Heatwaves and droughts are becoming more intense and frequent with climate change. These extreme weather events often occur simultaneously and may alter organismal physiology, yet their combined impacts remain largely unknown. Here, we experimentally investigated physiological responses of a temperate ectotherm, the asp viper (Vipera aspis), to a simulated heatwave and drought. We applied a two-by-two factorial design by manipulating the daily temperature cycle (control vs. heatwave) and the water availability (water available vs. water-deprived) over a month followed by exposure to standard thermal conditions with ad libium access to water. Simulated heatwave and water deprivation additively increased mass loss, while water deprivation led to greater plasma osmolality (dehydration). Mass gain from drinking after the treatment period was higher in vipers from the heatwave and water-deprived group suggesting that thirst was synergistically influenced by thermal and water constraints. Heatwave conditions and water deprivation also additively increased baseline corticosterone levels but did not influence basal metabolic rates and plasma markers of oxidative stress. Our results demonstrate that a short-term exposure to combined heatwave and drought can exacerbate physiological stress through additive effects, and interactively impact behavioral responses to dehydration. Considering combined effects of temperature and water availability is thus crucial to assess organismal responses to climate change.

This work was performed by Mathias Dezetter during his PhD project cosupervised with Olivier Lourdais at CNRS, Chizé.

Citation: Mathias Dezetter, Jean-François Le Galliard, Mathieu Leroux-Coyau, François Brischoux, Fréderic Angelier, Olivier Lourdais; Two stressors are worse than one: combined heatwave and drought affect hydration state and glucocorticoid levels in a temperate ectotherm. J Exp Biol 2022; jeb.243777. doi: https://doi.org/10.1242/jeb.243777