The interactive effect of an emerging infectious disease and an emerging contaminant on Woodhouse's toad (Anaxyrus woodhousii) tadpoles

Abstract

Two factors that influence amphibian population declines are infectious diseases and exposure to anthropogenic contaminants. The authors examined an emerging fungal pathogen, Batrachochytrium dendrobatidis (Bd), and its interaction with an emerging contaminant, the antimicrobial triclosan. They first conducted a 2 × 2 × 4 factorial study to examine the interactive impacts of dragonfly predator cues, Bd, and triclosan (0 µg/L, 10 µg/L, 100 µg/L, and 1000 µg/L) on Woodhouse's toad (Anaxyrus woodhousii) tadpoles. The authors measured the lethal and sublethal impacts of these stressors on tadpoles over 4 wk. All tadpoles in the 100-µg/L and 1000-µg/L concentrations of triclosan died within 24 h of exposure, but tadpoles in the low concentration (10 µg/L) survived. Tadpoles exposed to only Bd (no triclosan) exhibited a low survival rate (67.5%), whereas those exposed to both 10 µg/L triclosan and Bd exhibited a high survival rate (91.1%), implying that triclosan inhibits effects of Bd on tadpoles. Batrachochytrium dendrobatidis and predator cue exposure individually increased the developmental rate of the surviving tadpoles, but this effect was absent when these factors were combined with triclosan. In a follow-up study, the authors found Bd growth in culture was significantly inhibited at the 10-µg/L concentration of triclosan and completely inhibited at 100 µg/L. These findings suggest that interactions among multiple stressors can be complex and require examination in conjunction with one another to evaluate actual impacts to aquatic fauna.