Meeting Abstract
Many of the adverse effects of anthropogenic changes on biodiversity might be mediated by their impacts on organismal stress levels. To test this hypothesis it is necessary to cross anthropogenic stressors with compounds that block the synthesis of stress hormones. As an example, the herbicide atrazine (ATZ) and the introduced fungal pathogen, Batrachochytrium dendrobatidis (Bd), both increase the stress hormone corticosterone (CORT) in amphibians. Additionally, both can have adverse effects on the growth, development, and survival of amphibians. We assessed how much CORT mediates these adverse effects of ATZ and Bd by exposing Cuban tree frog tadpoles, Osteopilus septentrionalis, to ATZ and the CORT synthesis blocker metyrapone (MTP, for six days in a fully crossed design) and then challenging tadpoles and metamorphs with Bd or not. MTP successfully countered the CORT elevation induced by ATZ and Bd. However, reductions in body condition and development caused by ATZ and Bd were not mediated by CORT because they persisted even when CORT was blocked. Additionally, MTP exposure did not significantly affect tolerance of Bd as tadpoles, but reduced tolerance as adults because adults previously exposed to MTP lost more weight per Bd zoospore than adults not previously exposed to MTP. ATZ exposure decreased Bd load in the absence of MTP but increased Bd load with MTP, a result that is consistent with intermediate CORT levels induced by ATZ enhancing immunity. Our results suggest that the effects of ATZ and Bd on amphibian growth and development, and the effects of ATZ on amphibian tolerance of Bd are not a function of their effects on stress hormones. Instead, these effects are likely a function of energy lost from 1) ATZ detoxification, 2) defense against Bd, and 3) repair from any damage caused by ATZ and Bd. Additional studies are needed to evaluate how often the effects of anthropogenic stressors are mediated by their impacts on stress hormones.
