Physiological state influences evaporative water loss and microclimate preference in the snake Vipera aspis

Cutaneous water loss and epidermal lipid content in lanceheads (Crotalinae: Bothrops)

Cutaneous evaporation is the primary route of water loss in snakes. Species from arid environments typically show lower cutaneous water loss (CWL) rates due in part to higher epidermal lipid content. However, past comparative studies have used distantly related taxa or lacked phylogenetic comparative methods, limiting their conclusions. We measured CWL and lipid content (LC) in shed skins of eight lancehead species (Bothrops) from habitats with varying canopy coverage. Using phylogenetic comparative methods, we examined the effects of canopy coverage, snout-vent length (SVL), sex, and species on CWL and assessed its correlation with LC. Our results show that canopy coverage significantly influences CWL, independent of phylogeny. Snakes from open habitats exhibited lower CWL rates than those restricted to forests, which showed greater individual variation. Species from the most xeric habitat (Caatinga) displayed the lowest CWL. Neither sex nor SVL affected CWL, and phylogenetic signal was negligible (λ ≈ 0), suggesting weak phylogenetic constraints. CWL and LC were inversely correlated, with LC higher in open-habitat species. These findings indicate that habitat type, particularly canopy coverage, drives interspecific variation in CWL among closely related species, while phylogenetic effects are more relevant at higher taxonomic levels. Lipid content in the epidermis plays a critical role in regulating CWL, though differences in lipid composition may also contribute.

Hydrothermal physiology and vulnerability to climatic change: insight from European vipers

Clarifying physiological adaptations is crucial to understand species distribution and predict vulnerability to changing climatic conditions. Considering energy and water constraints jointly is necessary because these facets are intertwined in ectotherms. The genus Vipera is a diversified group of Palearctic snakes with parapatric distributions and contrasted climatic affinities. These species are active thermoregulators relying on basking to maintain their body temperature. While some species such as V. berus and V. seoanei are adapted to cold and wet environments, other species have intermediate (temperate-oceanic) affinities (V. aspis), and some such as V. latastei and V. ammodytes inhabit warm and semi-arid climates. We studied physiological traits related to energy and water balance in these five species to better understand species' vulnerability to climate change. First, using open-flow respirometry we quantified standard metabolic rate (SMR) and evaporative water loss (TEWL) at three temperatures (15 °C, 25 °C and 33 °C). Cold- and wet-adapted species exhibited higher metabolic rates and evaporative water loss, reflecting adaptations to colder, wetter environments, while warm- and dry-adapted species showed lower rates. Second, we used these data to investigate their physiological responses to extreme climatic events (ECE). Simulated responses to summer heat spells revealed a major increase in energy expenditure and water loss rates across species. However, the effect was more prominent in cold- and wet-adapted species. This study underscores the physiological constraints that cold and wet-adapted species face during extreme climate events, providing insights into the vulnerabilities of ectotherms to ongoing environmental changes.

Gehyra Geckos Prioritize Warm Over Humid Environments

Maintaining stable hydric and thermal states are dual challenges for reptiles that inhabit terrestrial environments with variable conditions across time and space. Under some conditions, reptiles face a conundrum where both physiological parameters cannot be simultaneously maintained at preferred levels by behavioral or physiological means. Prioritization of behavioral regulation of hydric or thermal state, and at which point this prioritization changes, was tested for nine species of congeneric tropical geckos by assessing their use of microhabitats with distinct thermal and hydric conditions in a controlled environment. Gehyra geckos were presented with two crevices of contrasting humidity levels, and time spent in either crevice was recorded across three ambient temperature treatments of 32°C, 27°C, and 22°C. Temperatures in the humid crevice matched ambient air temperature, whereas temperature in the dry crevice was maintained at 32°C. In these trials, all species showed greater use of the dry (and warm) crevice in the 27°C and 22°C treatments, while there was no strong preference for the humid or dry crevice in the 32°C treatment. Thus, Gehyra geckos prioritized thermoregulation and maintained thermal state through behavioral responses, and humid microhabitats were not selected even when it did not compromise the animal's thermal state. Although selection for preferred thermal conditions was prioritized in the short term, this does not preclude the possibility that hydric state can be regulated on a seasonal time scale.

