Phylogeography of the tailed frog (Ascaphus truei): Implications for the biogeography of the Pacific Northwest

Tailed frogs are distributed in high-gradient streams within the disjunct m esic forests of the Pacific North west and represent the basal lineage of t he anurans. We sequenced 1530 nucleotides of the mitochondrial cytochrome b and NADH dehydrogenase subunit two genes from 23 populations and used pars imony, maximum-likelihood, and nested-clade analyses to estimate relationsh ips among populations and infer evolutionary processes. We found two diverg ent haplotype clades corresponding with inland Rocky Mountain populations a nd coastal populations and separated by up to 0.133 substitutions per site. Within the coastal assemblage, haplotypes formed clades by mountain range with 0.010-0.024 substitutions per site divergence among populations. Inlan d haplotypes exhibited minimal genetic structure, with the exception of 0.0 21 substitutions per site distance between populations from the East Fork o f the South Fork of the Salmon River and all other inland haplotypes. The m agnitude of divergence between inland and coastal populations, as well as t he paleobotanical record, suggest isolation of these lineages occurred duri ng the late Miocene to early Pliocene, probably in response to the rise of the Cascade Mountains. Genetic structure within coastal and inland populati ons is consistent with isolation in refugia during the late Pliocene and ea rly Pleistocene. Closely related inland haplotypes reflect range expansion following glaciation. The depth of divergence between inland and coastal po pulations supports the persistence of mesic forests within the inland Pacif ic Northwest throughout the Pleistocene and is congruent with patterns foun d in several other mesic forest species. Based on mitochondrial divergence and previous allozyme and morphological data, we recommend recognition of i nland populations as a distinct species, Ascaphus montanus.