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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]

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]

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]

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.

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]

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]

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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]

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]

It is unclear whether torpor really is uncommon amongst passerine birds. We therefore examined body temperature and thermoregulatory strategies of an Austral passerine, the white-browed babbler (Pomatostomus superciliosus), which has characteristics related to a high probability of torpor use; it is a sedentary, insectivorous, cooperative breeding species, which we studied during winter in a temperate habitat. Wild, free-living babblers maintained normothermy overnight, even at sub-zero ambient temperatures, with a mean minimum body temperature of 38.5±0.04°C that was independent of minimum black bulb temperature. Physiological variables measured in the laboratory revealed that babblers had a low basal metabolic rate and evaporative water loss, but their body temperature and thermal conductance were typical of those of other birds and they had a typical endothermic response to low ambient temperature. Huddling yielded significant energy savings at low temperatures and a roost nest created a microclimate that buffered against low temperatures. Low basal energy requirements, communal roosting and the insulation of a roost nest confer sufficient energetic benefits, allowing babblers to meet energy requirements without resorting to heterothermia, even in their depauperate, low-productivity landscape, suggesting that passerine birds use alternatives to torpor to balance their energy budgets when possible. [ABSTRACT FROM AUTHOR]

Seasonal acclimatisation of thermal tolerance, evaporative water loss and metabolic rate, along with regulation of the hive environment, are key ways whereby hive-based social insects mediate climatic challenges throughout the year, but the relative importance of these traits remains poorly understood. Here, we examined seasonal variation in metabolic rate and evaporative water loss of worker bees, and seasonal variation of hive temperature and relative humidity (RH), for the stingless bee Austroplebeia essingtoni (Apidae: Meliponini) in arid tropical Australia. Both water loss and metabolic rate were lower in the cooler, dry winter than in the hot, wet summer at most ambient temperatures between 20°C and 45°C. Contrary to expectation, thermal tolerance thresholds were higher in the winter than in the summer. Hives were cooler in the cooler, dry winter than in the hot, wet summer, linked to an apparent lack of hive thermoregulation. The RH of hives was regulated at approximately 65% in both seasons, which is higher than unoccupied control hives in the dry season, but less than unoccupied control hives in the wet season. Although adaptations to promote water balance appear more important for survival of A. essingtoni than traits related to temperature regulation, their capacity for water conservation is coincident with increased thermal tolerance. For these small, eusocial stingless bees in the arid tropics, where air temperatures are relatively high and stable compared with temperate areas, regulation of hive humidity appears to be of more importance than temperature for maintaining hive health. [ABSTRACT FROM AUTHOR]

A typical explanation for ecologically stable strategies that apply to only a proportion of a population, is bet hedging, where increased reproductive success offsets reduced reproductive rate. One such is partial migration, where only a proportion of a population moves seasonally to avoid inclement climatic conditions. Bet hedging may overlook unseen costs to maintain broad physiological resilience, implied by encountering a breadth of environmental conditions. We investigated the physiological correlates of partial migration by measuring standard metabolic rates, and rates of evaporative water loss, and then estimating upper and lower thermal tolerance in males and females of two hoverfly species, Episyrphus balteatus and Eristalis tenax. In central Europe, females of these species may either migrate or overwinter, whereas males may migrate south to the Mediterranean, but have not been found overwintering. Both species were sexually dimorphic; female Ep. balteatus were lighter than males, but female Er. tenax were heavier than males. While allometrically- corrected metabolic rate in both species increased with temperature, the most parsimonious models included no sex-specific differences in metabolic rate for either species. Evaporative water loss of both species also increased with temperature, but was higher for females of both species than males. Assuming that resting metabolism is congruent with the activity requirements of migration, highly consistent thermal tolerance and metabolic rate suggests that any given fly could migrate, although water loss patterns suggest that females may be less well-adapted to Mediterranean climates. We infer that partial migration probably results from the imperatives of their reproductive strategies. [ABSTRACT FROM AUTHOR]