Rain-harvesting behavior in free-ranging prairie rattlesnakes (Crotalus viridis)

Organisms inhabiting arid environments face challenges to obtain dietary water. To prevent desiccation, some organisms possess unique adaptations to harvest water from infrequent and unpredictable rainfall, including several squamates (snakes and lizards). While most squamates consume precipitation as it pools in the environment, a small number engage in behaviors to enhance water collection by capturing precipitation from their own skin, referred to as rain-harvesting behavior (RHB). Details of this behavior remain unclear, particularly the sequence of behaviors associated with RHB. We developed a method to simulate rainfall to observe RHB in prairie rattlesnakes (Crotalus viridis) in situ and recorded 72 events in 94 snakes, the most robust sampling of RHB to date. Using video analysis, we describe the postures and kinematics of RHB and develop the first illustrated ethogram of this behavior for any vertebrate. Our results demonstrate that RHB contains fixed and variable patterns useful in cross-species comparisons and in exploring proximate causes of the behavior. In addition, we describe novel features of RHB including suspended head drinking, body levering, and drinking from neighboring snakes. Our results reveal RHB to be an intricate suite of movements and actions, some of which allude to acute sensory abilities of these animals that warrant further study. Furthermore, observations of RHB at dens and rookeries suggest a potential, novel benefit of snake aggregation is the formation of large, communal surfaces for rain harvesting. We suggest that the extremely elongated body plan of snakes may be well-suited for a rapidly deployed, modular rain-harvesting system effective at capitalizing on fleeting rainstorms characteristic of arid ecosystems of the world.

Flexibility of cutaneous evaporative water loss in response to hydration in pregnant prairie rattlesnakes (Crotalus viridis) and their neonates

Viviparous snakes may be particularly vulnerable to predicted increases in drought because of the high hydric costs associated with embryonic development and gestation, and their reliance on limited free-standing bodies of water or rain events for hydration. Drought will have negative implications for viper populations if females become increasingly water stressed and resorb developing embryos to conserve bodily water. We conducted a study to investigate the importance of drinking water in late-term pregnancy and its effect on cutaneous evaporative water loss (CEWL). We measured hydration and water loss in response to supplemental hydration during the final stages of embryonic development and gestation in arid-adapted prairie rattlesnakes (Crotalus viridis). Our goal was to assess how supplemental water affects hydration status and water loss (via CEWL) of females during and after pregnancy, and of their neonates before and after their first ecdysis. Supplemental hydration of pregnant C. viridis improved their hydration state and their neonates were also born more hydrated than those from control mothers, showing that they transfer water to neonates via the placenta even over a very short period in the late stages of pregnancy. The supplementally hydrated maternal C. viridis experienced slightly higher rates of CEWL compared with control snakes, but CEWL was primarily driven by ambient temperature and vapor pressure deficit at the time of measurement. At birth, neonate plasma osmolality and CEWL were both directly associated with their mothers' plasma osmolality and CEWL. Additionally, we found that neonate CEWL increased after the first ecdysis, suggesting that natal skin may help neonates avoid desiccation. Investigating and quantifying physiological implications of water shortage and dehydration can help us better understand the effects of drought and predict how wild populations of arid-adapted reptiles may respond to the predicted increase in frequency and severity of droughts.

