Adaptive Transgenerational Effects Offset the Increased Toxicity of the Pesticide Chlorpyrifos under Heat Stress

Although the importance of transgenerational effects and multiple stressors in ecotoxicology is well-established, transgenerational interactions between toxicants and natural stressors remain largely unexplored, yet are critical for advancing ecological risk assessment. In this study, we exposed the water flea <i>Daphnia magna</i> to a heat spike (25 °C vs 32 °C) followed by exposure to chlorpyrifos at an environmentally relevant concentration (0.5 μg/L) across the parental and grand-offspring generations using a full-factorial design. In both generations, chlorpyrifos reduced survival and acute heat tolerance, which, as expected, were further magnified by the preceding heat spike. Notably, parental exposure to chlorpyrifos decreased the sensitivity of grand-offspring to the toxicant, and more strikingly, offset the synergistic interaction between the heat spike and chlorpyrifos. Both the increased toxicity of the pesticide after exposure to the heat spike and the mitigating impact of the transgenerational effects on this synergism could be explained by changes in acetylcholinesterase activity and hemoglobin concentration. These findings underscore the critical role of transgenerational effects in ecotoxicology, including their potential to shape toxicant-warming interactions. Our results emphasize the necessity of incorporating transgenerational effects and multistressor scenarios into ecological risk assessments of toxicants in the context of global warming.