Thermoregulatory Capacity Research Articles

Heat Transfer by Sweat Droplet Evaporation.

Sweating regulates the body temperature in extreme environments or during exercise. Here, we investigate the evaporative heat transfer of a sweat droplet at the microscale to unveil how the evaporation complexity of a sweat droplet would affect the body's ability to cool under specific environmental conditions. Our findings reveal that, depending on the relative humidity and temperature levels, sweat droplets experience imperfect evaporation dynamics, whereas water droplets evaporate perfectly at equivalent ambient conditions. At low humidity, the sweat droplet fully evaporates and leaves a solid deposit, while at high humidity, the droplet never reaches a solid deposit and maintains a liquid phase residue for both low and high temperatures. This unprecedented evaporation mechanism of a sweat droplet is attributed to the intricate physicochemical properties of sweat as a biofluid. We suppose that the sweat residue deposited on the surface by evaporation is continuously absorbing the surrounding moisture. This route leads to reduced evaporative heat transfer, increased heat index, and potential impairment of the body's thermoregulation capacity. The insights into the evaporative heat transfer dynamics at the microscale would help us to improve the knowledge of the body's natural cooling mechanism with practical applications in healthcare, materials science, and sports science.

Metabolic adjustments to winter severity in two geographically separated great tit (Parus major) populations.

Understanding the potential limits placed on organisms by their ecophysiology is crucial for predicting their responses to varying environmental conditions. A main hypothesis for explaining avian thermoregulatory mechanisms is the aerobic capacity model, which posits a positive correlation between basal (basal metabolic rate [BMR]) and summit (Msum) metabolism. Most evidence for this hypothesis, however, comes from interspecific comparisons, and the ecophysiological underpinnings of avian thermoregulatory capacities hence remain controversial. Indeed, studies have traditionally relied on between-species comparisons, although, recently, there has been a growing recognition of the importance of intraspecific variation in ecophysiological responses. Therefore, here, we focused on great tits (Parus major), measuring BMR and Msum during winter in two populations from two different climates: maritime-temperate (Gontrode, Belgium) and continental (Zvenigorod, Russia). We tested for the presence of intraspecific geographical variation in metabolic rates and assessed the predictions following the aerobic capacity model. We found that birds from the maritime-temperate climate (Gontrode) showed higher BMR, whereas conversely, great tits from Zvenigorod showed higher levels of Msum. Within each population, our data did not fully support the aerobic capacity model's predictions. We argued that the decoupling of BMR and Msum observed may be caused by different selective forces acting on these metabolic rates, with birds from the continental-climate Zvenigorod population facing the need to conserve energy for surviving long winter nights (by keeping their BMR at low levels) while simultaneously being able to generate more heat (i.e., a high Msum) to withstand cold spells.

Capillaroscopic differences between primary Raynaud phenomenon and healthy controls indicate potential microangiopathic involvement in benign vasospasms.

For primary Raynaud phenomenon (PRP), an otherwise unexplained vasospastic disposition is assumed. To test the hypothesis of an additional involvement of distinct ultrastructural microvascular alterations, we compared the nailfold capillary pattern of patients with PRP and healthy controls. A total of 120 patients with PRP (with a median duration of vasospastic symptoms of 60 [IQR: 3-120] months) were compared against 125 controls. In both groups, nailfold capillaroscopy was performed to record the presence of dilatations, capillary edema, tortuous capillaries, ramifications, hemorrhages, and reduced capillary density and to determine a semiquantitative rating score. Further, the capacity of finger skin rewarming was investigated by performing infrared thermography in combination with cold provocation. Unspecific morphologic alterations were found in both, PRP, such as controls, whereby the risk for PRP was four times as high in the presence of capillary dilations (CI: 2.3-7.6) and five times as high if capillary density was reduced (CI: 1.9-13.5). Capillary density correlated with thermoregulatory capacity in both hands in the PRP group, but not in controls. In addition, a negative correlation between the microangiopathy score and the percentage degree of rewarming in both hands was found for patients with PRP only. We found specific differences within the microvascular architecture between patients with PRP and controls. As a conclusion, PRP may not be an entirely benign vasospastic phenomenon, but might be associated with subtle microcirculatory vasculopathy. In addition, we suggest that the implementation of a scoring system might serve as guidance in the diagnostic process at least of patients with long-standing PRP.

