John Wiley & Sons, Ltd.

The interactive effects of chytrid fungus, pesticides, and exposure timing on gray treefrog (Hyla versicolor) larvae

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Aquatic organisms are often exposed to a wide variety of perturbations in nature, including pathogens and chemical contaminants. Despite the co‐occurrence of these two stressors, few studies have examined the effects of chemical contaminants on host‐pathogen dynamics. We tested the individual and combined effects of two commonly used pesticides (Roundup® and Sevin®) and the pathogenic fungus Batrachochytrium dendrobatidis (Bd) on gray treefrog (Hyla versicolor) tadpoles. We used a fully factorial design and exposed tadpoles to Bd, Roundup, or Sevin alone, or a combination of Bd and either pesticide at three points during larval development (Early, Mid, Late). We predicted that pesticides would mediate the effect of Bd on tadpoles and reduce the likelihood of negative consequences of infection, and that timing of exposure would influence these effects. Tadpoles exposed to Bd at the Mid point experienced higher survival through metamorphosis than those exposed to Bd at the Early or Late points, while tadpoles exposed to Sevin at the Early point experienced reduced survival compared to those exposed to Roundup or no‐pesticide control at the same exposure point. Roundup ameliorated the effects of Bd on survival compared to tadpoles exposed to Bd alone, while there was no interactive effect of Sevin on survival. Additionally, Sevin reduced mass of new metamorphs compared to Roundup and reduced snout‐vent‐length compared to all other treatments. Our study supports the hypothesis that pesticides can mitigate the effects of Bd on amphibian hosts, and such effects may depend upon the timing of exposure. Environ Toxicol Chem © 2013 SETAC

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