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Recent experimental studies indicate that mitochondria in mammalian cells are maintained at temperatures of at least 50 °C. While acknowledging the limitations of current experimental methods and their interpretation, we here consider the ramifications of this finding for cellular functions and for evolution. We consider whether mitochondria as heat‐producing organelles had a role in the origin of eukaryotes and in the emergence of homeotherms. The homeostatic responses of mitochondrial temperature to externally applied heat imply the existence of a molecular heat‐sensing system in mitochondria. While current findings indicate high temperatures for the innermost compartments of mitochondria, those of the mitochondrial surface and of the immediately surrounding cytosol remain to be determined. We ask whether some aspects of mitochondrial dynamics and motility could reflect changes in the supply and demand for mitochondrial heat, and whether mitochondrial heat production could be a factor in diseases and immunity. [ABSTRACT FROM AUTHOR]

Summary: Current estimates of temperature effects on plants mostly rely on air temperature, although it can significantly deviate from leaf temperature (Tleaf). To address this, some studies have used canopy temperature (Tcan). However, Tcan fails to capture the fine‐scale variation in Tleaf among leaves and species in diverse canopies.We used infrared radiometers to study Tleaf and Tcan and how they deviate from air temperature (ΔTleaf and ΔTcan) in multispecies tropical tree plantations at three sites along an elevation and temperature gradient in Rwanda.Our results showed high Tleaf (up to c. 50°C) and ΔTleaf (on average 8–10°C and up to c. 20°C) of sun‐exposed leaves during 10:00 h–15:00 h, being close to or exceeding photosynthetic heat tolerance thresholds. These values greatly exceeded simultaneously measured values of Tcan and ΔTcan, respectively, leading to strongly overestimated leaf thermal safety margins if basing those on Tcan data. Stomatal conductance and leaf size affected Tleaf and Tcan in line with their expected influences on leaf energy balance.Our findings highlight the importance of leaf traits for leaf thermoregulation and show that monitoring Tcan is not enough to capture the peak temperatures and heat stress experienced by individual leaves of different species in tropical forest canopies. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effect of organic selenium (SE) supplementation on blood constituents related to hematology and serum biochemistry of dairy goats in the productive phase. A total of 16 lactating Saanen × Toggenburg crossbred goats, aged between 2 and 3, lactating, nonpregnant, clinically healthy, and having a body weight (BW) of 40.75 ± 8.31 kg were selected for this study. Higher SE concentrations were observed on the 42nd day of supplementation, and on the 63rd day, the SE concentrations were similar ( P > 0.05 ) to the 21st and 42nd days. There was no interaction for plasma constituents comparing treatment effects and days of supplementation ( P > 0.05 ). SE supplementation reduced ( P = 0.04 ) plasma proteins with a gradual increase in available SE. There was no difference ( P > 0.05 ) for the blood count comparing the effects of treatment and days of supplementation. There was no interaction ( P > 0.05 ) for serum biochemical constituents between treatments and periods, except for urea ( P = 0.045 ). Animals that received SE supplementation had similar plasma urea concentrations before and after supplementation, while animals that did not receive SE in the diet had increased serum urea concentrations. The main action of selenium in metabolism occurred in the reduction of plasma proteins and urea levels, which leads us to conclude that it influenced protein metabolism. Finally, hematology, liver function, and energy metabolism are not affected by selenium supplementation in dairy goats reared in semiarid conditions. [ABSTRACT FROM AUTHOR]

Unlike numerous other members of the holarctic Tribe Marmotini of the squirrel family (Sciuridae) that typically exhibit spontaneous bouts of torpor that progress into an annual season of hibernation, members of the genus Ammospermophilus (antelope ground squirrels) do not enter torpor, and they remain active throughout the year in nature. We have experimentally evaluated seasonal patterns of variation in the circadian rhythm of body temperature in captive A. leucurus over a two-and-a-half-year period by exposing groups to either a constant daily photoperiod of 12 h light or a seasonally changing photoperiod that cycled between a summer maximum of 16 h per day and a winter minimum of 8 h; ambient air temperature was maintained at 26 °C. All squirrels showed continuous, year-round diurnal locomotor activity, and the group exposed to seasonally changing photoperiod adjusted onset and end of activity to changes in duration of the photoperiod. Animals in both groups showed a marked circadian rhythm of core body temperature with a typical daytime level of about 38 °C and nighttime level of about 35 °C for most of each year, but the group exposed to naturally changing daylength surprisingly reduced the level of its circadian oscillation by about 2 °C at the winter seasonal extreme of shortest daily illumination to a daytime level about 36 °C and a nocturnal level of about 33 °C. Despite this modest experimentally induced reduction in the level of the circadian rhythm of body temperature, we conclude that A. leucurus shows an overall stable annual pattern of circadian rhythmicity of its core body temperature that is consistent with a lack of any other evidence that the species engages in torpor or hibernation. [ABSTRACT FROM AUTHOR]

