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Simple Summary: Many reptiles actively regulate their body temperature and during thermoregulation, they lose water from the body. The amount of body water lost in maintaining an adequate body temperature can vary from species to species. In this study, we compared the preferred body temperatures and the amount of water loss in males of two lacertid lizard species—the meadow lizard (Darevskia praticola) and the common wall lizard (Podarcis muralis)—that share the habitat at the western edge of the meadow lizard's distribution area. We hypothesized that the meadow lizard would exhibit higher water loss than the common wall lizard, as it generally prefers humid and forested places. However, the results showed that, at this locality, water loss is similar for both species, although the meadow lizard preferred lower ambient temperatures than the common wall lizard. We concluded that the meadow lizard has developed mechanisms to control water loss. Its preference for lower temperatures could be due to both historical factors and local adaptations. This information could help us to better understand how lizards cope with environmental changes and, more importantly, what we should do to prevent the species' decline in the wake of climate change. 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. [ABSTRACT FROM AUTHOR]

The role of atmospheric humidity in the evolution of endotherms' thermoregulatory performance remains largely unexplored, despite the fact that elevated humidity is known to impede evaporative cooling capacity. Using a phylogenetically informed comparative framework, we tested the hypothesis that pronounced hyperthermia tolerance among birds occupying humid lowlands evolved to reduce the impact of humidity‐impeded scope for evaporative heat dissipation by comparing heat tolerance limits (HTLs; maximum tolerable air temperature), maximum body temperatures (Tbmax), and associated thermoregulatory variables in humid (19.2 g H2O m−3) versus dry (1.1 g H2O m−3) air among 30 species from three climatically distinct sites (arid, mesic montane, and humid lowland). Humidity‐associated decreases in evaporative water loss and resting metabolic rate were 27%–38% and 21%–27%, respectively, and did not differ significantly between sites. Decreases in HTLs were significantly larger among arid‐zone (mean ± SD = 3.13 ± 1.12°C) and montane species (2.44 ± 1.0°C) compared to lowland species (1.23 ± 1.34°C), with more pronounced hyperthermia among lowland (Tbmax = 46.26 ± 0.48°C) and montane birds (Tbmax = 46.19 ± 0.92°C) compared to arid‐zone species (45.23 ± 0.24°C). Our findings reveal a functional link between facultative hyperthermia and humidity‐related constraints on evaporative cooling, providing novel insights into how hygric and thermal environments interact to constrain avian performance during hot weather. Moreover, the macrophysiological patterns we report provide further support for the concept of a continuum from thermal specialization to thermal generalization among endotherms, with adaptive variation in body temperature correlated with prevailing climatic conditions. [ABSTRACT FROM AUTHOR]

Heat waves are becoming increasingly common due to climate change, making it crucial to identify and understand the capacities for insect pollinators, such as honey bees, to avoid overheating. We examined the effects of hot, dry air temperatures on the physiological and behavioral mechanisms that honey bees use to fly when carrying nectar loads, to assess how foraging is limited by overheating or desiccation. We found that flight muscle temperatures increased linearly with load mass at air temperatures of 20 or 30 °C, but, remarkably, there was no change with increasing nectar loads at an air temperature of 40 °C. Flying, nectar-loaded bees were able to avoid overheating at 40 °C by reducing their flight metabolic rates and increasing evaporative cooling. At high body temperatures, bees apparently increase flight efficiency by lowering their wingbeat frequency and increasing stroke amplitude to compensate, reducing the need for evaporative cooling. However, even with reductions in metabolic heat production, desiccation likely limits foraging at temperatures well below bees' critical thermal maxima in hot, dry conditions. [ABSTRACT FROM AUTHOR]

Populations inhabiting several biomes may experience different abiotic and biotic conditions, exerting local selection pressures. Temperature and water regimes are interconnected variables, that may differ between biomes, and greatly influence ecophysiological traits, such as metabolic and evaporative water loss rates. We hypothesized that Ptyodactylus guttatus (Sinai Fan‐fingered Gecko) individuals, which occupy the Mediterranean and desert biomes across Israel, would follow the "metabolic cold adaptation" hypothesis and be adapted to the microclimate in the biome they inhabit. We thus predicted that desert individuals would prefer lower temperatures, and have lower resting metabolic rates and evaporative water loss rates at higher ambient temperatures than Mediterranean individuals. We also predicted that Mediterranean individuals would have a better body condition than individuals from the desert, because of higher primary productivity in the Mediterranean biome, and would therefore have higher mite loads. We further predicted that geckos from the desert would have longer limbs, enabling them to lose more heat to the environment, according to Allen's rule. To test these hypotheses, we measured the temperature preferences, field body temperatures, resting metabolic rates, evaporative water loss rates, body conditions, mite loads, and limb lengths of 82 P. guttatus individuals collected from four localities two from the desert biome and two from the Mediterranean biome. There were no significant differences in any of the tested traits when comparing between biomes. However, we found some differences in the evaporative water loss rates, body temperatures, body condition, and forelimb lengths between the northernmost and southernmost, and driest and wettest localities, supporting some of our predictions. Our results highlight the importance of the resolution of the analysis. Although some ecophysiological traits of P. guttatus seem to be conserved across localities and biomes, thermal plasticity in these traits may have helped this species reach its current distribution and occupy two biomes. [ABSTRACT FROM AUTHOR]

Aim: Physiological and metabolic performance are key mediators of the functional response of species to environmental change. Few environments offer such a multifaceted array of stressors as high‐altitude habitats, which differ markedly in temperature, water availability, UV radiation and oxygen pressure compared to low‐altitude habitats. Species that inhabit large altitudinal gradients are thus excellent models to study how organisms respond to environmental variation. Location: Tenerife island, Canary Islands archipelago (Spain). Taxon: Tenerife lizard (Gallotia galloti, Lacertidae). Methods: We integrated data on age structure, thermal and hydric regulatory behaviour and four metabolic and stress‐related biomarkers for an insular lizard that inhabits an extreme altitudinal range (sea level to 3700 m a.s.l.), to understand how an ectotherms' age, ecophysiology and metabolism can be affected by extreme environmental variation. Results: We found marked differences in metabolic stress markers associated with altitude (particularly in the abundance of carbonyl metabolites and relative telomere length), but without a linear pattern along the altitudinal cline. Contrary to expectations, longer telomeres and lower carbonyl content were detected at the highest altitude, suggesting reduced stress in these populations. Evaporative water loss differed between populations but did not follow a linear altitudinal gradient. Lizard age structure or thermal physiological performance did not markedly change across different altitudes. Mixed signals in life‐history and thermal ecology across populations and altitude suggest complex responses to variable conditions across altitude in this species. Main Conclusions: Our integrative study of multiple functional traits demonstrated that adaptation to highly divergent environmental conditions in this lizard is potentially linked to an interplay between plasticity and local adaptation variably associated with different functional traits. [ABSTRACT FROM AUTHOR]

Physical and chemical characteristics of organic bedding materials determine how well they will absorb and retain moisture and may influence the environment in livestock facilities where bedding is used. The objective of this study was to determine water holding capacity (WHC) and rate of evaporative water loss (EWL) of organic materials used as bedding in livestock facilities. Corn stover, soybean stover, wheat straw, switch grass, paper, corn cobs, and wood (pine and cedar) were evaluated; coarse, medium, and fine particle sizes of each bedding material were measured. The WHC was determined by submerging bedding materials in permeable nylon bags for 1, 3, 5, 10, 20, and 30 min, and 1, 3, 6, 9, 12, 24, 48, and 72 h. Generally, finely ground particles had higher WHC (P < 0.05) than the medium or coarsely ground particles of the same material. Corn stover (3.2 g g-1) and wheat straw (3.3 g g-1) had the highest WHC. Switch grass, dry cedar, green cedar, and corn cobs (1.4, 1.5, 1.6 and 1.9 g g-1, respectively) absorbed the least amount of water. Corn cobs retained water the longest when EWL was measured at 100 °C, 25 °C, and 15 °C (6.0, 33.0, and 38.1 days, respectively). Based on N, P, and K content, corn stover, wheat straw, and soybean stover bedding had the highest fertilizer value of the bedding materials studied. Considering all characteristics, wheat straw, corn stover, and soybean stover are the most favorable bedding materials to use in livestock housing systems. [ABSTRACT FROM AUTHOR]