Subterranean rodents face unique thermoregulatory challenges. Evaporative water loss (EWL) is a crucial mechanism for maintaining heat balance in endotherms subjected to heat stress but also leads to potential dehydration. EWL depends on gradients of temperature and humidity between the surface of the individual and the surrounding environment. Underground burrows generally provide a stable water vapor saturated atmosphere which may impede evaporative heat loss (EHL). This will mainly occur when ambient temperature exceeds the upper limit of individual's thermoneutral zone, or when body temperature rises as result of digging activities. Here we evaluate the effect of ambient temperature on EWL and energy metabolism in the subterranean rodent Ctenomys talarum (tuco-tucos), which inhabits sealed burrows, but makes an extensive use of the aboveground environment. We observed that EWL is increased when ambient temperature rises above thermoneutrality; below this point, evaporation remains stable. Though EWL contributes to total heat loss by increasing ∼1.3 times at 35 °C, dry thermal conductance is raised four times. In tuco-tucos' burrows both non-evaporative and, to some extent, evaporative and behavioral mechanisms are essential for body temperature regulation, preventing overheating at high ambient temperatures in a water vapor-saturated atmosphere. [ABSTRACT FROM AUTHOR]

Species with sexual dimorphism provide powerful study systems for understanding adaptation to different lifestyles as it removes the potentially confounding effects of phylogeny. Thynnine wasps have a stark sexual dimorphism where males fly patrols in search of the flightless, predominantly fossorial females with which to mate. Using flow-through respirometry, we tested the prediction that the highly active males of the thynnine wasp Zaspilothynnus nigripes would have high metabolic rates (VCO 2 ) relative to females. Further, the females, which spend more time underground, were predicted to exhibit lower evaporative water loss (EWL) than males. Metabolic rate of both sexes increased exponentially between 12 and 28 °C. As predicted, males had higher mass-corrected VCO 2 at identical temperatures than females. Alternatively, there were no differences in the EWL at identical temperatures between sexes, suggesting that experiencing the same environmental conditions during mating may favour similar EWL. Interestingly, Z. nigripes were estimated to undergo a decrease in metabolism at approximately 30 °C. It is proposed that Z. nigripes persist despite sensitivity to high temperatures using a combination of behavioural strategies and emergence during a period of relatively benign climate that ameliorates the impacts of high temperatures. [ABSTRACT FROM AUTHOR]

Many birds can defend body temperature (Tb) far below air temperature (Ta) during acute heat exposure, but relatively little is known about how avian heat tolerance and evaporative cooling capacity varies with body mass (Mb), phylogeny or ecological factors. We determined maximum rates of evaporative heat dissipation and thermal end points (Tb and Ta associated with thermoregulatory failure) in three southern African ploceid passerines, the scalyfeathered weaver (Sporopipes squamifrons, Mb≈10 g), sociable weaver (Philetairus socius, Mb≈25 g) and white-browed sparrow-weaver (Plocepasser mahali, Mb≈40 g). Birds were exposed to a ramped profile of progressively increasing Ta, with continuous monitoring of behaviour and Tb used to identify the onset of severe hyperthermia. The maximum Ta birds tolerated ranged from 48°C to 54°C, and was positively related to Mb. Values of Tb associated with severe heat stress were in the range of 44 to 45°C. Rates of evaporative water loss (EWL) increased rapidly when Ta exceeded Tb, and maximum evaporative heat dissipation was equivalent to 141-222% of metabolic heat production. Fractional increases in EWL between Ta<40°C and the highest Ta reached by each species were 10.8 (S. squamifrons), 18.4 (P. socius) and 16.0 (P. mahali). Resting metabolic rates increased more gradually with Ta than expected, probably reflecting the very low chamber humidity values we maintained. Our data suggest that, within a taxon, larger species can tolerate higher Ta during acute heat stress. [ABSTRACT FROM AUTHOR]

Mongolian gerbils ( Meriones unguiculatus ) have a large-scale distribution in northern China. Geographic physiological variations which related to energy and water metabolism are critical to animals' local adaptation and distribution. However, the underlying biochemical mechanism of such variation and its role in adaptation remains largely unknown. We used GC–MS metabolomics approach to investigate the biochemical adaptation of Mongolian gerbils from xeric (desert), transition (desert steppe) and mesic (typical steppe) environments. Gerbils in desert population had lower resting metabolic rate (RMR) and total evaporative water loss (TEWL) than mesic population. Serum metabolomics revealed that concentrations of five tricarboxylic acid cycle intermediates (citrate, cis-aconitate, α-ketoglutarate, fumarate and malate) were lower in desert population than mesic population. Gastrocnemius metabolomics and citrate synthase activity analysis showed a lower concentration of citrate and lower citrate synthase activity in desert population. These findings suggest that desert dwelling gerbils decrease RMR and TEWL via down-regulation of aerobic respiration. Gastrocnemius metabolomics also revealed that there were higher concentrations of glucose and glycolytic intermediates, but lower concentrations of lipids, amino acids and urea in desert population than mesic population. This geographic variation in metabolic substrates may enhance metabolic water production per oxygen molecule for desert population while constraining aerobic respiration to reduce RMR and TEWL. [ABSTRACT FROM AUTHOR]