• Canopy temperature was warmer than air temperature during most of the growing season. • T c :T air slopes increased following a water- to energy-limited gradient. • We introduced a framework linking canopy temperature, radiation, and soil moisture. Canopy temperature (T c) plays an important role in regulating the rates of mass and energy fluxes at the leaf surface. Better understanding of the relationship between T c and water availability may enable more accurate monitoring of ecosystem functioning in a changing climate. Here, we used high spatiotemporal resolution thermal infrared cameras deployed at three eddy covariance flux tower sites along a water- to energy-limited gradient – including a predominately water-limited grassland/shrubland site, a seasonally water-limited evergreen needleleaf forest, and a predominantly energy-limited deciduous broadleaf forest – to determine T c seasonality and its relationship with gross primary productivity (GPP) and environmental drivers. We found midday T c was generally warmer than air temperature (T air) during the growing season (T c :T air slope: 1.14–1.27) for all sites. Water-limited sites exhibited higher positive T c deviations from T air (2.30 ± 0.06 °C) compared to the energy-limited site (1.29 ± 0.09 °C) partly due to their reduced latent heat fluxes during water-limited periods. We further found that the T c :T air slope increased with site aridity, namely for 1.14 slope for the grassland, 1.15 for the evergreen forest, and 1.27 for the broadleaf forest. Peak GPP occurred when T c was higher than T air across all sites, with peak GPP at the grassland site occurring at +1.1 °C (T c -T air) and peak GPP at the broadleaf evergreen site occurring at +2.2 °C (T c -T air). T c -T air dynamics were mostly associated with soil water content at water-limited sites where canopies undergo a substantial cooling during the transition from dormancy to the peak GPP, while net radiation played a crucial role at the energy-limited site where the canopy heats up compared to T air over the same phenological transition. Our findings provide novel insights into T c -ecosystem water availability links, highlighting the drivers of T c -T air across diverse ecosystems in various phenological stages, which has implications for ecosystem management in a changing climate. [ABSTRACT FROM AUTHOR]

Understanding and predicting the relationship between leaf temperature (Tleaf) and air temperature (Tair) is essential for projecting responses to a warming climate, as studies suggest that many forests are near thermal thresholds for carbon uptake. Based on leaf measurements, the limited leaf homeothermy hypothesis argues that daytime Tleaf is maintained near photosynthetic temperature optima and below damaging temperature thresholds. Specifically, leaves should cool below Tair at higher temperatures (i.e., > ~25-30°C) leading to slopes <1 in Tleaf/Tair relationships and substantial carbon uptake when leaves are cooler than air. This hypothesis implies that climate warming will be mitigated by a compensatory leaf cooling response. A key uncertainty is understanding whether such thermoregulatory behavior occurs in natural forest canopies. We present an unprecedented set of growing season canopy-level leaf temperature (Tcan) data measured with thermal imaging at multiple well-instrumented forest sites in North and Central America. Our data do not support the limited homeothermy hypothesis: canopy leaves are warmer than air during most of the day and only cool below air in mid to late afternoon, leading to Tcan/Tair slopes >1 and hysteretic behavior. We find that the majority of ecosystem photosynthesis occurs when canopy leaves are warmer than air. Using energy balance and physiological modeling, we show that key leaf traits influence leaf-air coupling and ultimately the Tcan/Tair relationship. Canopy structure also plays an important role in Tcan dynamics. Future climate warming is likely to lead to even greater Tcan, with attendant impacts on forest carbon cycling and mortality risk. [ABSTRACT FROM AUTHOR]

Simple Summary: The optimal temperature for laboratory mice has been under discussion for some time. Current standard temperature is 20 °C–24 °C but it has been suggested to elevate the standard to 30 °C, which is the thermoneutral zone for mice. In this study, the effect of different cage temperatures (20 °C, 25 °C, 30 °C) on reproduction and stress hormone metabolite excretion was evaluated in lactating females of two commonly used mouse strains. Pup loss was higher, and weights of mothers and pups were reduced at 30 °C compared to the lower temperatures. In addition, pups showed increased tail length at weaning under the high temperature (30 °C). There was no difference in stress hormone metabolite excretion in mice between temperature groups. We could not show any detrimental effects of the lower or higher cage temperature on stress hormone metabolite excretion, but found decreased reproductive outcome under the higher temperature. Ambient temperature is an important non-biotic environmental factor influencing immunological and oncological parameters in laboratory mice. It is under discussion which temperature is more appropriate and whether the commonly used room temperature in rodent facilities of about 21 °C represents a chronic cold stress or the 30 °C of the thermoneutral zone constitutes heat stress for the animals. In this study, we selected the physiological challenging period of lactation to investigate the influence of a cage temperature of 20 °C, 25 °C, and 30 °C, respectively, on reproductive performance and stress hormone levels in two frequently used mouse strains. We found that B6D2F1 hybrid mothers weaned more pups compared to C57BL/6N mothers, and that the number of weaned pups was reduced when mothers of both strains were kept at 30 °C. Furthermore, at 30 °C, mothers and pups showed reduced body weight at weaning and offspring had longer tails. Despite pronounced temperature effects on reproductive parameters, we did not find any temperature effects on adrenocortical activity in breeding and control mice. Independent of the ambient temperature, however, we found that females raising pups showed elevated levels of faecal corticosterone metabolites (FCMs) compared to controls. Peak levels of stress hormone metabolites were measured around birth and during the third week of lactation. Our results provide no evidence of an advantage for keeping lactating mice in ambient temperatures near the thermoneutral zone. In contrast, we found that a 30 °C cage temperature during lactation reduced body mass in females and their offspring and declined female reproductive performance. [ABSTRACT FROM AUTHOR]