Thermal physiology helps us understand how ectotherms respond to novel environments and how they persist when introduced to new locations. Researchers generally measure thermal physiology traits immediately after animal collection or after a short acclimation period. Because many of these traits are plastic, the conclusions drawn from such research can vary depending on the duration of the acclimation period. In this study, we measured the rate of change and extent to which cold tolerance (critical thermal minimum [CTmin]) of nonnative Italian wall lizards (Podarcis siculus) from Hempstead, New York, changed during a cold acclimation treatment. We also examined how cold acclimation affected heat tolerance (critical thermal maximum [CTmax]), thermal preference (T pref), evaporative water loss (EWL), resting metabolic rate (RMR), and respiratory exchange ratio (RER). We predicted that CTmin, CTmax, and T pref would decrease with cold acclimation but that EWL and RMR would increase with cold acclimation. We found that CTmin decreased within 2 wk and that it remained low during the cold acclimation treatment; we suspect that this cold tolerance plasticity reduces risk of exposure to lethal temperatures during winter for lizards that have not yet found suitable refugia. CTmax and T pref also decreased after cold acclimation, while EWL, RMR, and RER increased after cold acclimation, suggesting trade-offs with cold acclimation in the form of decreased heat tolerance and increased energy demands. Taken together, our findings suggest that cold tolerance plasticity aids the persistence of an established population of invasive lizards. More generally, our findings highlight the importance of accounting for the plasticity of physiological traits when investigating how invasive species respond to novel environments. [ABSTRACT FROM AUTHOR]

We evaluate if the iconic Australian Zebra Finch (Taeniopygia guttata) has a unique physiology or if its metabolic, thermal and hygric physiology are similar to other Australian poephiline finches, by comparing it with three other species, the arid-habitat Painted Finch (Emblema pictum) and the mesic-habitat Double-barred (Taeniopygia bichenovii) and Red-browed (Neochmia temporalis) Finches. All physiological variables responded to ambient temperature as expected. There were no species differences for any of the standard physiological variables, consistent with the hypotheses that birds are pre-adapted to arid habitats, the recent development of Australian deserts has limited opportunity for physiological adaptation, and all four species share similar behavioural and ecological traits. Nevertheless, the ambient temperature where metabolic water production equals evaporative water loss (point of relative water economy) was highest for the Zebra (19.1 °C), lower for Double-barred (16.4 °C) and Painted (15.2 °C) and lowest for Red-Browed (4.1 °C) Finches, corresponding with their general patterns of habitat aridity. The point of relative water economy may be a sensitive index for assessing a species’ tolerance of aridity because it integrates individual physiological variables. We conclude that the Zebra Finch is not a physiological outlier amongst Australian finches, but is at the end of a continuum of aridity tolerance for the four study species.

As anthropogenic activities are increasing the frequency and severity of droughts, understanding whether and how fast populations can adapt to sudden changes in their hydric environment is critically important. Here, we capitalize on the introduction of the Cuban brown anole lizard (Anolis sagrei) in North America to assess the contemporary evolution of a widespread terrestrial vertebrate to an abrupt climatic niche shift. We characterized hydric balance in 30 populations along a large climatic gradient. We found that while evaporative and cutaneous water loss varied widely, there was no climatic cline, as would be expected under adaptation. Furthermore, the skin of lizards from more arid environments was covered with smaller scales, a condition thought to limit water conservation and thus be maladaptive. In contrast to environmental conditions, genome-averaged ancestry was a significant predictor of water loss. This was reinforced by our genome-wide association analyses, which indicated a significant ancestry-specific effect for water loss at one locus. Thus, our study indicates that the water balance of invasive brown anoles is dictated by an environment-independent introduction and hybridization history and highlights genetic interactions or genetic correlations as factors that might forestall adaptation. Alternative water conservation strategies, including behavioral mitigation, may influence the brown anole invasion success and require future examination. [ABSTRACT FROM AUTHOR]

Maintaining homeothermy may be a major challenge when species are confronted with ambient temperatures beyond their thermoneutral zone. Bird species occupying open landscapes are inherently exposed to acute heat loss and heat gain, which force them to adopt a suite of behavioural and physiological strategies to maintain homeothermy. Both types of responses could be influenced by their relative bill and leg sizes, but experimental data are lacking. Here, we evaluated how variation in body postural adjustments, panting, and locomotor activity in the dunlin Calidris alpina can be explained by experimental ambient temperature and relative bill and leg sizes. Additionally, we estimated resting metabolic rate and evaporative water loss to assess potential links between both physiological traits and relative bill and leg sizes. Temperatures below the thermoneutral zone were counteracted by enhancing metabolic heat production through increased locomotor activity, while body postural adjustments were used less than expected. Within the thermoneutral zone, back rest (tucking the bill under body feathers) and unipedal (standing on one leg) were preferred by dunlins, probably as being more comfortable for resting. At temperatures above the thermoneutral zone, dunlins were inactive and increased the time of bill exposure and wet-sitting and ultimately panting when challenged with temperatures above 37 °C. Interestingly, above the thermoneutral zone, but below their body temperature, birds with relatively longer bills and legs spent more time exposing them, probably to increase dry heat transfer into the environment. Our findings also highlighted the importance of the availability of wet substrates for minimising heat stress in wetland species. Significance statement: Recent correlational field studies found support for a relationship between relative bill and leg sizes and thermoregulatory behaviour in birds inhabiting open landscapes. However, experimental data are lacking, and the mechanisms underlying this relationship remain poorly understood. Here, we performed an experiment to model behavioural and physiological responses to ambient temperature change and relative bill and leg sizes in the dunlin Calidris alpina, a long-billed and long-legged shorebird. Additionally, we also examined potential links among metabolic rates, evaporative water loss and relative appendage sizes. Our findings showed a strong experimental relationship between behavioural and physiological responses and ambient temperature, as well as a link between appendage size and resting body postures. Our findings also have a conservation message by highlighting that the type of substrate available for roosting is important for minimising heat stress in wetland species. [ABSTRACT FROM AUTHOR]

Thermo-hydroregulation strategies involve concurrent changes in functional traits related to energy, water balance and thermoregulation and play a key role in determining life-history traits and population demography of terrestrial ectotherms. Local thermal and hydric conditions should be important drivers of the geographical variation of thermo-hydroregulation strategies, but we lack studies that examine these changes across climatic gradients in different habitat types. Here, we investigated intraspecific variation of morphology and thermo-hydroregulation traits in the widespread European common lizard (Zootoca vivipara louislantzi) across a multidimensional environmental gradient involving independent variation in air temperature and rainfall and differences in habitat features (access to free-standing water and forest cover). We sampled adult males for morphology, resting metabolic rate, total and cutaneous evaporative water loss and thermal preferences in 15 populations from the rear to the leading edge of the distribution across an elevational gradient ranging from sea level to 1750 m. Besides a decrease in adult body size with increasing environmental temperatures, we found little effect of thermal conditions on thermo-hydroregulation strategies. In particular, relict lowland populations from the warm rear edge showed no specific ecophysiological adaptations. Instead, body mass, body condition and resting metabolic rate were positively associated with a rainfall gradient, while forest cover and water access in the habitat throughout the season also influenced cutaneous evaporative water loss. Our study emphasizes the importance of rainfall and habitat features rather than thermal conditions for geographical variation in lizard morphology and physiology. [ABSTRACT FROM AUTHOR]

Desiccation is a fundamental challenge confronted by all terrestrial organisms, particularly insects. With a relatively small body size and large surface-to-volume ratio, insects are susceptible to rapid evaporative water loss and dehydration. To counter these physical constraints, insects have acquired specialized adaptations, including a hydrophobic cuticle that acts as a physical barrier to transpiration. We previously reported that genetic ablation of the oenocytes - specialized cells required to produce cuticular hydrocarbons (HCs) - significantly reduced survivorship under desiccative conditions in the fruit fly, Drosophila melanogaster. Although increased transpiration - resulting from the loss of the oenocytes and HCs - was hypothesized to be responsible for the decrease in desiccation survival, this possibility was not directly tested. Here, we investigated the underlying physiological mechanisms contributing to the reduced survival of oenocyte-less (oe-) flies. Using flow-through respirometry, we show that oe- flies, regardless of sex, exhibited an increased rate of transpiration relative to wild-type controls, and that coating oe- flies with fly-derived HC extract restored the rate to near-wild-type levels. Importantly, total body water stores, including metabolic water reserves, as well as dehydration tolerance, measured as the percentage of total body water lost at the time of death, were largely unchanged in oe- flies. Together, our results directly demonstrate the critically important role played by the oenocytes and cuticular HCs to promote desiccation resistance., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Climate change is increasing aridity in grassland and desert habitats across the southwestern United States, reducing available resources and drastically changing the breeding habitat of many bird species. Increases in aridity reduce sound propagation distances, potentially impacting habitat soundscapes, and could lead to a breakdown of the avian soundscapes in the form of loss of vocal culture, reduced mating opportunities, and local population extinctions. We developed an agent‐based model to examine how changes in aridity will affect both sound propagation and the ability of territorial birds to audibly contact their neighbors. We simulated vocal signal attenuation under a variety of environmental scenarios for the south, central semi‐arid prairies of the United States, ranging from contemporary weather conditions to predicted droughts under climate change. We also simulated how changes in physiological conditions, mainly evaporative water loss (EWL), would affect singing behavior. Under contemporary and climate change‐induced drought conditions, we found that significantly fewer individuals successfully contacted all adjacent neighbors than did individuals in either the contemporary or predicted climate change conditions. We also found that at higher sound frequencies and higher EWL, fewer individuals were able to successfully contact all their neighbors, particularly in drought and climate change drought conditions. These results indicate that climate change‐mediated aridification may alter the avian soundscape, such that vocal communication no longer effectively functions for mate attraction or territorial defense. As climate change progresses, increased aridity in current grasslands may favor shifts toward low‐frequency songs, colonial resource use, and altered songbird community compositions. [ABSTRACT FROM AUTHOR]