Previous research has demonstrated that dehydration increases the threshold temperature for panting and decreases the thermal preference of lizards. Conversely, it is unknown whether thermoregulatory responses such as shuttling and gaping are similarly influenced. Shuttling, as an active behavioural response, is considered one of the most effective thermoregulatory behaviours, whereas gaping has been proposed to be involved in preventing brain over-heating in lizards. In this study we examined the effect of salt loading, a proxy for increased plasma osmolality, on shuttling and gaping in Pogona vitticeps. Then, we determined the upper and lower escape ambient temperatures (UETa and LETa), the percentage of time spent gaping, the metabolic rate (Vo2), the evaporative water loss (EWL) during gaping and non-gaping intervals and the evaporative effectiveness (EWL/o2 of gaping. All experiments were performed under isotonic (154 mmol I-1) and hypertonic saline injections (625, 1250 or 2500 mmol I-1). Only the highest concentration of hypertonic saline altered the UETa and LETa, but this effect appeared to be the result of diminishing the animal's propensity to move, instead of any direct reduction in thermoregulatory set-points. Nevertheless, the percentage of time spent gaping was proportionally reduced according to the saline concentration; o2 was also decreased after salt loading. Thermographic images revealed lower head than body surface temperatures during gaping; however this difference was inhibited after salt loading. Our data suggest that EWL/o2 is raised during gaping, possibly contributing to an increase in heat transfer away from the lizard, and playing a role in head or brain cooling. [ABSTRACT FROM AUTHOR]

Basal metabolic rate (BMR) is thought to be a major hub in the network of physiological mechanisms connecting life history traits. Evaporative water loss (EWL) is a physiological indicator that is widely used to measure water relations in inter- or intraspecific studies of birds in different environments. In this study, we examined the physiological responses of summer-acclimatized Hwamei Garrulax canorus to temperature by measuring their body temperature (T b ), metabolic rate (MR) and EWL at ambient temperatures (T a) between 5 and 40°C. Overall, we found that mean body temperature was 42.4°C and average minimum thermal conductance (C) was 0.15ml O2 g−1 h−1 °C−1 measured between 5 and 20°C. The thermal neutral zone (TNZ) was 31.8–35.3°C and BMR was 181.83ml O2 h−1. Below the lower critical temperature, MR increased linearly with decreasing T a according to the relationship: MR (ml O2 h−1)=266.59–2.66 T a . At T a s above the upper critical temperature, MR increased with T a according to the relationship: MR (ml O2 h−1)=−271.26+12.85 T a . EWL increased with T a according to the relationship: EWL (mg H2O h−1)=−19.16+12.64 T a and exceeded metabolic water production at T a >14.0°C. The high T b and thermal conductance, low BMR, narrow TNZ, and high evaporative water production/metabolic water production (EWP/MWP) ratio in the Hwamei are consistent with the idea that this species is adapted to warm, mesic climates, where metabolic thermogenesis and water conservation are not strong selective pressures. [ABSTRACT FROM AUTHOR]

Abstract: In terms of total number of publications, the laboratory mouse (Mus musculus) has emerged as the most popular test subject in biomedical research. Mice are used as models to study obesity, diabetes, CNS diseases and variety of other pathologies. Mice are classified as homeotherms and regulate their core temperature over a relatively wide range of ambient temperatures. However, researchers find that the thermoregulatory system of mice is easily affected by drugs, chemicals, and a variety of pathological conditions, effects that can be exacerbated by changes in ambient temperature. To this end, a thorough review of the thermal physiology of mice, including their sensitivity and regulatory limits to changes in ambient temperature is the primary focus of this review. Specifically, the zone of thermoneutrality for metabolic rate and how it corresponds to that for growth, reproduction, development, thermal comfort, and many other variables is covered. A key point of the review is to show that behavioral thermoregulation of mice is geared to minimize energy expenditure. Their zone of thermal comfort is essentially wedged between the thresholds to increase heat production and heat loss; however, this zone is above the recommended guidelines for animal vivariums. Future work is needed to better understand the behavioral and autonomic thermoregulatory responses of this most popular test species. [Copyright &y& Elsevier]

