What does infrared thermography tell us about the evolutionary potential of heat tolerance in endotherms?

Non-invasive methods for measuring thermal tolerance and thermoregulation in large numbers of individuals under natural environmental conditions are useful to understand the capacity of species to adapt to future climate scenarios. Infrared thermography (IRT) is one such tool in research on thermal adaptation, but concerns have been raised about its reliability, specifically the correlation between surface temperature (Ts) and body temperature (Tb) (Monge et al., (2025). What does IRT tell us about the evolutionary potential of heat tolerance in endotherms? Evolution Letters, 9(2),184–188). Here, we discuss the biological inferences that can be made from data on Ts and Tb, and whether Ts needs to be correlated with Tb to be informative in studies of thermoregulation in free-living organisms. We also present a framework illustrating biological insights that can be gained by integrating IRT with data on different phenotypic traits, fitness metrics, pedigree information and other physiological traits, including Tb. We illustrate the utility of this new framework by demonstrating how it has increased our understanding of the evolution of thermal tolerance in a large animal where Tb is not easily measured, the ostrich (Struthio camelus) (Svensson et al., (2024). Heritable variation in thermal profiles is associated with reproductive success in the world’s largest bird. Evolution Letters, 8(2), 200–211). Integrating IRT with individual fitness data and pedigree information in field studies can aid our biological interpretation of Ts in future research on the ecology and evolution of thermal tolerance in both endotherms and ectotherms.

The (wind) chill factor controlled

Simple SummaryStressful events can trigger body temperature variations in mammals. The most commonly used methods for measuring temperature in laboratory mice are stressful and invasive in nature, and can themselves cause stress-induced hyperthermia (SIH). This raises concerns regarding both animal welfare and research output. Infrared thermography (IRT) offers a non-invasive alternative, if proven to accurately identify SIH. We exposed mice to mild handling-induced stress, by either tail-picking or the reportedly less-impactful tunnel-handling technique. Temperature was measured by reading microchip devices (PIT-tags) implanted subcutaneously (Tsc), and by a thermal camera to measure mean body surface temperature (Tbody) and mean tail surface temperature (Ttail). As expected, during acute stress exposure, both Tsc and Tbody increased, while Ttail decreased. No differences in stress-induced hyperthermia were found between the two handling techniques. This suggests that such differences may not be detectable in the context of co-occurring stressful events, such as opening of the cage lid, exposure to light, or presence of the handler. Within the same cage, animals handled last consistently showed higher body temperatures than those handled first, raising the issue of minding the order by which animals are tested. Our results suggest IRT offers a reliable non-invasive method for assessing SIH in laboratory rodents.Stress-induced hyperthermia (SIH) is a physiological response to acute stressors in mammals, shown as an increase in core body temperature, with redirection of blood flow from the periphery to vital organs. Typical temperature assessment methods for rodents are invasive and can themselves elicit SIH, affecting the readout. Infrared thermography (IRT) is a promising non-invasive alternative, if shown to accurately identify and quantify SIH. We used in-house developed software ThermoLabAnimal 2.0 to automatically detect and segment different body regions, to assess mean body (Tbody) and mean tail (Ttail) surface temperatures by IRT, along with temperature (Tsc) assessed by reading of subcutaneously implanted PIT-tags, during handling-induced stress of pair-housed C57BL/6J and BALB/cByJ mice of both sexes (N = 68). SIH was assessed during 10 days of daily handling (DH) performed twice per day, weekly voluntary interaction tests (VIT) and an elevated plus maze (EPM) at the end. To assess the discrimination value of IRT, we compared SIH between tail-picked and tunnel-handled animals, and between mice receiving an anxiolytic drug or vehicle prior to the EPM. During a 30 to 60 second stress exposure, Tsc and Tbody increased significantly (p < 0.001), while Ttail (p < 0.01) decreased. We did not find handling-related differences. Within each cage, mice tested last consistently showed significantly higher (p < 0.001) Tsc and Tbody and lower (p < 0.001) Ttail than mice tested first, possibly due to higher anticipatory stress in the latter. Diazepam-treated mice showed lower Tbody and Tsc, consistent with reduced anxiety. In conclusion, our results suggest that IRT can identify and quantify stress in mice, either as a stand-alone parameter or complementary to other methods.