Previous research demonstrated that cities are similar to individual mammals in their relationship between the rate of energy use for heating and outdoor air temperature (Ta). At Tas requiring heating of indoor living spaces, the energy-Ta plot of a city contains information on city-wide thermal insulation (I), making it possible to quantify city-wide I by use of the city as the unit of measure. We develop methods for extracting this insulation information, deriving the methods from prior research on mammals. Using these methods, we address the question: in North America, are cities built in particularly cold locations constructed in ways that provide greater thermal insulation than ones built in thermally more moderate locations? Using data for 42 small and medium-size cities and two information-extraction methods, we find that there is a statistically significant inverse relationship between city-wide I and T10-year, the average city Ta over a recent 10-year period (range of T10-year: − 11 to 26 °C). This relationship represents an energy-conserving trend, indicating that cities in cold climates have greater built-in thermal insulation than cities in warm climates. However, the augmentation of insulation in cold climates is only about half as great as would be required to offset fully the increased energy cost of low Tas in a cold climate, and T10-year explains just 5–11% of the variance in measured insulation, suggesting that cities in North America vary greatly in the extent to which thermal insulation has been a priority in city development. [ABSTRACT FROM AUTHOR]

Maintaining a high and stable body temperature as observed in endothermic mammals and birds is energetically costly. Thus, it is not surprising that we discover more and more heterothermic species that can reduce their energetic needs during energetic bottlenecks through the use of torpor. However, not all heterothermic animals use torpor on a regular basis. Torpor may also be important to an individual's probability of survival, and hence fitness, when used infrequently. We here report the observation of a single, ~ 5.5 h long hypothermic bout with a decrease in body temperature by 12 °C in the native Australian bush rat (Rattus fuscipes). Our data suggest that bush rats are able to rewarm from a body temperature of 24 °C, albeit with a rewarming rate lower than that expected on the basis of their body mass. Heterothermy, i.e. the ability to withstand and overcome periods of reduced body temperature, is assumed to be an evolutionarily ancestral (plesiomorphic) trait. We thus argue that such rare hypothermic events in species that otherwise appear to be strictly homeothermic could be heterothermic rudiments, i.e. a less derived form of torpor with limited capacity for rewarming. Importantly, observations of rare and extreme thermoregulatory responses by wild animals are more likely to be discovered with long-term data sets and may not only provide valuable insight about the physiological capability of a population, but can also help us to understand the constraints and evolutionary pathways of different phenologies. [ABSTRACT FROM AUTHOR]

Ambient temperature is an important non-biotic environmental factor influencing immunological and oncological parameters in laboratory mice. It is under discussion which temperature is more appropriate and whether the commonly used room temperature in rodent facilities of about 21 °C represents a chronic cold stress or the 30 °C of the thermoneutral zone constitutes heat stress for the animals. In this study, we selected the physiological challenging period of lactation to investigate the influence of a cage temperature of 20 °C, 25 °C, and 30 °C, respectively, on reproductive performance and stress hormone levels in two frequently used mouse strains. We found that B6D2F1 hybrid mothers weaned more pups compared to C57BL/6N mothers, and that the number of weaned pups was reduced when mothers of both strains were kept at 30 °C. Furthermore, at 30 °C, mothers and pups showed reduced body weight at weaning and offspring had longer tails. Despite pronounced temperature effects on reproductive parameters, we did not find any temperature effects on adrenocortical activity in breeding and control mice. Independent of the ambient temperature, however, we found that females raising pups showed elevated levels of faecal corticosterone metabolites (FCMs) compared to controls. Peak levels of stress hormone metabolites were measured around birth and during the third week of lactation. Our results provide no evidence of an advantage for keeping lactating mice in ambient temperatures near the thermoneutral zone. In contrast, we found that a 30 °C cage temperature during lactation reduced body mass in females and their offspring and declined female reproductive performance.

