Evaporative water loss simulation improves models’ prediction of habitat suitability for a high-elevation forest skink

Behavioural hydroregulation protects against acute effects of drought in a dry-skinned ectotherm

During extreme climate events, behavioural thermoregulation may buffer ectotherms from thermal stress and overheating. However, heatwaves are also combined with dry spells and limited water availability, and how much individuals can behaviourally mitigate dehydration risks through microclimate selection remains largely unknown. Herein, we investigated the behavioural and physiological responses to changes in air and microhabitat humidity in a terrestrial ectotherm, the asp viper (Vipera aspis). We exposed individuals to a simulated heatwave together with water deprivation for 3 weeks, and manipulated air water vapour density (wet air vs. dry air) and microclimate (wet shelter vs. dry shelter) in a two-by-two factorial design. Dry air conditions led to substantial physiological dehydration and muscle wasting. Vipers exposed to dry air used more often a shelter that offered a moist microclimate, which reduced dehydration and muscle wasting at the individual level. These results provide the first experimental evidence that active behavioural hydroregulation can mitigate specific physiological stress responses caused by a dry spell in an ectotherm. Future studies investigating organismal responses to climate change should consider moisture gradient in the habitat and integrate both hydroregulation and thermoregulation behaviours.

Climate Change Impacts on Tropical Reptiles: Likely Effects and Future Research Needs Based on Sri Lankan Perspectives

The tropical island nation of Sri Lanka has a rich terrestrial and aquatic reptilian fauna. However, like most other tropical countries, the threat of climate change to its reptile diversity has not been adequately addressed, in order to manage and mitigate the extinction threats that climate change poses. To address this shortfall, a review of the international literature regarding climate change impacts on reptiles was undertaken with specific reference to national requirements, focusing on predicted changes in air temperature, rainfall, water temperature, and sea level. This global information base was then used to specify a national program of research and environmental management for tropical countries, which is urgently needed to address the shortcomings in policy-relevant data, its availability and access so that the risks of extinction to reptiles can be clarified and mitigated. Specifically, after highlighting how climate change affects the various eco-physiological features of reptiles, we propose research gaps and various recommendations to address them. It is envisaged that these assessments will also be relevant to the conservation of reptilian biodiversity in other countries with tropical and subtropical climatic regimes

Landscape forest impacts the potential activity time of an invasive lizard and its possibilities for range expansion in Taiwan under climate warming

Climate warming may have an impact on invasive species and their ecological consequences. Invasive reptiles, which have temperature-dependent physiology, are expected to be greatly impacted by climate warming, though data supporting this is limited. We investigated the potential impact of a warmer climate on an invasive lizard, Eutropis multifasciata, in Taiwan. A mechanistic model, NicheMapR, was used to simulate the maximum activity time available at three elevations, with varying forest densities, under the current climate and a warmer scenario. The results show that climate warming will provide this species more time for activity in the currently occupied lowland region but not in the mountain areas, which are covered with dense forests. However, if the landscape becomes more open in mountain areas, it will become more suitable for this species and may enable an expansion upslope. Our results show that climate warming has a positive impact on this species, and that landscape's characteristics profoundly modulate its impact and the possibilities for elevational expansion in the future.

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

Thermoregulation is critical for ectotherms as it allows them to maintain their body temperature close to an optimum for ecological performance. Thermoregulation includes a range of behaviors that aim at regulating body temperature within a range centered around the thermal preference. Thermal preference is typically measured in a thermal gradient in fully-hydrated and post-absorptive animals. Short-term effects of the hydric environment on thermal preferences in such set-ups have been rarely quantified in dry-skinned ectotherms, despite accumulating evidence that dehydration might trade-off with behavioral thermoregulation. Using experiments performed under controlled conditions in climatic chambers, we demonstrate that thermal preferences of a ground-dwelling, actively foraging lizard (Zootoca vivipara) are weakly decreased by a daily restriction in free-standing water availability (less than 0.5°C contrast). The influence of air humidity during the day on thermal preferences depends on time of the day and sex of the lizard, and is generally weaker than those of of free-standing water (less than 1°C contrast). This shows that short-term dehydration can influence, albeit weakly, thermal preferences under some circumstances in this species. Environmental humidity conditions are important methodological factors to consider in the analysis of thermal preferences.

Comparative thermal ecology parameters of the mexican dusky rattlesnake (Crotalus triseriatus)

Montane habitats exhibit a high degree of thermal heterogeneity, and thus provide considerable thermoregulatory challenges for ectotherms. Comparative analyses provide an opportunity to understand how variation in abiotic factors (e.g., operative temperatures, thermal quality) can affect life history traits within species. We studied the thermal ecology of three populations of the rattlesnake Crotalus triseriatus inhabiting different volcanoes in the central region of Mexico using the Hertz et al. (1993) protocol. The average body temperature of dusky rattlesnakes from the three study sites was 22.4 °C; mean active body temperature was higher in site 2 than in sites 1 and 3, but no differences between females, males and juveniles nor an interaction among site and sex was found. The thermal quality was low in the three sites, particularly in sites 1 and 3. Thermoregulation accuracy statistically differed among populations: individuals from site 2 were more accurate thermoregulating, while individuals from site 1 were the least accurate. Compared to other snakes, dusky rattlesnakes can be considered as a eurythermic species, which can often be active at relatively low body temperatures.

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

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.

The functional significance of panting as a mechanism of thermoregulation and its relationship to the critical thermal maxima in lizards

Because most desert-dwelling lizards rely primarily on behavioral thermoregulation for the maintenance of active body temperatures, the effectiveness of panting as a thermoregulatory mechanism for evaporative cooling has not been widely explored. We measured changes in body temperature (Tb) with increasing air temperature (Ta) for seventeen species of lizards that range across New Mexico and Arizona and quantified the temperatures associated with the onset of panting, the capacity of individuals to depress Tb below Ta while panting and estimated the critical thermal maxima (CTmax) for each individual. We examined these variables as a function of phylogeny, body mass, and local acclimatization temperature. We found that many species can depress Tb 2-3°C below Ta while panting, and the capacity to do so appears to be a function of each species’ ecology and thermal environment, rather than phylogeny. Panting thresholds and CTmax’s are phylogenetically conserved within groups. Understanding the functional significance of panting and its potential importance as a thermoregulatory mechanism will improve our understanding of the potential for species’ persistence in an increasingly warmer world.