Pesticide exposure reinforces the stabilizing effect of thermal evolution on predator-prey systems under warming

Pollution and warming are major threats to freshwater ecosystems, yet their joint effects on predator-prey interactions structuring these ecosystems and how thermal evolution may modulate these impacts are largely unknown. Under common-garden settings, we investigated how exposure to the widespread pesticide chlorpyrifos and warming affected predator life history, metabolic rate and functional response, and prey population dynamics to predict the long-term interaction strength (intrinsic stability) of low- and high-latitude populations of Ischnura elegans damselfly larvae preying on Daphnia magna water fleas. Warming magnified the negative impact of pesticide exposure on predator performance and predation rates, but remarkably, for high-latitude predators, pesticide exposure mitigated some of the negative impacts of warming on long-term predator-prey system stability. This reversed the stressor interaction types at different biological organization levels, from negative synergistic and antagonistic to positive synergistic and antagonistic. Under warmer future conditions, thermal plasticity destabilized the predator-prey system for high-latitude predators. Interestingly, pesticide exposure helped to stabilize this system under warming, while having no effect under the current cooler thermal regime. Using a space-for-time substitution, our results suggest that joint thermal plasticity and evolution of high-latitude predators could contribute to stabilizing predator-prey systems under warming, with pesticide exposure further enhancing this effect, providing evidence that thermal evolution could alter the stressor interaction type. Our findings highlight the importance of considering thermal evolution, multiple-stressor interactions, and biotic interactions into ecotoxicology to better predict the impact of pollutants on the local persistence of species in increasingly stressed environments.