Living on the edge: thermoregulation at the niche margin in the Bedriaga’s rock lizard

Abstract Thermoregulation is essential for ectotherms but its relative cost, especially under ongoing climate change, depends on the thermal quality of habitats. Populations at the warm margin of a thermal niche could be negatively affected by environmental temperatures that approach the limits of a species’ thermoregulation capacity. This study aims to define the thermal niche of the Bedriaga’s rock lizard, Archaeolacerta bedriagae, a rock-dwelling species endemic to the Corsica and Sardinia islands (western Mediterranean Sea), and to investigate its thermoregulation effectiveness at the warm edge of its niche. We collected data on climate, body temperature, and microhabitat temperature throughout the species’ range to characterize its thermal niche. We found that A. bedriagae does not occupy the entire climatic space available across its distribution range; rather, it selects temperate climates. Remarkably, thermoregulation effort increases when the habitat thermal quality decreases towards warmer sites. Populations at the warm edge of the thermal niche show the best thermoregulation effectiveness, but they are also more sensitive to the effects of climate change as they may already be at (or beyond) the species’ maximum thermal capacity under the current conditions. We observed such a pattern at the extreme hot side of the thermal niche. This study provides key information on the thermoregulatory response of A. bedriagae to ongoing climate change that can be useful to identify populations facing a higher extinction risk either currently or in the near future.

Climate change and depressive disorders in middle-aged and older people in China: A quasi-experimental study

Global climate change has been increasingly recognized as one of the most significant threats to global health, including mental health. Although many studies have explored the link between mental health problems and climate change, the findings are inconclusive, especially regarding the effect on depressive disorders. A possible limitation is the lack of comprehensive assessment of climate change.This study aimed to comprehensively investigate the effects of temperature-related consequences of climate change (including changes in average temperature, temperature variability, heat waves, cold spells, and hot nights) on depressive disorders among middle-aged and older people who are more vulnerable to climate change because of their reduced thermoregulation capacity with aging. Our findings suggest that both hot nights and cold spells significantly exacerbate depressive disorders (hot nights: Excess Risk (ER) = 9.60% (95%CI: 1.59%, 18.24%); cold spells: ER = 3.63% (95%CI: 0.77%, 6.57%)). However, we did not find sufficient evidence to support the effect of average temperature, temperature variability, and heat waves on depressive disorders among middle-aged and older people in China. To conclude, depressive disorders was sensitive to extreme hot at night and cold. The government should propose some measures to mitigate the impact of extreme temperature events, such as launching campaigns to promote air conditioning in rural areas where the penetration rate of air conditioning is low.

Heritable variation in thermal profiles is associated with reproductive success in the world's largest bird.

Organisms inhabiting extreme thermal environments, such as desert birds, have evolved spectacular adaptations to thermoregulate during hot and cold conditions. However, our knowledge of selection for thermoregulation and the potential for evolutionary responses is limited, particularly for large organisms experiencing extreme temperature fluctuations. Here we use thermal imaging to quantify selection and genetic variation in thermoregulation in ostriches (Struthio camelus), the world's largest bird species that is experiencing increasingly volatile temperatures. We found that females who are better at regulating their head temperatures ("thermoregulatory capacity") had higher egg-laying rates under hotter conditions. Thermoregulatory capacity was both heritable and showed signatures of local adaptation: females originating from more unpredictable climates were better at regulating their head temperatures in response to temperature fluctuations. Together these results reveal that past and present evolutionary processes have shaped genetic variation in thermoregulatory capacity, which appears to protect critical organs, such as the brain, from extreme temperatures during reproduction.