Abstract There is growing evidence on the role of legs and bill as ‘thermal windows’ in birds coping with heat stress. However, there is a lack of empirical work examining the relationship between the relative bill and/or leg surface areas and key thermoregulatory traits such as the limits of the thermoneutral zone (TNZ) or the cooling efficiency at high temperatures. Here, we explored this relationship in a Mediterranean population of Great tit (Parus major) facing increasing thermal stress in its environment. The lower and upper critical limits of the TNZ were found to be 17.7 ± 1.6ºC and 34.5 ± 0.7°C, respectively, and the basal metabolic rate was 0.96 ± 0.12 ml O2 min−1 on average. The evaporative water loss (EWL) inflection point was established at 31.85 ± 0.27°C and was not significantly different from the value of the upper critical limit. No significant relationship was observed between the relative bill or tarsi size and TNZ critical limits, breadth, mass‐independent VO2, or mass‐independent EWL at any environmental temperature (from 10 to 40°C). However, Great tit males (but not females) with larger tarsi areas (a proxy of leg surface area) showed higher cooling efficiencies at 40°C. We found no support for the hypothesis that the bill surface area plays a significant role as a thermal window in Great tits, but the leg surface areas may play a role in males’ physiological responses to high temperatures. On the one hand, we argue that the studied population occupies habitats with available microclimates and fresh water for drinking during summer, so active heat dissipation by EWL might be favored instead of dry heat loss through the bill surface. Conversely, male dominance behaviors could imply a greater dependence on cutaneous EWL through the upper leg surfaces as a consequence of higher exposure to harsh environmental conditions than faced by females.

Anthropogenic land use changes, such as deforestation and commercial forestry, have substantially reduced natural roost sites for European bats. A common conservation solution is to provide artificial roosts (i.e. bat boxes), but there are concerns that these can become hotter than natural roosts in summer and could be death traps during heat waves. Nevertheless, females of several bat species form maternity colonies in these boxes, thus occupying hotter and more humid microclimates than solitarily roosting males. We tested if cooling efficiency and heat tolerance differ between sexes in European bats, and estimated the evaporative water requirements for bats living in bat boxes during hot summer days.We used indirect calorimetry and thermometry to quantify thermoregulation at high air temperatures (Ta) in four species of verspitilionid bats that regularly occupy artificial roosts. We measured resting metabolic heat production, evaporative water loss rates (EWL) and body temperature (Tb) at Ta between 28°C and 48°C during summer. We predicted that females have higher evaporative cooling efficiency (evaporative heat loss/metabolic heat production) than males, allowing them to reach their heat tolerance limit at higher Ta.We found no sex differences in maximum evaporative cooling efficiency, maximum Tb, and maximum Ta tolerated. However, the patterns of increasing EWL with Ta differed between sexes. Females tolerated higher Ta before increasing EWL than males and then rapidly increased EWL to higher values than males at the maximum Ta tolerated. These sex differences in heat dissipation strategies may reflect varying ecological and physiological constraints associated with different summer roosting habits.Synthesis and applications. Our study revealed that some small European bat species are already at risk of succumbing to lethal dehydration during present‐day heat waves, with daytime evaporative water requirements equivalent to ~30% of body mass in sun‐exposed boxes. For conservation managers working with common European bat species, particularly those in monoculture forests with woodcrete bat‐boxes, our physiologically informed recommendations include positioning boxes in diverse locations varying in aspect and sun exposure. This will ensure thermal heterogeneity of roost sites and provide a wide gradient of microclimate conditions, allowing for roost switching when necessary. [ABSTRACT FROM AUTHOR]

Integration of multiple approaches is key to understand the evolutionary processes of local adaptation and speciation. Reptiles have successfully colonized desert environments, that is, extreme and arid conditions that constitute a strong selective pressure on organisms. Here, we studied genomic, physiological and morphological variations of the lizard Liolaemus fuscus to detect adaptations to the Atacama Desert.By comparing populations of L. fuscus inhabiting the Atacama Desert with populations from the Mediterranean forests from central Chile, we aimed at characterizing features related to desert adaptation.We combined ddRAD sequencing with physiological (evaporative water loss, metabolic rate and selected temperature) and morphological (linear and geometric morphometrics) measurements. We integrated the genomic and phenotypic data using redundancy analyses.Results showed strong genetic divergence, along with a high number of fixed loci between desert and forest populations. Analyses detected 110 fixed and 30 outlier loci located within genes, from which 43 were in coding regions, and 12 presented non‐synonymous mutations. The candidate genes were associated with cellular membrane and development. Desert lizards presented lower evaporative water loss than those from the forest. Morphological data showed that desert lizards had smaller body size, different allometry, larger eyeballs and more dorsoventrally compressed heads.Our results suggest incipient speciation between desert and forest populations. The adaptive signal must be cautiously interpreted since genetic drift could also contribute to the divergence pattern. Nonetheless, we propose water and resource availability, and changes in habitat structure, as the most relevant challenges for desert reptiles. This study provides insights of the mechanisms that allow speciation as well as desert adaptation in reptiles at multiple levels, and highlights the benefit of integrating independent evidence. [ABSTRACT FROM AUTHOR]

Simple Summary: Zebra Finches (Taeniopygia guttata) are the most widespread Australian finches, occurring throughout much of Australia's semi-arid and arid zones. They have a similar physiology (body temperature, metabolic rate, evaporative water loss, thermal conductance) to other finches but differ in having a higher point of relative economy, the ambient temperature at which metabolic water production exceeds evaporative water loss. Overall physiological similarities of these species likely reflect evolutionary, ecological and behavioural factors. Our study highlights the utility of relatively water economy for evaluating integrated physiological adaptations to heat and aridity. We evaluate if the iconic Australian Zebra Finch (Taeniopygia guttata) has a unique physiology or if its metabolic, thermal and hygric physiology are similar to other Australian poephiline finches, by comparing it with three other species, the arid-habitat Painted Finch (Emblema pictum) and the mesic-habitat Double-barred (Taeniopygia bichenovii) and Red-browed (Neochmia temporalis) Finches. All physiological variables responded to ambient temperature as expected. There were no species differences for any of the standard physiological variables, consistent with the hypotheses that birds are pre-adapted to arid habitats, the recent development of Australian deserts has limited opportunity for physiological adaptation, and all four species share similar behavioural and ecological traits. Nevertheless, the ambient temperature where metabolic water production equals evaporative water loss (point of relative water economy) was highest for the Zebra (19.1 °C), lower for Double-barred (16.4 °C) and Painted (15.2 °C) and lowest for Red-Browed (4.1 °C) Finches, corresponding with their general patterns of habitat aridity. The point of relative water economy may be a sensitive index for assessing a species' tolerance of aridity because it integrates individual physiological variables. We conclude that the Zebra Finch is not a physiological outlier amongst Australian finches, but is at the end of a continuum of aridity tolerance for the four study species. [ABSTRACT FROM AUTHOR]

Abstract Natural history collections provide an unparalleled resource for documenting population responses to past anthropogenic change. However, in many cases, traits measured on specimens may vary temporally in response to a number of different anthropogenic pressures or demographic processes. While teasing apart these different drivers is challenging, approaches that integrate analyses of spatial and temporal series of specimens can provide a robust framework for examining whether traits exhibit common responses to ecological variation in space and time. We applied this approach to analyze bill morphology variation in California Savannah Sparrows (Passerculus sandwichensis). We found that bill surface area increased in birds from higher salinity tidal marshes that are hotter and drier. Only the coastal subspecies, alaudinus, exhibited a significant increase in bill size through time. As with patterns of spatial variation, alaudinus populations occupying higher salinity tidal marshes that have become warmer and drier over the past century exhibited the greatest increases in bill surface area. We also found a significant negative correlation between bill surface area and total evaporative water loss (TEWL) and estimated that observed increases in bill size could result in a reduction of up to 16.2% in daily water losses. Together, these patterns of spatial and temporal variation in bill size were consistent with the hypothesis that larger bills are favored in freshwater‐limited environments as a mechanism of dissipating heat, reducing reliance on evaporative cooling, and increasing water conservation. With museum collections increasingly being leveraged to understand past responses to global change, this work highlights the importance of considering the influence of many different axes of anthropogenic change and of integrating spatial and temporal analyses to better understand the influence of specific human impacts on population change over time.

