Water restriction induces behavioral fight but impairs thermoregulation in a dry‐skinned ectotherm

Abstract

Behavioral fight responses to desiccation risk are important to predict the vulnerability of terrestrial animals to climate change and yet, they have received little attention so far. In terrestrial ectotherms, behavioral regulation of the water balance (i.e. hydroregulation) is likely to be plastic and may tradeoff with thermoregulation behavior because water loss rates are generally higher in warmer environments and body temperatures. When low water availability and heat stress cause physiological dehydration, we expect to highlight a shift to behavioral water‐conservation strategies including changes in activity patterns, micro‐habitat selection and thermoregulation strategies. Here, we compared the behavior of adult common lizards Zootoca vivipara in indoor arenas that either had a permanent access to water or underwent a one‐week long experimental water restriction. Water‐restricted lizards reduced their behavioral activity, selected more often cooler and wetter refuges during daytime, and performed less accurate thermoregulation than control lizards. The activity of water‐restricted gravid females shifted towards the cooler and wetter early hours of the day. In addition, they had lower body temperatures and preferred lower body temperatures at the end of the experiment (i.e. thermal depression). Water‐restricted lizards suffered from a mild physiological dehydration and had a lower mass change. Heat stress was simulated every second day, which led to a range of heat avoidance and water conservation strategies independent from water restriction. Altogether, these results confirm that chronic water restriction and dehydration induce responses towards water conservation that conflict with thermoregulation accuracy.

Short-term changes in air humidity and water availability weakly constrain thermoregulation in a dry-skinned ectotherm

“…The analysis of daily thermoregulation patterns reveals subtler effects of water conditions. In general, lizards bask at higher temperatures at the beginning than at the end of the day, as highlighted in our previous work using the same protocol with a thermal gradient [40,46] or with more complex experimental arenas [30]. The effects of free-standing water availability are more pronounced at the end of the day than at the beginning: in the presence of free water, lizards maintain a higher preferred temperature that is more stable over time during the day, whereas a decrease in body temperatures is observed at the end of the day under water restriction conditions, especially in females (effect size of ca.…”

“…It also explains why overall effects of our manipulation on thermal preference were generally small since experiments lasted only one day, an insufficient time to induce a severe dehydration. Other studies have shown that changes in thermoregulation and activity were proportional to the dehydration status of individuals in several species of reptiles [29,30,34]. In contrast, Sannolo and Carretero [28] observed short-term behavioral responses to water restriction suggesting that Podarcis lizards might be sensitive to the perception of dehydration risk.…”

“…Yet, we still poorly know the effects of short-term changes in individual water balance on the thermoregulatory behavior of dry-skinned ectotherms, such as lizards and snakes [27,28]. Further studies of the effects of dehydration on thermal preferences in dry-skinned ectotherms are needed to understand their thermo-hydroregulation mechanisms and to reveal how different species of ectotherms respond both to hydric and thermal constraints in their environment [e.g., 29,30].…”

“…A chronic dehydration caused by a restriction of drinking water in the laboratory or a lack of free water under natural conditions can compromise thermoregulatory behavior in lizards. For example, prolonged water restriction over several days may lead lizards to select lower body temperatures and reduce their activity [30,34]. Under natural conditions, several reptile species can also modify their activity behavior and their choice of micro-habitats depending on rainfall intensity and availability of free-standing water in the habitat [35][36][37].…”

“…Here, we tested for short-term effects of daily changes in free water availability and air humidity on the thermoregulatory behavior of a ground-dwelling lizard species, Zootoca vivipara, that typical inhabits cold and humid environments across Eurasia. In this species, chronic restriction in water availability leads to individual dehydration and is associated with a decrease in locomotor activity and thermal preferences, and changes in the selection of thermal and moist refuges during the daytime [30,[38][39][40]. In order to study the short-term flexibility of thermoregulation behavior to the risk of dehydration, we measured PBT in thermal gradients installed in climatic chambers maintained under perfectly controlled environmental conditions (temperature, humidity, ventilation, and light).…”