Lineage diversification on an evolving landscape: phylogeography of the California newt, Taricha torosa (Caudata: Salamandridae)

Abstract

We used mitochondrial cytochrome b sequences (up to 778 bp) and starch gel electrophoresis (45 loci) to examine the phylogeographical history of 39 populations of the California newt, Taricha torosa. Phylogenetic and population genetic methods were integrated to infer history at deep and shallow time depths. Using a molecular clock, the subspecies T. t. torosa and T. t. sierrae were estimated to have diverged 7–13 Mya. Within T. t. torosa, genetically differentiated groups were identified along coastal California, in southern California, and in the southern Sierra Nevada. The coastal group exhibited isolation by distance, but a lack of genetic variation north of present-day Monterey was indicative of a recent range expansion. In southern California, a disjunct population in central San Diego County was genetically diverged from coastal populations to the north (Nei’s genetic distance of 0.113). However, mtDNA and protein data were geographically discordant regarding the boundary between the coastal and southern Californian groups, and a biogeographical scenario was developed to account for this discordance. The southern Sierran clade of T. t. torosa was weakly diverged from coastal populations for mtDNA sequence variation, yet was strongly differentiated for allozyme variation (Nei’s genetic distance of 0.17–0.20). Populations of T. t. sierrae exhibited substantial population structure, and showed a steeper pattern of isolation by distance than did coastal populations of T. t. torosa. These results are interpreted in consideration of the known geomorphological history of California. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89, 213–239.