Microhabitat humidity rather than food availability drives thermo-hydroregulation responses to drought in a lizard

The regulation of energy, water and thermal balance involves integrated processes that should drive ecological responses of ectotherms to climate change. Functional tradeoffs between thermoregulation and hydroregulation are exacerbated during hot or dry spells, but how microhabitat hydric properties and trophic resource availability influence these tradeoffs remains unknown. Here, we investigated the effects of microhabitat humidity and food availability on thermo-hydroregulation strategies in the ground-dwelling common lizard Zootoca vivipara during a simulated hot and dry spell event. We exposed lizards to a five-day long acute water restriction in hot conditions in the laboratory and manipulated hydric quality of the retreat site (wet or dry shelter) as well as food availability (ad libitum food or food deprivation). Water restriction and food deprivation caused physiological responses such as muscle catabolism and mobilization of caudal energy reserves. Lizards also developed behavioural strategies to conserve water or energy via decreased thermoregulation effort, higher shelter use and increased eye closure behaviours through time. These physiological and behavioural changes were importantly buffered by the presence of a wet shelter but not by food availability. A wet retreat site reduced the behavioural conflicts between thermoregulation and hydroregulation, allowed lizards to maintain a better condition and reduced physiological dehydration. Instead, food intake did not play a major role in the regulation of hydration state and increased behavioural conflicts between thermoregulation and hydroregulation. A better consideration of thermo-hydroregulation behaviours and microhabitat hydric quality is required to address ectotherm responses to future climate change.