Comparing Preferred Temperatures and Evaporative Water Loss Rates in Two Syntopic Populations of Lacertid Lizard Species

Many reptiles actively regulate their body temperature. During thermoregulation, they suffer evaporative water loss (EWL). Since evaporation increases with temperature, EWL could limit the activity of ectotherms when water is not available. In this study, we compared the preferred body temperatures (Tp) and EWL of two lacertid lizard species, Darevskia praticola and Podarcis muralis, at the western edge of D. praticola's range, where they live in syntopy. We hypothesized that D. praticola, a species that inhabits forested and humid environments, would have a higher EWL than the more widespread P. muralis. Our results show that D. praticola prefers lower temperatures (mean Tp = 28.1 °C) than P. muralis (mean Tp = 30.6 °C). Despite the differences in their thermal preferences, both species showed similar total EWL (2.76% for D. praticola and 2.67% for P. muralis), although their daily patterns of water loss differed. Our results suggest that D. praticola has developed mechanisms to control water loss and that its lower thermal preference may be due to both historical factors and local adaptations. These results contribute to the understanding of how environmental factors influence the physiology of lizards, which in turn has implications for predicting the effects of climate change on species distribution.

Coping with drought? The hidden microhabitat selection and underground movements of amphisbaenians under summer drought conditions

Habitat selection is a dynamic process that depends on many environmental variables that can vary with weather conditions. This is important because, within a context of global change, extreme weather events, such as severe droughts, are predicted to become more frequent. We examined the patterns of microhabitat selection and underground movements (using PIT-tag telemetry) of a strictly fossorial reptile, the North African checkboard amphisbaenian Trogonophis wiegmanni, during the summer drought period. We aimed to test whether changes in strategies of habitat use and movements could allow this amphisbaenian to cope with unfavorable weather. We found that during the summer drought period, T. wiegmanni did not use the microhabitats in relationship to their availability, but particularly selected sites with high abundance of rocks but also areas under a high cover of bushes, where environmental conditions were more favorable. We also found, using PIT-tag telemetry, that the numbers of T. wiegmanni individuals located under rocks and their activity (number of days with movements) decreased largely in summer. However, the animals were not entirely inactive, but, especially males were active below the ground under bushes and made some relatively long underground hidden movements between favorable areas.

Prey consumption does not restore hydration state but mitigates the energetic costs of water deprivation in an insectivorous lizard

To cope with limited availability of drinking water in their environment, terrestrial animals have developed numerous behavioral and physiological strategies including maintaining an optimal hydration state through dietary water intake. Recent studies performed in snakes, which are generalist carnivorous reptiles, suggest that the benefits of dietary water intake are negated by hydric costs of digestion. Most lizards are generalist insectivores that can shift their prey types, but firm experimental demonstration of dietary water intake is currently missing in these organisms. Here, we performed an experimental study in the common lizard Zootoca vivipara, a keystone mesopredator from temperate climates exhibiting a great diversity of prey in its mesic habitats, in order to investigate the effects of food consumption and prey type on physiological responses to water deprivation. Our results indicate that common lizards cannot improve their hydration state through prey consumption, irrespective of prey type, suggesting that they are primarily dependent upon drinking water. Yet, high-quality prey consumption reduced the energetic costs of water deprivation, potentially helping lizards to conserve a better body condition during periods of limited water availability. These findings have important implications for understanding the physiological responses of ectotherms to water stress, and highlight the complex interactions between hydration status, energy metabolism and feeding behavior in insectivorous lizards.

Dehydrated snakes reduce postprandial thermophily

Transient thermophily in ectothermic animals is a common response during substantial physiological events. For example, ectotherms often elevate body temperature after ingesting a meal. In particular, the increase in metabolism during the postprandial response of pythons - known as specific dynamic action - is supported by a concurrent increase in preferred temperature. The objective of this study was to determine whether hydration state influences digestion-related behavioral thermophily. Sixteen (8 male and 8 female) Children's pythons (Antaresia childreni) with surgically implanted temperature data loggers were housed individually and provided with a thermal gradient of 25-45°C. Body temperature was recorded hourly beginning 6 days prior to feeding and for 18 days post-feeding, thus covering pre-feeding, postprandial and post-absorptive stages. Each snake underwent this 24 day trial twice, once when hydrated and once when dehydrated. Our results revealed a significant interaction between temperature preference, digestive stage and hydration state. Under both hydrated and dehydrated conditions, snakes similarly increased their body temperature shortly after consuming a meal, but during the later days of the postprandial stage, snakes selected significantly lower (∼1.5°C) body temperature when they were dehydrated compared with when they were hydrated. Our results demonstrate a significant effect of hydration state on postprandial thermophily, but the impact of this dehydration-induced temperature reduction on digestive physiology (e.g. passage time, energy assimilation) is unknown and warrants further study.

