Distribution and Pathogenicity of Batrachochytrium dendrobatidis in Boreal Toads from the Grand Teton Area of Western Wyoming
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The pathogen Batrachochytrium dendrobatidis (Bd), which causes the skin disease chytridiomycosis, has been linked to amphibian population declines and extinctions worldwide. Bd has been implicated in recent declines of boreal toads, Bufo boreas boreas, in Colorado but populations of boreal toads in western Wyoming have high prevalence of Bd without suffering catastrophic mortality. In a field and laboratory study, we investigated the prevalence of Bd in boreal toads from the Grand Teton ecosystem (GRTE) in Wyoming and tested the pathogenicity of Bd to these toads in several environments. The pathogen was present in breeding adults at all 10 sites sampled, with a mean prevalence of 67%. In an experiment with juvenile toadlets housed individually in wet environments, 106 zoospores of Bd isolated from GRTE caused lethal disease in all Wyoming and Colorado animals within 35 days. Survival time was longer in toadlets from Wyoming than Colorado and in toadlets spending more time in dry sites. In a second trial involving Colorado toadlets exposed to 35% fewer Bd zoospores, infection peaked and subsided over 68 days with no lethal chytridiomycosis in any treatment. However, compared with drier aquaria with dry refuges, Bd infection intensity was 41% higher in more humid aquaria and 81% higher without dry refuges available. Our findings suggest that although widely infected in nature, Wyoming toads may escape chytridiomycosis due to a slight advantage in innate resistance or because their native habitat hinders Bd growth or provides more opportunities to reduce pathogen loads behaviorally than in Colorado.
KeywordsBatrachochytrium dendrobatidis chytridiomycosis boreal toads Wyoming
The authors thank Debra Patla for providing the locations of breeding sites and field assistance, and Hank Harlowe for logistical help and his expertise in local boreal toad ecology. Erin Muths, Jason Jones, Aaron Inouye, Blake Hossack, and Andrew Lilley also helped in the field. Susan Wolff helped obtain project funding. Joyce Longcore provided advice on chytrid culture. We thank the Colorado Division of Wildlife for providing us with animals from the John W. Mumma Native Aquatic Species Restoration Facility. This project was funded by USGS Park-Oriented Biological Support (#77-NRMS), the University of Wyoming-National Park Service Research Station, and the Office of Research at Idaho State University. All lab and field protocols were approved by the ISU Institutional Animal Care and Use Committee.
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