Are the adverse effects of stressors on amphibians mediated by their effects on stress hormones?
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Adverse effects of anthropogenic changes on biodiversity might be mediated by their impacts on the stress response of organisms. To test this hypothesis, we crossed exposure to metyrapone, a synthesis inhibitor of the stress hormone corticosterone, with exposure to the herbicide atrazine and the fungal pathogen Batrachochytrium dendrobatidis (Bd) to assess whether the effects of these stressors on tadpoles and post-metamorphic frogs were mediated by corticosterone. Metyrapone countered atrazine- and Bd-induced corticosterone elevations. However, atrazine- and Bd-induced reductions in body size were not mediated by corticosterone because they persisted despite metyrapone exposure. Atrazine lowered Bd abundance without metyrapone but increased Bd abundance with metyrapone for tadpoles and frogs. In contrast, atrazine reduced tolerance of Bd infections because frogs exposed to atrazine as tadpoles had reduced growth with Bd compared to solvent controls; this effect was not countered by metyrapone. Our results suggest that the adverse effects of atrazine and Bd on amphibian growth, development, and tolerance of infection are not mediated primarily by corticosterone. A possible mechanism for these effects is energy lost from atrazine detoxification, defense against Bd, or repair from damage caused by atrazine and Bd. Additional studies are needed to evaluate how often the effects of anthropogenic stressors are mediated by stress hormones.
KeywordsAtrazine Batrachochytrium dendrobatidis Chytrid Contaminants Pathogen
We thank J. Middlemis Maher for help with using metyrapone, E. Sauer for help with preparing Bd for inoculations, and N. Halstead for help with atrazine methodology, and early discussions with L. Martin and R. Boughton on this topic. We thank R. Earley for helpful discussion on the experimental design. We also thank K. Cunningham for measuring tadpoles, J. Reyes for help running hormone plates, M. Ehrsam for help with feeding and recording behavior, A. Dubour and V. Caponera for help with water-borne hormone collection, D. Pike for help with swabbing tadpoles for Bd, and S. Sehgal and S. Peters for help with animal husbandry.
Author contribution statement
CRG, SAK, and JRR designed the experiments, CRG, SAK, and EAR carried out the research. CRG and JRR conducted the analyses and primarily wrote the manuscript. All authors gave final approval for publication.
Compliance with ethical standards
C. R. G. was funded by a REP Grant from Texas State University. J. R. R. was funded by the National Science Foundation (EF-1241889), National Institutes of Health (R01GM109499, R01TW010286), US Department of Agriculture (NRI 2006-01370, 2009-35102-0543), and US Environmental Protection Agency (CAREER 83518801).
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable institutional and/or national guidelines for the care and use of animals were followed. This project was approved by the Texas State University Animal Care and Use Committee # 201485314.
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