Abstract: We examine here the thermal physiology of the ash-grey mouse, as there is a paucity of data to explain how Australian rodents meet thermoregulatory demands. Most ash-grey mice remained normothermic over a range of ambient temperatures (10°C to 30°C), although they became hyperthermic at high ambient temperatures. One individual entered torpor at ambient temperatures of 20°C and 25°C, with minimal body temperatures of 24.5°C and 28.4°C respectively, before spontaneously arousing. This is the first evidence of torpor use by an Australian murine rodent. Our data suggest that although ash-grey mice have the physiological ability to use torpor, it is used rarely, presumably due to other behavioural and physiological adaptations. Their higher-than-expected basal metabolic rate (1.56±0.25mLO2 g−1 h−1) indicates that ash-grey mice do not have a frugal approach to energy expenditure. Other standard physiological variables were typical of a generalised rodent. A readily-available omnivorous diet, nocturnal activity, semi-fossorial habit and social behaviour presumably allow a high energy lifestyle. A reluctance to use torpor, despite an apparent physiological ability to do so, supports the idea that the use of torpor reflects a net balance between the costs and benefits of a heterothermic thermoregulatory strategy. [Copyright &y& Elsevier]

Stripe-faced dunnarts (Sminthopsis macroura) and Ooldea dunnarts (S. ooldea) were acclimated for 2weeks to ambient temperature (Ta) regimes of 12-22°C, 18-28°C and 25-35°C, and then measured for standard, basal (BMR) and maximum (MMR) metabolic rate using flow-through respirometry. Sminthopsis macroura maintained a stable body temperature under all experimental Ta and acclimation regimes. Although its BMR was not statistically different between the three acclimation regimes, the lower end of the thermoneutral zone (TNZ) shifted from 30°C under the 18-28°C and 12-22°C acclimation regimes to 35°C under the 25-35°C acclimation regime. MMR increased significantly at the cooler acclimation regimes. EWL increased at ra=35°C, compared with lower Ta, in all acclimation regimes, but an increase in evaporative water loss (EWL) at ra=10°C observed in cool acclimations did not occur at the 25-35°C regime. In contrast, S. ooldea had variable body temperature between experimental Ta in all acclimation regimes, but no acclimational shift in TNZ, which was between 30 and 35°C. Neither BMR nor MMR was affected by exposure to the three acclimation regimes. EWL did not change across Ta or with acclimation regime. Sminthopsis macroura was flexible in many aspects of its thermoregulation (involving energy and water balance) in response to thermal acclimation, presumably allowing it to balance its energy and water requirements over a broad range of climatic conditions. Sminthopsis ooldea seems to have an inflexible energetic and water balance in response to thermal acclimation, but has low nominal expenditure of either resource on thermoregulation because it thermoregulates less precisely than S. macroura. It seems that S. ooldea is adapted to a more narrow, stable climate. [ABSTRACT FROM AUTHOR]

High ambient temperatures can adversely affect insects through high evaporative water loss ( EWL) and reduction of metabolic activity through enzyme denaturation. Establishing the relationship between the temperature at which these processes become detrimental and regulatory behaviour is critical in resolving the mechanisms by which insects cope with physiologically stressful environments. Here, we compare levels of metabolic rate and EWL measured by flow-through respirometry with field activity in the ichneumonid wasp Lissopimpla excelsa. Metabolic rate increased to a maximum of 10.8 ± 0.4 mLCO2.g−1.h−1 at 35° C before decreasing to 8.4 ± 0.4 mLCO2.g−1.h−1 at Ta = 40° C. EWL showed an exponential pattern of increase, with a significant increase in EWL from Ta = 12° C to Ta = 35 and 40° C. Male wasps were active in the field from Ta = 20.1 to 36.8° C (peak activity Ta = 26.5° C and relative humidity = 44.4%), though activity levels were most strongly correlated with time of day. Being active in the mornings may be advantageous in that temperatures are warm enough to maintain activity but avoid excess energy expenditure and EWL. Furthermore, food or calling females may be most abundant during this period. Based on a consensus allometric scaling relationship derived for insect resting metabolic rates, the metabolic rate of L. excelsa at Ta = 25° C was higher than predicted, as was EWL. Since the present study is the first describing the metabolic physiology of an ichneumonid wasp, it remains unclear whether this pattern is characteristic of ichneumonids in general of L. excelsa in particular. [ABSTRACT FROM AUTHOR]

