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Project

Combined effects of global warming and pesticide exposure on mosquitoes: integrating temporal aspects within and across generations in ecotoxicology

Pesticides and warming are two major environmental stressors in aquatic ecosystems that can cause biodiversity loss and can interact with each other. Therefore, investigating the combined effects of warming and pesticide exposure is important for assessing the net impact of pesticides on non-target aquatic species. Despite the growing awareness of the roles of temporal aspects in stressor interactions and of the effects of warming in ecotoxicological studies, current knowledge about the interactive effects between warming and pesticides is largely based on empirical studies of simultaneous exposure to both stressors. The purpose of this thesis was to evaluate the importance of considering realistic temporal exposure scenarios to warming for the risk assessment of pesticides. I thereby studied the within- and across-generation combined effects of warming-related factors (increase in mean temperature and heat extremes) and pesticide exposure on the mosquito species Culex pipiens

In chapters 1 and 2, I tested whether and how the toxicity of the pesticide chlorpyrifos was modulated by the sequential exposure to a heat spike within a generation. I found that the heat spike applied in the first larval stage caused considerable direct and delayed mortality, and the survivors were less sensitive to the subsequent exposure to chlorpyrifos in the final larval stage which probably was caused by survival selection and cross-tolerance (chapter 1). In contrast, the heat spike strongly magnified the toxicity of chlorpyrifos when the heat spike was applied in the final larval stage and directly followed by the chlorpyrifos exposure, and this synergism disappeared or was weakened when the exposure order was reserved (chapter 2). 

In chapters 3 and 4, I investigated whether and how the duration of exposure to warming can predictably modify pesticide toxicity. I thereby contrasted the effects of acute, developmental and transgenerational warming on the toxicity of chlorpyrifos. The net impact of chlorpyrifos on life history and physiology (chapter 3) and on heat tolerance and antipredator behaviour (chapter 4) was weakened under warming, caused by the warming-induced increase in the degradation rate of chlorpyrifos. In addition, the impact of chlorpyrifos under warming was affected by the exposure duration to warming, where acute warming increased the toxicity of chlorpyrifos more compared to developmental and transgenerational warming.

In chapter 5, I tested for the sequential exposure of a heat spike followed by exposure to chlorpyrifos and this in a full factorial way in the parental and offspring generations. Parental exposure to chlorpyrifos caused adaptive transgenerational effects in terms of increased tolerance to chlorpyrifos in the offspring, suggesting an underestimation of the risk of a toxicant in field-collected animals in case that their parents already experienced the toxicant. Nevertheless, the synergism between the heat spike and exposure to chlorpyrifos did not change in the offspring when parents had been exposed to chlorpyrifos.

In general, my thesis provides considerable evidence from life history, heat tolerance, physiology and antipredator behaviour that global warming-related factors can strongly modulate the impact of exposure to a pesticide, and importantly that this can be strongly dependent on the temporal exposure scenario. Hence, my results emphasize the importance of integrating ecologically relevant temporal exposure scenarios in ecotoxicological studies and risk assessment of pollutants.

 

Date:16 Oct 2017 →  5 Oct 2021
Keywords:warming, pesticide, temporal aspect
Disciplines:Ecology, Environmental science and management, Other environmental sciences, Geology, Aquatic sciences, challenges and pollution, Animal biology, Veterinary medicine, Fisheries sciences
Project type:PhD project