Abstract Arctic animals inhabit some of the coldest environments on the planet and have evolved physiological mechanisms for minimizing heat loss under extreme cold. However, the Arctic is warming faster than the global average and how well Arctic animals tolerate even moderately high air temperatures (Ta) is unknown. Using flow‐through respirometry, we investigated the heat tolerance and evaporative cooling capacity of snow buntings (Plectrophenax nivalis; ≈31 g, N = 42), a cold specialist, Arctic songbird. We exposed buntings to increasing Ta and measured body temperature (Tb), resting metabolic rate (RMR), rates of evaporative water loss (EWL), and evaporative cooling efficiency (the ratio of evaporative heat loss to metabolic heat production). Buntings had an average (±SD) Tb of 41.3 ± 0.2°C at thermoneutral Ta and increased Tb to a maximum of 43.5 ± 0.3°C. Buntings started panting at Ta of 33.2 ± 1.7°C, with rapid increases in EWL starting at Ta = 34.6°C, meaning they experienced heat stress when air temperatures were well below their body temperature. Maximum rates of EWL were only 2.9× baseline rates at thermoneutral Ta, a markedly lower increase than seen in more heat‐tolerant arid‐zone species (e.g., ≥4.7× baseline rates). Heat‐stressed buntings also had low evaporative cooling efficiencies, with 95% of individuals unable to evaporatively dissipate an amount of heat equivalent to their own metabolic heat production. Our results suggest that buntings’ well‐developed cold tolerance may come at the cost of reduced heat tolerance. As the Arctic warms, and this and other species experience increased periods of heat stress, a limited capacity for evaporative cooling may force birds to increasingly rely on behavioral thermoregulation, such as minimizing activity, at the expense of diminished performance or reproductive investment.

Abstract In multihost disease systems, differences in mortality between species may reflect variation in host physiology, morphology, and behavior. In systems where the pathogen can persist in the environment, microclimate conditions, and the adaptation of the host to these conditions, may also impact mortality. White‐nose syndrome (WNS) is an emerging disease of hibernating bats caused by an environmentally persistent fungus, Pseudogymnoascus destructans. We assessed the effects of body mass, torpid metabolic rate, evaporative water loss, and hibernaculum temperature and water vapor deficit on predicted overwinter survival of bats infected by P. destructans. We used a hibernation energetics model in an individual‐based model framework to predict the probability of survival of nine bat species at eight sampling sites across North America. The model predicts time until fat exhaustion as a function of species‐specific host characteristics, hibernaculum microclimate, and fungal growth. We fit a linear model to determine relationships with each variable and predicted survival and semipartial correlation coefficients to determine the major drivers in variation in bat survival. We found host body mass and hibernaculum water vapor deficit explained over half of the variation in survival with WNS across species. As previous work on the interplay between host and pathogen physiology and the environment has focused on species with narrow microclimate preferences, our view on this relationship is limited. Our results highlight some key predictors of interspecific survival among western bat species and provide a framework to assess impacts of WNS as the fungus continues to spread into western North America.

Microscale differences in the habitats organisms occupy can influence selection regimes and promote intraspecific variation of traits. Temperature‐dependent traits can be locally adapted to climatic conditions or be highly conserved and insensitive to directional selection under all but the most extreme regimes, and thus be similar across populations. The opposing slopes of Nahal Oren canyon in the Carmel Mountains, Israel, are strikingly different: the south‐facing slope receives intensive solar radiation, is hot and supports mostly annual vegetation, whereas the north‐facing slope is ~10°C cooler, more humid, and supports Mediterranean woodland. We examined whether these differences manifest in the thermal physiology of a common gecko species Ptyodactylus guttatus in controlled laboratory conditions. We predicted that geckos from the hotter south‐facing slope would prefer higher temperatures, have faster gut passage times, lower metabolic and evaporative water loss rates, and start diel activity earlier compared with north‐facing slope conspecifics. Contrary to these predictions, there were no differences between any of the ecophysiological traits in geckos from the opposing slopes. Nevertheless, our data showed that individuals from the north‐facing slope were generally more active in earlier hours of the afternoon compared with south‐facing individuals. We suggest that P. guttatus individuals disperse between the slopes and either gene‐flow or behavioral plasticity deter local adaptation, resulting in similar physiological traits. Perhaps a stronger contrast in climatic conditions and a stronger barrier are needed to result in interpopulation divergence in temperature‐dependent traits. Research Highlights: Similar ecophysiological traits of gecko populations across slopes of the same canyon, despite contrasting microclimatic conditions.Gene‐flow or behavioral plasticity mask local adaptation of ecophysiological traits to adjacent microclimates. [ABSTRACT FROM AUTHOR]

Individual survival is influenced by interactions between local environmental conditions and an organism's morphological, behavioural and physiological traits. Studies examining the effects of individual phenotypes on survival under variable conditions are relatively rare among early transitional life stages, although the vital rates of these life stages can importantly influence population dynamics.We experimentally examined the effects of initial body mass, movement, standard metabolic rate (SMR) and respiratory surface area water loss (RSAWL) on survival in the transitional juvenile life stage of two biphasic amphibian species (Ambystoma maculatum and A. opacum) in a 7‐month mark–recapture study under semi‐natural conditions.Juveniles with a larger initial body mass, lower initial SMR and/or a lower tendency to change locations had a higher likelihood of known survival. In contrast, we found no significant effect of RSAWL on juvenile survival.The relationships between individual phenotypes and survival did not differ between species, but equivalent species‐specific survival rates may have been attributed to larger initial body sizes in A. maculatum and lower SMR in A. opacum.Our results illuminate the complex ways in which individual traits influence survival during the early transitional life stage of two ambystomatid species under varying abiotic conditions. More generally, our findings illustrate potential advantages of simultaneously examining multiple traits to evaluate survival. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Species with broad geographic ranges may experience varied environmental conditions throughout their range leading to local adaptation. Variation among populations reflects potential adaptability or plasticity, with implications for populations impacted by disease, climate change, and other anthropogenic influences. However, behavior may counteract divergent selection among populations. We studied intraspecific variation in hibernation physiology of Myotis lucifugus (little brown myotis) and Corynorhinus townsendii (Townsend's big-eared bat), two species of bats with large geographic ranges. We studied M. lucifugus at three hibernacula which spanned a latitudinal gradient of 1500 km, and C. townsendii from 6 hibernacula spread across 1200 km latitude and 1200 km longitude. We found no difference in torpid metabolic rate among populations of either species, nor was there a difference in the effect of ambient temperature among sites. Evaporative water loss was similar among populations of both species, with the exception of one C. townsendii pairwise site difference and one M. lucifugus site that differed from the others. We suggest the general lack of geographic variation is a consequence of behavioral microhabitat selection. As volant animals, bats can travel relatively long distances in search of preferred microclimates for hibernation. Despite dramatic macroclimate differences among populations, hibernating bats are able to find preferred microclimate conditions within their range, resulting in similar selection pressures among populations spread across wide geographic ranges. [ABSTRACT FROM AUTHOR]

