The genetics of amphibian declines: population substructure and molecular differentiation in the Yosemite Toad, Bufo canorus (Anura, Bufonidae) basedon single-strand conformation polymorphism analysis (SSCP) and mitochondrial DNA sequence data

We present a comprehensive survey of genetic variation across the range of the narrowly distributed endemic Yosemite toad Bufo canorus, a declining am phibian restricted to the Sierra Nevada of California. Based on 322 bp of m itochondrial cytochrome b sequence data, we found limited support for the m onophyly of B. canorus and its closely related congener B. exsul to the exc lusion of the widespread western toad B. boreas. However, B. exsul was alwa ys phylogenetically nested within B. canorus, suggesting that the latter ma y not be monophyletic. SSCP (single-strand conformation polymorphism) analy sis of 372 individual B. canorus from 28 localities in Yosemite and Kings C anyon National Parks revealed no shared haplotypes among these two regions and lead us to interpret these two parks as distinct management units for B . canorus. Within Yosemite, we found significant genetic substructure both at the level of major drainages and among breeding ponds. Kings Canyon samp les show a different pattern, with substantial variation among breeding sit es, but no substructure among drainages. Across the range of B. canorus as well as among Yosemite ponds, we found an isolation-by-distance pattern sug gestive of a stepping stone model of migration. However, in Kings Canyon we found no hint of such a pattern, suggesting that movement patterns of toad s may be quite different in these nearby parklands. Our data imply that man agement for B. canorus should focus at the individual pond level, and effec tive management may necessitate reintroductions if local extirpations occur . A brief review of other pond-breeding anurans suggests that highly struct ured populations are often the case, and thus that our results for B. canor us may be general for other species of frogs and toads.