It is unusual to re-visit a paper a half-century after first reading it, as I have done with the classic publication of Per Scholander, Raymond Hock, Vladimir Walters and Lawrence Irving published in The Biological Bulletin in 1950 (Scholander et al., 1950). My first reading of this paper, and others by Scholander and colleagues on temperature adaptation in aquatic and terrestrial ectotherms (Scholander et al., 1953; Scholander et al., 1957), occurred around 1962, early in my doctoral studies when I trekked to Antarctica to study cold adaptation in fish. These papers provided much of the conceptual and empirical foundation for the work I anticipated doing with notothenioid fishes. My interests in polar birds and mammals at that time were largely confined to their roles as photographic subjects. However, my reading of the 1950 Biological Bulletin paper turned out to be highly important in broadening my scientific horizons and helping me to formulate a perspective on evolutionary adaptation to temperature that spanned the full range of biological (body) temperatures and the adaptive patterns observed among all taxa, whether endothermic or ectothermic. A fresh reading of this paper by scientists of my generation and, even more, a first reading by scientists whose parents may not have been born when the paper first appeared, still has much to offer in teaching us about thermal biology and how scientific research in comparative and evolutionary physiology has evolved.The studies of thermal biology by Scholander and colleagues that were initiated shortly after the end of World War II and conducted with major logistical support from the US military helped in important ways to define the evolutionary strategies used by endothermic homeotherms – mammals and birds – to cope with differences in ambient temperature. Importantly, the focus of these initial studies was on evolutionary adaptation, not phenotypic acclimation or acclimatization to cold, phenomena that later took center stage in analysis of thermal biology in endotherms. The 1950 paper was one in a series from this group that elucidated the roles of what they termed three possible ‘avenues for cold adaptation’ in mammals and birds: variations in the body-to-air thermal gradient, insulation level and basal metabolic rate. In other words, how were heat production and heat exchange altered to allow mammals and birds to maintain a stable and high body temperature? The previous papers by these authors, plus earlier literature cited in the 1950 paper, led to the tentative conclusion that adaptive changes in body temperature to reduce the body-to-air thermal gradient and, thereby, reduce heat flux between animal and environment, are unlikely to play a role in cold adaptation in active adult mammals and birds. To quote the 1950 paper, ‘…there are no signs so far that body temperature of mammals and birds is adaptive to the different climates on earth.’ This well-buttressed conclusion leads to another – and yet unanswered – set of questions: What is the basis for selection of temperatures near 37–40°C for avian and mammalian core body temperatures? Is there something special about this particular range of temperatures? If so, what is it?The remaining two ‘avenues for cold adaptation’ had also been partially explored in earlier studies by Scholander and colleagues. It was clear from their work and that of others that insulation played a critical role. As stated in the 1950 paper, ‘…we established, by insulation measurements, the general rule that arctic mammals have warmer furs than do tropical mammals.’ However, this adaptive mechanism, while of importance, could not at that time be regarded as offering the full story. The final ‘avenue for cold adaptation’, the role of evolved temperature-adaptive differences in basal metabolic rate, remained a possible mechanism of cold adaptation, with animals from cold polar environments possibly exhibiting higher metabolic rates per unit mass than animals from warmer temperate locations. Most existing basal metabolic rate data were from studies on temperate species; there was not an adequate diversity of environments represented in these data sets to fully evaluate whether basal metabolic rates reflected evolutionary thermal history. To resolve this issue, it was necessary to conduct additional studies of mammals and birds from thermal environments that were as different as possible in terms of maximal temperature. Thus the dual focus – Arctic versus tropical – of the studies presented in the 1950 paper. The metabolic rate measurements made with endemic species from Point Barrow, Alaska, and Barro Colorado Island in the Central American tropics essentially put the final nail in the coffin of this potential mechanism of adaptation to cold. The metabolic rate measurements presented in the 1950 paper were made with animals spanning a wide range of sizes and rate measurements were made as closely as possible under ‘resting’ or ‘basal’ conditions and in the absence of acute cold stress. Appropriately, the data gathered by Scholander et al. were analyzed in the context of Francis Benedict's famous ‘mouse to elephant’ relationship of metabolic scaling (Benedict, 1938). The results of these experiments seemed unambiguous: ‘…we may state as a tentative generalization that the basal metabolic rate of terrestrial mammals from tropics to arctic is fundamentally determined by a size relation according to the formula Cal./day = 70 kg3/4 and is phylogenetically nonadaptive to external temperature conditions. Equally nonadaptive is the body temperature, and the phylogenetic adaptation to cold therefore rests entirely upon the plasticity of the factors which determine the heat loss, mainly the fur insulation.’ Thus, natural selection seemed not to have packed more metabolic capacity into a gram of an arctic mammal than into a gram of a similar-sized tropical mammal. At least this seemed to be the case when analyses involved normothermic adult animals, such as those used by Scholander et al. However, as the caveat in the above quotation (‘tentative generalization’) seems to hint, later work showed that there was more to the story.As is the case of many foundational papers, observations and comments made in the 1950 paper seem prescient when examined in the context of what has subsequently been discovered. One such comment is the brief mention that a small mammal, the arctic weasel, showed an extraordinarily high rate of heat production when exposed to cold; this species' metabolic rate was well above the regression line of the ‘mouse to elephant’ curve. Scholander et al. remarked that it seemed ‘somewhat odd’ that the weasel didn't simply increase its insulation when exposed to cold. This ‘oddity’ and similar observations on other small, cold-stressed mammals helped to pave the way for the discovery of the thermogenic role of brown adipose tissue (BAT) (Cannon and Nedergaard, 2004; Smith, 1961). The discovery of this specialized heat-generating tissue casts metabolic adaptation to cold by mammals (no avian equivalent of BAT is known) in a new light. The importance of heat generation by BAT is arguably the most significant extension of our understanding of thermal biology in mammals made since the 1950 paper was published. I'd like to think that the ‘oddity’ noted by Scholander and colleagues puzzled readers enough to catalyze a deeper look at non-basal metabolic capacities, namely those of BAT, the one type of thermogenic tissue known in mammals.A second easily missed point in the 1950 paper is one that is not explicitly indicated by the paper's title. In addition to addressing the adaptations required to withstand cold, Scholander et al. pay heed to the challenges faced by tropical mammals and birds. Thus they state, ‘It seems then that the problem for tropical mammals is neither overheating nor cooling, but, actually, both.’ Moreover, the authors emphasize (presciently, as things are turning out) that, ‘Many parts of the tropics are so hot and humid that a few degrees’ rise in the temperature would mean death for mammals and birds because they cannot adapt to it by raising their body temperatures.' My re-examination of this paper over 50 years since first reading it was done in concert with the appearance in 2010 of articles by Sherwood and Huber and McMichael and Dear that dealt with this threat to low latitude mammals and birds, a danger that would have seemed completely ‘academic’ back in 1950 when concerns about global warming – an expression that seems to have been introduced to the scientific literature only in 1975 in a classic paper by Wallace Broecker in Science (Broecker, 1975) – were still well off in the future (Sherwood and Huber, 2010; McMichael and Dear, 2010). In their analysis of the capacities of birds and mammals to cope with the combination of rising temperatures and humidity, these authors build on (but, regrettably, do not cite) the types of studies found in the 1950 classic by Scholander et al. The 2010 papers point out that, as the need for effective evaporative cooling becomes more critical in a warming world, capacities to evaporate water from the body surfaces becomes increasingly challenging. The basic physics of the situation shows that, when wet bulb temperatures (TW) exceed 35°C, evaporative dissipation of metabolic heat by mammals and birds ceases to be possible. How close are we to this situation of ‘melt down’, the exclusion of habitats from occupancy by endothermic homeotherms due to TW values >35°C? Currently, TW never exceeds 31°C, even in the hottest climates (Sherwood and Huber, 2010). However, TW is predicted to rise with global mean temperature at a ratio of 3°C for every 4°C of global warming. The models used to predict rates of global warming offer a range of estimates and are typically limited for extrapolating trends beyond the current century. However, as Sherwood and Huber emphasize, using models based on realistic assumptions about release of greenhouse gases and extending these models beyond 2100, within two or three centuries the temperatures of some regions may increase by ~7°C and, therefore, have combinations of heat and humidity that result in TW near 35°C. Because such a large fraction of the human population resides at low latitudes, Sherwood and Huber conjecture that global warming of 11–12°C would lead to intolerable values of TW in the regions where most of the human population is currently found (Sherwood and Huber, 2010). Moreover, these low latitude regions are zones where the greatest biodiversity is commonly found. The early studies of Scholander and colleagues help to put into sharp relief the challenges faced by endothermic homeotherms in confronting rising temperatures and humidity. Birds and mammals are ‘stuck’, evolutionarily, with high mass-specific metabolic (heat generation) rates. It seems inconceivable that they can evolve a physiological solution that would allow them to cope with the threats posed by TW values greater than 35°C.In summary, reading (or re-reading) this classic paper offers a number of rewards. First, in terms of its primary question about fundamental evolutionary strategies for cold adaptation, we can come to appreciate how the principal ‘avenue’ taken by birds and mammals for maintaining high and stable body temperatures regardless of ambient temperature was elucidated. Second, we find a nice example of how an experimental ‘oddity’ can lead to further work that, in this case, helped open up the broad field of BAT physiology. Third, and certainly without the intention of the authors, the paper has provided a valuable context for evaluating the challenges posed to endothermic homeotherms by global climate change. And, lastly, there are rewards from (re)visiting this work that deal less with specific scientific discoveries than with the ways in which doing science have evolved. These lessons seem especially valuable for younger scientists for whom the practice of reading literature that is more than a year or two old may not exist. In our (usually futile) obsession to stay on top of the current literature, the classics of the past – the formative publications that built the foundation for our field – are too often neglected or just downright forgotten entirely. As Sydney Brenner recently commented, ‘…most scientists are too busy working in the present and thinking anxiously about the future and have no time to view their work in the context of what has gone before’ (Brenner, 2012). Disregarding the past is a shame, for several reasons. One is that, by neglecting the foundational literature of one's field, one is apt to lack an appreciation of how the shaping principles (‘paradigms’) of one's discipline have originated and subsequently evolved. Another benefit of examining the older literature is to get a sense of how different it was to do science at a time when major questions were first being addressed experimentally. For comparative physiology, the first two or three decades after World War II were an era of both intellectual and geographical explorations of exciting new territory. These were halcyon days when opening up entirely new lines of study could be done with simple instruments, minimal needs for costly reagents, and, therefore, relatively tiny budgets (with the exception of travel costs for exploring distant and exotic lands). And, as the working and writing styles of early, intrepid explorers of comparative physiology such as Per Scholander and his collaborators, Knut Schmidt-Nielsen, and others suggest, doing research was probably a lot more fun and adventurous back then. Writing could be a bit more colorful too, compared with the prose found in the space-limited pages of contemporary journals. Can you think of a recent paper in which there occurs something equivalent to a statement that the sample size was low because the sled dogs ate one-third of the fish that were caught (Scholander et al., 1957)? In these incredibly busy times, it is worthwhile to pause, read some of the classics and contemplate what life was like back in the days when the ratio of novelty of discovery to grant dollars expended was arguably relatively high compared with the present. Classic papers such as those published by Scholander and colleagues over a half-century ago give their readers a clear sense of not only how the foundational discoveries of our field were made, but also of the adventure that was associated with these early intellectual and geographical explorations. Having been his faculty colleague for two decades, I think I can safely say that when Per Scholander chose the title for his autobiography, Enjoying a Life in Science (Scholander, 1990), he was at once giving an honest summary of a great career and challenging his readers to follow an example that, while increasingly tough to meet, should still be our goal.

