Pesticides in aquatic systems: An ecological and evolutionary perspective

Disturbances play important roles in shaping ecological and evolutionary processes. By using disturbances to perturb natural systems, biologist can both develop generalizable predictions about how disturbances alter natural systems as well as utilize disturbances as a tool to test ecological and evolutionary theory. Using pesticide disturbances in aquatic systems, the first half of this thesis integrates ecology, evolution, and toxicology to develop predictions about the consequences of pesticides in aquatic communities and patterns of pesticide tolerance across populations of wood frogs (Lithobathes sylvaticus). Towards this goal, I first conducted a mesocosm study tracking the direct and indirect effects of four insecticides–applied individually and as a mixture– across 18 weeks and demonstrated that insecticides applied individually and in a mixture have complex direct and indirect consequences on aquatic system response and recovery not predicted by traditional laboratory tests. Second, I investigated the potential for cross-tolerance in non-target populations of wood frogs and demonstrate that amphibian populations with tolerance to one pesticide may be cross-tolerant to many other pesticides. \ud \ud The second half of this dissertation uses pesticides as a tool, to test theoretical predictions about the role of phenotypic plasticity in evolutionary innovation to novel environments. I investigated whether natural populations of wood frogs can respond plastically to pesticides (i.e. by inducing increased tolerance) and whether there is evidence supporting the process of genetic assimilation. This study is the first to demonstrate that sublethal and ecologically relevant concentrations of a common insecticide can, within the same generation, induce adaptive tolerance in amphibians and the population-level patterns of inducibility are consistent with predictions of genetic assimilation. Induced pesticide tolerance would be particularly beneficial to non-target species if it were to confer increased tolerance not only against the pesticide it first experienced, but also against many other pesticides (e.g., induced cross-tolerance). Using wood frogs, the final chapter of this dissertation demonstrated the phenomenon of induced cross-tolerance and suggests that cross-tolerance is not limited to insecticides that share mode of action. Overall, the inducible tolerance and cross-tolerance findings suggest that phenotypic plasticity may play a role in shaping patterns of species abundance in nature.\u