Day-flying lepidoptera larvae have a poorer ability to thermoregulate than adults.

Changes to ambient temperatures under climate change may detrimentally impact small ectotherms that rely on their environment for thermoregulation; however, there is currently a limited understanding of insect larval thermoregulation. As holometabolous insects, Lepidoptera differ in morphology, ecology and behaviour across the life cycle, and so it is likely that adults and larvae differ in their capacity to thermoregulate. In this study, we investigated the thermoregulatory capacity (buffering ability) of 14 species of day-flying Lepidoptera, whether this is influenced by body length or gregariousness, and whether it differs between adult and larval life stages. We also investigated what thermoregulation mechanisms are used: microclimate selection (choosing locations with a particular temperature) or behavioural thermoregulation (controlling temperature through other means, such as basking). We found that Lepidoptera larvae differ in their buffering ability between species and body lengths, but gregariousness did not influence buffering ability. Larvae are worse at buffering themselves against changes in air temperature than adults. Therefore Lepidoptera may be more vulnerable to adverse temperature conditions during their larval life stage. Adults and larvae rely on different thermoregulatory mechanisms; adults primarily use behavioural thermoregulation, whereas larvae use microclimate selection. This implies that larvae are highly dependent on the area around their foodplant for effective thermoregulation. These findings have implications for the management of land and species, for example, highlighting the importance of creating and preserving microclimates and vegetation complexity surrounding Lepidoptera foodplants for larval thermoregulation under future climate change.

Establishing resilience in times of climate change—a perspective on humans and buildings

With a contribution of 40% to the annual global CO2-emissions, the built environment needs to drastically reduce its impact, while also providing pleasant and healthy indoor spaces and protecting people from weather extremes. Over time, particularly in western and industrialized countries, buildings have evolved to shield occupants almost completely from outdoor conditions. As a consequence, humans have become so used to a constant, comfortable indoor environment that we struggle to cope with thermal fluctuations. The time has come to shift perspective, as the very protective character of buildings and provision of omnipresent comfort are neither feasible nor desirable any longer. An enormous amount of energy and resources are spent to provide tightly controlled thermal environments, often with the same target temperature all year round. However, being mostly exposed to constant, comfortable indoor temperatures can have negative impacts on health and deteriorate our human capability to deal with thermal challenges. Importantly, spending time outside the thermal comfort zone is known to enhance human thermoregulatory capacities and thermal resilience, while also improving metabolic and cardiovascular health. This perspective essay aims to draw attention to novel and yet underrepresented avenues of coping with climate challenges, both with respect to the built environment and humans. Allowing more thermal variation indoors will save precious resources, decrease the negative impact of building CO2-footprints, and stimulate physiological and psychological adaptation in humans, which can lead to improved resilience and health.

Transcriptomic Response of Differentiating Porcine Myotubes to Thermal Stress and Donor Piglet Age.

Climate change is a current concern that directly and indirectly affects agriculture, especially the livestock sector. Neonatal piglets have a limited thermoregulatory capacity and are particularly stressed by ambient temperatures outside their optimal physiological range, which has a major impact on their survival rate. In this study, we focused on the effects of thermal stress (35 °C, 39 °C, and 41 °C compared to 37 °C) on differentiating myotubes derived from the satellite cells of Musculus rhomboideus, isolated from two different developmental stages of thermolabile 5-day-old (p5) and thermostable 20-day-old piglets (p20). Analysis revealed statistically significant differential expression genes (DEGs) between the different cultivation temperatures, with a higher number of genes responding to cold treatment. These DEGs were involved in the macromolecule degradation and actin kinase cytoskeleton categories and were observed at lower temperatures (35 °C), whereas at higher temperatures (39 °C and 41 °C), the protein transport system, endoplasmic reticulum system, and ATP activity were more pronounced. Gene expression profiling of HSP and RBM gene families, which are commonly associated with cold and heat responses, exhibited a pattern dependent on temperature variability. Moreover, thermal stress exhibited an inhibitory effect on cell cycle, with a more pronounced downregulation during cold stress driven by ADGR genes. Additionally, our analysis revealed DEGs from donors with an undeveloped thermoregulation capacity (p5) and those with a fully developed thermoregulation capacity (p20) under various cultivation temperature. The highest number of DEGs and significant GO terms was observed under temperatures of 35 °C and 37 °C. In particular, under 35 °C, the DEGs were enriched in insulin, thyroid hormone, and calcium signaling pathways. This result suggests that the different thermoregulatory capacities of the donor piglets determined the ability of the primary muscle cell culture to differentiate into myotubes at different temperatures. This work sheds new light on the underlying molecular mechanisms that govern piglet differentiating myotube response to thermal stress and can be leveraged to develop effective thermal management strategies to enhance skeletal muscle growth.