Early morning and midday body temperatures of rams and ewes of three breeds of sheep were measured once weekly for a period of 10 months in Northern Rhodesia and 12 months in Southern Rhodesia.1. In all breeds seasonal fluctuations in body temperature were due to concurrent fluctuations in ambient air temperature.2. Mean annual body temperatures were: Merino 102·2° F.; Persian 101·7° F. and Native 101·7° F. Wool and hair breeds differed considerably in their early morning temperatures and in their body temperature increases from 6.30 a.m. to 12.30 p.m. Mean annual values for these measurements were Merino 101·73 and 1·92° F.; Persian 100·81 and 1·83° F.; Native 100·73 and 1–92° F. At all times Merinos showed markedly greater uniformity of body temperature than either hair breed. There was no evidence to show that the thermoregulatory mechanisms of these animals had been stressed unduly.3. Sex had no consistent effect on body temperature or on rise in body temperature.In general, lactating ewes showed a significantly higher initial body temperature than either empty or pregnant ewes, but the respective heat tolerances as measured by body temperature increase did not differ appreciably. Body temperature differed little in empty and pregnant ewes.4. Although the youngest group of ewes in each breed showed the highest early morning temperature, there was no evidence that heat tolerance was less in young than in old animals.5. Black-coated Native ewes had higher initial body temperatures and a smaller body temperature increase during the summer months in Southern Rhodesia than brown or broken-coloured Native ewes. These effects were due to differences in coat density rather than to differences in coat colour or skin pigmentation.6. In all breeds the magnitude of the diurnal and annual variation in body temperature was different in Northern and Southern Rhodesia. Differences were largely of climatic origin but low plane of nutrition in Southern Rhodesia possibly reduced critical body temperature and impaired thermoregulatory ability.