Metabolic rate and evaporative water loss (EWL) were measured to quantify the thermoregulatory patterns of two dasyurids, the stripe-faced dunnart (Sminthopsis macroura) and the Ooldea dunnart (S. ooldea) during acute exposure to T[sub a] between 10 and 35°C. S. macroura maintained consistent T[sub b] across the T[sub a] range, whereas S. ooldea was more thermolabile. The metabolic rate of both species decreased from T[sub a] = 10°C to BMR at T[sub a] = 30°C. Mass-adjusted BMR at T[sub a] = 30°C was the same for the two species, but there was no common regression of metabolic rate below the thermoneutral zone (TNZ). There was no significant difference between the species in allometrically corrected EWL at T[sub a] = 30°C. Total EWL increased significantly at T[sub a] = 10 and 35°C compared with the TNZ for S. macroura, but was consistent across the T[sub a] range for S. ooldea. At any T[sub a] below the TNZ, S. macroura required more energy per gram of body mass than S. ooldea, and had a higher EWL at the lower critical T[sub a]. By being thermolabile S. ooldea reduced its energetic requirements and water loss at low T[sub a]. The more constant thermoregulatory strategy of S. macroura may allow it to exploit a broad climatic envelope, albeit at the cost of higher energetic and water requirements. Since S. ooldea does not expend as much energy and water on thermoregulation this may be a response to the very low productivity, 'hyperarid' conditions of its central Australian distribution. Thermoregulation of Sminthopsis macroura and S. ooldea were measured. Sminthopsis macroura thermoregulated well, whereas S. ooldea was more thermolabile, which had implications for metabolism and water loss. Thermoregulation may adapt S. macroura to a broad climate, but thermolability may adapt S. ooldea to very low productivity conditions of central Australia. [ABSTRACT FROM AUTHOR]

Quolls ( Dasyurus) are medium-sized carnivorous dasyurid marsupials. Tiger (3,840 g) and eastern quolls (780 g) are mesic zone species, northern quolls (516 g) are tropical zone, and chuditch (1,385 g) were once widespread through the Australian arid zone. We found that standard physiological variables of these quolls are consistent with allometric expectations for marsupials. Nevertheless, inter-specific patterns amongst the quolls are consistent with their different environments. The lower Tb of northern quolls (34°C) may provide scope for adaptive hyperthermia in the tropics, and they use torpor for energy/water conservation, whereas the larger mesic species (eastern and tiger quolls) do not appear to. Thermolability varied from little in eastern (0.035°C °C−1) and tiger quolls (0.051°C ºC−1) to substantial in northern quolls (0.100°C ºC−1) and chuditch (0.146°C ºC−1), reflecting body mass and environment. Basal metabolic rate was higher for eastern quolls (0.662 ± 0.033 ml O2 g−1 h−1), presumably reflecting their naturally cool environment. Respiratory ventilation closely matched metabolic demand, except at high ambient temperatures where quolls hyperventilated to facilitate evaporative heat loss; tiger and eastern quolls also salivated. A higher evaporative water loss for eastern quolls (1.43 ± 0.212 mg H2O g−1 h−1) presumably reflects their more mesic distribution. The point of relative water economy was low for tiger (−1.3°C), eastern (−12.5°C) and northern (+3.3) quolls, and highest for the chuditch (+22.6°C). We suggest that these differences in water economy reflect lower expired air temperatures and hence lower respiratory evaporative water loss for the arid-zone chuditch relative to tropical and mesic quolls. [ABSTRACT FROM AUTHOR]