This study investigated the effect of season on the endocrine and adaptive profiles of a Brazilian Creole goat population in a semi-arid region of Brazil during the dry and the rainy season. We considered physiological, morphological, biochemical, haematological, hormonal and anatomical profiles. The experiment used 80 adult goats (2- to 5-year-old) and lactating (160 ± 14 days of lactation length) goats, with an average daily milk yield of 500.9 ± 13 g. Physiological parameters (rectal temperature, RT; respiratory rate, RR; heart rate, HR; skin temperature, ST) were high (p

This review aimed to present the current status of the studies about the role of physiological, hematological, biochemical and hormonal variables on the blood of goats raised in adverse environments. Scientific work in recent years has allowed for the evaluation of how goats of distinct breeds react to edaphoclimatic effects to maintain homeothermy according to adaptability to the environment. The exposure of goats to heat stress causes changes in the physiological functions with impact on production and productivity of the animals. There is evidence that the central nervous system is sensitive to temperature changes, and some cells are agiler in the cold than in heat. In conclusion, we say that regardless of the breed, the raising environment and its climatic variables can trigger physiological, biochemical, hematological and hormonal alterations that result in a reduction of the heat production for maintenance of homeothermy. All these changes have a substantial impact on production and productivity.

The principal focus of this study was to describe how the coat characteristics could affect the heat exchanges in animals managed in a hot environment. The Morada Nova ewes were monitored once a month, during 10 consecutive months, in three commercial flocks. Initially, an analysis was performed to measure the differences regarding the coat color in the thermoregulation mechanisms. The animals were grouped into 4 different groups according to coat tonality, as follows: dark red animals (group 1, N = 23), intermediate red color (group 2, N = 27), light red animals (group 3, N = 30), and white-coated animals (group 4, N = 30). The data were collected from 1100 to 1400 h, after the animals were exposed to 30 min of direct sunlight. The cluster analysis was performed considering the hair structural characteristics such as coat thickness (CT, cm), hair length (HL, mm), hair diameter (HD, m), and number of hairs (NH, hairs per unit area), after that these clusters were compared in relation to thermoregulatory mechanisms that include rectal temperature (RT, °C), respiratory rate (RR, breaths min−1), cutaneous evaporation (CE, °C), and respiratory evaporation (RE, W m−2). The groups were characterized and compared using mean and standard deviation, and the differences between the clusters were compared using the Tukey test with a 5% probability of error. In relation to coat color, no differences were found in groups 1, 2, and 3 regarding the activation of the thermoregulation mechanisms. The most different was observed in the totally white coat that presented different thermoregulatory responses as the highest sweating rate. White-coated animals showed a non-pigmented epidermis, and the hair structure is responsible to promote skin protection as necessary, such as a dense coat (1242.7 hair cm−2), long hair (14.2 mm), and thicker coat (7.38 mm). In red-coated animals, the hair structure favored heat loss to the environment, such as short hairs, less thick coat, and less hairs per square centimeter. All evaluated animals showed the rectal temperature within the reference limits for the ovine species, regardless of the coat color. In the analysis of clusters related to the physical structure of hair, it was possible to observe that the animals with thick hair, short hair, and less dense coat tended to have a higher capacity to eliminate heat through their respiratory rate and showed less intense heat loss by cutaneous evaporation. We verified that coat color presents a direct influence on the hair structure and the activation of mechanisms related to thermoregulation. [ABSTRACT FROM AUTHOR]

Organisms survive environmental variation by combining homeostatic regulation of critical states with allostatic variation of other traits, and species differences in these responses can contribute to coexistence in temporally variable environments.In this paper, we simultaneously record variation in three functional traits—body temperature (Tb), heart rate and activity—in relation to three forms of environmental variation—air temperature (Ta), photoperiod and experimentally manipulated resource levels—in free‐ranging snowshoe hares and North American red squirrels to characterize distinctions in homeotherm responses to the extreme conditions of northern boreal winters.Hares and squirrels differed in the level and precision of Tb regulation, but also in the allostatic pathways necessary to maintain thermal homeostasis. Hares demonstrated a stronger metabolic pathway (through heart rate variation reflective of the thermogenesis), while squirrels demonstrated a stronger behavioural pathway (through activity variation that minimizes cold exposure).As intermediate‐sized, winter‐active homeotherms, hares and squirrels share many functional attributes, yet, through the integrated monitoring of multiple functional traits in response to shared environmental variation, our study reveals many pairwise species differences in homeostatic and allostatic traits, that both define and are defined by the natural history, functional niches and coexistence of sympatric species. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Background: Mammals, particularly large domestic ones, are considered to be year-round homeotherms. Surprisingly, however, very few long-term studies of the stability of core temperature of large domestic mammals have been conducted. Methods: We monitored the auricular temperature and rectal temperature of goats, sheep, cows, and donkeys monthly for 2 years and compared their annual variation with their daily and day-to-day variations. Results: Although ambient temperature varied from 8 °C in the winter to 30 °C in the summer, auricular temperature varied less than 0.5 °C, and rectal temperature varied less than 0.3 °C. We found that the daily oscillation in body temperature was up to three times as large as the day-to-day and month-to-month variations and that month-to-month variation was negligibly larger than day-to-day variation. Conclusion: Our results confirm persistent homeothermy in large domestic mammals with unrestricted access to food and water and provide a quantitative measure of the relationship between long-term homeothermy and the wider range of daily/circadian oscillation. [ABSTRACT FROM AUTHOR]