Novel Technological Advances to Protect People Who Exercise or Work in Thermally Stressful Conditions: A Transition to More Personalized Guidelines

Background: Prevention plays a key role in ensuring health and safety and is particularly important in scenarios when life is threatened. Adverse thermal conditions are experienced by billions of people daily, affecting the human capacity for thermoregulation and increasing the risks of life-threatening accidents, diseases, and fatalities. The aim of this study was to develop and validate a new, freely accessible method that will ultimately allow health, as well as exercise and labour organizations, to predict and potentially mitigate the physiological strain experienced by people who exercise or work in thermally stressful environmental conditions. Methods: First, we used concurrent technological advances and thermophysiological modelling to (i) develop a mobile phone application that predicts the physiological heat strain experienced by individuals conducting physical activity in adverse environmental conditions, and (ii) provide them with individualized heat mitigation strategies. Second, to examine the construct validity of the newly developed mobile phone application, core body temperature was recorded using gastrointestinal thermometry in 37 healthy soldiers during different activities. These data were used to examine the predictive capacity of our application in pre-classifying individuals with an increased risk of experiencing elevated physiological heat strain during work based on the guidelines (core body temperature ≥ 38 °C) of the World Health Organization. Results: The core body temperature predictions made by the mobile phone application were positively related (r = 0.57, p < 0.05) with the actual physiological measurements taken by our participants (mean absolute error: 0.28 °C). More importantly, our application correctly predicted 93% of occurrences of elevated physiological heat strain and 90% of those that were not (overall accuracy: 92%). Conclusions: Mobile phone applications integrating thermophysiological models can predict the physiological heat strain experienced by an individual, but it remains to be studied whether the suggested heat mitigation strategies can reduce or prevent adverse impacts.

Measuring Brain Temperature in Youth Bipolar Disorder Using a Novel Magnetic Resonance Imaging Approach: A Proof-of-concept Study.

There is evidence of alterations in mitochondrial energy metabolism and cerebral blood flow (CBF) in adults and youth with bipolar disorder (BD). Brain thermoregulation is based on the balance of heat-producing metabolism and heat-dissipating mechanisms, including CBF. To examine brain temperature, and its relation to CBF, in relation to BD and mood symptom severity in youth. This study included 25 youth participants (age 17.4 ± 1.7 years; 13 BD, 12 control group (CG)). Magnetic resonance spectroscopy data were acquired to obtain brain temperature in the left anterior cingulate cortex (ACC) and the left precuneus. Regional estimates of CBF were provided by arterial spin labeling imaging. Analyses used general linear regression models, covarying for age, sex, and psychiatric medications. Brain temperature was significantly higher in BD compared to CG in the precuneus. A higher ratio of brain temperature to CBF was significantly associated with greater depression symptom severity in both the ACC and precuneus within BD. Analyses examining the relationship of brain temperature or CBF with depression severity score did not reveal any significant finding in the ACC or the precuneus. The current study provides preliminary evidence of increased brain temperature in youth with BD, in whom reduced thermoregulatory capacity is putatively associated with depression symptom severity. Evaluation of brain temperature and CBF in conjunction may provide valuable insight beyond what can be gleaned by either metric alone. Larger prospective studies are warranted to further evaluate brain temperature and its association with CBF concerning BD.