Of the many mysteries surrounding the life history of dinosaurs, one of the more enduring is how such gigantic organisms—some reaching 42 feet tall and weighing 90 tons—regulated their body temperature. For many years, scientists had assumed that dinosaurs, which evolved from reptiles, were also cold blooded (ectotherms), with a slow metabolism that required the sun's heat to thermoregulate. But, in the late 1960s, the notion emerged that dinosaurs, like mammals and birds, might have been warm blooded (endotherms) with relatively constant, high body temperatures that were internally regulated like their avian descendants (and mammals). Still others argued that while most dinosaurs had a metabolism similar to contemporary reptiles, the large dinosaurs managed a higher, more-constant body temperature through thermal inertia, which is how modern alligators, Galapagos tortoises, and Komodo dragons retain heat. Thermal inertia allows the body to approach homeothermy, or constant body temperature, when the ratio of body mass to surface area is high enough. If this “inertial homeothermy” hypothesis is correct, dinosaur body temperature should increase with body size. In a new study, James Gillooly, Andrew Allen, and Eric Charnov revisit—and resolve—this debate. The researchers used a model that provided estimates of dinosaur body temperature based on developmental growth trajectories inferred from juvenile and adult fossil bones of the same species. The model predicts that dinosaur body temperature did increase with body mass, and that large dinosaurs had body temperatures similar to those of modern birds and mammals, while smaller dinosaurs' temperatures were more like contemporary reptiles. These results suggest that the largest dinosaurs (but not the smaller ones) had relatively constant body temperatures maintained through thermal inertia. Gillooly et al. compiled data from eight dinosaur species from the early Jurassic and late Cretaceous periods that ranged in size from 30 pounds to 28 tons. The growth trajectories, taken from the published research papers, were determined by using bone histology (microscopic study) and body size estimates to estimate the maximum growth rate and mass at the time of maximum growth. The recent availability of these data, the researchers explain, along with advances in understanding how body size and temperature affect growth, allowed them to use a novel mathematical model to estimate dinosaur body temperatures. The researchers modified the model to estimate the body temperature of each dinosaur species, based on its estimated maximum growth rate and mass at the time of maximum growth. The model shows that body temperature increases with body size for seven dinosaur species. The model shows that dinosaur body temperature increased with body size, from roughly 77 °F at 26 pounds to 105.8 °F at 14 tons. These results, the researchers explain, suggest that the body temperatures of the smaller dinosaurs (77 °F) were close to the environmental temperature—just as occurs for modern smaller reptiles—which meant they acquired heat from external sources (in addition to the internal heat generated by metabolism). The results also suggest that body temperature rose as an individual dinosaur grew, increasing by about 37.4 °F for species weighing about 661 pounds as adults and nearly 68 °F for those reaching about 27 tons (Apatosaurus excelsus). Predicted body temperature for the largest dinosaur ( Sauroposeidon proteles at about 60 tons) was about 118 °F—just past the limit for most animals, suggesting that body temperature may have prevented dinosaurs from becoming even bigger. Gillooly et al. demonstrate the validity of these results by showing that the model successfully predicts documented increases in body temperature with size for existing crocodiles. Altogether, these results indicate that dinosaurs were reptiles and that their body temperature increased with body size—providing strong evidence for the inertial homeothermy hypothesis.

