A phylogeny of some taxa of masked shrews (Sorex cinereus) based on mitochondrial-DNA, D-loop sequences

Parsimony analysis of sequence variation in the mitochondrial (mt) DNA, D-loop region indicated that the masked shrew (Sorer cinereus) and the prairie shrew (S. haydeni) are monophyletic taxa, but mtDNA from S. cinereus has introgressed into S. haydeni. Within S. cinereus there was a rack of concordance between mtDNA clades and currently accepted subspecific designations. The taxonomic designation S. c. acadicus corresponded to a mtDNA clade composed of specimens found predominantly in Nova Scotia and New Brunswick. This clade shared a more recent ancestor with a lineage common to Ontario and Quebec than it did with mtDNA haplotypes from specimens sampled in Michigan and Alberta. S. c. cinereus is, therefore, a paraphyletic assemblage based on mtDNA haplotypes. Little support for currently recognized subspecific designations was found from an analysis of molecular variance among the populations of S. c. cinereus. The mtDNA clades fit a biogeographic hypothesis in which populations of shrews were isolated by factors associated with the Wisconsinan, glaciation and then reinvaded Canada from coastal and southern continental refugia. However, divergence times preceding the recent Wisconsinan glaciation are indicated by applying a molecular clock calibrated for shrews to observed genetic-distance values.