Theoretical modelling predicts that the thermoregulatory strategies of endothermic animals range from those represented by thermal generalists to those characteristic for thermal specialists. While the generalists tolerate wide variations in body temperature (Tb), the specialists maintain Tb at a more constant level. The model has gained support from inter-specific comparisons relating to species and population levels. However, little is known about consistent among-individual variation within populations that could be shaped by natural selection. We studied the consistency of individual heterothermic responses to environmental challenges in a single population of yellow-necked mice (Apodemus flavicollis), by verifying the hypothesis that Tb variation is a repeatable trait. To induce the heterothermic response, the same individuals were repeatedly food deprived for 24 h. We measured Tb with implanted miniaturised data loggers. Before each fasting experiment, we measured basal metabolic rate (BMR). Thus, we also tested whether individual variation of heterothermy correlates with individual self-maintenance costs, and the potential benefits arising from heterothermic responses that should correlate with body size/mass. We found that some individuals clearly entered torpor while others kept Tb stable, and that there were also individuals that showed intermediate thermoregulatory patterns. Heterothermy was found to correlate negatively with body mass and slightly positively with the BMR achieved 1-2 days before fasting. Nonetheless, heterothermy was shown to be highly repeatable, irrespective of whether we controlled for self-maintenance costs and body size. Our results indicate that specialist and generalist thermoregulatory phenotypes can co-exist in a single population, creating a heterothermy continuum. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the physiological parameters and thermal comfort indices of commercial layers fed diets containing different levels of vegetable glycerin. A total of 378 Hy-Line White layers at 32 weeks of age were housed in a shed at nine birds per cage. The experiment lasted 84 days. Treatments consisted of a control diet (without glycerin) plus five diets with increasing levels of vegetable glycerin (3, 6, 9, 12, and 15%). The black globe humidity index (BGHI) and radiant heat load (RHL) were out of the thermal comfort zone and were higher in the afternoon period in all production cycles. Respiratory frequency was lower in the morning, when 3% glycerin were added to the diet. The surface temperatures of comb, wattle, back, wings, head, and feet did not differ with the glycerin levels and were higher in the 2nd cycle, but within the range recommended for the species. Glycerin inclusion levels of up to 12% can be used to partially replace corn in diets for layers housed in sheds covered with ceramic tiles without compromising their thermoregulation in a hot environment. [ABSTRACT FROM AUTHOR]

The evolutionary success of endothermy in mammals and birds represents an enduring enigma. Relative to an ectotherm of equivalent body size, endotherms expend many times the energy to maintain high, stable body temperatures. What source or sources of selection could have favored such an energetically costly strategy? Several hypotheses have been proposed for agents of selection that may have facilitated the rise of endothermy, with mixed support for each. Here, I discuss the possibility that an additional agent of selection, pathogens, may have played an important role in the evolution and maintenance of obligate endothermy in mammals and birds. I draw on recent work demonstrating that the immune system is highly thermally sensitive and individuals that maintain warm body temperatures have enhanced ability to reduce pathogen burdens. To further increase immune function when encountering a pathogen, ectotherms often employ the environmentally constrained and costly strategy of behavioral fever, whereas endotherms maintain body temperatures close to the optimum for immune performance at most times, essentially 'priming' their immune systems for a rapid response to infection. An evolutionary arms race in an ancient ectotherm, in which better behavioral thermoregulators were favored by increasingly virulent pathogens (and vice versa) could have contributed to the evolution of obligate endothermy in mammals and birds. [ABSTRACT FROM AUTHOR]

This article is a Commentary on Drake et al. (2020), 228: 1511–1523. [ABSTRACT FROM AUTHOR]

