Phylogeography, evolution, and conservation in forest-associated Pacific Northwest salamanders

Phylogeographic studies of six Pacific Northwest forest-associated salamanders provide insight into historical and contemporary processes on population genetic structure. Among Larch Mountain Salamanders (Plethodon larselli), cytochrome b mitochondrial (mtDNA) sequences (381 bp) and random amplified polymorphic DNA (RAPDs; 34 loci) supported separate Management Units for northern and southern populations (12 populations, N = 184 individuals) as delineated by the Columbia River. Southern populations exhibited significantly reduced expected heterozygosity at RAPD loci, which may be a consequence of a founder event or bottleneck. Similarly, significant population structure was found in Oregon Slender Salamanders (Batrachoseps wrighti). Cytochrome b sequences (744 bp) revealed two historical lineages among 22 populations (N = 339 individuals). RAPD markers further differentiated mid-range populations. Therefore, overlapping Management Units are warranted for northern-most, mid-range, and southern-most populations. Phylogenetic relationships, taxonomic identity, and population differentiation was examined among four morphologically conserved Torrent Salamanders species (Family Rhyacotritonidae). Analysis of three mitochondrial genes (cytochrome b, 16S, and 12S ribosomal RNA) indicated each species represented a well-supported monophyletic group. Results agreed with allozyme data (Good et al. 1987, Good and Wake 1992) suggesting three groups of Torrent Salamanders (Rhyacotriton variegatus, R. cascadae, and the ancestor of R. olympicus and R. kezeri) diverged during the Miocene. A more recent divergence appears to have occurred between R. olympicus and R. kezeri during the late Pliocene/early Pleistocene. Populations within R. variegatus appear to be as diverged as R. olympicus and R. kezeri, supporting conservation unit designation within R. variegatus. MtDNA 16S ribosomal RNA sequences and allozymes (5 loci) identified Cascade and Southern Torrent Salamanders recently discovered in the Central Oregon Cascades. Results indicate a range extension for both species and suggest the Middle Fork of the Willamette River may provide a geographic barrier to dispersal. Phylogenetic analyses of Southern Torrent Salamanders (72 localities) based upon cytochrome b sequences revealed three divergent clades (north coast, Oregon, and California) that coincide with possible geographic barriers to dispersal. Merging mtDNA results with previous allozyme studies provides support for an Evolutionary Significant Unit for the California clade and separate Management Units for the north coast and Oregon clades.