Ectotherm reproduction is vulnerable to acute heat stress, yet the longitudinal impacts of transient thermal events on male reproduction remain poorly understood. Using the stored-product pest Plodia interpunctella, a sperm-heteromorphic moth, we investigated how acute thermal stress (4 h at 40°C) impacts males' lifetime reproductive resource allocation and offspring fitness. Heat-exposed adult males and controls (26°C) were paired daily with non-stressed females. We found that transient heat stress did not significantly impact pre-courtship duration, courtship duration, copulation latency, longevity, or lifetime mating frequency, nor did it alter offspring developmental duration. Total offspring production and lifetime eupyrene (fertile) sperm transfer also remained unaffected. However, heat-exposed males exhibited a massive hyper-allocation of non-fertilising sperm, ejaculating 53.4% more apyrene sperm at a 56.8% faster rate, increasing lifetime apyrene production by 41.0%. This hyper-allocation suggests that non-fertilising apyrene sperm act as a critical compensatory mechanism, buffering eupyrene sperm to maintain intact reproductive output following severe thermal stress. Although male reproductive performance proved resilient, we observed a subtle inter-generational cost: a 3.5% reduction in male offspring body weight. Our findings highlight a novel, potential adaptive role for sperm heteromorphism, demonstrating that sperm-heteromorphic insects can leverage plastic, morph-specific ejaculate tailoring to safeguard fertility against acute thermal extremes.
Extreme temperatures can compromise reproduction in viviparous reptiles. We evaluated whether thermal stress affects male reproductive traits in Barisia imbricata, a eurythermic and cryophilic high-elevation lizard. Males were exposed for 12 h per day during 7 days to low (10 °C) or high (35 °C) temperatures, and testicular histology, gonadosomatic and epididymosomatic indices, circulating testosterone concentrations, and sperm performance were assessed. Sperm progressive motility was additionally evaluated over a 12-h incubation period at five temperatures (5, 10, 26, 35, and 38 °C). Both low and high treatments reduced gonadosomatic and epididymosomatic indices. Histological analyses revealed largely preserved seminiferous tubule organization, with mild epithelial alterations at low temperature and greater disorganization at high temperature, but without complete structural damage. Testosterone concentrations decreased under low-temperature exposure but remained similar to controls at high temperature. Sperm progressive motility remained detectable throughout the 12-h experimental period at low temperatures (5 to 10 °C), whereas exposure to warmer temperatures (26 to 38 °C) caused a rapid decline in sperm motility, with complete immobility occurring fastest at 38 °C. These results indicate that B. imbricata shows considerable reproductive tolerance to thermal extremes, although warmer temperatures constrain sperm performance. Our findings partially support the proposed hypothesis by demonstrating that short-term thermal sensitivity varies among reproductive traits, with testicular structure remaining largely preserved despite mild histological alterations, whereas sperm performance showed greater vulnerability to warming. These findings highlight the importance of reproductive thermal physiology in understanding reptile vulnerability under climate warming.
Understanding how shallow marine species cope with ocean warming is essential for developing climate-smart conservation strategies. Realistic projections require detailed knowledge of thermal limits across life stages, since these can vary with development, sex and reproductive status. However, most thermal tolerance studies focus exclusively on adults, potentially underestimating species vulnerability. To address this gap, we examined the thermal tolerance of the ditch shrimp Palaemon varians, across its full life cycle through a Critical Thermal maximum (CTmax) experiment, integrating different developmental stages (Zoea 1-5, Postlarvae and Adult), while accounting for sex (Males vs. Females), and female reproductive status (Ovigerous, Spent and Immature). Early larval stages (Zoea 1- 3) exhibited lower CTmax (36.7, 37.1 and 36.8 °C, respectively) than later stages (Zoea 4- 5, Postlarvae and Adults), with Postlarvae (37.9 °C) showing the highest values. Larval development represents a bottleneck for this species' thermal tolerance. The largest increase was observed after the transition from larval life to the postlarvae stage (1.9 %), indicating that this life stage represents a physiological milestone in the acquisition of thermal tolerance in this species. Females were generally more sensitive to heat than males (37.7 °C), with those that had released their larvae recently (spent females 37.2 °C), showing the lowest CTmax values, indicating a potential energetic cost associated with reproduction. Overall, our findings show that focusing solely on adult thermal limits overlooks key vulnerabilities across development and reproduction. Integrating these factors provides a more realistic assessment of shallow-water species’ tolerance to global warming.
