The Influence of Temperature on Chytridiomycosis In Vivo
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Chytridiomycosis, an amphibian disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is an ideal system for studying the influence of temperature on host–pathogen relationships because both host and pathogen are ectothermic. Studies of Bd in culture suggest that optimal growth occurs between 17 and 23°C, and death of the fungus occurs above 29 or below 0°C. Amphibian immune systems, however, are also temperature dependent and often more effective at higher temperatures. We therefore hypothesized that pathogen load, probability of infection and mortality in Bd-exposed frogs would peak at a lower temperature than that at which Bd grows best in vitro. To test this, we conducted a study where Bd- and sham-exposed Northern cricket frogs (Acris crepitans) were incubated at six temperatures between 11 and 26°C. While probability of infection did not differ across temperatures, pathogen load and mortality were inversely related to temperature. Survival of infected hosts was greatest between 20 and 26°C, temperatures where Bd grows well in culture. These results demonstrate that the conditions under which a pathogen grows best in culture do not necessarily reflect patterns of pathogenicity, an important consideration for predicting the threat of this and other wildlife pathogens.
Keywordsamphibian Batrachochytrium dendrobatidis ecophysiology fungal pathogen in vitro thermal
The authors thank David Heins, Sunshine Van Bael and Warren Porter for feedback on earlier drafts. Thanks also to Gina Zwicky, Megan Exnicios, Tammy Vo, Xander Rose, Megan McWilliams, and Ian Buchta who assisted with animal husbandry and data collection and Mary Neligh who assisted with database design. This work was funded by grants from the National Science Foundation (Award No. 1649443) and Louisiana Board of Regents (Award No. LEQSF (2011-14)-RD-A-26) to CLRZ. Permission to collect A. crepitans was provided by the Louisiana Department of Wildlife and Fisheries (Permit Nos. WL-Research-2012-06 and LNHP-14-060). This study and its methods were approved by the Institutional Animal Care and Use Committees (IACUC) at Tulane University (Protocol Nos. 0391 – 0391R2).
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