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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]

Threatened species monitoring is challenging for small, cryptic endotherms that are most effectively detected at night. Low detectability is a challenge for monitoring programmes, resulting in low statistical power and sparse or zero‐inflated datasets. To advance conservation management programmes, efforts to address this are required. In recent years thermal scanners have emerged as an effective tool for detecting small endotherms, but the diversity of available thermal tools, focal habitats and target species mean that their applicability in many key scenarios remain untested. We directly compared vehicle‐mounted thermal surveys with vehicle‐based spotlighting targeting small endotherms in Australian native grasslands. Our targets included both common species that occur at high densities, and species that are notoriously difficult to detect with spotlights, which may occur at very low densities. We completed paired surveys of roosting grassland birds, and nocturnally active small mammals at 22 sites, once using thermal scanners and once using spotlights. Ultimately, distance sampling was conducted across 136 km of transects. Thermal scanners facilitated greater detection distances and higher total detections for small endotherms when compared with spotlighting. Species of greatest conservation concern, the Plains‐wanderer (Pedionomus torquatus—Pedionomidae) and Fat‐tailed Dunnart (Sminthopsis crassicaudata—Dasyuridae) were only detected using thermal scanners. Detection distances generated for thermal scanners were reduced by higher vegetation density; however, thermal scanners continued to outperform spotlights under this scenario. Observers also detected more stationary animals and fewer birds were flushed upon detection using thermal scanners when compared with spotlighting. Thermal scanners have the potential to improve the quality of monitoring datasets by increasing detection probabilities for small endotherms. We recommend the adoption of thermal scanners as a best‐practice tool for monitoring small endotherms in open grassland habitats at night, offering new opportunities to monitor endotherms where monitoring has historically been challenging, inadequate or impossible. [ABSTRACT FROM AUTHOR]

Bergmann's rule states that endotherms have a large body size in high latitudes and cold climates. However, previous empirical studies have reported mixed evidence on the relationships between body size and latitude, raising the question of why some clades of endotherms follow Bergmann's rule, whereas others do not. Here, we synthesized the interspecific relationships between body size and latitude among 16,187 endothermic species (5422 mammals and 10,765 birds) using Bayesian phylogenetic generalized linear mixed models to examine the strength and magnitude of Bergmann's rule. We further assessed the effect of biological and ecological factors (i.e., body mass categories, dietary guild, winter activity, habitat openness, and climate zone) on the variations in the body mass–latitude relationships by adding an interaction term in the models. Our results revealed a generally weak but significant adherence to Bergmann's rule among all endotherms at the global scale. Despite taxonomic variation in the strength of Bergmann's rule, the body mass of species within most animal orders showed an increasing trend toward high latitudes. Generally, large‐bodied, temperate species, non‐hibernating mammals, and migratory and open‐habitat birds tend to conform to Bergmann's rule more than their relatives do. Our results suggest that whether Bergmann's rule applies to a particular taxon is mediated by not only geographic and biological features, but also potential alternate strategies that species might have for thermoregulation. Future studies could explore the potential of integrating comprehensive trait data into phylogenetic comparative analysis to re‐assess the classic ecogeographic rules on a global scale. [ABSTRACT FROM AUTHOR]

Detection is essential to studying and monitoring wild animals; however, detection is challenging for small endotherms that are nocturnal or best detected at night. Techniques such as trapping or spotlighting disturb focal species, and the effectiveness of spotlighting can be limited for cryptic species, resulting in low detection rates that hinder our ability to monitor and study some endotherms at night. Thermal scanners detect infrared wavelengths not otherwise visible to humans. With improvements in equipment size and cost, thermal scanners have emerged as a valuable tool for passive detection of endotherms. Here we seek to provide objective guidance on thermal tool selection to practitioners who wish to adopt such tools to detect and monitor small endotherms. We compared the efficacy of three handheld thermal scanners (of varying resolutions) and a traditional spotlight for detecting small, cryptic endotherms at night. Random arrays of artificially heated small bird models (representing small, cryptic endotherms) were established along transects in native grasslands that support a range of small threatened endotherms, including the Critically Endangered Plains‐wanderer (Pedionomus torquatus). Transects were independently surveyed by five observers, blind to model locations and model density. Performance measures representing detection capability were assessed for all devices, and usability of each device was assessed with a survey completed by all observers. Detection rates, detection distances, and survey accuracy were greater for thermal scanners with resolutions of 320 × 240 and 640 × 480 than for the spotlight. A low‐resolution thermal scope (160 × 120) performed poorly for all performance measures. There was a consensus among users that a video camera‐style thermal scanner was most comfortable to hold and view while traversing the transect, as opposed to thermal scopes where users look directly through the lens. These results suggest that high‐resolution thermal scanners (≥320 × 240) provide improved detection capabilities compared to traditional spotlights. Higher detection rates provide opportunities for detecting and monitoring small endotherms at night where this was once difficult or impossible. [ABSTRACT FROM AUTHOR]