The Association Between Ambient Temperature and Snakebite in Georgia, USA: A Case-Crossover Study

The World Health Organization has identified snakebite envenoming as a highest priority neglected tropical disease, yet there is a dearth of epidemiologic research on environmental risk factors, including outdoor temperature. Temperature may affect snakebites through human behavior or snake behavior; snakes are ectotherms, meaning outdoor temperatures influence their internal body temperature and thus their behavior. Here we investigate the relationship between short-term temperature and snakebites in Georgia, one of the most biodiverse US states in terms of herpetofauna. We acquired emergency department (ED) visit data for Georgia between 1 January 2014 and 31 December 2020. Visits for venomous and non-venomous snakebites were identified using diagnosis codes. For comparison, we also considered visits for non-snake (e.g., insects, spiders, scorpions) envenomation. Daily meteorology from the Daymet 1 km product was linked to patient residential ZIP codes. We applied a case-crossover design to estimate associations of daily maximum temperature and snakebite ED visits. During the 7-year study period, there were 3,908 visits for venomous snakebites, 1,124 visits for non-venomous bites and 65,187 visits for non-snake envenomation. Across the entire period, a 1°C increase in same-day maximum temperature was associated with a 5.6% (95%CI: 4.0-7.3) increase in the odds of venomous snakebite and a 5.8% (95%CI: 3.0-8.8) increase in non-venomous snakebite. Associations were strongest in the spring. We also observed a positive and significant (p < 0.05) association for non-snake envenomation, albeit slightly smaller and more consistent across seasons compared to those for snakebites.

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.

Hydric status influences salinity-dependent water selection in frogs from coastal wetlands

The environment is heterogeneous across spatial and temporal scales, and the behavioural responses required to adjust individuals' needs to resource availability across such variable environments should be under selective pressure. Coastal wetlands are characterized by a diversity of habitats ranging from fresh- to salt water; and individuals occurring in such complex habitats need to adjust their habitat use based on their osmotic status. In this study, we experimentally tested whether an amphibian species (Pelophylax sp.) occurring in coastal wetlands was able to discriminate and select between different salinity concentrations (0, 4, 8 and 12 g.l^-1) and whether hydric status (hydrated versus dehydrated) influenced salinity-dependent water selection. We found that frogs selected water based on salinity differentially between hydrated and dehydrated individuals, with the later favoring lower salinities likely to improve their osmotic status. Interestingly, we highlighted the ability of frogs to select lower salinity before having access to water, suggesting that frogs can assess water salinity without actual contact. In coastal wetlands where salinity of water bodies can dynamically vary through space and time, such behavioural osmoregulation process is potentially a key factor affecting individual movements, habitat choice and thus species distribution. Our study further highlights the importance of salinity-dependent habitat heterogeneity and especially the presence of freshwater environments as structuring factors for the amphibian community.

Two stressors are worse than one: combined heatwave and drought affect hydration state and glucocorticoid levels in a temperate ectotherm

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.

Could plasticity mediate highlands lizards' resilience to climate change? A case study of the leopard iguana (Diplolaemus leopardinus) in Central Andes of Argentina

