Aquatic communities and agrochemicals: Combining the perspectives of eco- and evo-toxicology
The ubiquitous use of agrochemicals such as pesticides has resulted in the contamination of aquatic ecosystems around the world. As a result, there is a growing need to understand how such contamination affects the communities of organisms that live in these systems. While toxicology has traditionally focused on direct toxicity of pesticides on individual species, we are beginning to understand that these tests inadequately predict the complex suite of pesticide-mediated impacts on communities and ecosystems including the transmission of indirect effects. Making this situation even more challenging to understand is the potential for evolutionary responses to pesticides. For example, repeated exposures to pesticides may select for increased resistance in some non-target species, a phenomenon that has received little empirical attention. Whereas the evolution of increased resistance is the bane of pest control efforts, it may be highly beneficial to non-target individuals and populations. Moreover, evolved resistance has the potential to dramatically stabilize food webs when the most sensitive taxa become resilient to pesticide exposures and thereby prevent pesticide-induced trophic cascades.
This symposium talk will provide a broad overview on the complex effects of pesticides on aquatic communities. These effects range from direct toxic effects to indirect effects that occur when a sensitive taxon is eliminated from a community, which can trigger a chain of events through the food web that causes dramatic effects on the growth, development, and survival of other species are not affected in traditional single-species experiments. As we add more reality to these communities, such as aquatic macrophytes, we find that pesticide impacts can be attenuated via mechanisms that are outside of the current paradigms. Overlaid on this complexity is our recent discovery that evolved resistance in non-target species is common from zooplankton to amphibians. This increased resistance appears to be operating through a combination of induction and selection and its effects can be felt well beyond the levels of individuals and populations. Indeed, we demonstrate that highly sensitive taxa that have evolved increased resistance to pesticides can prevent the triggering of pesticide-induced trophic cascades. Collectively, our work demonstrates that understanding the consequences of agrochemical exposures in nature requires a synergistic approach that combines ecological and evolutionary perspectives.