Temperature regulation is an indispensable physiological activity critical for animal survival. However, relatively little is known about the origin of thermoregulatory regimes in a phylogenetic context, or the genetic mechanisms driving the evolution of these regimes. Using bats as a study system, we examined the evolution of three thermoregulatory regimes (hibernation, daily heterothermy, and homeothermy) in relation to the evolution of leptin, a protein implicated in regulation of torpor bouts in mammals, including bats. A threshold model was used to test for a correlation between lineages with positively selected lep, the gene encoding leptin, and the thermoregulatory regimes of those lineages. Although evidence for episodic positive selection of lep was found, positive selection was not correlated with lineages of heterothermic bats, a finding that contradicts results from previous studies. Evidence from our ancestral state reconstructions suggests that the most recent common ancestor of bats used daily heterothermy and that the presence of hibernation is highly unlikely at this node. Hibernation likely evolved independently at least four times in bats—once in the common ancestor of Vespertilionidae and Molossidae, once in the clade containing Rhinolophidae and Rhinopomatidae, and again independently in the lineages leading to Taphozous melanopogon and Mystacina tuberculata. Our reconstructions revealed that thermoregulatory regimes never transitioned directly from hibernation to homeothermy, or the reverse, in the evolutionary history of bats. This, in addition to recent evidence that heterothermy is best described along a continuum, suggests that thermoregulatory regimes in mammals are best represented as an ordered continuous trait (homeothermy ← → daily torpor ← → hibernation) rather than as the three discrete regimes that evolve in an unordered fashion. These results have important implications for methodological approaches in future physiological and evolutionary research. We explored the relationship between an ecologically important gene, lep, and the evolution of thermoregulatory regimes (hibernation, daily torpor, and homeothermy) in bats. Contrary to previous findings, we found no relationship here. We provide one of the first ancestral state reconstructions of thermoregulatory regimes in a mammalian group and present evidence suggesting that thermoregulatory regimes evolved in a continuous and ordered fashion rather than in a discrete and unordered manner. [ABSTRACT FROM AUTHOR]

This review aimed to present the current status of the studies about the role of physiological, hematological, biochemical and hormonal variables on the blood of goats raised in adverse environments. Scientific work in recent years has allowed for the evaluation of how goats of distinct breeds react to edaphoclimatic effects to maintain homeothermy according to adaptability to the environment. The exposure of goats to heat stress causes changes in the physiological functions with impact on production and productivity of the animals. There is evidence that the central nervous system is sensitive to temperature changes, and some cells are agiler in the cold than in heat. In conclusion, we say that regardless of the breed, the raising environment and its climatic variables can trigger physiological, biochemical, hematological and hormonal alterations that result in a reduction of the heat production for maintenance of homeothermy. All these changes have a substantial impact on production and productivity. [ABSTRACT FROM AUTHOR]

Ten (10) multiparous hair ewes from white genotype, non-pregnant and non-lactating, were confined in order to determine diurnal variations of physiological variables and some blood metabolite concentrations through hot summer months (June to September) in an desert region of the northwest Mexico. While blood metabolite concentrations were measured at 6 and 18 h, physiological variables were evaluated at 0, 6, 12 and 18 h during 4-d in each month (weekly measurements). Temperature and temperature-humidity index monthly averages during the study were 33.6 oC and 78.6 units, respectively, being August the hottest month. Live weight and body condition did not change (P>0.05) across the summer months. Compared with other months, rectal temperatures in August were lower (P<0.05) between 0 and 12 h, and then increased (P<0.05) at 18 h. Respiration frequency decreased (P<0.05) at 6 h in all the months, but at 0 and 18 h this was higher in August than in other months. Higher (P<0.05) glucose concentration and lower (P<0.05) cholesterol and triglyceride concentration were observed in June and July than in August and September. In conclusion, under desert climatic conditions, hair ewes had the ability to maintain homeothermy during all summer warm months because they changed their diurnal rhythms of physiological and metabolic variables according to the intensity of the heat stress in each month [ABSTRACT FROM AUTHOR]

The present paper aimed to show the thermoregulatory responses of locally adapted Morada Nova sheep with different coat colors that were exposed to direct solar radiation in an equatorial semiarid region. Animals were classified into four groups according to the coat color as follows: (1) dark red, (2) intermediate red, (3) light red, and (4) white coats. Forty Morada Nova ewes were observed in for 7 consecutive months. The experimental variables measured were rectal temperature (RT), skin surface temperature (ST), respiratory rate (RR), skin surface evaporation (CE), respiratory evaporation (RE), and heat exchange by convection (HC) and radiation (R). Data were collected from 1100 to 1400 h after the animals were exposed to 30 min direct sunlight. The results showed that all groups maintained homeothermy. The RR was higher in the animals of groups 1 to 3, which also showed higher values for ST when compared to the white-coated animals. Sensible heat exchange mechanisms were not important for heat loss, and R was a significant source of heat gain from the environment for the animals. Groups 1, 2, and 3 used RR more intensely than group 4 (P value = 0.001); however, CE was higher for the white-coated animals. It was concluded that Morada Nova sheep are well adapted to the semiarid environment, regardless of coat color. [ABSTRACT FROM AUTHOR]