Abstract Detection is essential to studying and monitoring wild animals; however, detection is challenging for small endotherms that are nocturnal or best detected at night. Techniques such as trapping or spotlighting disturb focal species, and the effectiveness of spotlighting can be limited for cryptic species, resulting in low detection rates that hinder our ability to monitor and study some endotherms at night. Thermal scanners detect infrared wavelengths not otherwise visible to humans. With improvements in equipment size and cost, thermal scanners have emerged as a valuable tool for passive detection of endotherms. Here we seek to provide objective guidance on thermal tool selection to practitioners who wish to adopt such tools to detect and monitor small endotherms. We compared the efficacy of three handheld thermal scanners (of varying resolutions) and a traditional spotlight for detecting small, cryptic endotherms at night. Random arrays of artificially heated small bird models (representing small, cryptic endotherms) were established along transects in native grasslands that support a range of small threatened endotherms, including the Critically Endangered Plains‐wanderer (Pedionomus torquatus). Transects were independently surveyed by five observers, blind to model locations and model density. Performance measures representing detection capability were assessed for all devices, and usability of each device was assessed with a survey completed by all observers. Detection rates, detection distances, and survey accuracy were greater for thermal scanners with resolutions of 320 × 240 and 640 × 480 than for the spotlight. A low‐resolution thermal scope (160 × 120) performed poorly for all performance measures. There was a consensus among users that a video camera‐style thermal scanner was most comfortable to hold and view while traversing the transect, as opposed to thermal scopes where users look directly through the lens. These results suggest that high‐resolution thermal scanners (≥320 × 240) provide improved detection capabilities compared to traditional spotlights. Higher detection rates provide opportunities for detecting and monitoring small endotherms at night where this was once difficult or impossible.

As researchers, teachers, and practitioners we often encounter young professionals and lay adults who do not understand basics of mammalian body temperature regulation. Often their single solid piece of knowledge is that some vertebrates (mammals and birds) are warm-blooded and some (fish, amphibians, and reptile) are cold-blooded, which is incorrect. There are many thermal capabilities and regulatory strategies. We provide basics of body temperature regulation, including definitions, its evolution, examples of body temperature variability, unique examples of hibernation and torpor, and we explain how a better understanding benefits individuals in personal and professional lives. We suggest a simple replacement of the warm-blooded paradigm that can be used to inform even young students. As a starting point, students young and old are familiar with species of mammals (e.g., platypus and opossums) that do not maintain as constant or as warm of a body temperature as humans and dogs. Students also know that humans do not maintain a constant body temperature over time (they have a "temperature" when sick) or all part of their body (they have cold hands and feet outside in winter). [ABSTRACT FROM AUTHOR]

Insectivorous bats are particularly susceptible to heat loss due to their relatively large surface area to volume ratio. Therefore, to maintain a high normothermic body temperature, bats require large amounts of energy for thermoregulation. This can be energetically challenging for small bats during cold periods as heat loss is augmented and insect prey is reduced. To conserve energy many bats enter a state of torpor characterized by a controlled reduction of metabolism and body temperature in combination with selecting roosts based upon thermal properties. Our study aimed to quantify torpor patterns and roost preferences of free-ranging little forest bats (Vespadelus vulturnus) during winter to identify physiological and behavioral mechanisms used by this species for survival of the cold season. All bats captured were male (body mass 4.9 ± 0.7 g, n = 6) and used torpor on every day monitored, with bouts lasting up to 187.58 h (mean = 35.5 ± 36.7 h, n = 6, total number of samples [N] = 61). Torpor bout duration was significantly correlated with daily minimum and maximum ambient temperature, mean skin temperature, insect mass, and body mass of individuals and the multiday torpor bouts recorded in the cold qualify as hibernation. The lowest skin temperature recorded was 5.2°C, which corresponded to the lowest ambient temperature measurement of –5.8°C. Most bats chose tall, large, live Eucalyptus trees for roosting and to leave their roost for foraging on warmer days. Many individuals often switched roosts (every 3–5 days) and movements increased as spring approached (every 1–2 days). Our data suggest that V. vulturnus are capable of using the environmental temperature to gauge potential foraging opportunities and as a cue to reenter torpor when conditions are unsuitable. Importantly, frequent use of torpor and appropriate roost selection form key roles in the winter survival of these tiny bats. [ABSTRACT FROM AUTHOR]

