Temporal variability of food determines the outcome of pesticide exposure in Daphnia

Abstract

AbstractIn nature the effect that pollutants exert on exposed organisms could depend on the state and dynamics of natural environmental factors as well as on the internal state of the exposed organisms. In this study we evaluated how level and variability of food, as well as the age of exposure can modify the effects of the pesticide deltamethrin on the freshwater crustacean Daphnia magna. The effects of the pesticide were measured on life history and nutritional traits (lipid storage) of the test organisms, which were exposed at different juvenile ages under constant (high and low) food as well as food shortage treatments. Our results show that deltamethrin exerts significant effects on all evaluated traits of Daphnia, and several responses are shaped by deltamethrin interacting with food and age of exposure. Two novel results are remarkable. First, at constant food treatments the effects of the pesticide were stronger on younger individuals, whereas in food shortage treatments the effects were stronger on older individuals. Second, we observed that deltamethrin exerted stronger effects on certain traits (survival, body growth and median consumption time of lipids) in Daphnia exposed to food shortage, as compared to constant low food treatments. Our results highlight the importance of the dynamics of resources in freshwater systems for shaping the vulnerability of herbivores to pollutants released to the ecosystem and improve our understanding of how the organismal responses to environmental stress are determined by the ecological condition of the organisms at the instant of being exposed to perturbations.