Thermoregulatory capacity of goat kids from birth to weaning in a dry hot climate.

This study aimed to evaluate the thermoregulatory capacity and performance of Saanen goat kids from birth to weaning in a hot climate. Twelve newborn males and female goat kids with an initial body weight of 4.17 ± 0.81 kg were used. Physiological responses, climatic variables, and biometric traits data were collected. Univariate and multivariate analysis techniques were used. Heart rate (HR) was high up to the 6th week of life, with a reduction from the 7th week on (P < 0.001). Rectal temperature (RT) was lower in the first 2 weeks (P < 0.001), with an increase and stabilization occurring in the 7th and 8th weeks. Coat surface temperature (ST) was more activated from the 5th week onwards (P < 0.001). Body weight (BW) and withers height (WH) were higher in later weeks of the calving phase with a linear effect (P < 0.001). The first principal component demonstrated the relationship of sensible heat dissipation × body area of the goat kids; the second component shows the relationship of meteorological data with RT, having a positive relationship between RT with RH and negative with AT, and the third component points to the association of RR and HR. Of the animals, 81.3% were correctly classified in their group of origin in discriminant canonical analysis, with emphasis on the classification of the kids in the 1st-2nd and 3rd-4th weeks (classification percentage Ʃ = 95.8%). It is concluded that (i) newborn kids activate latent mechanisms to maintain their homoeothermic during the first 2 weeks of life, and as they grow, they use sensitive heat loss processes, especially from the 5th week of life onwards and (ii) male and female goats do not show sexual dimorphism effect on body performance and body morphometric measurements up to 60 days of life.

84 Puerto Rican Slick-Haired Holstein Cattle Exhibit Enhanced Mammary Gland Hemodynamics Compared with Their Wild-Type Haired Counterparts

Abstract A mutation of the prolactin receptor gene (PRLR) results in cattle with short and sleek hair coat and superior thermoregulatory capacity when exposed to heat stress conditions. This mutation, which is present in Puerto Rican Holstein cattle (SLICK) results in decreased vaginal temperatures and increased milk yield (MY) compared with wild-type haired Holstein cattle (WT) under tropical conditions. The superior performance of SLICK Holstein cows has been considered multifactorial in nature and physiological differences between genotypes still need to be elucidated. Thereby, the objective was to compare the mammary gland hemodynamics and udder skin temperature between SLICK (n = 7) and WT (n = 7) Holstein cows during the summer as possible contributors to such physiological differences. Animals were selected for differences in MY (23.77±1.24 vs.19.74±1.24 kg, SLICK vs. WT, respectively; P = 0.041) and stratified by body weight (BW), lactation number, and days in milk (DIM). At 160±3 DIM, left and right pudendoepigastric arteries were assessed transrectally via Doppler ultrasonography and the udder skin temperature was determined using a thermal camera. Data were analyzed by one-way ANOVA using the MIXED procedure of SAS with resistance index (RI), pulsatility index (PI), diameter, total mammary blood flow (MBF), MBF relative to BW, and udder skin temperature as dependent variables and hair coat as the independent variable. The CORR procedure of SAS was used to determine the correlation between MY and MBF. Statistical significance was declared at P ≤ 0.05 and tendencies were established at 0.05 ≤ P ≤ 0.10. The RI was less (P = 0.045) in SLICK Holsteins (0.56 ± 0.02) than WT (0.64 ± 0.02). The PI tended (P = 0.0589) to be less in SLICK Holsteins (0.94±0.07) compared with WT (1.15 ± 0.07). The average diameter of the left and right pudendoepigastric arteries was greater in the SLICK animals compared with WT (1.31 ± 0.07 vs..08±0.07 cm, respectively; P = 0.038). Total MBF was increased in SLICK cattle compared with WT (9.03 ± 1.11 vs. 5.14 ± 1.11 L/min; P = 0.0291). There was a tendency (P = 0.0577) for the MBF relative to BW to be greater in the SLICK Holsteins compared with the WT (16.75 ± 2.14 vs.0.38 ± 2.14 mL/min*kg). No differences were observed in udder skin temperature between SLICK and WT Holsteins (P ≥ 0.05). Lastly, a tendency for a positive correlation between MY and MBF was observed (r = 0.51, P = 0.066). In the current study, SLICK Holsteins had enhanced blood supply to the mammary gland which is indicative of greater amount of oxygen and nutrients available for milk synthesis. Therefore, the gene introgression of the PRLR mutation to a dairy herd may result in animals with superior physiological performance during heat stress conditions preventing economical losses in the dairy industry.