Physiological performance declines precipitously at high body temperature (Tb), but little attention has been paid to adaptive variation in upper Tb limits among endotherms. We hypothesized that avian maximum tolerable Tb (Tbmax) has evolved in response to climate, with higher Tbmax in species exposed to high environmental heat loads or humidity-related constraints on evaporative heat dissipation. To test this hypothesis, we compared Tbmax and related variables among 53 bird species at multiple sites in South Africa with differing maximum air temperature (Tair) and humidity using a phylogenetically informed comparative framework. Birds in humid, lowland habitats had comparatively high Tbmax (mean ± SD = 45.60 ± 0.58 °C) and low normothermic Tb (Tbnorm), with a significantly greater capacity for hyperthermia (Tbmax 2 Tbnorm gradient = 5.84 ± 0.77 °C) compared with birds occupying cool montane (4.97 ± 0.99 °C) or hot arid (4.11 ± 0.84 °C) climates. Unexpectedly, Tbmax was significantly lower among desert birds (44.65 ± 0.60 °C), a surprising result in light of the functional importance of hyperthermia for water conservation. Our data reveal a macrophysiological pattern and support recent arguments that endotherms have evolved thermal generalization versus specialization analogous to the continuum among ectothermic animals. Specifically, a combination of modest hyperthermia tolerance and efficient evaporative cooling in desert birds is indicative of thermal specialization, whereas greater hyperthermia tolerance and less efficient evaporative cooling among species in humid lowland habitats suggest thermal generalization. [ABSTRACT FROM AUTHOR]

Current camera traps use passive infrared triggers; therefore, they only capture images when animals have a substantially different surface body temperature than the background. Endothermic animals, such as mammals and birds, provide adequate temperature contrast to trigger cameras, while ectothermic animals, such as amphibians, reptiles, and invertebrates, do not. Therefore, a camera trap that is capable of monitoring ectotherms can expand the capacity of ecological research on ectothermic animals. This study presents the design, development, and evaluation of a solar-powered and artificial-intelligence-assisted camera trap system with the ability to monitor both endothermic and ectothermic animals. The system is developed using a central processing unit, integrated graphics processing unit, camera, infrared light, flash drive, printed circuit board, solar panel, battery, microphone, GPS receiver, temperature/humidity sensor, light sensor, and other customized circuitry. It continuously monitors image frames using a motion detection algorithm and commences recording when a moving animal is detected during the day or night. Field trials demonstrate that this system successfully recorded a high number of animals. Lab testing using artificially generated motion demonstrated that the system successfully recorded within video frames at a high accuracy of 0.99, providing an optimized peak power consumption of 5.208 W. No water or dust entered the cases during field trials. A total of 27 cameras saved 85,870 video segments during field trials, of which 423 video segments successfully recorded ectothermic animals (reptiles, amphibians, and arthropods). This newly developed camera trap will benefit wildlife biologists, as it successfully monitors both endothermic and ectothermic animals. [ABSTRACT FROM AUTHOR]

Explaining variation in the fitness of organisms is a fundamental goal in evolutionary ecology. Maintenance energy metabolism is the minimum energy required to sustain biological processes at rest (resting metabolic rate: RMR) and is proposed to drive or constrain fitness of animals; however, this remains debated. Hypotheses have been proposed as to why fitness might increase with RMR (the 'increased intake' or 'performance' hypothesis), decrease with RMR (the 'compensation' or 'allocation' hypothesis), or vary among species and environmental contexts (the 'context dependent' hypothesis). Here, we conduct a systematic review and meta-analysis of the literature, finding 114 studies with 355 relationships between RMR and traits that may be related to fitness. We show that individuals with relatively high RMR generally have high fitness overall, which might be supported by an increased energy intake. However, fitness proxies are not interchangeable: the nature of the RMR–fitness relationship varied substantially depending on the specific trait in question, and we found no consistent relationship between RMR and those traits most closely linked with actual fitness (i.e., lifetime reproductive success). We hypothesise that maintaining high RMR is not costly when resources are unlimited, and we propose ideas for future studies to identify mechanisms underlying RMR–fitness relationships. [ABSTRACT FROM AUTHOR]

Endothermic organisms typically maintain high and relatively constant body temperatures in the face of environmental variation by regulating their metabolic and water loss rates in conjunction with behavioural and postural adjustments. A mechanistic understanding of these processes provides a perspective of the fundamental niches of endotherms by quantifying their energy and water requirements, restrictions on habitat use and survival limits. Here we introduce and document the endotherm model of NicheMapR, an R package that includes a suite of programs for the mechanistic modelling of energy and mass exchange between organisms and their environments. The NicheMapR endotherm model is based on a Fortran program that simultaneously solves for the metabolic rate, water loss rate, fur/feather temperature and skin temperature required to balance the heat budget in a given microclimate. These calculations are a function of traits relating to insulation, shape, physiological and behavioural responses. The program contains algorithms for computing heat transfer through a porous insulative layer (fur/feathers), including solar and infrared radiation fluxes as well as convective and conductive exchange, and can handle differing dorsal and ventral traits and environments. Here we configure the program to be called from R as part of the NicheMapR package and describe the model in detail. We break the program into a set of modules that can be run in isolation, or jointly, and combined in different ways to capture species‐specific thermoregulatory responses. We explain the theory and underlying subroutines, and the default thermoregulatory settings. We discuss how the model can be adapted to incorporate species‐specific behaviours and extended to incorporate multiple body parts. We also compare the endotherm modelling setup with the ectotherm model of the NicheMapR package and discuss how the different modelling strategies they require reflect fundamental biological issues. [ABSTRACT FROM AUTHOR]