The predicted rise of global temperatures is of major concern for ectotherms because of its direct impact on their behavior and physiology. As physiological performance mediates a species' resilience to warming exposure, physiological plasticity could greatly reduce the susceptibility to climate change. We studied the degree to which Diplolaemus leopardinus lizards are able to adjust behavioral and physiological traits in response to short periods of temperature change. We used a split cross design to measure the acclimation response of preferred body temperature (Tp), and the thermal performance curve of resting metabolic rate (RMR) and evaporative water loss (EWL). Our results showed that plasticity differs among traits: whereas Tp and EWL showed lower values in warm conditions, the body temperature at which RMR was highest increased. Moreover, RMR was affected by thermal history, showing a large increase in response to cold exposure in the group initially acclimated to warm temperatures. The reduction of EWL and the increase in optimal temperature will give lizards the potential to partially mitigate the impact of rising temperatures in the energy cost and water balance. However, the decrease in Tp and the sensitivity to the warm thermal history of RMR could be detrimental to the energy net gain, increasing the species' vulnerability, especially considering the increase of heat waves predicted for the next 50 years. The integration of acclimation responses in behavioral and physiological traits provides a better understanding of the range of possible responses of lizards to cope with the upcoming climatic and environmental modifications expected as a result of climate change.

Bearded dragons (Pogona vitticeps) with reduced scalation lose water faster but do not have substantially different thermal preferences

Whether scales reduce cutaneous evaporative water loss in lepidosaur reptiles (Superorder Lepidosauria) such as lizards and snakes has been a contentious issue for nearly half a century. Furthermore, while many studies have looked at whether dehydration affects thermal preference in lepidosaurs, far fewer have examined whether normally hydrated lepidosaurs can assess their instantaneous rate of evaporative water loss and adjust their thermal preference to compensate in an adaptive manner. We tested both of these hypotheses using three captive-bred phenotypes of bearded dragon (Pogona vitticeps) sourced from the pet trade: 'wild-types' with normal scalation, 'leatherbacks' exhibiting scales of reduced prominence, and scaleless bearded dragons referred to as 'silkbacks'. Silkbacks on average lost water evaporatively at about twice the rate that wild-types did. Leatherbacks on average were closer in their rates of evaporative water loss to silkbacks than they were to wild-types. Additionally, very small (at most ∼1°C) differences in thermal preference existed between the three phenotypes that were not statistically significant. This suggests a lack of plasticity in thermal preference in response to an increase in the rate of evaporative water loss, and may be reflective of a thermal 'strategy' as employed by thermoregulating bearded dragons that prioritises immediate thermal benefits over the threat of future dehydration. The results of this study bolster an often-discounted hypothesis regarding the present adaptive function of scales and have implications for the applied fields of animal welfare and conservation.

Heat and water loss versus shelter: a dilemma in thermoregulatory decision making for a retreat-dwelling nocturnal gecko

Understanding the interaction between upper voluntary thermal limit (VTmax) and water loss may aid in predicting responses of ectotherms to increasing temperatures within microhabitats. However, the temperature at which climate heating will force cool-climate nocturnal lizards to abandon daytime retreats remains poorly understood. Here, we developed a new laboratory protocol for determining VTmax in the retreat-dwelling, viviparous Woodworthia 'Otago/Southland' gecko, based on escape behaviour (abandonment of heated retreat). We compared the body temperature (Tb) at VTmax, and duration of heating, between two source groups with different thermal histories, and among three reproductive groups. We also examined continuous changes in Tb (via an attached biologger) and total evaporative water loss (EWL) during heating. In the field, we measured Tb and microhabitat thermal profiles to establish whether geckos reach VTmax in nature. We found that VTmax and duration of heating varied between source groups (and thus potentially with prior thermal experience), but not among reproductive groups. Moreover, geckos reached a peak temperature slightly higher than VTmax before abandoning the retreat. Total EWL increased with increasing VTmax and with the duration of heating. In the field, pregnant geckos with attached biologgers reached VTmax temperature, and temperatures of some separately monitored microhabitats exceeded VTmax in hot weather implying that some retreats must be abandoned to avoid overheating. Our results suggest that cool-climate nocturnal lizards that inhabit daytime retreats may abandon retreats more frequently if climate warming persists, implying a trade-off between retention of originally occupied shelter and ongoing water loss due to overheating.