It is believed that increased livestock production is limited by tropical climate. Thermal imbalance in bulls can lead to hyperthermia and alter testicular metabolism, causing subfertility or infertility. Therefore, the thermoregulation of composite Canchim bulls (5/8 Charolais × 3/8 Zebu) raised in tropical climate as well as their consequences in the physiological, hematological, hormonal, and andrological parameters were evaluated monthly. The bulls (n = 18; 30.0 ± 1.5 months; 503.8 ± 23.0 kg) were kept on pasture, in a single group, from August 2015 to March 2016, comprising the winter, spring, and summer seasons. Biometeorological variables were continuously monitored, and the Temperature and Humidity Index (THI) was calculated. A greater thermal challenge occurred in spring and summer (THI ≥ 72.0). Nevertheless, the bulls exhibited normothermia (38.6 to 38.9 °C) in these seasons. The cortisol did not vary between seasons (7.0 vs. 8.7 vs. 6.8 ng/mL; P > 0.05) and remained within the physiological patterns. Independent of the seasons, stress leukogram was also not observed, refuting the incidence of acute or chronic thermal stress. It is noteworthy that T3 and testosterone increased (P < 0.0001, P < 0.05) in spring and summer, the time that coincides with the breeding season, when there is increased metabolic requirement from the bulls. The progressive thermal challenge increase did not affect the scrotal thermoregulatory capacity, and in general, scrotal temperature remained at 5.2 °C below the internal body temperature. In summer, there was a 5% reduction in the minor sperm defects (P < 0.05) and DNA fragmentation in 2.4% of spermatozoa, a compatible value for high fertility bulls. The results show that the studied composite bulls can be considered as climatically adapted and constitute a viable alternative to be used in production systems in a tropical climate, even if the breeding seasons occur during the most critical thermal condition periods of the year. [ABSTRACT FROM AUTHOR]

1. The accuracy of predictive models (also known as mechanistic or causal models) of animal responses to climate change depends on properly incorporating the principles of heat transfer and thermoregulation into those models. Regrettably, proper incorporation of these principles is not always evident. 2. We have revisited the relevant principles of thermal physiology and analysed how they have been applied in predictive models of large mammals, which are particularly vulnerable, to climate change. We considered dry heat exchange, evaporative heat transfer, the thermoneutral zone and homeothermy, and we examined the roles of size and shape in the thermal physiology of large mammals. 3. We report on the following misconceptions in influential predictive models: underestimation of the role of radiant heat transfer, misassignment of the role and misunderstanding of the sustainability of evaporative cooling, misinterpretation of the thermoneutral zone as a zone of thermal tolerance or as a zone of sustainable energetics, confusion of upper critical temperature and critical thermal maximum, overestimation of the metabolic energy cost of evaporative cooling, failure to appreciate that the current advantages of size and shape will become disadvantageous as climate change advances, misassumptions about skin temperature and, lastly, misconceptions about the relationship between body core temperature and its variability with body mass in large mammals. 4. Not all misconceptions invalidate the models, but we believe that preventing inappropriate assumptions from propagating will improve model accuracy, especially as models progress beyond their current typically static format to include genetic and epigenetic adaptation that can result in phenotypic plasticity. [ABSTRACT FROM AUTHOR]

This study investigated the effect of season on the endocrine and adaptive profiles of a Brazilian Creole goat population in a semi-arid region of Brazil during the dry and the rainy season. We considered physiological, morphological, biochemical, haematological, hormonal and anatomical profiles. The experiment used 80 adult goats (2- to 5-year-old) and lactating (160 ± 14 days of lactation length) goats, with an average daily milk yield of 500.9 ± 13 g. Physiological parameters (rectal temperature, RT; respiratory rate, RR; heart rate, HR; skin temperature, ST) were high (p<.05) in the afternoon in both seasons. There was a significant effect of season (p<.05) on anatomical parameters (hair diameter, HD; hair length, HL; coat thickness, CT). Haematological, biochemical and hormonal parameters were also significantly affected by season (p<.05). We measured the biochemical and hormonal characteristics changes during different seasons; metabolism was reduced during heat stress and accelerated during cold stress. These hormones facilitate the physiological parameters involved in the adaptation process. Our results confirm that the adaptive capacity of the animals cannot be described solely by RT and RR. [ABSTRACT FROM AUTHOR]

Recent research is revealing incredible diversity in the thermoregulatory patterns of wild and captive endotherms. As a result of these findings, classic thermoregulatory categories of 'homeothermy', 'daily heterothermy', and 'hibernation' are becoming harder to delineate, impeding our understanding of the physiological and evolutionary significance of variation within and around these categories. However, we lack a generalized analytical approach for evaluating and comparing the complex and diversified nature of the full breadth of heterothermy expressed by individuals, populations, and species. Here we propose a new approach that decomposes body temperature time series into three inherent properties-waveform, amplitude, and period-using a non-stationary technique that accommodates the temporal variability of body temperature patterns. This approach quantifies circadian and seasonal variation in thermoregulatory patterns, and uses the distribution of observed thermoregulatory patterns as a basis for intra- and inter-specific comparisons. We analyse body temperature time series from multiple species, including classical hibernators, tropical heterotherms, and homeotherms, to highlight the approach's general usefulness and the major axes of thermoregulatory variation that it reveals. [ABSTRACT FROM AUTHOR]