As the climate warms, endotherms are challenged with maintaining body temperature within a neutral range. Modifying behaviour to mitigate heat loads is a potentially low-cost response to avoid heat stress and may be critical to persistence in a changing environment, especially for large endotherms. We tested the hypothesis that bed sites are a thermal refuge and means of behavioural mitigation of heat loads for a large temperate ungulate especially prone to heat stress, the Shiras moose, Alces alces shirasi. We predicted that if bed sites are a thermal refuge, selection of bed sites should be consistent with sites that reduce heat gain or increase heat loss via convection or conduction. Moose selected cool bed sites with a substrate that was moist, wet or had standing water, and avoided bedding in open or sparse vegetation. On warm days and during the warmest periods of the day, moose increased selection for wet substrate and for bed sites in standing water with sparse vegetation, which they avoided on cool days and during cool periods of the day. Strong and context-dependent selection for bed sites that would reduce heat gain and ameliorate heat load supports the notion that bed sites are a thermal refuge and a way to behaviourally mitigate warming temperatures. Flexibility in habitat selection may be a primary way for large endotherms to combat a warming climate, although doing so is contingent on habitat assemblages that offer thermal refuge to limit heat gain and importantly, facilitate heat loss. • Moose select bed sites with wet ground or standing water to mitigate heat loads. • Canopy cover was not an influential factor in bed site selection. • Heat loss is more important for behavioural thermoregulation than limiting heat gain. • Flexibility in bed site selection may be a way for endotherms to combat warming. • Selection of wet ground increased on warm days and during the warmest diel periods. [ABSTRACT FROM AUTHOR]

Current camera traps use passive infrared triggers; therefore, they only capture images when animals have a substantially different surface body temperature than the background. Endothermic animals, such as mammals and birds, provide adequate temperature contrast to trigger cameras, while ectothermic animals, such as amphibians, reptiles, and invertebrates, do not. Therefore, a camera trap that is capable of monitoring ectotherms can expand the capacity of ecological research on ectothermic animals. This study presents the design, development, and evaluation of a solar-powered and artificial-intelligence-assisted camera trap system with the ability to monitor both endothermic and ectothermic animals. The system is developed using a central processing unit, integrated graphics processing unit, camera, infrared light, flash drive, printed circuit board, solar panel, battery, microphone, GPS receiver, temperature/humidity sensor, light sensor, and other customized circuitry. It continuously monitors image frames using a motion detection algorithm and commences recording when a moving animal is detected during the day or night. Field trials demonstrate that this system successfully recorded a high number of animals. Lab testing using artificially generated motion demonstrated that the system successfully recorded within video frames at a high accuracy of 0.99, providing an optimized peak power consumption of 5.208 W. No water or dust entered the cases during field trials. A total of 27 cameras saved 85,870 video segments during field trials, of which 423 video segments successfully recorded ectothermic animals (reptiles, amphibians, and arthropods). This newly developed camera trap will benefit wildlife biologists, as it successfully monitors both endothermic and ectothermic animals.

Before they develop competent endothermy, mammals and birds are sensitive to fluctuating temperature. It follows that early life thermal environment can trigger changes to the ontogeny of thermoregulatory control. At the ecological level, we have incomplete knowledge of how such responses affect temperature tolerance later in life. In some cases, changes to pre- and postnatal temperature prime an organism’s capacity to meet a corresponding thermal environment in adulthood. However, in other cases, developmental temperature seems to constrain temperature tolerance later in life. The timing, duration, and severity of a thermal challenge will determine whether its impact is ameliorating or constraining. However, the effects influencing the transition between these states remain poorly understood, particularly in mammals and during the postnatal period. As climate change is predicted to bring more frequent spells of extreme temperature, it is relevant to ask under which circumstances developmental thermal conditions predispose or constrain animals’ capacity to deal with temperature variation. Increasingly stochastic weather also implies increasingly decoupled early- and late-life thermal environments. Hence, there is a pressing need to understand better how developmental temperature impacts thermoregulatory responses to matched and mismatched thermal challenges in subsequent life stages. Here, we summarize studies on how the thermal environment before, and shortly after, birth affects the ontogeny of thermoregulation in birds and mammals, and outline how this might carry over to temperature tolerance in adulthood. We also identify key points that need addressing to understand how effects of temperature variation during development may facilitate or constrain thermal adaptation over a lifetime.