The influence of skin wettedness on thermal behavior responses during exercise was investigated under different ambient temperature and relative humidity at a fixed vapor pressure of 2.69 kPa (E1: 35.0°C, 48% relative humidity; E2: 31.0°C, 60% relative humidity; E3: 25.0°C, 85% relative humidity) in tropical natives. Eleven physically active, heat-acclimated males completed three trials: 15 min passive exposure before exercise, 45 min cycling at 60% V˙ O2peak and 15 min of passive exposure after exercise, with voluntary fan use to maintain thermal comfort. The results indicated that mean skin wettedness was significantly lower in E1 vs. E2 and E3 (0.68 ± 0.05 a.u. vs. 0.76 ± 0.06 and 0.88 ± 0.05 a.u., respectively, all P < 0.05) at the end of exercise. Despite these differences, no participants used the fan in any of the trials (P = 1.000). Rectal and mean skin temperatures were significantly higher in E1 and E2 compared to E3 at the end of exercise (all P < 0.05). Regarding sudomotor responses, forearm sweat rate was higher in E1 and E2 compared to E3 throughout the exercise, whereas forehead sweat rate was significantly higher in E1 than E3 at 45 min (P < 0.05). In contrast, no differences were observed in skin blood flow between environments at 45 min (P > 0.05). These findings indicated that behavioral thermal effectors were not recruited despite greater sudomotor responses, suggesting that tropical natives maintained their thermal perception via effective autonomic effector activation rather than relying on thermoregulatory behavior.
Chronic heat stress (HS) impairs intestinal barrier function and microbiota homeostasis. Taurine, a functional amino acid, is well characterized by anti-oxidation, anti-inflammation and cytoprotection. However, whether taurine can maintain intestinal barrier integrity and microbiota under chronic HS remains unknown. Mice (6-week-old; C57BL/6; Male) were randomly assigned one of three groups including a control group (CON, 23°C), a heat stress group (HS, 42°C), or a heat stress + taurine group (HT, received 0.5% taurine in drinking water under HS condition). This study investigated the effects of taurine supplementation on intestinal morphology, barrier function, endoplasmic reticulum stress (ERS), apoptosis, and gut microbiota in heat-stressed mice. Taurine supplementation contributed to decreased rectal temperature and body weight loss in heat-stressed mice. Taurine improved intestinal morphology as demonstrated by elevated villus height in HT group compared to HS group. HS-induced intestinal permeability indicative of increased d-lactate was inhibited by upregulating ZO-1 expression in mice administrated by Taurine. Supplementary taurine normalized the expression of endoplasmic reticulum (ER) stress proteins (BIP, IRE1α, XBP-1, CHOP) as well as proapoptotic proteins (BAX, Cytc, and Active-caspase 3) in HT mice. Taurine intervention resulted in expansion of taurine-utilizing Desulfovibrio in HT mice. Moreover, taurine supplementation enhanced enrichment of SCFA-producing microbiota such as Bifidobacterium, Dubosiella, and Faecalibaculum in heat-stressed mice. Collectively, these results suggested that taurine could attenuate HS-induced intestinal barrier dysfunction via reversing ER stress-mediated apoptosis and gut microbial dysbiosis, suggesting taurine as a promising dietary additive against the intestinal injury induced by HS in mice.
Twaite shad (Alosa fallax) is a protected anadromous fish of European estuaries with regionally threatened populations, yet temperature requirements for embryo and early larval development remain poorly resolved. We present new experimental data on embryonic and yolk-sac larval temperature sensitivity of A. fallax from the Elbe River and complement these results with a structured literature compilation of life-stage-specific thermal windows across A. fallax and five congeneric Alosa species (A. alosa, A. sapidissima, A. pseudoharengus, A. aestivalis, A. mediocris). Development of A. fallax embryos was examined across a controlled temperature gradient (9.7-26.1°C) spanning and extending spawning-season conditions. Embryos hatched successfully between 12.1 and 26.1°C, with an optimum range for hatching success of 13.9-22.4°C. Embryonic development rate increased exponentially with temperature, corresponding to an apparent activation energy of 0.46 eV and a Q10 of 1.9. Warmer incubation produced larger larvae at hatch with reduced yolk reserves, but these larvae reached a smaller size at 90% yolk depletion than larvae reared at colder temperatures. Integrating daily growth rate and yolk consumption indicated an upper threshold for post-hatch yolk utilization efficiency (YUEDay) at 24.2°C. The thermal windows of A. fallax embryos and yolk-sac larvae were broadly consistent with stage-specific data from other Alosa species in Europe and North America, supporting the pattern that thermal windows shift toward warmer conditions and broaden during ontogeny. Together, the experimental data and genus-level compilation provide a basis for assessing spawning and nursery habitat suitability and incorporating climate risks into conservation planning for vulnerable anadromous fishes.