Micro-geographic shift between negligible and actuarial senescence in a wild snake

While it has long been known that species have contrasted life expectancy (pace of mortality) and generation time (pace of reproduction), recent studies have also uncovered that the shape of adult age trajectories of mortality and reproduction can vary remarkably among species along a continuum of senescence ranging from strong deterioration (senescence), insignificant deterioration (negligible senescence) to improvement with advancing age (negative senescence). As for many long-lived ectotherms with asymptotic growth and increasing reproductive output with age, snakes are good candidates for negligible senescence to occur. Yet, intraspecific variation in the pace and shape of actuarial and reproductive senescence across wild populations of these species remains to be explored. Here, we used 37 years of mark-recapture data in two nearby habitats inside a meadow viper Vipera ursinii population to quantify life expectancies, generation times and the shape of actuarial and reproductive senescence. Female vipers maintained stable reproductive performances at old ages, even when accounting for the predicted increase of fertility with body size, providing evidence for negligible reproductive senescence in both habitats. Males had a higher adult mortality and a shorter life expectancy on average than females and actuarial senescence shifted from negligible senescence in the optimal habitat to strong senescence in the sub-optimal habitat. Overall, these results demonstrate that micro-geographic environmental variation can generate qualitative shifts in actuarial senescence patterns. This highlights that taking into account the within-species plasticity of age-dependent trajectories could prove useful in better understanding what determines the evolution of life-history age trajectories.

Mother-offspring conflict for water and its mitigation in the oviparous form of the reproductively bimodal lizard, Zootoca vivipara

Parent-offspring conflicts are widespread given that resources are often limited. Recent evidence has shown that availability of water can trigger such conflict during pregnancy in viviparous squamate species (lizards and snakes) and thus questions the role of water in the evolution of reproductive modes. Here, we examined the impact of water restriction during gravidity in the oviparous form of the bimodal common lizard (Zootoca vivipara), using a protocol previously used on the viviparous form. Females were captured in early gravidity from six populations along a 600 m altitudinal gradient to investigate whether environmental conditions (altitude, water access and temperature) exacerbate responses to water restriction. Females were significantly dehydrated after water restriction, irrespective of their reproductive status (gravid vs. non-reproductive), relative reproductive effort (relative clutch mass), and treatment timing (embryonic development stage). Female dehydration, together with reproductive performance, varied with altitude, probably due to long term acclimation or local adaptation. This moderate water-based intergenerational conflict in gravid females contrasts sharply with previous findings for the viviparous form, with implications to the evolutionary reversion from viviparity to oviparity. It is likely that oviparity constitutes a water-saving reproductive mode which might help mitigate intensive temperature-driven population extinctions at low altitudes.

Acclimation to Water Restriction Implies Different Paces for Behavioral and Physiological Responses in a Lizard Species

Chronic changes in climate conditions may select for acclimation responses in terrestrial animals living in fluctuating environments, and beneficial acclimation responses may be key to the resilience of these species to global changes. Despite evidence that climate warming induces changes in water availability, acclimation responses to water restriction are understudied compared with thermal acclimation. In addition, acclimation responses may involve different modes, paces, and trade-offs between physiological and behavioral traits. Here, we tested the dynamical acclimation responses of a dry-skinned terrestrial ectotherm to chronic water restriction. Yearling common lizards (Zootoca vivipara) were exposed to sublethal water restriction during 2 mo of the summer season in laboratory conditions, then released in outdoor conditions for 10 additional months. Candidate behavioral (exploration, basking, and thermal preferences) and physiological (metabolism at rest and standard water loss rate) traits potentially involved in the acclimation response were measured repeatedly during and after water restriction. We observed a sequential acclimation response in water-restricted animals (yearlings spent less time basking during the first weeks of water deprivation) that was followed by delayed sex-specific physiological consequences of the water restriction during the following months (thermal depression in males and lower standard evaporative water loss rates in females). Despite short-term negative effects of water restriction on body growth, annual growth, survival, and reproduction were not significantly different between water-restricted and control yearlings. This demonstrates that beneficial acclimation responses to water restriction involve both short-term flexible behavioral responses and delayed changes in thermal and water biology traits.