BackgroundHypothermia is associated with many adverse clinical outcomes in pediatric patients, and thus, it is important to find an effective and safe method for preventing peri-operative hypothermia and its associated adverse outcomes in pediatric patients. This study aimed to investigate the effect of forced-air warming blankets with different temperatures on changes in the transforming growth factor-β (TGF-β), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-10 levels in children undergoing surgical treatment for developmental displacement of the hip (DDH).MethodsThe study included 123 children undergoing surgery for DDH under general anesthesia. The patients were randomly assigned to three groups, using a random number table: the 32, 38, and 43°C groups according to the temperature setting of the forced-air warming blankets. For each patient, body temperature was recorded immediately after anesthesia induction and intubation (T0), at initial incision (T1), at 1 h after incision (T2), at 2 h after incision (T3), at the end of surgery (T4), immediately upon return to the ward after surgery (T5), and then at 12 h (T6), 24 h (T7), 36 h (T8), and 48 h (T9) after the surgery. The serum levels of TGF-β, TNF-α, IL-1β, and IL-10 were measured at T0 and T4 for all groups.ResultsThe number of patients with fever in the 38°C group was significantly less than those in the 32 and 43°C groups (χ2 = 6.630, P = 0.036). At T0, the body temperatures in the 38 and 43°C groups were significantly higher than that in the 32°C group (F = 17.992, P < 0.001). At T2, the body temperature was significantly higher in the 43°C group than those in the 32 and 38°C groups (F = 12.776, P < 0.001). Moreover, at T4, the serum levels of TGF-β (F = 3286.548, P < 0.001) and IL-10 (F = 4628.983, P < 0.001) were significantly increased in the 38°C group, and the serum levels of TNF-α (F = 911.415, P < 0.001) and IL-1β (F = 322.191, P < 0.001) were significantly decreased in the 38°C group, compared with the levels in the 32 and 43°C groups.ConclusionForce-air warming blankets set at 38°C maintained stable body temperature with less adverse outcome and effectively inhibited the inflammatory response in pediatric patients undergoing surgery for DDH.Clinical trial registrationChiCTR1800014820; http://www.chictr.org.cn/showproj.aspx?proj=25240.

