Acute warming increases pesticide toxicity more than transgenerational warming by reducing the energy budget.

There is increasing awareness that the toxicity of pesticides can to a large extent be modulated by warming, and that temporal exposure scenarios may strongly affect the impact of two stressors. Nevertheless, we lack information on how the exposure duration to warming may shape pesticide toxicity under warming. Furthermore, despite that bioenergetic responses have the potential to generate mechanistic insights in how toxicants interact with warming, this has been understudied in ecotoxicology. To investigate whether warming duration modifies pesticide toxicity, mosquito larvae were exposed to a control temperature at 20 °C or three warming treatments at 24 °C (acute, developmental and transgenerational warming), and to four pesticide treatments (solvent control, and three chlorpyrifos concentrations) in a full factorial design. Chlorpyrifos increased mortality, growth rate and the energy consumed, and reduced the AChE (acetylcholinesterase) activity, the energy available, and the net energy budget (estimated as cellular energy allocation). The warming treatments did not affect mortality, AChE activity, and the energy consumed. However, acute warming increased the growth rate and decreased the energy available, while both acute and developmental warming decreased the cellular energy allocation. A first key finding was that the lethal and sublethal effects of chlorpyrifos were less strong under warming because of a higher degradation in the medium under warming. A second key finding was that, among the warming treatments, the pesticide toxicity was more increased under acute warming than under transgenerational warming. This could be explained by the negative impact of acute warming but not transgenerational warming on the net energy budget. The results in this study provide mechanistic insights that the exposure duration to warming can play an important role in modulating the impact of pesticides under warming. Therefore, including ecologically relevant temporal scenarios of exposure to warming is important in ecotoxicological studies.

Temperature variation magnifies chlorpyrifos toxicity differently between larval and adult mosquitoes.

To improve risk assessment there is increasing attention for the effect of climate change on the sensitivity to contaminants and vice versa. Two important and connected topics have been largely ignored in this context: (i) the increase of daily temperature variation (DTV) as a key component of climate change, and (ii) differences in sensitivity to climate change and contaminants between developmental stages. We therefore investigated whether DTV magnified the negative effects of the organophosphate insecticide chlorpyrifos on mortality and heat tolerance and whether this effect was stronger in aquatic larvae than in terrestrial adults of the mosquito Culex pipiens. Exposure to chlorpyrifos at a constant temperature imposed mortality and reduced the heat tolerance in both larvae and adult males, but not in adult females. This provides the first evidence that the TICS ("toxicant-induced climate change sensitivity") concept can be sex-specific. DTV had no direct negative effects. Yet, consistent with the CITS ("climate-induced toxicant sensitivity") concept, DTV magnified the toxicity of the pesticide in terms of larval mortality. This was not the case in the adult stage indicating the CITS concept to be dependent on the developmental stage. Notably, chlorpyrifos reduced the heat tolerance of adult females only in the presence of DTV, thereby providing support for the reciprocal effects between DTV and contaminants, hence the coupling of the TICS and CITS concepts. Taken together, our results highlight the importance of integrating DTV and the developmental stage to improve risk assessment of contaminants under climate change.

Impact of temperature and pyrene exposure on the functional response of males and females of the copepod Calanus finmarchicus.

We know very little about the effects of two global stressors, elevated temperature and contaminants, on the grazing of marine copepods. To address this issue, we tested the hypotheses that the individual and combined effects of these two stressors may reduce grazing rates and may depend on food availability and gender. We exposed male and female Calanus finmarchicus copepods to pyrene at two temperatures (10 and 14 °C) and six food concentrations (25-800 µg C Rhodomonas baltica L-1) and measured fecal pellet size, and grazing rate (GR) from pellet production. Males had smaller fecal pellets and lower GR than did females. Temperature and pyrene exposure had no effect on pellet size. Temperature alone had no effect on GR of males, but females had lower GR at elevated temperature. Pyrene-exposed males and females had lower GR only at the food concentrations of 200-800 µg C R. baltica L-1 and those patterns were independent of temperature. Pyrene-induced reduction in GR was stronger in females than in males. The negative effects of both elevated temperature and pyrene may reduce the abundance and trophic success of C. finmarchicus in a warmer, more polluted future.

Impact of Pyrene Exposure during Overwintering of the Arctic Copepod Calanus glacialis.

While ongoing warming and sea ice decline threaten unique Arctic ecosystems, they improve the prospect of exploiting fossil fuels in the seafloor. Arctic Calanus copepods can accumulate oil compounds in the large lipid reserves that enable them to cope with highly seasonal food availability characteristic of the Arctic. While spending a significant part of their lives overwintering at depth, their vulnerability to oil contamination during winter remains unknown. We investigated effects of the hazardous crude oil component pyrene on overwintering Calanus glacialis, a key species in Arctic shelf areas. Females were exposed from December to March and then transferred to clean water and fed until April. We showed that long-term exposure during overwintering reduced survival and lipid mobilization in a dose-dependent manner at concentrations previously considered sublethal. After exposure, strong delayed effects were observed in lipid recovery, fecal pellet, and egg production. We showed that 50% lethal threshold concentrations were at least 300 times lower than expected, and that 50% effect thresholds for pellet and egg production were at least 10 times lower than previously documented. Our study provides novel insights to the effects of oil contamination during winter, which is essential to evaluate ecological impacts of Arctic oil pollution.