Systematic and biogeographic implications of biochemical variation in insular populations of Peromyscus from the Pacific Northwes

Biochemical variation at 24 presumptive gene loci was examined among samples (N = 683) of deer mice form Vancouver Island and associated islands in the Queen Charlotte Strait, the Strait of Georgia, and the Strait of Juan de Fuca. The genic data support the recognition of two species, Peromyscus maniculatus and P. oreas, as proposed from studies of karyotypic and morphological variation among the same samples. Although no biochemical characters serve as fixed markers for species identification, genotypic frequencies at three loci (ADH, ES-1, and GOT-1) are substantially different in populations of the two forms. Interspecific comparison of genetic similarity (S = 0.864) and genic distance (D$sb{rm N}$= 0.107) are comparable to values reported between other taxa within the maniculatus species group and are consistent with a mid-Pleistocene time of divergence.;Levels of genetic variability are high among the sampled populations of P. maniculatus, but low among the sampled populations of P. oreas. Furthermore, genetic variation in P. maniculatus is concentrated among individuals within populations, while variation in P. oreas is concentrated between populations. These data suggest that the effects of isolation are more pronounced in P. oreas, and this is substantiated by the greater level of gene flow estimated among samples of P. maniculatus. Consistent with recent morphological analyses, the patterns of biochemical variation support the recognition of a single subspecies of P. maniculatus (P. m. austerus, from mainland and insular localities) and two insular subspecies of P. oreas (P. o. interdictus, from Vancouver Island, and P. o. isolatus, from islands in the Queen Charlotte Strait), distinct from the mainland form (P. o. oreas).;A review of geologic and biogeographic data suggests that both species are best considered as recent colonizers of the insular habitat of the Pacific Northwest. Based on the results of a phylogenetic analysis of the biochemical data, it is hypothesized that P. oreas represents the older inhabitant of the islands, migrating onto Vancouver Island from a Washington refugium at the close of the Fraser Glaciation. P. maniculatus is also considered to have immigrated from the south, but has apparently radiated to occupy a larger insular range than that occupied by P. oreas. (Abstract shortened with permission of author.).