Ectothermic organisms respond to rapid environmental change through a combination of behavioral and physiological adjustments. As behavioral and physiological traits are often functionally linked, an effective ectotherm response to environmental perturbation will depend on the direction and magnitude of their association. The role of various modifiers in behavioral-physiological relationships remains largely unexplored. We applied a repeated-measures approach to examine the influence of body temperature and individual variation on the link between resting metabolic rate (RMR) and exploratory locomotor activity (ELA) in juvenile Alpine newts, Ichthyosaura alpestris. We analyzed trait relationships at two body temperatures separately and as parameters, intercepts and slopes, of thermal reaction norms for both traits. Body temperature affected the level of detectable among-individual variation in two different directions. Among-individual variation in ELA was detected at 12°C, while RMR was repeatable at 22°C. We found no support for a link between RMR and ELA at either temperature. While analysis of intercepts revealed among-individual variation in both traits, among-individual variation in slopes was detected in RMR only. Intercepts were positively associated at the individual, but not the whole-phenotypic, level. For ELA, the target of selection should be individual trait values across temperatures, rather than their thermal sensitivities. The positive association between intercepts of thermal reaction norms for ELA and RMR suggests that phenotypic selection acts on both traits in a correlated fashion. Measurements at one body temperature and within-individual variation hide the metabolic-behavioral relations. We conclude that correlative studies on flexible behavioral and physiological traits in ectotherms require repeated measurement at two or more body temperatures in order to avoid misleading results. This approach is needed to fully understand ectotherm responses to environmental change and its impact on their population dynamics.