87 Milk Yield, Vaginal Temperature, and Solar Radiation Exposure in Slick and Wild Type-Haired Puerto Rican Holstein Cows

Abstract As heat stress limits dairy cattle performance in the tropics, selection for heat resistant cattle has been proposed as a possible alternative for these countries. Such cattle should be able to regulate their body temperature efficiently so grazing activity is not compromised by environmental conditions. This is particularly important for Puerto Rico’s dairy industry, which depends on grazing as the principal or unique source of dietary fiber. Even though Puerto Rican slick-haired dairy cattle (SLICK) have been associated with superior thermoregulation, empirical data about their capacity to withstand greater solar radiation exposure while maintaining lower body temperature is scarce. The current study aimed to compare the vaginal temperature, solar radiation exposure, and milk yield between SLICK and wild type-haired (WT) cows. Evaluated groups were balanced for lactation number (P = 0.8101) and days in milk (DIM: P = 0.9619). Eight SLICK (2.00 ± 0.33 lactations and 160.33 ± 11.39 DIM) and 8 WT Holstein cows (1.89 ± 0.31 lactations and 159.44 ± 14.34 DIM) were compared. Initially, experimental groups were selected visually, then a genomic test confirmed each the hair coat type of each cow. Vaginal temperature was recorded by means of a HOBO TidbiT v2 Water Temperature datalogger secured to a blank CIDR. Light intensity exposure was recorded using a HOBO Pendant MX Temperature / Light datalogger secured to the top of a neck collar, as an index of solar radiation exposure (previously validated by our group). Data were recorded in each cow every 15 seconds for 48 consecutive hours (August 4-5, 2022) and averaged by hour for statistical analysis using the GLIMMIX Procedure of SAS. The week before the study SLICK cows showed greater milk yields than their WT counterparts (20.76 ± 0.55 vs.8.60 ± 0.56 kg/d; P = 0.0073). No time by hair coat type interaction was observed for vaginal temperatures (P = 0.1396). However, time (P &amp;lt; 0.0001) and hair coat type (P = 0.0042) affected vaginal temperature. The SLICK cows presented lower vaginal temperatures than their WT counterparts, with daily averages of 39.08 ± 0.09 and 39.45 ± 0.10°C, respectively. A time by hair coat type interaction (P = 0.0293) was observed for the light intensity exposure of the cows. The SLICK cows had greater light intensity exposure than their WT counterparts at 1,000 h (15,467.00 ± 1,584.92 vs.10,057.00 ± 787.35 lx; P &amp;lt; 0.0001), 1,100 h (12,028 ± 1,660 vs. 8,571.11 ± 888.13 lx; P = 0.0078), and 1,200 h (13,191.00 ± 2,188.86 vs.10,923.00 ± 1,904.31 lx; P = 0.0801). No other differences in light intensity exposure were observed. Slick-haired cows were able to maintain a lower daily vaginal temperature, even with a greater exposure to direct solar radiation, further suggesting a superior thermoregulatory capacity. Concurrently, a greater milk production was observed in the slick-haired group. Future studies should evaluate grazing activity under direct solar radiation exposure in both hair coat groups.