Climate change is likely to affect many mammalian phenotypes, yet little is known whether and how phenotypic plasticity is involved in responding to thermal challenges during mammalian development. We investigated the effect of continuous cold or warm exposure during development on morphological, behavioral, and functional variables of yellow-footed antechinus (Antechinus flavipes), a semelparous Australian marsupial mammal. Captive-bred young were exposed to two ambient temperatures (Ta), cold (17°C) or warm (25°C), once weaned. Treatments were reversed and metabolic rate (MR) measurements repeated after 2 months. We measured body mass weekly, activity continuously, and MRs over a range of Ta once they were adults. Growth rate was similar in both groups, but was faster in males. Antechinus in the warm group were initially more active than the cold group and decreased activity when exposed to cold, whereas the cold group increased activity when exposed to warm. Interestingly, females changed their night-time activity when Ta was changed, whereas males changed their daytime activity. MRs were originally lower in the warm group in comparison to the cold group for both sexes and increased slightly for females, but not for males, after being exposed to cold. After exposure to warm Ta, the MRs of the cold group decreased significantly over the entire Ta-range for both sexes. Our results reveal that temperatures experienced during development can influence behavioral and physiological traits in antechinus. Such phenotypic plasticity is vital for a species that within 1 year is dependent on a single breeding event and experiences a complete population turnover.

The heart has a high‐metabolic rate, and its "around‐the‐clock" vital role to sustain life sets it apart in a regenerative setting from other organs and appendages. The landscape of vertebrate species known to perform intrinsic heart regeneration is strongly biased toward ectotherms—for example, fish, salamanders, and embryonic/neonatal ectothermic mammals. It is hypothesized that intrinsic heart regeneration is exclusively limited to the low‐metabolic hearts of ectotherms. The biomedical field of regenerative medicine seeks to devise biologically inspired regenerative therapies to diseased human hearts. Falsification of the ectothermy dependency for heart regeneration hypothesis may be a crucial prerequisite to meaningfully seek inspiration in established ectothermic regenerative animal models. Otherwise, engineering approaches to construct artificial heart components may constitute a more viable path toward regenerative therapies. A more strict definition of regenerative phenomena is generated and several testable sub‐hypotheses and experimental avenues are put forward to elucidate the link between heart regeneration and metabolism. Also see the video abstract here https://youtu.be/fZcanaOT5z8. [ABSTRACT FROM AUTHOR]

Activity times structure the thermal environments experienced by organisms. In mammals, species shift from being nocturnal to diurnal and vice versa, but the thermal consequences of variable activity patterns remain largely unexplored. Here we used theoretical thermoregulatory polygons bounded by estimates of basal metabolic rates (BMR), maximum metabolic rates (MMR), and thermal conductance (C) in small mammals to explore the metabolic consequences of exposure to global-scale daytime and nighttime temperatures. Model predictions indicated higher metabolic scope for activity for nocturnal species at low latitudes and that reduced minimum C and larger body size increased the geographic range in which nocturnality was advantageous. Consistent with predictions, within rodents nocturnal species have low C. However, nocturnal mammals tend to be smaller than diurnal species, likely reflecting the importance of additional factors driving body size. Projections of warming impacts on small mammals suggest that diurnal species could lose habitable space globally. Conversely, warming could lift cool temperature constraints on nocturnal species and increase habitable space, suggesting that a shift toward nocturnal niches might be favored in a warming world. Taken together, these findings demonstrate the importance of energetic considerations for endotherms in managing global change impacts on nocturnal and diurnal species. [ABSTRACT FROM AUTHOR]

Before they develop competent endothermy, mammals and birds are sensitive to fluctuating temperature. It follows that early life thermal environment can trigger changes to the ontogeny of thermoregulatory control. At the ecological level, we have incomplete knowledge of how such responses affect temperature tolerance later in life. In some cases, changes to pre- and postnatal temperature prime an organism's capacity to meet a corresponding thermal environment in adulthood. However, in other cases, developmental temperature seems to constrain temperature tolerance later in life. The timing, duration, and severity of a thermal challenge will determine whether its impact is ameliorating or constraining. However, the effects influencing the transition between these states remain poorly understood, particularly in mammals and during the postnatal period. As climate change is predicted to bring more frequent spells of extreme temperature, it is relevant to ask under which circumstances developmental thermal conditions predispose or constrain animals' capacity to deal with temperature variation. Increasingly stochastic weather also implies increasingly decoupled early- and late-life thermal environments. Hence, there is a pressing need to understand better how developmental temperature impacts thermoregulatory responses to matched and mismatched thermal challenges in subsequent life stages. Here, we summarize studies on how the thermal environment before, and shortly after, birth affects the ontogeny of thermoregulation in birds and mammals, and outline how this might carry over to temperature tolerance in adulthood. We also identify key points that need addressing to understand how effects of temperature variation during development may facilitate or constrain thermal adaptation over a lifetime. [ABSTRACT FROM AUTHOR]

