Pesticides are a ubiquitous challenge for aquatic ecosystems. Despite the sensitivity of many aquatic species to pesticides, growing evidence suggests that populations can respond to pesticides by evolving constitutive tolerance or inducing tolerance via phenotypic plasticity. While both mechanisms allow organisms to persist when faced with pesticides, resource allocation theory predicts that pesticide tolerance may depend on resource availability. Using Daphnia pulex, we investigated how resource availability and prior exposure to sublethal concentrations of pesticides influence D. pulex tolerance to carbaryl, a common insecticide. Towards this goal, we conducted a two-phase experiment: In phase 1, we exposed D. pulex to one of the following treatments: high food- 0 ug/L carbaryl, high food- 0.05 ug/L carbaryl, low food- 0 ug/L carbaryl, or low food- 0.05 ug/L carbaryl. Next, in phase 2, to understand how resource availability and early exposure to pesticides affected later tolerance in life, D. pulexfrom each phase 1 treatment were subjected to a time to death (TTD) assay.
Results/Conclusions
In high resource environments, D. pulex had a higher baseline tolerance for carbaryl compared to the individuals reared in low resource environments. We also discovered that exposure to sublethal concentrations of carbaryl early in development allowed D. pulex to induce increased tolerance to a lethal concentration of carbaryl later in life. Although D. pulex reared in low resource environments had lower baseline tolerance compared to those in high resource environments, they were able to induce similar tolerances to carbaryl if exposed to the insecticide early in development. We found that only individuals in a low resource environment were able to induce carbaryl tolerance, which highlights the importance of considering resource availability in our understanding of pesticide tolerance.