Slowing down the metabolic engine: impact of early-life corticosterone exposure on adult metabolism in house sparrows (Passer domesticus)

Whole-organism metabolism is an integrative process that determines not only the energy cost of living but also the energy output that is available for behavioral and physiological processes during the life cycle. Developmental challenge is known to affect growth, development of several organs, and several physiological mechanisms (such as HPA responsiveness, oxidative stress or immunity), which may altogether affect adult metabolism. All of these developmental effects are likely to be mediated by glucocorticoids, but the impact of developmental glucocorticoid exposure on adult metabolism has rarely been studied and the results are equivocal. In this study, we examined the impact of developmental exposure to corticosterone (CORT, the main avian glucocorticoid hormone) on resting metabolic rate (RMR, measured in thermoneutrality, 25°C) and thermoregulatory metabolic rate (TMR, measured in cold challenge conditions, 5°C) in the house sparrow. Following experimental administration of CORT at the nestling stage, house sparrows were kept in captivity until adulthood, when their metabolism was measured. We found that post-natal CORT exposure decreased both RMR and TMR in adult sparrows. This CORT-mediated reduction of metabolism was also associated with a reduced overnight body mass loss. Therefore, our results suggest that developmental CORT exposure can orient the phenotype towards an energy-saving strategy, which may be beneficial in a constraining environmental context.

When water interacts with temperature: Ecological and evolutionary implications of thermo-hydroregulation in terrestrial ectotherms

The regulation of body temperature (thermoregulation) and of water balance (defined here as hydroregulation) are key processes underlying ecological and evolutionary responses to climate fluctuations in wild animal populations. In terrestrial (or semiterrestrial) ectotherms, thermoregulation and hydroregulation closely interact and combined temperature and water constraints should directly influence individual performances. Although comparative physiologists traditionally investigate jointly water and temperature regulation, the ecological and evolutionary implications of these coupled processes have so far mostly been studied independently. Here, we revisit the concept of thermo-hydroregulation to address the functional integration of body temperature and water balance regulation in terrestrial ectotherms. We demonstrate how thermo-hydroregulation provides a framework to investigate functional adaptations to joint environmental variation in temperature and water availability, and potential physiological and/or behavioral conflicts between thermoregulation and hydroregulation. We extend the classical cost-benefit model of thermoregulation in ectotherms to highlight the adaptive evolution of optimal thermo-hydroregulation strategies. Critical gaps in the parameterization of this conceptual optimality model and guidelines for future empirical research are discussed. We show that studies of thermo-hydroregulation refine our mechanistic understanding of physiological and behavioral plasticity, and of the fundamental niche of the species. This is illustrated with relevant and recent examples of space use and dispersal, resource-based trade-offs, and life-history tactics in insects, amphibians, and nonavian reptiles.

Evaluating temporal patterns of snakebite in Sri Lanka: the potential for higher snakebite burdens with climate change

Background

Snakebite is a neglected tropical disease that has been overlooked by healthcare decision makers in many countries. Previous studies have reported seasonal variation in hospital admission rates due to snakebites in endemic countries including Sri Lanka, but seasonal patterns have not been investigated in detail.

Methods

A national community-based survey was conducted during the period of August 2012 to June 2013. The survey used a multistage cluster design, sampled 165 665 individuals living in 44 136 households and recorded all recalled snakebite events that had occurred during the preceding year. Log-linear models were fitted to describe the expected number of snakebites occurring in each month, taking into account seasonal trends and weather conditions, and addressing the effects of variation in survey effort during the study and of recall bias amongst survey respondents.

Results

Snakebite events showed a clear seasonal variation. Typically, snakebite incidence is highest during November-December followed by March-May and August, but this can vary between years due to variations in relative humidity, which is also a risk factor. Low relative-humidity levels are associated with high snakebite incidence. If current climate-change projections are correct, this could lead to an increase in the annual snakebite burden of 31.3% (95% confidence interval: 10.7-55.7) during the next 25-50 years.