Polar and sub-polar animals evolved to thrive in cold climates and may thus be particularly sensitive to rising temperatures associated with climate change. Penguins may be especially vulnerable, due to their dual habitat, alternating between foraging in cold waters and breeding/moulting on an increasingly warm land. Here, we characterized heat stress occurrence in breeding king penguins through behavioural observations (e.g. panting occurrence) and body temperature measurements. We observed that behavioural signs of heat stress are frequent in king penguins breeding in the sub-Antarctic region (> 20% of observations at mid-day), and that subcutaneous temperatures increase under high heat load, especially in penguins observed panting. Subcutaneous and core body temperatures were moderately correlated and both increased with heat load. Yet, their responses were not parallel since core body temperature is markedly less sensitive to heat load than subcutaneous temperature. Air temperature alone was a poor predictor of heat stress occurrence, whereas the combination of high solar radiation, low wind speed and high air temperatures provided the strongest predictive power. Finally, reproductive failures were more likely to occur on warmer days, suggesting that heat stress may have significant sublethal effects on adults that could ultimately affect population dynamics.
We studied the thermal ecology of the endemic skink, Trachylepis atlantica, and applied a physiologically-based mechanistic model to assess its vulnerability to climate change. We estimated thermal performance curves, thermal safety margins (TSM), and hours of activity restriction (Hr), while evaluating environmental thermal quality, body-temperature accuracy, and thermoregulatory effectiveness. Field body temperatures frequently exceeded both preferred and optimal temperatures for locomotor performance, while TSM s were negative, indicating that individuals already operate close to their physiological limits. The species exhibited low thermoregulatory accuracy, and available habitats were generally thermally suboptimal, suggesting limited opportunities for effective thermoregulation. Our projections indicate a severe increase in daily Hr by 2070, with environmental temperatures frequently surpassing physiological thresholds. Under these climate scenarios, the archipelago’s thermal landscape becomes increasingly unsuitable, significantly compressing the species' viable activity periods. Our findings demonstrate the value of integrating physiological mechanisms into climate-vulnerability assessments and highlight the urgent need for conservation measures, such as microclimatic buffering and habitat management, to safeguard this island-endemic species.
Environmental variability significantly influences parental care, likely because parental care can buffer nest survival against environmental variations, enabling those receiving greater parental care to tolerate a wider range of conditions. Under harsh conditions (e.g., high temperatures), this buffering effect may be reinforced through increased parental cooperation. Here, using data from a coastal and an inland site, we examined the effects of high ambient temperature (Ta) and wind, and their variability, on nest attendance and behavioural thermoregulation in Kentish plovers (Anarynchus alexandrinus). To quantify plover activity at their nests in relation to Ta, low-cost dataloggers were fully customised. A system was designed around a single board computer, connected to a webcam, a temperature sensor, and a clock module to synchronise timestamps when comparing results from dataloggers. In the Kentish plover, males typically incubate at night, whereas females incubate during the day; however, at elevated Ta, males also contribute to diurnal incubation. We found that at higher Ta, the plovers increased the frequency of heat-dissipating behaviours and switched incubation bouts between pair members more frequently. Wind speed additionally influenced the thermoregulatory behaviour of plovers, likely through convective cooling, thereby allowing longer periods of uniparental incubation. Furthermore, we show that at the same temperature, males exhibited higher nest attendance at the more variable inland site. Because this involvement exceeded that observed at the coastal site under equivalent temperatures, it may provide a safety margin against environmental variability. These findings support the hypothesis that environmental variability contributes to variations in parental cooperation during incubation.