Climate change is likely to affect many mammalian phenotypes, yet little is known whether and how phenotypic plasticity is involved in responding to thermal challenges during mammalian development. We investigated the effect of continuous cold or warm exposure during development on morphological, behavioral, and functional variables of yellow-footed antechinus (Antechinus flavipes), a semelparous Australian marsupial mammal. Captive-bred young were exposed to two ambient temperatures (T a ), cold (17°C) or warm (25°C), once weaned. Treatments were reversed and metabolic rate (MR) measurements repeated after 2 months. We measured body mass weekly, activity continuously, and MRs over a range of T a once they were adults. Growth rate was similar in both groups, but was faster in males. Antechinus in the warm group were initially more active than the cold group and decreased activity when exposed to cold, whereas the cold group increased activity when exposed to warm. Interestingly, females changed their night-time activity when T a was changed, whereas males changed their daytime activity. MRs were originally lower in the warm group in comparison to the cold group for both sexes and increased slightly for females, but not for males, after being exposed to cold. After exposure to warm T a , the MRs of the cold group decreased significantly over the entire T a -range for both sexes. Our results reveal that temperatures experienced during development can influence behavioral and physiological traits in antechinus. Such phenotypic plasticity is vital for a species that within 1 year is dependent on a single breeding event and experiences a complete population turnover. [ABSTRACT FROM AUTHOR]

Mammals and birds provide food for their young after birth, but such provisioning is almost absent in other vertebrates. A recent theory suggested that, in addition to thermoregulation, the large discrepancy in size between adult and young ectothermic vertebrates precludes them from providing for their young, whereas the relatively large offspring of endotherms are easier to provision. I show here that reptile neonates and hatchlings are as large as those of mammals and birds. Differences in size between adults and young thus cannot explain the lack of parental provisioning in reptiles. I suggest that the large size at birth is the ancestral condition in amniotes as a whole and that provisioning has thus evolved after endothermy. [ABSTRACT FROM AUTHOR]

Das Verständnis der Terminologie einer Naturwissenschaft ist essentiell für eine erfolgreiche Teilnahme am Unterricht. Fachspezifische Begriffe sollen dabei nicht additiv, sondern am konkreten Fall gelernt werden. Der vorliegende Beitrag gibt zunächst eine problemorientierte Übersicht über Aufgaben und Lösungsvorschläge zu dem Phänomen der Thermoregulation bei Lebewesen und zeigt, wie uneinheitlich die dabei verwendeten Fachbegriffe homoiotherm/poikilotherm bzw. endo- und ektotherm in verschiedenen Lehrbüchern und Lehrmaterial präsentiert werden. Daran anschließend wird kurz diskutiert, unter welchen Bedingungen diese Begriffe im Unterricht eingeführt werden sollten und wobei es darauf zu achten gilt.

Several methods are routinely used to measure avian body temperature, but different methods vary in invasiveness. This may cause stress-induced increases in temperature and/or metabolic rate and, hence, overestimation of both parameters. Choosing an adequate temperature measurement method is therefore key to accurately characterizing an animal's thermal and metabolic phenotype. Using great tits (Parus major) and four common methods with different levels of invasiveness (intraperitoneal, cloacal, subcutaneous, cutaneous), we evaluated the preciseness of body temperature measurements and effects on resting metabolic rate (RMR) over a 40°C range of ambient temperatures. None of the methods caused overestimation or underestimation of RMR compared with un-instrumented birds, and body or skin temperature estimates did not differ between methods in thermoneutrality. However, skin temperature was lower compared with all other methods below thermoneutrality. These results provide empirical guidance for future research that aims to measure body temperature and metabolic rate in small bird models., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

The boundaries of glass-forming regions in the Sm2S3–Ga2S3–EuS system have been located using simultaneous thermal analysis, X-ray diffraction, and X-ray microanalysis. We have studied IR spectra of glass with the composition (Ga2S3)0.80(Sm2S3)0.10(EuS)0.10 and its stability in an inert atmosphere. The glass has been shown to soften at 985 K (Tg), which is accompanied by an endothermic peak. It crystallizes at 1112 K (Tx). Exothermic peaks observed in the range 1203–1222 K suggest that this glass has a tendency to decompose in several steps. In the IR spectra of the glasses, the bands due to the M–S (M = Sm, Ga, Eu) bonds have higher intensity and are shifted to higher frequencies relative to those in the spectra of their crystalline constituent components, which is probably due to the increase in M–S bond covalence. [ABSTRACT FROM AUTHOR]