Twenty-four castrated male pigs were used to determine the effect of ambient temperature on thermoregulatory responses during an acute heat stress test conducted for 48 hours. The animals were housed in two climatic chambers with controlled temperature, humidity and ventilation. The animals were maintained in thermal comfort for the category (22°C) in one of the chambers, and in the other, under heat stress (34°C). Twelve pigs were housed in each chamber, with the experimental unit composed of two animals in the stall, totaling six replicates. The environmental conditions of the climatic chambers and physiological parameters of respiratory rate and rectal and surface temperature were monitored at the beginning of the experiment and every 12 hours during the experimental period. Growing pigs presented effective thermoregulatory responses beginning at 12 hours under acute heat stress (34°C). [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the adaptive profile of the Garfagnina goat breed in two different seasons (spring and summer) through physiological, biochemical, haematological, and hormonal parameters. Fifty adult lactating females were studied twice a day (morning and afternoon) in each season. The air temperature, black globe temperature and air relative humidity was recorded using an automatic weather station. Physiological parameters recorded were rectal temperature, respiratory rate, heart rate, skin temperature and rectal-skin temperature gradient. The results of this study showed that there was a significant effect of season and period on all environmental variables. Physiological variables, rectal temperature, respiratory rate, heart rate and skin temperature showed higher values in the afternoon in both seasons. Both biochemical and hormonal parameters were significantly affected by season of the year. Biochemical and hormonal characteristics undergo changes during different seasons such that metabolism is reduced during heat stress and accelerated during cold stress; these metabolic changes are controlled by the thyroid hormones and cortisol. It has been shown from this study that these hormones facilitates the physiological parameters involved with the adaptation process confirming that adaptive capacity of animals cannot be described solely by rectal temperature and respiratory rate. [ABSTRACT FROM AUTHOR]

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This study aimed to examine thermoregulatory responses in birds facing two commonly experienced stressors, cold and fasting. Logging devices allowing long-term and precise access to internal body temperature were placed within the gizzards of ducklings acclimated to cold (CA) (58C) or thermoneutrality (TN) (258C). The animals were then examined under three equal 4-day periods: ad libitum feeding, fasting and re-feeding. Through the analysis of daily as well as short-term, or ultradian, variations of body temperature, we showed that while ducklings at TN show only a modest decline in daily thermoregulatory parameters when fasted, they exhibit reduced surface temperatures from key sites of vascular heat exchange during fasting. The CA birds, on the other hand, significantly reduced their short-term variations of body temperature while increasing long-term variability when fasting. This phenomenon would allow the CA birds to reduce the energetic cost of body temperature maintenance under fasting. By analysing ultradian regulation of body temperature, we describe a means by which an endotherm appears to lower thermoregulatory costs in response to the combined stressors of cold and fasting. [ABSTRACT FROM AUTHOR]

Altricial birds are unable to maintain body temperature when exposed to low ambient temperatures during the first days after hatching. Thermoregulatory capacity begins to form as postnatal development progresses, and eventually nestlings become homeothermic. Several factors may influence this development at both the level of the individual and the level of the whole brood, but to our knowledge no studies have focused on the effect of brood size per se on the development of endothermy in individual nestlings. We performed cooling experiments on blue tit (Cyanistes caeruleus) nestlings in the field, to study how different experimental brood sizes affected the development of endothermy in individual nestlings and the thermal environment experienced by the whole brood in the nest. Nestlings from all experimental brood sizes showed a decrease in cooling rate as they grew older, but birds from reduced broods showed an earlier onset of endothermy compared with nestlings from enlarged and control broods. This difference manifested during early development and gradually disappeared as nestlings grew older. The thermal environment in the nests differed between treatments during nestling development, such that nest temperature in reduced broods was lower than that in enlarged broods during all days and during nights at the end of the experimental period.We suggest that the development of endothermy in blue tit nestlings is not ontogenetically fixed, but instead may vary according to differences in developmental, nutritional and thermal conditions as determined by brood size. [ABSTRACT FROM AUTHOR]

Literature and own data on central effects of regulatory peptides (155 substances from 32 families) have been analyzed. Peptides produced by peripheral tissues affect the brain through the almost impermeable for them blood-brain barrier and evoke numerous central effects. The mechanisms of this impact are as follows: peptides bind to specific receptors located on vagal afferent terminals and in the circumventricular organs as well as (to a lesser extent) penetrate into the brain with the aid of specific transport systems or by simple diffusion. The number of these trans-barrier communications depends on the evolutionary age of the regulated physiological function: the more ancient the function is, the greater number of peripheral peptides are involved in such trans-barrier communications. [ABSTRACT FROM AUTHOR]