The hard tick Haemaphysalis longicornis serves as a vector for multiple pathogens and can cause severe tick-borne diseases. Temperature is a key environmental factor influencing its population dynamics and disease transmission risk. As a crucial molecular mechanism underlying thermal adaptation, the upregulation of heat shock protein 70 (Hsp70) is generally regarded as an important adaptive response of organisms to heat stress. We systematically identified seven Hsp70s (designated as HlHsp70.1, HlHsp70.2, HlHsp70.3, HlHsp70.4, HlHsp70.5, HlHspa5, HlHspa9) in H. longicornis and comprehensively analyzed their physicochemical properties, phylogenetic relationships, and expression patterns. Quantitative real-time PCR results revealed that the expression patterns of HlHsp70s were significantly influenced by the duration and intensity of heat treatment. Under 35°C treatment, most HlHsp70 genes (except HlHspa9) were upregulated after 2 h. After 45°C treatment, most HlHsp70 genes reached their expression peaks within 1 h. Notably, HlHsp70.1, HlHsp70.2, and HlHsp70.3 exhibited particularly remarkable upregulation, with HlHsp70.2 showing a maximum increase of 1973.71-fold, while HlHspa9 expression remained unchanged. At 45°C, the mortality of H. longicornis was significantly increased after RNA interference of HlHsp70.1, HlHsp70.2, and HlHsp70.3 (p < 0.01). It indicates that HlHsp70.1, HlHsp70.2, and HlHsp70.3 play critical roles in the thermotolerance of H. longicornis. This study elucidates the important function of the Hsp70 gene family in the heat stress response of H. longicornis, providing a theoretical basis for understanding its environmental adaptation and exploring control strategies for tick-borne diseases.
Understanding how organisms respond to temperature variation has become central to ecology and evolution because of its role in shaping species' physiology, distribution, and ecological interactions. Thermal tolerances are critical for ectothermic organisms, which have evolved a variety of behavioral and physiological strategies to manage thermal stress that vary widely across geographic and temporal scales. This study synthesizes existing information on bees' critical thermal maximum (CTmax) and minimum (CTmin) through a systematic review of published data. Despite bees' ecological importance, research on such common metrics of thermal tolerance remains scarce, with fewer than 50 accumulated studies over the past 30 years and less than 1% of species represented. Data are biased to North America, especially the USA, Oceania and Europe, leaving vast regions unexplored. We found that CTmax was correlated with variables related to body size and ramping rates during measurement, but not with mean, maximum and minimum temperatures; CTmin correlated only with the coldest month's minimum temperature and mean annual temperature. These patterns underscore the role of local climate in shaping thermal adaptation. However, major knowledge gaps persist, limiting predictions of climate change impacts. We call for broader studies on intra-specific thermal tolerance variation across geography, life stages, and social traits to predict climate change impacts and guide bee conservation.
Accurate prediction of transient tissue temperature fields is important for understanding the thermal response of mild moxibustion and supporting treatment-parameter screening. In this study, a two-dimensional axisymmetric physics-informed neural network (PINN) model was developed to simulate bioheat transfer during mild moxibustion. The Pennes bioheat equation, layered tissue properties, and coupled radiation-convection boundary conditions at the skin surface were embedded into the loss function. Nine L9 (34) orthogonal cases were designed to evaluate the effects of moxa-burning temperature, moxa-stick diameter, moxibustion distance, and ambient temperature on the temperature response at a depth of 5 mm. The training processes showed stable convergence, and the average training time for a single parameter case was approximately 10 min. An additional confirmation case was compared with an independent COMSOL finite-element numerical benchmark at t = 1200 s. The mean absolute error, root-mean-square error, and maximum absolute error between the PINN and COMSOL temperature fields were 0.159, 0.299, and 2.723 °C, respectively. Range analysis showed that the influence of the four parameters followed the order of moxa-stick diameter > moxibustion distance > ambient temperature > moxa-burning temperature. The candidate parameter combination obtained under the present model conditions was 18 mm moxa-stick diameter, 25 mm moxibustion distance, 32 °C ambient temperature, and 650 °C moxa-burning temperature. These results suggest that the proposed PINN framework can provide a physics-constrained computational tool for temperature-field reconstruction and preliminary parameter screening in mild moxibustion, while further experimental and clinical validation remains necessary.
In this study, calorimetry was used to measure metabolic heat flow of diapausing larvae of the freeze-tolerant sugarbeet root maggot (SBRM), Tetanops myopaeformis, and of developing third-instar Drosophila melanogaster larvae. Counter to expectations for ectothermic animals, ramping the temperature down from a 4°C isotherm to a -12°C isotherm induced a significant increase in heat flow rate in diapausing SBRM. Likewise, isothermal calorimetry of Drosophila larvae found a significant increase in heat flow at 14°C as compared to 23°C. Stepping SBRM though a sequential series of isotherms from 4°C to -12°C revealed a significant dose response in the increased heat flow as temperatures decreased. The observed increase in heat flow for both species was independent of the atmospheric conditions (normoxia or anoxia) that they were exposed to during the calorimetry trials. Even more unexpected, there was no significant difference in the SBRM heat flow between frozen and non-frozen larvae at -12°C. These results suggest that calorimetry can detect metabolic activity not captured by respirometry in insects exposed to suboptimal temperatures. The observed cold-induced heat flows indicate that SBRM are capable of adaptive thermogenesis.