Conclusions

Snakebite in Sri Lanka shows seasonal variation. Additionally, more snakebites can be expected during periods of lower-than-expected humidity. Global climate change is likely to increase the incidence of snakebite in Sri Lanka.

Climate and foraging mode explain interspecific variation in snake metabolic rates

The energy cost of self-maintenance is a critical facet of life-history strategies. Clarifying the determinant of interspecific variation in metabolic rate (MR) at rest is important to understand and predict ecological patterns such as species distributions or responses to climatic changes. We examined variation of MR in snakes, a group characterized by a remarkable diversity of activity rates and a wide distribution. We collated previously published MR data (n = 491 observations) measured in 90 snake species at different trial temperatures. We tested for the effects of metabolic state (standard MR (SMR) versus resting MR (RMR)), foraging mode (active versus ambush foragers) and climate (temperature and precipitation) while accounting for non-independence owing to phylogeny, body mass and thermal dependence. We found that RMR was 40% higher than SMR, and that active foragers have higher MR than species that ambush their prey. We found that MR was higher in cold environments, supporting the metabolic cold adaptation hypothesis. We also found an additive and positive effect of precipitation on MR suggesting that lower MR in arid environments may decrease dehydration and energetic costs. Altogether, our findings underline the complex influences of climate and foraging mode on MR and emphasize the relevance of these facets to understand the physiological impact of climate change.

Water availability and environmental temperature correlate with geographic variation in water balance in common lizards

Water conservation strategies are well documented in species living in water-limited environments, but physiological adaptations to water availability in temperate climate environments are still relatively overlooked. Yet, temperate species are facing more frequent and intense droughts as a result of climate change. Here, we examined variation in field hydration state (plasma osmolality) and standardized evaporative water loss rate (SEWL) of adult male and pregnant female common lizards (Zootoca vivipara) from 13 natural populations with contrasting air temperature, air humidity, and access to water. We found different patterns of geographic variation between sexes. Overall, males were more dehydrated (i.e. higher osmolality) than pregnant females, which likely comes from differences in field behaviour and water intake since the rate of SEWL was similar between sexes. Plasma osmolality and SEWL rate were positively correlated with environmental temperature in males, while plasma osmolality in pregnant females did not correlate with environmental conditions, reproductive stage or reproductive effort. The SEWL rate was significantly lower in populations without access to free standing water, suggesting that lizards can adapt or adjust physiology to cope with habitat dryness. Environmental humidity did not explain variation in water balance. We suggest that geographic variation in water balance physiology and behaviour should be taken account to better understand species range limits and sensitivity to climate change.

Water deprivation increases maternal corticosterone levels and enhances offspring growth in the snake Vipera aspis

Circulating glucocorticoids (GCs) levels may increase as a result of reproductive effort or in response to unpredictable events. However, the GCs secretion can vary with the availability of vital trophic resources such as energy. While water represents another critical resource, the impact of water deprivation on GCs secretion during reproduction has not yet been thoroughly investigated. Here, we examined the effects of water deprivation on plasma corticosterone (CORT) concentrations of female aspic vipers (Vipera aspis), and we determined the impacts of water deprivation on offspring traits. We exposed both pregnant and non-reproductive females to a 20-day water deprivation and compared their pre- and post-deprivation CORT levels to those of control females. At the end of the treatment, only water-deprived pregnant females showed a significant increase in CORT levels. In pregnant females, changes in baseline CORT level were correlated to changes in female hydration state. Changes in baseline CORT levels were also negatively influenced by maternal reproductive effort in pregnant control females, while such relationship was not apparent in pregnant water-deprived females. Finally, we found that offspring from water-deprived females had higher growth rates than offspring from control females. Offspring growth was also positively correlated to changes in both maternal osmolality and baseline CORT levels. Together, our results suggest that dehydration increases maternal CORT levels which may subsequently influence offspring development. Further long-term field studies are therefore required to assess whether there is an adaptive significance of this response.