Physiological and behavioral responses of northern elephant seals (Mirounga angustirostris) to global change among three northern California rookeries

The California coast provides a unique study system for investigating the effects of warming and habitat quality on the thermoregulatory capacity of the northern elephant seal (NES). In California, island rookeries such as the offshore site at the Farallon Islands National Wildlife Refuge are experiencing habitat loss and reduced suitable haul-out surfaces due to erosion from storm events. Extreme weather events are increasing in frequency and severity with global change. Semi-aquatic animals face a unique thermal challenge. They possess adaptations to conserve heat when immersed in cold water during deep dives but must compensate for such heat-conserving properties of their physiology when transitioning to heat exposure on land. Therefore, these animals must precisely thermoregulate with physiological and behavioral adjustments across a broad thermal range. We investigated how environmental variables affect seal thermoregulation at three northern California rookeries, the southeast Farallon Island (SEFI), Point Reyes National Seashore (PORE) and Año Nuevo State Park (ANSP). Infrared thermography was used to determine seal skin surface temperature and weather data was collected at each site. We found that average surface temperature increases with solar radiation, maximum surface temperature decreases with increasing wind speed, and thermal window area percentage decreases with relative humidity and increases with ambient temperature. Climatic variation may present physiological and behavioral challenges for marine mammals that experience significant life-history stages on land. Such ongoing findings will be fundamental in predicting climate change vulnerabilities and will be critical in mitigating the impacts of anthropogenic warming and promoting resilience in these populations. Carol Baird Graduate Student Award for Field Research; The Neubacher Fund for Marine Science at Point Reyes National Seashore. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Heat Stress-Induced Intestinal Barrier Impairment: Current Insights into the Aspects of Oxidative Stress and Endoplasmic Reticulum Stress.

Heat stress (HS) occurs when the sensible temperature of animals exceeds their thermoregulatory capacity, a condition that exerts a detrimental impact on health and growth. The intestinal tract, as a highly sensitive organ, has been shown to respond to HS by exhibiting mucosal injury, intestinal leakage, and disturbances in the gut microbiota. Oxidative stress and endoplasmic reticulum stress (ERS) are both potential outcomes of long-term exposure to high temperatures and have been linked to apoptosis, autophagy, and ferroptosis. In addition, HS alters the composition of the gut microbiota accompanied by changed levels of bacterial components and metabolites, rendering the gut more vulnerable to stress-related injury. In this review, we present recent advances in mechanisms of oxidative stress-associated ERS in response to HS, which is destructive to intestinal barrier integrity. The involvement of autophagy and ferroptosis in ERS was highlighted. Further, we summarize the relevant findings regarding the engagement of gut microbiota-derived components and metabolites in modulation of intestinal mucosal injury induced by HS.

Seasonality of pollinators in montane habitats: Cool‐blooded bees for early‐blooming plants

AbstractUnderstanding the factors that drive community‐wide assembly of plant‐pollinator systems along environmental gradients has considerable evolutionary, ecological, and applied significance. Variation in thermal environments combined with intrinsic differences among pollinators in thermal biology have been proposed as drivers of community‐wide pollinator gradients, but this suggestion remains largely speculative. We test the hypothesis that seasonality in bee pollinator composition in Mediterranean montane habitats of southeastern Spain, which largely reflects the prevalence during the early flowering season of mining bees (Andrena), is a consequence of the latter's thermal biology. Quantitative information on seasonality of Andrena bees in the whole plant community (275 plant species) and their thermal microenvironment was combined with field and laboratory data on key aspects of the thermal biology of 30 species of Andrena (endothermic ability, warming constant, relationships of body temperature with ambient and operative temperatures). Andrena bees were a conspicuous, albeit strongly seasonal component of the pollinator assemblage of the regional plant community, visiting flowers of 153 different plant species (57% of total). The proportion of Andrena relative to all bees reached a maximum among plant species which flowered in late winter and early spring, and declined precipitously from May onward. Andrena were recorded only during the cooler segment of the annual range of air temperatures experienced at flowers by the whole bee assemblage. These patterns can be explained by features of Andrena's thermal biology: null to weak endothermy; ability to forage at much lower body temperature than strongly endothermic bees (difference ~ 10°C); low upper tolerable limit of body temperature, beyond which thermal stress presumably precluded foraging at the warmest period of year; weak thermoregulatory capacity; and high warming constant enhancing ectothermic warming. Our results demonstrate the importance of lineage‐specific pollinator traits as drivers of seasonality in community‐wide pollinator composition; show that exploitation of cooler microclimates by bees does not require strong endothermy; and suggest that intense endothermy and precise thermoregulation probably apply to a minority of bees. Medium‐ and large‐sized bees with low upper thermal limits and weak thermoregulatory ability can actually be more adversely affected by climate warming than large, hot‐blooded, extremely endothermic species.