Military personnel and athletes increasingly use non-invasive methods to estimate body core temperature during heat acclimation. This study determined the responsiveness of the CALERA Research Sensor (CRS) to changes in resting and end-exercise body core temperature induced by heat acclimation as well as the criterion validity for determining the thermal dose, defined as time spent with a body core temperature ≥38.5 °C.Fifteen participants completed a nine-day controlled-hyperthermia heat acclimation protocol. Body core temperature was continuously monitored prior to and during heat exposures using both the CRS (Tcrs) and a rectal temperature (Tre) probe. This study assessed responsiveness and criterion validity using Bland-Altman analysis and intraclass correlation coefficients (ICC). Additionally, the analyses included a linear mixed model to further analyze responsiveness.Tcrs showed limited responsiveness to heat acclimation-induced changes in resting and end-exercise Tre with wide limits of agreement (±0.32 °C), proportional bias (indicating increasing underestimation with larger adaptations), and low ICC (≤0.18). Additionally, resting and end-exercise Tre decreased to a greater extent than Tcrs, which showed a downward trend during end-exercise over the nine-day heat acclimation (P < 0.001). The CRS showed limited criterion validity for estimating thermal dose, with wide limits of agreement (±20 min), proportional bias (indicating increasing underestimation at higher thermal doses), and low ICC of 0.35.These results indicate that the current version of the CRS underestimates both heat acclimation-induced changes in Tre and the thermal dose during controlled hyperthermia.
Although different studies are using ThermoHuman software to delimitate regions of interest (ROI) of lower limbs, no study has validated this automatic analysis. This work evaluated the level of agreement and time efficiency of the automated ThermoHuman software compared with manual determination of the regions of interest in assessing lower-limb skin temperature before and after exercise. Seventy-six thermographic images from 19 recreational runners (10 males, 9 females) were analyzed before and after a 10-km outdoor run. Automated analysis using ThermoHuman was compared with Manual analysis (ROI delineation based on general template) and Manual-TH (manual replication of the same ROI delimitations generated by ThermoHuman). Agreement was assessed using concordance correlation coefficients (CCC), mean absolute error (MAE), Bland-Altman analysis, and linear mixed models. High agreement was observed between methods, with CCC values ranging from 0.95 to 0.98 and MAE between 0.3 °C and 0.5 °C, and bias of 0.0 °C for all comparisons. Mixed-model analysis revealed no significant main effect of method. Additionally, the ROI selection criterion (Manual-TH vs. Manual) did not result in significant differences. Compared with Manual (13.9 h) and Manual-TH (28.7 h), ThermoHuman required substantially less time for image analysis (2.0 h), representing time savings of 85.6 % and 93 %, respectively. In conclusion, automated analysis using ThermoHuman showed high agreement with both manual approaches, including a higher time efficiency.
This study investigates whether salinity affects the upper thermal tolerance (CTmax) of the euryhaline mummichog (Fundulus heteroclitus). Mummichogs were acclimated to seawater (38 ppt, SW) or freshwater (<1 ppt, FW) at 18.5°C (Tacc), then transferred to the opposite salinity. CTmax and physiological profiles were assessed on days 0, 1, 3, 6, and 13 post-transfer. CTmax was consistently lower in FW than in SW, regardless of prior acclimation. Compared to the Tacc controls, CTmax exposure reduced plasma ion levels in FW-transferred fish and increased them in SW-transferred fish. In both salinities, CTmax exposure raised plasma cortisol, glucose, lactate, and hematocrit.Second-order Akaike Information Criterion (AICc) modeling identified the Salinity/Acclimation time interaction as the most parsimonious predictor of CTmax. Furthermore, multivariate analysis reveals that potential underlying mechanisms of thermal shock diverged by environment. In FW, CTmax progressively declined over time, constrained by a direct metabolic tax—the recruitment of high-overhead, residual (ouabain-insensitive) ATPase activity required to maintain ionic stability—alongside a unique stress-erythropoiesis response. Conversely, in SW, thermal performance improved over time and was tightly coupled to osmolality, glucose and cortisol. Additionally, lactate accumulation was a shared response across salinities. We conclude that the synergy of ion-poor environments and rising temperatures creates a unique performance trade-off that imposes a permanent thermal penalty, potentially increasing the climate vulnerability of estuarine populations beyond current ecological forecasts.
