P. o. interdictus, and P. o. isolatus) from Pacific regions of British Columbia and Washington, may stem from genetic factors related to peripheral isolation of P. oreas from P. maniculatus and interspecific differences in dispersal abilities.