12 ways to take a temperature

Severe injury and shock are frequently associated with abnormalities in patient body temperature. Substantial increases in mortality have been associated with profound hypothermia, especially below 35 degrees C. The purpose of this study was to further characterize the impact of hypothermia in a large dataset of trauma patients. This study was a retrospective analysis of the 2004 version of the National Trauma Data Bank (NTDB), which contains approximately 1.1 million patients from over 400 trauma centers. Admission temperature was analyzed with respect to mortality, injury severity score (ISS), base deficit (BD), Glasgow Coma Score (GCS), and hospital outcomes. The NTDB contained 701,491 patients with temperatures recorded upon trauma center admission. Of these, 11,026 patients had admission temperatures <35 degrees C, and 802 had temperatures <32 degrees C. Comparison of core temperature versus mortality revealed that as temperature decreased, the mortality rate increased, reaching approximately 39% at 32 degrees C, and remained constant at lower temperatures. Surprisingly, 477 patients (59.5%) survived with temperatures <32 degrees C. Similarly, BD increased as hypothermia worsened until body temperature reached 31 degrees C, below which there was little further increase. Patients with admission temperatures less than 35 degrees C had significantly greater mortality (25.5% vs. 3.0%, P < 0.001) and BD (7.8 vs. 3.7, P < 0.001) when compared with patients with temperatures >or=35 degrees C. In survivors, average ventilator days and intensive care unit (ICU) days were 14.4 and 12.8, respectively, for patients with temperatures <35 degrees C as opposed to more normothermic patients who demonstrated an average of 9.5 ventilator days and 9.1 ICU days (P < 0.001). When grouped by individual ISS, BD level, and GCS motor score, mortality was significantly greater when admission temperature was below 35 degrees C (ISS mean difference = 11.4%, BD mean difference = 22.8%, and GCS motor mean difference = 9.85%). Logistic regression revealed that hypothermia remains an independent determinant of mortality after correction for confounding variables (odds ratio = 1.54, 95% confidence interval 1.40-1.71). Admission hypothermia is associated with greater mortality, increased injury severity, more profound acidosis, and prolonged ICU/ventilator courses. However, although mortality at <32 degrees C is high, patients with temperatures this low do survive. As temperatures drop below 32 degrees C, mortality rates remain constant, which may indicate a threshold below which physiologic mechanisms are unable to correct body temperature regardless of injury severity. Although shock severity is highly indicative of outcome, hypothermia independently contributes to the substantial mortality associated with severe injury.

The aim of this study was to determine the extent to which several environmental variables were associated with body temperatures of three species of garter snakes (Thamnophis) on Vancouver Island, and whether or not these associations changed with different activities of snakes. Perhaps because the data set was quite heterogeneous, no differences were observed between body temperatures of different species or sexes. In all activity groups, environmental temperatures were the variables most highly correlated with body temperatures; factors such as visible light intensity and cloud cover also were correlated with body temperature in some cases, but added little to the "explained" variation of body temperature. There was little evidence of seasonal or diel fluctuation in body temperature, but more careful data collection may be required to detect these. The correlation between body and environmental temperatures was highest for snakes under cover and lowest for moving snakes. Basking snakes in general were intermediate between these two groups, but snakes basking in the sun under sunny skies showed low correlation between body and environmental temperatures. Snakes, therefore, had body temperatures relatively independent of environmental temperatures under certain circumstances, but conclusions about thermoregulation could not be drawn from these data.

Marathon runners are famed for pasta packing in the days before a big run but when tiny passerine birds set out on their epic migrations, the distances are too great to cover on the reserves with which they embark. MichałWojciechowski and Berry Pinshow explain that most birds stop off en route to their destination to refuel. One of the Eurasian blackcaps' preferred refuelling stops is Midreshet Ben-Gurion, Israel, where the birds fill up on fruit and insects before setting off again. Knowing that birds expend twice as much energy during stopovers than they use in transit, the duo wondered whether the tiny aviators may drop their body temperature at night during stopovers to save energy and build up their reserves faster(p. 3068).Collecting migrating blackcaps at their stopover site on the Sede Boqer Campus of Ben-Gurion University, Wojciechowski and Pinshow weighed the birds and monitored their body temperatures and metabolic rates as the birds stocked up on fruit supplemented with mealworms. During the day the birds' body temperatures hovered around 42.5°C, but as dusk fell, their temperatures began to drop. The average normal body temperature at night was about 38.8°C, while one particularly skinny individual's temperature plummeted to 33°C. And when the team plotted the birds' body masses against their nocturnal body temperatures, the smaller birds' (<16.3 g) temperatures correlated with their body masses but the larger birds' (>16.3 g) body temperatures did not.Finally, the team looked at the relationship between the birds'temperatures and their metabolic rates and found that the heavier birds dropped their metabolic rates least, while the lightest birds dropped their metabolic rates most. Some conserved a remarkable 30% of their energy by becoming hypothermic.Knowing that small birds also conserve energy by huddling together for warmth, Wojciechowski and Pinshow suggest that migrating birds may combine both strategies to shorten refuelling stopovers to fatten up fast before hastening on their way.

