Increased Daily Temperature Fluctuations Overrule the Ability of Gradual Thermal Evolution to Offset the Increased Pesticide Toxicity under Global Warming

Abstract

The widespread evidence that global warming can increase species sensitivities to chemical toxicants and vice versa, and the recent insight that thermal evolution may mitigate these effects is crucial to predict the future impact of toxicants in a warming world. Nevertheless, a major component of global warming, the predicted increase in daily temperature fluctuations (DTFs), has been ignored at the interface of evolutionary ecotoxicology and global change biology. We studied whether 4°C warming and an 5°C DTF increase (to 10°C DTF) magnified the negative impact of the insecticide chlorpyrifos (CPF) in larvae of low-and high-latitude populations of the damselfly Ischnura elegans. While 4°C warming only increased CPF-induced mortality in high-latitude larvae, the high (10°C) DTF increased CPF-induced larval mortality at both latitudes. CPF reduced the heat tolerance, however, this was buffered by latitude-specific thermal adaptation to both mean temperature and DTF. Integrating our results in a space-for-time substitution indicated that gradual thermal evolution in high-latitude larvae may offset the negative effects of CPF on heat tolerance under warming, unless the expected DTF increase is taken into account. Our results highlight the crucial importance of jointly integrating DTFs and thermal evolution to improve risk assessment of toxicants under global warming.

Shrinking Body Size and Physiology Contribute to Geographic Variation and the Higher Toxicity of Pesticides in a Warming World

“…Exposure to CPF increased mortality and reduced growth rate of I. elegans damselfly larvae thereby confirming previous studies in the study species [29][30][31] . CPF-induced growth reductions can be explained by an energy allocation away from growth towards maintenance 32 , respiration 33 and/or defense and repair mechanisms 34 .…”

Genetic compensation rather than genetic assimilation drives the evolution of plasticity in response to mild warming across latitudes in a damselfly

“…De Block et al., 2013; Debecker & Stoks, 2019; Van Dievel et al., 2019). Taken together, this sets the stage for applying space‐for‐time substitutions, as has been successfully applied to predict the life history, behaviour and physiology of the northern populations in response to 4°C warming by 2,100 (De Block et al., 2013; Debecker & Stoks, 2019; Dinh Van et al., 2013, 2014; Janssens et al., 2014; Verheyen et al., 2019).…”

Negative bioenergetic responses to pesticides in damselfly larvae are more likely when it is hotter and when temperatures fluctuate

“…As for mean temperatures, DTFs can greatly differ in magnitude across spatial gradients (Wang and Dillon, 2014), and are predicted to increase under global warming (Colinet et al, 2015;IPCC, 2013;Vázquez et al, 2017). Notably, there is increasing evidence that DTFs may make pesticides more toxic (Delnat et al, 2019b;Verheyen et al, 2019;Verheyen and Stoks, 2019b;Willming et al, 2013;Willming and Maul, 2016). For example, while a given environmentally realistic concentration of the organophosphate insecticide chlorpyrifos was not toxic at a constant temperature of 20 °C, it did increase mortality fivefold under DTFs in damselfly larvae (Verheyen and Stoks, 2019b).…”

“…For example, while a given environmentally realistic concentration of the organophosphate insecticide chlorpyrifos was not toxic at a constant temperature of 20 °C, it did increase mortality fivefold under DTFs in damselfly larvae (Verheyen and Stoks, 2019b). To increase the realism of current and future risk assessment it is therefore crucial to study the combined effects of a mean temperature and DTF on pesticide toxicity (Verheyen et al, 2019) To better understand interactions between pesticides and natural stressors, it is important to consider effects on physiological traits (Côté et al, 2016;Gunderson et al, 2016;Hooper et al, 2013;Jackson et al, 2016). There is particularly poor knowledge about how pesticide toxicity is affected by DTF through physiological changes (but see Verheyen and Stoks, 2019a;Willming et al, 2013).…”