Here today, gone tomorrow: Induction and retention of pesticide tolerance in amphibians
Phenotypic plasticity—the ability of a single genotype to produce multiple distinct phenotypes in response to a given environmental cue—enables species to persist within heterogeneous environments, and may aid populations in response to novel anthropogenic stressors. Although beneficial, pesticide use has led to the ubiquitous contamination of natural habitats, which has inadvertently increased pesticide tolerance in both target and non-target species. Historically, increased pesticide tolerance has been attributed to natural selection on tolerance among individuals of affected populations. Recent research, however, has discovered that pesticide tolerance can be increased through phenotypic plasticity. Though induced pesticide tolerance may benefit organisms experiencing contaminated systems, little is known about its occurrence in vertebrates, its retention through ontogeny, or potential life-history tradeoffs. We investigated the induction and retention of increased pesticide tolerance by first exposing gray treefrog tadpoles (Hyla versicolor) to one of three sublethal carbaryl (Sevin®) concentrations, and then to either a no-carbaryl control or lethal carbaryl concentration at two developmental windows (5 and 23 d post-sublethal exposure). To examine the tradeoffs associated with inducing increased pesticide tolerance, a subset of tadpoles from each treatment were raised to metamorphosis, collected, and measured (snout-vent length and body mass).
We discovered that gray treefrogs tadpoles that were exposed to sublethal carbaryl concentrations were more tolerant to a lethal concentration of carbaryl at 5 d post-sublethal exposure than those without previous carbaryl exposure. However, at 23 d post-sublethal exposure, there was no difference in tolerance among the three sublethal exposure treatments, indicating the loss, or reversion, of induced pesticide tolerance. Lastly, we found that the initial exposure to sublethal carbaryl concentrations early in life, and subsequent induction of increased pesticide tolerance, had no long-term effects on the life-history traits of the animals. Gray treefrogs are only the second vertebrate species and second amphibian family to exhibit this pattern of induced pesticide tolerance. Given the high plastic ability of amphibians, induced pesticide tolerance following sublethal exposure may be a generalizable response across many amphibian families. Moreover, the ability to induce pesticide tolerance in amphibians may play a critical role in conservation efforts, given that exposure to pesticides has been implicated as a possible factor in global amphibian population declines.