The microsites that animals occupy during the rest phase of their circadian activity cycle influence their physiology and behaviour, but relatively few studies have examined correlations between interspecific variation in thermal physiology and roost microclimate. Among bats, there is some evidence that species exposed to high roost temperatures (Troost) possess greater heat tolerance and evaporative cooling capacity, but the small number of species for which both thermal physiology and roost microclimate data exist mean that the generality of this pattern remains unclear.Here, we test the hypothesis that bat heat tolerance and evaporative cooling capacity have co‐evolved with roost preferences. We predicted that species occupying roosts poorly buffered from high outside environmental temperature exhibit higher heat tolerance and evaporative cooling capacity compared to species inhabiting buffered roosts in which Troost remains well below outside conditions.We used flow‐through respirometry to investigate thermoregulation at air temperatures (Ta) approaching and exceeding normothermic body temperature (Tb) among six species with broadly similar body mass but differing in roost microclimate (hot vs. cool roosts). We combined these data with empirical measurements of Troost for each study population.Hot‐roosting species tolerated Ta ~4°C higher than cool‐roosting bats before the onset of loss of coordinated locomotion and non‐regulated hyperthermia. The evaporative scope (i.e. ratio of maximum evaporative water loss [EWL] to minimum thermoneutral EWL) of hot‐roosting species (16.1 ± 2.4) was substantially higher than that of cool‐roosting species (5.9 ± 2.4). Maximum evaporative cooling capacities (i.e. evaporative heat loss/metabolic heat production) of hot‐roosting species were >2, while the corresponding values for cool‐roosting species were ≤1.The greater heat tolerance and higher evaporative cooling capacity of hot‐roosting species compared with those occupying cooler roosts reveal variation in bat evaporative cooling capacity correlated with roost microclimate, supporting the hypothesis that thermal physiology has co‐evolved with roost preference. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

There is growing evidence on the role of legs and bill as 'thermal windows' in birds coping with heat stress. However, there is a lack of empirical work examining the relationship between the relative bill and/or leg surface areas and key thermoregulatory traits such as the limits of the thermoneutral zone (TNZ) or the cooling efficiency at high temperatures. Here, we explored this relationship in a Mediterranean population of Great tit (Parus major) facing increasing thermal stress in its environment. The lower and upper critical limits of the TNZ were found to be 17.7 ± 1.6°C and 34.5 ± 0.7°C, respectively, and the basal metabolic rate was 0.96 ± 0.12 ml O2 min-1 on average. The evaporative water loss (EWL) inflection point was established at 31.85 ± 0.27°C and was not significantly different from the value of the upper critical limit. No significant relationship was observed between the relative bill or tarsi size and TNZ critical limits, breadth, mass-independent VO2, or mass-independent EWL at any environmental temperature (from 10 to 40°C). However, Great tit males (but not females) with larger tarsi areas (a proxy of leg surface area) showed higher cooling efficiencies at 40°C. We found no support for the hypothesis that the bill surface area plays a significant role as a thermal window in Great tits, but the leg surface areas may play a role in males' physiological responses to high temperatures. On the one hand, we argue that the studied population occupies habitats with available microclimates and fresh water for drinking during summer, so active heat dissipation by EWL might be favored instead of dry heat loss through the bill surface. Conversely, male dominance behaviors could imply a greater dependence on cutaneous EWL through the upper leg surfaces as a consequence of higher exposure to harsh environmental conditions than faced by females. [ABSTRACT FROM AUTHOR]

Motivation: The understanding of physiological adaptations, of evolutionary radiations and of ecological responses to global change urges for global, comprehensive databases of the functional traits of extant organisms. The ability to maintain an adequate water balance is a critical functional property influencing the resilience of animal species to climate variation. In terrestrial or semi‐terrestrial organisms, total water loss includes a significant contribution from evaporative water loss (EWL). The analysis of geographic and phylogenetic variation in EWL rates must however account for differences in methods and potential confounding factors, which influence standard measures of whole‐organism water loss. We compiled the global and standardized SquamEWL database of total, respiratory and cutaneous EWL for 325 species and subspecies of squamate reptiles (793 samples and 2,536 estimates) from across the globe. An extensive set of companion data and annotations associated with the EWL measurements of potential value for future investigation, including metabolic rate data, is provided. We present preliminary descriptive statistics for the compiled data, discuss gaps and biases, and identify promising avenues to update, expand and explore this database. Main types of variables contained: Standard water loss rates, geographic data, metabolic rates. Spatial location: Global. Time period: Data were obtained from extant species and were collected between 1945 and 2020. Major taxa: Reptilia, Squamata including lizards, snakes and amphisbaenians. Level of measurements: Individual samples of animals from the same species, locality, age class and sex category. Software format: csv. [ABSTRACT FROM AUTHOR]

For small endotherms inhabiting desert ecosystems, defending body temperatures (T b) is challenging as they contend with extremely high ambient temperatures (T a) and limited standing water. In the arid zone, bats may thermoconform whereby T b varies with T a , or may evaporatively cool themselves to maintain T b < T a. We used an integrative approach that combined both temperature telemetry and flow through respirometry to investigate the ecological and physiological strategies of lesser long-eared bats (Nyctophilus geoffroyi) in Australia's arid zone. We predicted individuals would exhibit desert-adapted thermoregulatory patterns (i.e., thermoconform to prioritise water conservation), and that females would be more conservative with their water reserves for evaporative cooling compared to males. Temperature telemetry data indicated that free-ranging N. geoffroyi were heterothermic (T skin = 18.9–44.9 °C) during summer and thermoconformed over a wide range of temperatures, likely to conserve water and energy during the day. Experimentally, at high T a s, females maintained significantly lower T b and resting metabolic rates, despite lower evaporative water loss (EWL) rates compared to males. Females only increased EWL at experimental T a = 42.5 °C, significantly higher than males (40.7 °C), and higher than any bat species yet recorded. During the hottest day of this study, our estimates suggest the water required for evaporative cooling ranged from 18.3% (females) and 25.5% (males) of body mass. However, if we extrapolate these results to a recent heatwave these values increase to 36.5% and 47.3%, which are likely beyond lethal limits. It appears this population is under selective pressures to conserve water reserves and that these pressures are more pronounced in females than males. Bats in arid ecosystems are threatened by both current and future heatwaves and we recommend future conservation efforts focus on protecting current roost trees and creating artificial standing water sites near vulnerable populations. • Significant sex differences exist in the thermoregulatory strategies in desert bats. • Females can withstand higher temperatures than males. • Females are more conservative in their use of evaporative water loss. • Desert bats are under a severe threat from current and future heat waves. [ABSTRACT FROM AUTHOR]

The present study attempts to assess changes in soccer players' physical and technical activity profiles due to thermal stress, measured with the Universal Thermal Climate Index (UTCI), in training centres and during matches of the 2018 FIFA World Cup in Russia. The study also verifies the theoretical models of soccer players' physiological parameters. The study sample consisted of 945 observations of 340 players of national teams taking part in the World Cup in Russia. The measured variables included physical activities: total distance covered, distances covered with an intensity of 20–25 km/h, number of sprints; technical activities: number of shots, number of passes, pass accuracy and physiological indicators: evaporative water loss and heart rate. In addition, the final ranking places of each national team were also used in the study. The UTCI was calculated based on meteorological data recorded at training centres and during matches. The UTCI records were then classified into two ranges: NTS—no thermal stress (UTCI 9–26 °C) and TS—thermal stress (UTCI > 26 °C). Climatic conditions at soccer training centres assessed as involving "no thermal stress" are found to be more beneficial for increasing the total distance covered and the number of sprints performed by players during a match. The theoretical models for determining soccer players' physiological parameters used in the study reduce the players' heart rate effort and evaporative water loss, which is in line with findings in studies by other authors. The climatic conditions at soccer training centres and during tournament matches should be taken into account in planning preparations for future World Cup tournaments, especially those in hotter countries. [ABSTRACT FROM AUTHOR]

Heat tolerance for many birds under climate and land use change scenarios could be compromised in the future. Common Nighthawks (Chordeiles minor) belong to the Caprimulgiformes, a generally heat-tolerant order, but few studies have assessed heat tolerance in Caprimulgiform chicks, which might be particularly susceptible to heat stress. In the midwestern United States, nighthawks primarily nest on flat graveled rooftops in urban areas, as natural nesting habitats are limited. Urban rooftop-nesting nighthawks are likely exposed to higher environmental temperatures than birds nesting at more thermally buffered natural sites, and evaporative cooling might be impeded by the typically high summer humidity in their Midwest breeding range. This combination of heat and humidity might negatively impact heat tolerance of nighthawk chicks. We exposed 7-to 14-day-old nighthawk chicks (n = 15) from rooftop nests to ambient temperatures (Tas) up to 51°C and at typical summer dew points. Chicks initiated gular flutter at a mean ambient temperature of 42.4 ± 3.4°C (mean ± SE). Evaporative water loss (EWL) rates increased significantly with increasing temperature above 44.0 ± 1.5°C. Chicks showed little evidence of lower and upper bounds of the thermal neutral zone over the range of temperatures (30-44°C) for which we measured oxygen consumption. Body mass loss was significantly positively correlated with temperature during heat exposure trials. Chicks tolerated Tas up to 51°C and body temperatures (Tbs) up to 48°C, which, along with the high temperatures at which gular flutter and high rates of EWL were initiated, suggest that nighthawk chicks are tolerant of high ambient temperatures, even with relatively high humidity. Given the high rates of mass loss and high Tbs at hot ambient temperatures, chick heat tolerance mechanisms could be detrimental for rooftop-nesting nighthawks given projected increasing trends for both heat and humidity in the midwestern United States. [ABSTRACT FROM AUTHOR]

