COS 62-9
Splitting hairs: Preliminary results from the range-wide population genetics study of the endangered salt marsh harvest mouse (Reithrodontomys raviventris)
The salt marsh harvest mouse (SMHM, Reithrodontomys raviventris) is a state and federally listed endangered species that is found only in salt and brackish marshes of the San Francisco, San Pablo and Suisun Bays of California. The decline of the species is mainly attributed to fragmentation and loss of habitat through reclamation of tidal areas, urban development, erosion and vegetation change. This fragmentation is anticipated to increase with the advent of rising sea levels due to climate change. Small and/or fragmented populations such as those of the SMHM are susceptible to inbreeding and localized extinction through random events. The SMHM is sympatric with the morphologically similar western harvest mouse (R. megalotis). In the field, individuals of intermediate morphology are found which makes species identification difficult, and thus raises the question, do the species hybridize. To aid in conservation prioritization we were interested in determining the genetic substructure, and diversity of SMHM populations. We also wished to determine if there is an underlying genetic basis for the subspecies (R. r. raviventris and R. r. halicoetes). We addressed these questions using genetic analyses of mtDNA and microsatellites performed on hair samples taken in the field.
Results/Conclusions
Analyses of our novel microsatellite loci and mtDNA were in 100% agreement regarding species assignment and together indicated no hybridization between the harvest mice species. However, we identified multiple instances of individuals mis-assigned to species in the field, resulting in an inflated estimate of SMHM abundance, which thwarts conservation efforts. Within SMHM (n = 90) mtDNA indicated a relatively close relationship (ΦST 0.09) and shared haplotypes between populations in the two northern bays (San Pablo and Suisun), and major differentiation from the southern San Francisco bay population (average ΦST 0.37). Similarly, admixture analyses of SMHM microsatellite data indicated major differentiation between northern and southern populations. The deep division we find across marker types is consistent with recognized subspecies (R. r. raviventris and R. r. halicoetes). The delimitation of distinct genetic units is an important management tool to facilitate the preservation of the maximum amount of evolutionary potential of this endangered species. Future work will be directed towards other isolated remnant populations of SMHM, particularly those intermediate to northern and southern populations.