Observations of animal thermoregulatory behavior are labor‐intensive, and human presence may disturb the normal behavior of the animal. Therefore, we investigated whether a remote biologging technique could be used to detect orientation to solar radiation in savanna antelope. We predicted that when a mammal was orientated perpendicular to solar radiation, the subcutaneous temperature on the side of the body facing the sun would be greater than that on the opposite side, whereas when the mammal was orientated parallel to solar radiation, subcutaneous temperatures on both sides would be similar. A pilot study showed that the difference between left‐ and right‐side temperatures under a pelt reflected orientation to solar radiation if a pelt‐covered cylinder had been orientated for 15 min or longer. In addition, the rate of change in temperature difference could detect orientation that had changed within the previous 5 min. We implanted temperature‐sensitive data loggers subcutaneously into the flanks of eight black (Connochaetes gnu) and eight blue (Connochaetes taurinus) wildebeest. By incorporating both the rate of change and subcutaneous temperature differences and excluding times when wildebeest were lying down, our predictions correctly matched behavioral observations of wildebeest orientation to solar radiation 71% of the time. Our technique tended to fail when wildebeest were lying down, wind speeds were high and the sun was overhead. But those are conditions in which the benefits of manipulating orientation to solar radiation is of diminishing importance to a free‐living mammal. Therefore, subcutaneous temperatures provide physiologically relevant information on the importance of solar radiation to mammals. HIGHLIGHTS: Subcutaneous temperature measured remotely by biologgers could be used to identify orientation to solar radiation of free‐living wildebeest correctly 71% of the time and to quantify heat gain during orientation behaviors. [ABSTRACT FROM AUTHOR]

Mechanistic approaches for predicting the ranges of endotherms are needed to forecast their responses to environmental change. We test whether physiological constraints on maximum metabolic rate and the factor by which endotherms can elevate their metabolism (metabolic expansibility) influence cold range limits for mammal and bird species. We examine metabolic expansibility at the cold range boundary (MECRB) and whether species' traits can predict variability in MECRB and then use MECRB as an initial approach to project range shifts for 210 mammal and 61 bird species. We find evidence for metabolic constraints: the distributions of metabolic expansibility at the cold range boundary peak at similar values for birds (2.7) and mammals (3.2). The right skewed distributions suggest some species have adapted to elevate or evade metabolic constraints. Mammals exhibit greater skew than birds, consistent with their diverse thermoregulatory adaptations and behaviors. Mammal and bird species that are small and occupy low trophic levels exhibit high levels of MECRB. Mammals with high MECRB tend to hibernate or use torpor. Predicted metabolic rates at the cold range boundaries represent large energetic expenditures (>50% of maximum metabolic rates). We project species to shift their cold range boundaries poleward by an average of 3.9° latitude by 2070 if metabolic constraints remain constant. Our analysis suggests that metabolic constraints provide a viable mechanism for initial projections of the cold range boundaries for endotherms. However, errors and approximations in estimating metabolic constraints (e.g., acclimation responses) and evasion of these constraints (e.g., torpor/hibernation, microclimate selection) highlight the need for more detailed, taxa‐specific mechanistic models. Even coarse considerations of metabolism will likely lead to improved predictions over exclusively considering thermal tolerance for endotherms. We find evidence for metabolic constraints at cold range boundaries: the distributions of metabolic expansibility peaks at similar values for birds and mammals. Right skewed distributions suggest some species have adapted to elevate or evade metabolic constraints. Species' traits help explain which species are able to evade metabolic constraints [ABSTRACT FROM AUTHOR]

From its earliest days of domestication, the domestic chicken ( Gallus gallus domesticus ) has been selectively bred for specific traits. Decades of genetic selection have resulted in significant dissimilarities in metabolism and growth between breeds, in particular fast-growing broilers and highly productive layers. A chicken develops the capacity to elevate metabolism in response to decreases in ambient temperature upon hatching, including well-developed methods of regulating thermogenesis. However, a differential timing between incipient endothermic capacities of broiler and layer strains exists. Although both broiler and layer chicks show the hallmark rapid attainment of endothermic capacity of precocial birds, endothermic capacity of broilers matures faster than that of layers. Here we characterized changes in morphology and mitochondria physiology during the developmental transition as the animals become endothermic. Changes in body mass occurred at a faster rate in broilers, with hatching embryos showing significant increases over embryonic body mass, while layers did not exhibit significant differences in mass until after hatch. Heart and liver both exhibited rapid growth upon hatching that occurred with little change in body mass in both breeds. Skeletal and cardiac mitochondrial respiration capacity in broilers increased from the embryonic stage through hatching. Oxidative phosphorylation was more tightly coupled to ATP production in broilers than layer muscles during external pipping. By selecting for faster growth and higher meat yield, the physiological transition from ectothermy to endothermy was also affected: differences in whole-animal, tissue, and organelle responses are evident in these two divergent breeds of chicken. [ABSTRACT FROM AUTHOR]