Scholander-Irving curves describe the relationship between ambient temperature and metabolic rate and are fundamental to understanding the energetic demands of homeothermy. However, Scholander-Irving curves are typically measured in dry air, which is not representative of the humidity many organisms experience in nature. Consequently, it is unclear (1) whether Scholander-Irving curves (especially below thermoneutrality) are altered by humidity, given the effects of humidity on thermal properties of air, and (2) whether physiological responses associated with Scholander-Irving curves in the lab reflect organismal performance in humid field conditions. We used laboratory experiments and biophysical models to test the effects of humidity on the thermoregulatory physiology of tree swallows (Tachycineta bicolor). We also tested whether physiological responses measured under lab conditions were correlated with field body temperatures and nestling provisioning rates. We found that humidity reduced rates of evaporative water loss but did not have large effects on body temperature or metabolic rate, suggesting that swallows can decouple evaporative cooling, body temperature and metabolic rate. Although the effect of humidity on metabolic rate in the lab was small, our biophysical models indicated that energetic costs of thermoregulation were ∼8% greater in simulations that used metabolic rates from birds in humid compared with dry conditions. Finally, we found mixed evidence that physiological responses measured in the lab under humid or dry conditions were associated with body temperature and nest provisioning rates in the field. Our results help clarify the effect of humidity on endotherm thermoregulation, which may help forecast organismal responses to environmental change., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Arctic animals inhabit some of the coldest environments on the planet and have evolved physiological mechanisms for minimizing heat loss under extreme cold. However, the Arctic is warming faster than the global average and how well Arctic animals tolerate even moderately high air temperatures (Ta) is unknown.Using flow‐through respirometry, we investigated the heat tolerance and evaporative cooling capacity of snow buntings (Plectrophenax nivalis; ≈31 g, N = 42), a cold specialist, Arctic songbird. We exposed buntings to increasing Ta and measured body temperature (Tb), resting metabolic rate (RMR), rates of evaporative water loss (EWL), and evaporative cooling efficiency (the ratio of evaporative heat loss to metabolic heat production).Buntings had an average (±SD) Tb of 41.3 ± 0.2°C at thermoneutral Ta and increased Tb to a maximum of 43.5 ± 0.3°C. Buntings started panting at Ta of 33.2 ± 1.7°C, with rapid increases in EWL starting at Ta = 34.6°C, meaning they experienced heat stress when air temperatures were well below their body temperature. Maximum rates of EWL were only 2.9× baseline rates at thermoneutral Ta, a markedly lower increase than seen in more heat‐tolerant arid‐zone species (e.g., ≥4.7× baseline rates). Heat‐stressed buntings also had low evaporative cooling efficiencies, with 95% of individuals unable to evaporatively dissipate an amount of heat equivalent to their own metabolic heat production.Our results suggest that buntings' well‐developed cold tolerance may come at the cost of reduced heat tolerance. As the Arctic warms, and this and other species experience increased periods of heat stress, a limited capacity for evaporative cooling may force birds to increasingly rely on behavioral thermoregulation, such as minimizing activity, at the expense of diminished performance or reproductive investment. [ABSTRACT FROM AUTHOR]

Before constructing an orb web, an araneoid spider takes down and ingests the previous day's web. Nocturnal species do this either during the early evening or in the early morning and diurnal species during the early morning, times of the day when relative humidity (RH) is high. Under these conditions the hygroscopic glue droplets of a web's viscous prey capture thread attract atmospheric moisture, providing a net gain of water when a spider ingests its web. The contribution of web recycling to a spider's water budget has been estimated, but not determined empirically. This study does so for adult females of four species (Araneus marmoreus Clerck, 1757, Argiope trifasciata (Forsk°al, 1775), Leucauge venusta (Walckenaer, 1841), and Micrathena gracilis (Walckenaer, 1805)) by first determining the total volume of a web's glue droplets at 20% and 37% RH to estimate the water invested in web during construction. Subtracting each of these values from the web's total droplet volume at 90% RH approximates the range of water harvested when the web is recycled. High estimates of the net water gained range from 0.45% of a spider's body mass (3.01 μl water gained) in A. marmoreus to 0.88% of body mass (0.19 μl water gained) in L. venusta. In A. trifasciata, the water gained when a web is ingested is equivalent to 29% of a spider's daily evaporative water loss. [ABSTRACT FROM AUTHOR]

Natural history collections provide an unparalleled resource for documenting population responses to past anthropogenic change. However, in many cases, traits measured on specimens may vary temporally in response to a number of different anthropogenic pressures or demographic processes. While teasing apart these different drivers is challenging, approaches that integrate analyses of spatial and temporal series of specimens can provide a robust framework for examining whether traits exhibit common responses to ecological variation in space and time. We applied this approach to analyze bill morphology variation in California Savannah Sparrows (Passerculus sandwichensis). We found that bill surface area increased in birds from higher salinity tidal marshes that are hotter and drier. Only the coastal subspecies, alaudinus, exhibited a significant increase in bill size through time. As with patterns of spatial variation, alaudinus populations occupying higher salinity tidal marshes that have become warmer and drier over the past century exhibited the greatest increases in bill surface area. We also found a significant negative correlation between bill surface area and total evaporative water loss (TEWL) and estimated that observed increases in bill size could result in a reduction of up to 16.2% in daily water losses. Together, these patterns of spatial and temporal variation in bill size were consistent with the hypothesis that larger bills are favored in freshwater‐limited environments as a mechanism of dissipating heat, reducing reliance on evaporative cooling, and increasing water conservation. With museum collections increasingly being leveraged to understand past responses to global change, this work highlights the importance of considering the influence of many different axes of anthropogenic change and of integrating spatial and temporal analyses to better understand the influence of specific human impacts on population change over time. [ABSTRACT FROM AUTHOR]

In multihost disease systems, differences in mortality between species may reflect variation in host physiology, morphology, and behavior. In systems where the pathogen can persist in the environment, microclimate conditions, and the adaptation of the host to these conditions, may also impact mortality. White‐nose syndrome (WNS) is an emerging disease of hibernating bats caused by an environmentally persistent fungus, Pseudogymnoascus destructans. We assessed the effects of body mass, torpid metabolic rate, evaporative water loss, and hibernaculum temperature and water vapor deficit on predicted overwinter survival of bats infected by P. destructans. We used a hibernation energetics model in an individual‐based model framework to predict the probability of survival of nine bat species at eight sampling sites across North America. The model predicts time until fat exhaustion as a function of species‐specific host characteristics, hibernaculum microclimate, and fungal growth. We fit a linear model to determine relationships with each variable and predicted survival and semipartial correlation coefficients to determine the major drivers in variation in bat survival. We found host body mass and hibernaculum water vapor deficit explained over half of the variation in survival with WNS across species. As previous work on the interplay between host and pathogen physiology and the environment has focused on species with narrow microclimate preferences, our view on this relationship is limited. Our results highlight some key predictors of interspecific survival among western bat species and provide a framework to assess impacts of WNS as the fungus continues to spread into western North America. [ABSTRACT FROM AUTHOR]

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Extreme weather events (e.g. heatwaves and droughts) can expose animals to environmental conditions outside of their zones of physiological tolerance, and even resistance, and impact long-term viability of populations and species. We examined the thermal and hygric physiology of the critically endangered western ringtail possum (Pseudocheirus occidentalis), a member of a family of marsupial folivores (Pseudocheiridae) that appear particularly vulnerable to environmental extremes. Basal metabolic rate and other standard physiological variables measured at an ambient temperature of 30°C conformed to values for other marsupials. At lower temperatures, body temperature decreased slightly, and metabolic rate increased significantly at 5°C. At higher temperatures, possums experienced mild hyperthermia and increased evaporative heat loss by licking rather than panting. Their point of relative water economy (–8.7°C) was more favourable than other pseudocheirid possums and the koala (Phascolarctos cinereus). We predict that western ringtail possums should tolerate low ambient temperatures well and be more physiologically tolerant of hot and dry conditions than common (Pseudocheirus peregrinus) and particularly green (Pseudochirops archeri) ringtail possums, and koalas. Our physiological data can be incorporated into mechanistic species distribution models to test our hypothesis that western ringtail possums should physiologically tolerate the climate of habitat further inland than their current distribution, and withstand moderate impacts of climate change in the south-west of Western Australia. Extreme weather events (e.g. heatwaves) limit where animals live by creating environmental conditions beyond their physiological resistance. The critically endangered western ringtail possum is sensitive to high temperatures, but is more tolerant of heat and aridity than other ringtail possum species. Understanding the possum's physiological limitations will inform conservation planning by better predicting regions with climates favourable for future survival. Photo by Christine Cooper. [ABSTRACT FROM AUTHOR]