Small differences in physiological responses are known to influence demographic rates such as survival. We tested for differences in the physiological acclimation responses of two closely-related salamander species that often co-occur, Ambystoma maculatum and A. opacum. Specifically, we measured changes in critical thermal maxima (CT max), standard metabolic rates (SMRs), and respiratory surface area water loss (RSAWL) following exposure to three temperature treatments under laboratory conditions. While the magnitude of RSAWL and CT max acclimation responses to warming did not differ between the study species, SMR was maintained across acclimation temperatures among A. maculatum, but declined among A. opacum acclimated to warmer temperatures. Metabolic compensation may facilitate maintained A. maculatum activity levels during warm periods following the relatively cool spring breeding season. In contrast, metabolic suppression may allow A. opacum to conserve energy when exposed to surface conditions during fall breeding and nest guarding. We simulated how these different SMR responses would likely alter post-metamorphic survival in our study species using previously collected data representing six weeks under relatively warm seminatural conditions. Our simulation indicated that, following warming and under identical study conditions, metabolic compensation may allow juvenile A. maculatum to maintain survival likelihoods, whereas metabolic depression may cause juvenile A. opacum to experience increased survivorship. These findings underscore that comparable physiological responses among ecologically similar, sympatric species cannot be assumed. Further, results of this study suggest that metabolic responses may play an important role in amphibian species persistence as temperatures increase due to habitat modification and climate change. • Terrestrial spotted and marbled salamanders physiologically acclimate to warming. • Metabolism and thermal tolerance responded to warming; water loss rate did not. • The study species showed different metabolic acclimation responses to warming. • Distinct acclimation responses correspond with differing species phenologies. • Species-specific metabolic responses will likely affect survivorship post-warming. [ABSTRACT FROM AUTHOR]

The thermal and metabolic physiology of Chalinolobus gouldii, an Australian vespertilionid bat, was studied in the laboratory using flow-through respirometry. Chalinolobus gouldii exhibits a clear pattern of euthermic thermoregulation, typical of endotherms with respect to body temperature and rate of oxygen consumption. The basal metabolic rate of euthermic Chalinolobus gouldii is approximately 86% of that predicted for a 17.5-g mammal and falls into the range of mass-specific basal metabolic rates ascribed to vespertilionid bats. However, like most vespertilionid bats, Chalinolobus gouldii displays extreme thermolability. It is able to enter into torpor and spontaneously arouse at ambient temperatures as low as 5 °C. Torpid bats thermoconform at moderate ambient temperature, with body temperature ≈ ambient temperature, and have a low rate of oxygen consumption determined primarily by Q10 effects. At low ambient temperature (< 10 °C), torpid C. gouldii begin to regulate their body temperature by increased metabolic heat production; they tend to maintain a higher body temperature at low ambient temperature than do many northern hemisphere hibernating bats. Use of torpor leads to significant energy savings. The evaporative water loss of euthermic bats is relatively high, which seems unusual for a bat whose range includes extremely arid areas of Australia, and is reduced during torpor. The thermal conductance of euthermic C. gouldii is less than that predicted for a mammal of its size. The thermal conductance is considerably lower for torpid bats at intermediate body temperature and ambient temperature, but increases to euthermic values for torpid bats when thermoregulating at low ambient temperature. [ABSTRACT FROM AUTHOR]

The intensity and frequency of extreme weather events, such as heat waves, are increasing as a consequence of global warming. Acute periods of extreme heat can be more problematic for wildlife than a chronic increase in mean temperature, to which animals can potentially acclimatise. Predicting effects of heat exposure requires a clear understanding of the capacity of individuals to respond to heat waves, so we examined the physiological response of a small desert bird, the zebra finch (Taeniopygia guttata), after acute previous exposure to high ambient temperature, simulating heatwave-like conditions. The standard physiology of the zebra finches was unaffected by prior exposure to heatwave-type conditions, suggesting that periodic exposure to heatwaves is unlikely to impact their longer-term day-to-day energy and water requirements. When finches were thermally challenged, prior experience of heatwave-like conditions did not impact overall body temperature and evaporative water loss, but birds previously experiencing high temperatures did reduce their metabolic heat production, and the variance in water loss and metabolism between individuals was significantly lower. This suggests that some individuals are more likely to become dehydrated if they have not had prior experience of high temperatures, and do not prioritise water conservation over thermoregulation. However, our observations overall suggest that acute periods of heat exposure do little to modify the general physiology of small birds, supporting the hypothesis that periodic extreme heat events may be more problematic for them than chronic warming. Unlabelled Image • Intensity and frequency of extreme weather is increasing and may be problematic for wildlife. • Basic physiology of zebra finches was unaffected by prior exposure to heatwave-type conditions. • At high temperature acclimated finches reduced metabolic rate and water loss variance. • Overall, short periods of heat exposure do little to modify the general physiology of small birds. [ABSTRACT FROM AUTHOR]