A data-intensive documentation of plant ecosystem thermoregulation across spatial and temporal scales.

This article is a Commentary on Guo et al. (2023), 238: 1004–1018.

Seasonal variation in thermoregulatory capacity of three closely related Afrotropical Estrildid finches introduced to Europe

A species' potential geographical range is largely determined by how the species responds physiologically to its changing environment. It is therefore crucial to study the physiological mechanisms that species use to maintain their homeothermy in order to address biodiversity conservation challenges, such as the success of invasions of introduced species. The common waxbill Estrilda astrild, the orange-cheeked waxbill E. melpoda, and the black-rumped waxbill E. troglodytes are small Afrotropical passerines that have established invasive populations in regions where the climate is colder than in their native ranges. As a result, they are highly suitable species for studying potential mechanisms for coping with a colder and more variable climate. Here, we investigated the magnitude and direction of seasonal variation in their thermoregulatory traits, such as basal (BMR), summit (Msum) metabolic rates and thermal conductance. We found that, from summer to autumn, their ability to resist colder temperatures increased. This was not related to larger body masses or higher BMR and Msum, but instead, species downregulated BMR and Msum toward the colder season, suggesting energy conservation mechanisms to increase winter survival. BMR and Msum were most strongly correlated with temperature variation in the week preceding the measurements. Common waxbill and black-rumped waxbill, whose native ranges encompass the highest degree of seasonality, showed the most flexibility in metabolic rates (i.e., stronger downregulation toward colder seasons). This ability to adjust thermoregulatory traits, combined with increased cold tolerance, may facilitate their establishment in areas characterized by colder winters and less predictable climates.

High or hot-Perspectives on altitude camps and heat-acclimation training as preparation for prolonged stage races.

Adaptation to heat stress and hypoxia are relevant for athletes participating in Tour de France or similar cycling races taking place during the summertime in landscapes with varying altitude. Both to minimize detrimental performance effects associated with arterial desaturation occurring at moderate altitudes in elite athletes, respectively, reduce the risk of hyperthermia on hot days, but also as a pre-competition acclimatization strategy to boost blood volume in already highly adapted athletes. The hematological adaptations require weeks of exposure to manifest, but are attractive as an augmented hemoglobin mass may improve arterial oxygen delivery and hence benefit prolonged performances. Altitude training camps have in this context a long history in exercise physiology and are still common practice in elite cycling. However, heat-acclimation training provides an attractive alternative for some athletes either as a stand-alone approach or in combination with altitude. The present paper provides an update and practical perspectives on the potential to utilize hypoxia and heat exposure to optimize hematological adaptations. Furthermore, we will consider temporal aspects both in terms of onset and decay of the adaptations relevant for improved thermoregulatory capacity and respiratory adaptations to abate arterial desaturation during altitude exposure. From focus on involved physiological mechanisms, time course, and responsiveness in elite athletes, we will provide guidance based on our experience from practical implementation in cyclists preparing for prolonged stage races such as the Tour de France.