The maintenance of optimal body temperatures has profound consequences on all aspects of ectotherms life history, like fitness and performance, and has been the subject of research for decades. In contrast, for reptiles, comparatively less is known on the potential effects of water balance on physiology, ecology and behaviour. In recent years, several recent studies are pointing out the importance of studying thermoregulation and water balance within the same framework. Here, we used a Mediterranean lizard, Psammodromus algirus, to investigate how field body temperature and water loss rates may vary among populations, between sexes and along an altitudinal gradient. We found little variation in field body temperatures among populations, while within each population, field body temperature may change daily, seasonally and differ between sexes. On the contrary, water loss rates decreased with elevation and showed no seasonal trend or difference between sexes. Microclimatic data indicated that highland lizards experienced more fluctuating conditions, a factor that may explain their lower water loss rates. Other factors, like inter‐population differences in ectoparasite intensity, might also contribute in explaining the observed patterns. We present here the first data for a lacertid lizard on the inter‐population variability and sexual difference in water loss rates and point out that water balance may play a fundamental role in regulating lizard activity during the hottest and driest period of the year. [ABSTRACT FROM AUTHOR]

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 shortterm negative effectsofwater restrictiononbodygrowth, 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. [ABSTRACT FROM AUTHOR]

When amphibians thermoregulate, they face a fundamental trade-off between the ability to maintain activity and an increased rate of dehydration at higher temperatures. Canopy coverage affects both the thermal and hydric conditions of the environment and can therefore influence amphibian thermoregulation. Frogs require proper conditions to thermoregulate to successfully grow, survive, and reproduce. But while we know how canopy and environmental variables typically affect operative temperature, less is known about effects on amphibian water loss rates. In this study, we measure the effect of canopy coverage on the conditions available for thermoregulation at a breeding pond of the California red-legged frog, Rana draytonii. We use agar frog models to estimate the thermal and hydric capacities frogs would experience in locations with different canopy coverage and microhabitats. At each site, we deployed models under four microhabitat treatments: wet/sun, wet/shade, dry/sun, and dry/shade. We modeled how environmental variables affected operative temperature and evaporative water loss from agar frogs. We found positive effects of air temperature, the sun treatment, and reduced canopy cover on operative temperature, and negative direct or indirect effects of these variables on evaporative water loss, consistent with the hypothesized trade-off between thermoregulatory behavior to increase temperature and the increased desiccation risk due to higher water loss. Additionally, our results indicate that the availability of wet microhabitats can allow frogs to reduce water loss, potentially mitigating the risk of desiccation when thermoregulating to achieve higher operative temperatures. Our findings suggest, that with access to proper microhabitats, amphibians can mitigate the fundamental trade-off and receive benefits of thermoregulating at high temperatures. • We investigated environmental effects on frog body temperature and water loss. • We placed agar frog models in locations with variable canopy coverage and microhabitats. • Air temperature, sun, and lower canopy cover increased operative body temperature. • Thermoregulating at higher body temperatures increases water loss. • Water access and higher humidity decrease evaporative water loss. [ABSTRACT FROM AUTHOR]

Temperature and water availability are two of the most important variables affecting all aspects of an anuran’s key physiological processes such as body temperature (Tb), evaporative water loss (EWL) and standard metabolic rate (SMR). Since anurans display pronounced sexual dimorphism, evidence suggests that these processes are further influenced by other factors such as vapour pressure deficit (VPD), sex and body mass (Mb). However, a limited number of studies have tested the generality of these results across a wide range of ecologically relevant ambient temperatures (Ta), while taking habitat use into account. Thus, the aim of this study was to investigate the role of Ta on Tb, whole-animal EWL and whole-animal SMR in three wild caught African anuran species with different ecological specialisations: the principally aquatic African clawed frog (Xenopus laevis), stream-breeding common river frog (Amietia delalandii), and the largely terrestrial raucous toad (Sclerophrys capensis). Experiments were conducted at a range of test temperatures (5–35 °C, at 5 °C increments). We found that VPD better predicted rates of EWL than Ta in two of the three species considered. Moreover, we found that Tb, whole-animal EWL and whole-animal SMR increased with increasing Ta, while Tb increased with increasing Mb in A. delalandii and S. capensis but not in X. laevis. Whole-animal SMR increased with increasing Mb in S. capensis only. We did not find any significant effect of VPD, Mb or sex on whole-animal EWL within species. Lastly, Mb did not influence Tb, whole-animal SMR and EWL in the principally aquatic X. laevis. These results suggest that Mb may not have the same effect on key physiological variables, and that the influence of Mb may also depend on the species ecological specialisation. Thus, the generality of Mb as an important factor should be taken in the context of both physiology and species habitat specialisation.

Many mammals hibernate during winter, reducing energy expenditure via bouts of torpor. The majority of a hibernator's energy reserves are used to fuel brief, but costly, arousals from torpor. Although arousals likely serve multiple functions, an important one is to restore water stores depleted during torpor. Many hibernating bat species require high humidity, presumably to reduce torpid water loss, but big brown bats (Eptesicus fuscus) appear tolerant of a wide humidity range. We tested the hypothesis that hibernating female E. fuscus use behavioural flexibility during torpor and arousals to maintain water balance and reduce energy expenditure. We predicted: (1) E. fuscus hibernating in dry conditions would exhibit more compact huddles during torpor and drink more frequently than bats in high humidity conditions; and (2) the frequency and duration of torpor bouts and arousals, and thus total loss of body mass would not differ between bats in the two environments. We housed hibernating E. fuscus in temperature- and humidity-controlled incubators at 50% or 98% relative humidity (8°C, 110 days). Bats in the dry environment maintained a more compact huddle during torpor and drank more frequently during arousals. Bats in the two environments had a similar number of arousals, but arousal duration was shorter in the dry environment. However, total loss of body mass over hibernation did not differ between treatments, indicating that the two groups used similar amounts of energy. Our results suggest that behavioural flexibility allows hibernating E. fuscus to maintain water balance and reduce energy costs across a wide range of hibernation humidities., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Trade-offs shaping behavioral variation are often influenced by the environment. We investigated the role that the environment plays in mediating trade-offs using a widespread frog with a conspicuous mating display, Pseudacris crucifer. We first demonstrated, using playback and desiccation experiments, that calling site selection involves a trade-off between sound transmission and desiccation. We then determined the influence of local environmental conditions on the intensity of the trade-off by examining range-wide behavioral and environmental data. We showed that the benefit of improved call transmission is positively influenced by vegetation density and ground cover. Behavioral data are consistent with this relationship: sites with a greater transmission benefit have increased prevalence of arboreally calling males. We also found that the prevalence of arboreal calling behavior increases with relative humidity and air temperature, suggesting an influence of these environmental variables on the desiccation cost of arboreal calling. This study provides a clear example of the role of the environment in mediating trade-off intensities and shaping critical behavioral traits. Local environment mediates the intensity of a trade-off associated with arboreal calling behavior in a treefrog. Combining observational and experimental approaches, we show that arboreal calling behavior increases the transmission of a mating call while potentially subjecting individuals to a rate of desiccation six times greater than terrestrial calling. Local environmental conditions influence both the benefit and the cost of this trade-off, subjecting different populations to varying trade-off intensities and shaping arboreal calling behavior. [ABSTRACT FROM AUTHOR]

