Short‐term change in water availability influences thermoregulation behaviours in a dry‐skinned ectotherm

Abstract

Mechanistic models of terrestrial ectotherms predict that climate warming will induce activity restriction due to heat stress and loss of shade, leading to the extinction of numerous populations. Such models rely on the assumption that activity patterns are dictated by simple temperature thresholds independent of changes in water availability. However, changes in water availability may further influence thermoregulation behaviour of ectotherms through dehydration risk perception, changes in water balance or changes in microclimatic conditions. Here, we experimentally assess the interactive effects of thermal conditions and water availability on activity patterns, shade selection and thermoregulation efficiency in a model ectothermic species. Thermoregulation behaviour of adult common lizards Zootoca vivipara was monitored in outdoor mesocosms as we manipulated water availability, providing water as mist in the morning and free‐standing water during the daytime. We recorded operative temperatures and micro‐meteorological conditions to infer thermal constraints and dehydration risk. Activity and shade selection were better predicted by continuous changes in thermal conditions and dehydration risk, respectively, than by threshold functions. In addition, water supplementation increased activity in males and reduced shade selection in both sexes, most probably as a behavioural response to the perception of a stronger dehydration risk. Water supplementation also influenced the thermal quality of the environment, which in turn altered daily activity patterns and thermoregulation statistics. This demonstrates that dual effects of heat and water stress on activity patterns may lead to stronger activity restriction as a result of climate change than currently predicted.

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

“…Since lizards of the genus Podarcis are species with a more sit-and-wait foraging mode, they might have less opportunities to adjust their behavioral activity and their "only" behavioral solution is therefore to lower importantly their body temperature in the absence of water. Unfortunately, we did not record movement activity in this study but previous investigations with lizards have shown that dehydration can reduce locomotor activity [29,43]. These hypotheses will have to be tested by studying a greater number of contrasting species with distinct foraging styles in the future and recording both body temperature and movement activity.…”

Habitat Partitioning and Overlap by Large Lacertid Lizards in Southern Europe

“…Climate is a powerful environmental factor driving the process of niche diversification in reptiles [1,2]. Tolerance to maximum temperatures in reptiles is evolutionarily constrained, possibly because of the importance of external heat sources in maintaining activity and for bodily water balance [3,4]. For these reasons, there is a significant association between the composition of reptile assemblages and thermal latitudinal gradients [5].…”

Global changes explain the long-term demographic trend of the Eurasian common lizard (Squamata: Lacertidae)

“…The performance of most ectotherms improves smoothly with increasing body temperature until reaching an optima, and thereafter it drastically decreases ( Huey and Stevenson 1979 ). Zootoca vivipara ’s preferred body temperature in May/June, that is, during reproduction, is between 30 °C and 34 °C in males and around 29.5 °C in gravid females, and the range over which its performance is at least 80% of maximal performance is quite narrow ±2–5 °C ( Van Damme et al 1991 ; Gvoždík and Castilla 2001 ; Rozen-Rechels et al 2020 ). Its critical thermal maxima is between 43.8 °C and 44.1 °C.…”

“…At this temperature its righting reflex is lost, leg spasms happen, and lethal or near lethal injury occurs ( Gvoždík and Castilla 2001 ; Leon and Bouchama 2015 ). Operative temperatures, that is, the body temperature of a perfectly thermoconforming animal ( Dzialowski 2005 ), reach more than 50 °C in the early afternoon at the beginning of May and on most study days, they were much above Z. vivipara ’s preferred body temperature (measured in May 2018, Rozen-Rechels et al 2020 ). However, in May, the daily maximal temperatures are much below the daily maxima occurring in summer (e.g., in May they were −7.2 °C lower than in summer 2018 in Nemours les Saint-Pierre, France, where Rozen-Rechels et al [2020] recorded operative temperatures [click on this weblink to see the daily maximal temperatures at Nemours les Saint-Pierre] ).…”

“…Operative temperatures, that is, the body temperature of a perfectly thermoconforming animal ( Dzialowski 2005 ), reach more than 50 °C in the early afternoon at the beginning of May and on most study days, they were much above Z. vivipara ’s preferred body temperature (measured in May 2018, Rozen-Rechels et al 2020 ). However, in May, the daily maximal temperatures are much below the daily maxima occurring in summer (e.g., in May they were −7.2 °C lower than in summer 2018 in Nemours les Saint-Pierre, France, where Rozen-Rechels et al [2020] recorded operative temperatures [click on this weblink to see the daily maximal temperatures at Nemours les Saint-Pierre] ). As a consequence, Z. vivipara exhibits a unimodal activity pattern with an activity peak around midday when daily maximal temperatures are below 34 °C and evapotranspiration is not too high.…”