Behavioral thermoregulation is an important defense against the negative impacts of climate change for ectotherms. In this study we examined the use of burrows by a common intertidal crab, Minuca pugnax, to control body temperature. To understand how body temperatures respond to changes in the surface temperature and explore how efficiently crabs exploit the cooling potential of burrows to thermoregulate, we measured body, surface, and burrow temperatures during low tide on Sapelo Island, GA in March, May, August, and September of 2019. We found that an increase in 1°C in the surface temperature led to a 0.70-0.71°C increase in body temperature for females and an increase in 0.75-0.77°C in body temperature for males. Body temperatures of small females were 0.3°C warmer than large females for the same surface temperature. Female crabs used burrows more efficiently for thermoregulation compared to the males. Specifically, an increase of 1°C in the cooling capacity (the difference between the burrow temperature and the surface temperature) led to an increase of 0.42-0.50°C for females and 0.34-0.35°C for males in the thermoregulation capacity (the difference between body temperature and surface temperature). The body temperature that crabs began to use burrows to thermoregulate was estimated to be around 24°C, which is far below the critical body temperatures that could lead to death. Many crabs experience body temperatures of 24°C early in the reproductive season, several months before the hottest days of the year. Because the use of burrows involves fitness trade-offs, these results suggest that warming temperatures could begin to impact crabs far earlier in the year than expected.

Brown adipose tissue (BAT) thermogenesis occurs episodically in an ultradian manner approximately every 80-100 min during the waking phase of the circadian cycle, together with highly correlated increases in brain and body temperatures, suggesting that BAT thermogenesis contributes to brain and body temperature increases. We investigated this in conscious Sprague-Dawley rats by determining whether inhibition of BAT thermogenesis via blockade of beta-3 adrenoceptors with SR59230A interrupts ultradian episodic increases in brain and body temperatures and whether SR59230A acts on BAT itself or via sympathetic neural control of BAT. Interscapular BAT (iBAT), brain, and body temperatures, tail artery blood flow, and heart rate were measured in unrestrained rats. SR59230A (1, 5, or 10 mg/kg ip), but not vehicle, decreased iBAT, body, and brain temperatures in a dose-dependent fashion (log-linear regression P < 0.01, R(2) = 0.3, 0.4, and 0.4, respectively, n = 10). Ultradian increases in BAT, brain, and body temperature were interrupted by administration of SR59230A (10 mg/kg ip) compared with vehicle, resuming after 162 ± 24 min (means ± SE, n = 10). SR59230A (10 mg/kg ip) caused a transient bradycardia without any increase in tail artery blood flow. In anesthetized rats, SR59230A reduced cooling-induced increases in iBAT temperature without affecting cooling-induced increases in iBAT sympathetic nerve discharge. Inhibition of BAT thermogenesis by SR59230A, thus, reflects direct blockade of beta-3 adrenoceptors in BAT. Interruption of episodic ultradian increases in body and brain temperature by SR59230A suggests that BAT thermogenesis makes a substantial contribution to these increases.

Available sleep deprivation studies lack data on simultaneous changes in hypothalamic, cortical and body temperature during sleep deprivation and recovery. Ten adult male Wistar rats chronically implanted with electroencephalogram, electro-oculogram and electromyogram electrodes for recording sleep were used in this study. Hypothalamic and cortical temperatures were measured by pre-implanted thermocouples. A radio transmitter (TA10TAF-40, DSI USA) was implanted intraperitoneally to measure body temperature. All the temperatures were measured simultaneously at 15-s intervals during baseline conditions, sleep deprivation and recovery sleep. Sleep deprivation was carried out for 24hr by the gentle handling method; however, sleep and temperature were only recorded during the first 12hr of deprivation. During sleep deprivation the body, hypothalamic and cortical temperatures increased significantly as compared to baseline. During recovery sleep, body and cortical temperature recovered earlier than the hypothalamic temperature. Hypothalamic temperature remained higher than the baseline values throughout 12hr of recovery sleep. In the recovery sleep, cortical temperature decreased immediately and reached near baseline by 4hr. We observed a quicker return of cortical temperature towards control temperature during recovery sleep compared with hypothalamic and body temperature. The results of the present study show that acute sleep deprivation results in a rise in both cortical and hypothalamic temperature, along with body temperature. A rise in cortical temperature may be a contributing factor for cognitive dysfunction resulting from sleep deprivation.