Temperature and water availability are two of the most important variables affecting all aspects of an anuran’s key physiological processes such as body temperature (Tb), evaporative water loss (EWL) and standard metabolic rate (SMR). Since anurans display pronounced sexual dimorphism, evidence suggests that these processes are further influenced by other factors such as vapour pressure deficit (VPD), sex and body mass (Mb). However, a limited number of studies have tested the generality of these results across a wide range of ecologically relevant ambient temperatures (Ta), while taking habitat use into account. Thus, the aim of this study was to investigate the role of Ta on Tb, whole-animal EWL and whole-animal SMR in three wild caught African anuran species with different ecological specialisations: the principally aquatic African clawed frog (Xenopus laevis), stream-breeding common river frog (Amietia delalandii), and the largely terrestrial raucous toad (Sclerophrys capensis). Experiments were conducted at a range of test temperatures (5–35 °C, at 5 °C increments). We found that VPD better predicted rates of EWL than Ta in two of the three species considered. Moreover, we found that Tb, whole-animal EWL and whole-animal SMR increased with increasing Ta, while Tb increased with increasing Mb in A. delalandii and S. capensis but not in X. laevis. Whole-animal SMR increased with increasing Mb in S. capensis only. We did not find any significant effect of VPD, Mb or sex on whole-animal EWL within species. Lastly, Mb did not influence Tb, whole-animal SMR and EWL in the principally aquatic X. laevis. These results suggest that Mb may not have the same effect on key physiological variables, and that the influence of Mb may also depend on the species ecological specialisation. Thus, the generality of Mb as an important factor should be taken in the context of both physiology and species habitat specialisation. [ABSTRACT FROM AUTHOR]

Roosts are critical for the reproduction and survival of bats and many species spend a significant portion of their lives in them; thus, individuals should carefully select sites that reduce predation risk while providing ideal microclimatic conditions. Many studies have determined that bats select warmer and more humid roosts in temperate regions, but few studies have determined if roosts selected by tropical species also provide suitable conditions. In this study we compare temperature and humidity within and outside furled tubular leaves of plants in the order Zingiberales, which are used by several tropical species as roost-sites, to determine if these structures provide microclimatic advantages to bats. We found very small differences between the internal and external temperatures of tubular leaves, and the difference further decreased as leaves developed. However, we found large differences in humidity within the tubular leaf compared to external conditions, which were strongly dependent on a leaf's diameter and genus. The internal humidity was often 20% above the external, particularly when leaves were narrower, and tubular leaves in the genus Heliconia were more humid than those in the genus Calathea. Our findings suggest that, despite being fairly exposed structures, furled tubular leaves provide suitable microclimatic conditions for tropical species. [ABSTRACT FROM AUTHOR]

Environmental humidity is thought to be a major determinant of evaporative cooling capacity at high air temperatures (Ta), but the technical challenges of experimentally manipulating humidity in respirometry chambers have resulted in far less being known about the effects of humidity compared to those of Ta. We tested the prediction that at Ta approaching and exceeding normothermic body temperature (Tb), high humidity would result in higher Tb, lower evaporative water loss (EWL) and/or higher resting metabolic rate (RMR) in a passerine bird, the white-browed sparrow-weaver (Plocepasser mahali). We used open-system flow-through respirometry to measure EWL, RMR and Tb in sparrow-weavers experiencing Ta = 36-44 °C and chamber humidities of 6, 13, 19 or 25 g m− 3. Increasing humidity was associated with significantly higher Tb. The strongest effect of humidity, however, involved significant increases in RMR; at Ta = 40 °C, RMR at a humidity of 25 g m− 3 was ~ 40% higher compared to a humidity of 6 g m− 3. Moreover, the interaction between Ta and humidity exerted a significant effect on the ratio of evaporative heat loss (EHL) to metabolic heat production (MHP), evident as an increasing effect of humidity with increasing Ta. Our results, when compared with those of the limited number of previous studies that involved similar ranges of Ta and humidity, reveal that the relative effects of humidity on EWL and RMR vary among avian taxa, and support the notion that the overall effect of high humidity is a reduction in maximum EHL/MHP. [ABSTRACT FROM AUTHOR]

An animal's physiology should be closely adapted to its environment to optimize organismal function, so physiological traits may be mismatched when animals are introduced to new locations. For introduced amphibians, mismatched traits involving hydric balance or performance across hydric states could have profound impacts on their abundance and distribution, and thus their invasion success. We examined susceptibility to dehydration in invasive Cuban treefrogs (Osteopilus septentrionalis) and two sympatric native treefrogs (Hyla spp.) in Florida, USA, by measuring rates of evaporative water loss, rates of water uptake, and sensitivity of locomotor performance to dehydration. Of the three species, Cuban treefrogs were the most susceptible to dehydration by experiencing the highest rate of evaporative water loss and lowest rate of water uptake. Green treefrogs (Hyla cinerea) were the most resistant to dehydration by losing water the slowest and gaining water the fastest, and squirrel treefrogs (Hyla squirella) were intermediate in rates of water loss and uptake. Dehydrating frogs by 20% of their fully hydrated body masses affected the locomotor performance of all species by decreasing maximum jump lengths, decreasing speed, and increasing successive jump lengths. The maximum jump lengths of Cuban treefrogs and green treefrogs were more sensitive to dehydration than those of squirrel treefrogs. Despite this sensitivity, Cuban treefrogs still outperformed both native species in maximum jump length and speed, even when controlling for body size. Consequently, the performance of dehydrated Cuban treefrogs was similar to that of fully hydrated native treefrogs. Our results suggest that Cuban treefrogs are more susceptible to dehydration and its effects than several native competitors; however, they may be able to at least partly compensate for these effects with their large body size, superior locomotor performance, and strong affinity for refugia. Our findings highlight different strategies used by frogs to maintain water balance and suggest that Cuban treefrog densities may be higher in areas with greater moisture availability and habitat complexity, including urban and densely forested areas. Native treefrogs may experience stronger competition and predation from Cuban treefrogs in these areas, which supports anecdotal reports of native frog declines.

Much recent work on avian physiological adaptation to desert environments has focused on larks (Passeriformes: Alaudidae). We tested the prediction that the threatened red lark (Calendulauda burra), a species restricted to very arid parts of South Africa and which is not known to drink, exhibits highly efficient evaporative cooling and makes pronounced use of facultative hyperthermia when exposed to high air temperatures (Ta). We also predicted that C. burra possesses similarly low basal metabolic rate (BMR) and total evaporative water loss (EWL) at moderate Ta as reported for species from the deserts of the Middle East. Rest-phase thermoregulation in C. burra was characterized by an unusually low lower critical limit of thermoneutrality at Ta = ~ 21 °C and a BMR of 0.317 ± 0.047 W, the lowest BMR relative to allometrically-expected values yet reported in any lark. During the diurnal active phase, red larks were able to tolerate Ta up to 50 °C, with the onset of panting occurring at Ta = 38 °C. Maximum EWL was 1.475 ± 0.107 g h− 1 at Ta = 50 °C, equivalent to 620% of minimum EWL at thermoneutrality. The maximum ratio of evaporative heat dissipation to metabolic heat production was 1.58, a value towards the lower end of the range reported for passerines. Our data support the prediction that C. burra shows metabolic traits similar to those of other larks inhabiting extremely arid climates, but not the notion that evaporative cooling at high Ta in this species is more efficient than in most passerines. [ABSTRACT FROM AUTHOR]

Small mammals, and particularly shrews and mice, have relatively high mass‐specific metabolic rates and may be constrained to habitats where they can avoid extreme temperatures. Although their phylogeny differs, shrews and rodents often inhabit the same environments and compete for resources due to their similar body masses and dietary overlap. Our aim was to elucidate the variation in thermal parameters of sympatric species. We examined Myosorex varius, Crocidura flavescens and Mus minutoides, by measuring metabolic rate, evaporative water loss (EWL), body temperature (Tb) and thermal conductance over a range of ambient temperatures (Ta). Body temperatures of all three species remained above 32°C across the range of Ta. For all species, there was no relation between Ta <35°C and EWL, although EWL in C. flavescens was considerably lower compared to the other two species. Dry thermal conductance was much higher in Mu. minutoides than in either of the shrews. Resting metabolic rate of all three species declined with Ta <35°C. The thermoneutral zone of My. varius was between Ta = 35°C and Ta = 40°C, whereas that of C. flavescens was between Ta = 30°C and Ta = 33°C. No discernible thermoneutral zone was evident for Mu minutoides. Our data reveal considerable variation in thermal physiology among three sympatric species of small mammal at a single site and generally conform to the plesiomorphic–apomorphic endothermy model. Differences in body size, life‐history traits and evolutionary history may all play a role in the thermoregulatory patterns of these sympatric species. Three sympatric small mammals from South Africa's Eastern Cape province, one of which is southern Africa's smallest mammal, vary substantially in their thermal physiology. Body temperatures of two of the species are near the boundary between baso‐ and mesoendothermy, and the capacity for evaporative cooling appears limited. Photo credit: Maria Froneman. [ABSTRACT FROM AUTHOR]