As human populations continue to grow, the effects of anthropogenic stressors such as pesticides on wildlife have increased. Populations that are frequently exposed to pesticides can evolve increased tolerance via natural selection over multiple generations; however, recent evidence suggests that many organisms are also able to induce pesticide tolerance in a single generation via phenotypic plasticity. This suggests that induced pesticide tolerance could be a generalizable phenomenon that plays an important role in enhancing survival during exposure to a novel contaminant. Recent studies have shown that exposure to both a sublethal pesticide concentration as well as a naturally occurring stressor both can induce pesticide tolerance. Moreover, evidence suggests that levels of the stress hormone corticosterone (CORT) are altered by the presence of both types of stressors. Thus, we hypothesized that induced pesticide tolerance is the result of a generalized stress response mediated by CORT. We tested this hypothesis by first exposing larval wood frogs (Lithobates sylvaticus) to either a sublethal carbaryl concentration (0.67 mg/L), cues from a predator, or one of two concentrations of exogenous CORT (62.5 nM and 125 nM). We then exposed the wood frogs to a lethal carbaryl treatment (27 mg/L) to assess time-to-death.
Results/Conclusions
Results/Conclusions
We found that prior exposure to both 62.5 and 125 nM of exogenous CORT induced tolerance to a lethal concentration of carbaryl in larval wood frogs, with 62.5 nM CORT increasing median survival time by 50% and 125 nM CORT increasing median survival time by 78.6%. Similarly, exposure to cues from a lethal predator induced tolerance to a lethal concentration of carbaryl, increasing median survival time by 21.4%. Although not significant, exposure to 0.67 mg/L carbaryl tended to increase tolerance to subsequent exposure to a lethal carbaryl concentration. Our study provides evidence that induced tolerance to pesticides is linked to a generalized stress response. Because the stress axis is highly conserved across taxa, these results suggest that inducible pesticide tolerance via a generalized stress response may be a ubiquitous mechanism of contaminant tolerance.