Population isolation exacerbates conservation genetic concerns in the endangered Amargosa vole, Microtus californicus scirpensis

The ability of a taxon to maintain adaptive flexibility in a stochastic environment is a function of the genetic diversity within the population. In small, fragmented populations, genetic variation can become depleted more quickly than in larger, more contiguous populations. Characterizing the patterns of genetic variation and differentiation associated with these processes is an important step in establishing conservation priorities. The Amargosa vole, Microtus californicus scirpensis, is an endangered rodent persisting in the small, fragmented marsh complex surrounding the Amargosa River near Death Valley, California. This naturally patchy system has existed since the end of the Pleistocene (approximately 10,000 y.b.p.), however, fragmentation has been exacerbated by recent anthropogenic changes. For this study, I used five nuclear microsatellite loci and the cytochrome-b region of the mitochondrial genome to quantify levels of genetic variation, population substructure, and patterns of gene flow in M.c. scirpensis. These data were compared to a broadly distributed subspecies, Microtus californicus sanctidiegi. Overall levels of nuclear genetic variation were significantly lower in M.c. scirpensis, whether measured in terms of diversity or heterozygosity, compared to more broadly distributed conspecifics. Moreover, only two haplotypes were recovered from the mitochondrial data with over 90% of the observed haplotypes being identical. Despite low genetic diversity, significant genetic subdivision among M.c. scirpensis populations was detected using both pairwise F_ST and Bayesian clustering methods. Furthermore, isolation by distance analyses reveal that an important landscape feature, ephemeral tributaries, is critical for dispersal among population clusters. Recommendations for conservation management are presented.