Many hibernating animals thermoregulate during torpor and defend their body temperature (Tb) near 0°C by an increase in metabolic rate. Above a critical temperature (Tcrit), animals usually thermoconform. We investigated the physiological responses above and below Tcrit for a small tree-dwelling bat (Chalinolobus gouldii, ~14 g) that is often exposed to sub-zero temperatures during winter. Through simultaneous measurement of heart rate (fH) and oxygen consumption (...O2), we show that the relationship between oxygen transport and cardiac function is substantially altered in thermoregulating torpid bats between 1 and -2°C, compared with thermoconforming torpid bats at mild ambient temperatures (Ta 5-20° C). Tcrit for this species was at a Ta of 0.7±0.4°C, with a corresponding Tb of 1.8±1.2°C. Below Tcrit, animals began to thermoregulate, as indicated by a considerable but disproportionate increase in both fH and ...O2. The maximum increase in fH was only 4-fold greater than the average thermoconforming minimum, compared with a 46-fold increase in ...O2. The differential response of fH and ...O2 to low Ta was reflected in a 15-fold increase in oxygen delivery per heart beat (cardiac oxygen pulse). During torpor at low Ta, thermoregulating bats maintained a relatively slow fH and compensated for increased metabolic demands by significantly increasing stroke volume and tissue oxygen extraction. Our study provides new information on the relationship between metabolism and fH in an unstudied physiological state that may occur frequently in the wild and can be extremely costly for heterothermic animals. [ABSTRACT FROM AUTHOR]

Animals store metabolic energy as electrochemical gradients. At least 50% of mammalian energy is expended to maintain electrochemical gradients across the inner mitochondrial membrane (H+), the sarcoplasmic reticulum (Ca++), and the plasma membrane (Na+/K+). The potential energy of these gradients can be used to perform work (e.g., transport molecules, stimulate contraction, and release hormones) or can be released as heat. Because ectothermic species adapt their body temperature to the environment, they are not constrained by energetic demands that are required to maintain a constant body temperature. In fact, ectothermic species expend seven to eight times less energy than similarly sized homeotherms. Accordingly, ectotherms adopt low metabolic rates to survive cold, hypoxia, and extreme bouts of fasting that would result in energy wasting, lactic acidosis and apoptosis, or starvation in homeotherms, respectively. Ectotherms have also evolved unique applications of ion gradients to allow for localized endothermy. Endothermic avian species, which lack brown adipose tissue, have been integral in assessing the role of H+ and Ca++ cycling in skeletal muscle thermogenesis. Accordingly, the diversity of non-mammalian vertebrate species allows them to serve as unique models to better understand the role of ion gradients in heat production, metabolic flux, and adaptation to stressors, including obesity, starvation, cold, and hypoxia.

Birds have many physiological characteristics that are convergent with mammals. In the light of recent evidence that mammals can maintain a constant insensible evaporative water loss (EWL) over a range of perturbing environmental conditions, we hypothesized that birds might also regulate insensible EWL, reflecting this convergence. We found that budgerigars (Melopsittacus undulatus) maintain EWL constant over a range of relative humidities at three ambient temperatures. EWL, expressed as a function of water vapour pressure deficit, differed from a physical model where the water vapour pressure deficit between the animal and the ambient air is the driver of evaporation, indicating physiological control of EWL. Regulating EWL avoids thermoregulatory impacts of varied evaporative heat loss; changes in relative humidity had no effect on body temperature, metabolic rate or thermal conductance. Our findings that a small bird can regulate EWL are evidence that this is a common feature of convergently endothermic birds and mammals, and may therefore be a fundamental characteristic of endothermy. [ABSTRACT FROM AUTHOR]

Animals store metabolic energy as electrochemical gradients. At least 50% of mammalian energy is expended to maintain electrochemical gradients across the inner mitochondrial membrane (H+), the sarcoplasmic reticulum (Ca++) and the plasma membrane (Na+/K+). The potential energy of these gradients can be used to perform work (e.g., transport molecules, stimulate contraction and release hormones) or can be released as heat. Because ectothermic species adapt their body temperature to the environment, they are not constrained by energetic demands that are required to maintain a constant body temperature. In fact, ectothermic species expend seven to eight times less energy than similarly sized homeotherms. Accordingly, ectotherms adopt low metabolic rates to survive cold, hypoxia and extreme bouts of fasting that would result in energy wasting, lactic acidosis and apoptosis, or starvation in homeotherms, respectively. Ectotherms have also evolved unique applications of ion gradients to allow for localized endothermy. Endothermic avian species, which lack brown adipose tissue, have been integral in assessing the role of H+ and Ca++ cycling in skeletal muscle thermogenesis. Accordingly, the diversity of non-mammalian vertebrate species allows them to serve as unique models to better understand the role of ion gradients in heat production, metabolic flux and adaptation to stressors, including obesity, starvation, cold and hypoxia. [ABSTRACT FROM AUTHOR]