Recent Emergence of a Chytrid Fungal Pathogen in California Cascades Frogs (Rana cascadae)
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The pathogenic fungus Batrachochytrium dendrobatidis (Bd) has been associated with global amphibian declines, but it is often difficult to discern the relative importance of Bd as a causal agent in declines that have already occurred. Retrospective analyses of museum specimens have allowed researchers to associate the timing of Bd arrival with the timing of past amphibian declines. Cascades frogs (Rana cascadae) have experienced dramatic declines in northern California, but it is not clear whether the onset of these declines corresponds to the arrival of Bd. We used quantitative real-time PCR assays of samples collected from museum specimens to determine historical Bd prevalence in the northern California range of Cascades frogs. We detected Bd in 13 of 364 (3.5%) Cascades frog specimens collected between 1907 and 2003, with the first positive result from 1978. A Bayesian analysis suggested that Bd arrived in the region between 1973 and 1978, which corresponds well with the first observations of declines in the 1980s.
Keywordschytridiomycosis museum specimen quantitative PCR Klamath Mountains Cascade Mountains
This project was supported by a grant from the United States Fish and Wildlife Service Contaminants Branch to JPS and grants from the National Science Foundation to VV (DEB-11202283 and IOS-1258133). We thank Janet Foley for providing access to her laboratory, Ben Phillips for providing advice on statistical analyses, and Karen Pope for providing comments on a draft of the manuscript; Colleen Kamoroff helped assemble the list of samples, Laurence Cyril Henson helped create the map, and David Tran helped with computing.
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