Mitochondrial DNA variation in water shrews (Sorexpalustris,Sorexbendirii) from western North America: implications for taxonomy and phylogeography

Abstract

Inter- and intra-specific variations in cytochrome b (Cytb) sequence were assessed in 22 specimens of Sorex palustris Richardson, 1828 and 6 specimens of Sorex bendirii (Merriam, 1884) from 20 locations in western North America. Phylogenetic analyses revealed three distinct clades: Boreal (S. p. palustris), Cordilleran (S. p. brooksi, S. p. navigator), and Coastal (S. b. palmeri, S. b. bendirii). Sequence divergence between the Boreal and the Coastal–Cordilleran lineages was 6.9%, while the divergence between the Coastal and the Cordilleran clades was 3.1%. Sorex palustris brooksi, a subspecies endemic to Vancouver Island, showed minor divergence from mainland samples of S. p. navigator. The results suggest that S. palustris may consist of two species: a boreal eastern form (S. palustris) and a Cordilleran form (S. navigator). The taxonomic validity of S. p. brooksi is unresolved. Distribution of the three clades are consistent with vicariance and isolation in coastal, Cordilleran, and eastern refugia in the Late Pliocene or Pleistocene. The Vancouver Island subspecies S. p. brooksi is probably derived from postglacial colonization in the Late Pleistocene.