Metabolism,thermoregulation and evaporative water loss in the Chaotung Vole (Eothenomys olitor) in Yunnan-Kweichow Plateau in summer

Proper adjustment of thermoregulatory mechanisms ensures the survival of mammals when they are subjected to seasonal changes in their natural environment. To understand the physiological and ecological adaptations of Eothenomys olitor, we measured their metabolic rate, thermal conductance, body temperature (T_b) and evaporative water loss at a temperature range of 5–30 °C in summer. The thermal neutral zone (TNZ) of E. olitor was 20–27.5 °C, and the mean body temperature was 35.81±0.15 °C. Basal metabolic rate (BMR) was 2.81±0.11 ml O₂/g h and mean minimum thermal conductance (C_m) was 0.18±0.01 ml O₂/g h °C. Evaporative water loss (EWL) in E. olitor increased when the ambient temperature increased. The maximal evaporative water loss was 6.74±0.19 mg H₂O/g h at 30 °C. These results indicated that E. olitor have relatively high BMR, low body temperature, low lower critical temperature, and normal thermal conductance. EWL plays an inportant role in temperature regulation. These characteristics are closely related to the living habitat of the species, and represent its adaptive strategy to the climate of the Yunnan-Kweichow Plateau, a low-latitude, high-altitude region where annual temperature fluctuations are small, but daily temperature fluctuations are greater.     

Change in the thermal biology of tadpoles of Odontophrynus occidentalis from the Monte desert, Argentina: Responses to photoperiod

We determined if the photoperiod regime affects the thermal biology of the tadpoles of Odontophrynus occidentalis from the Monte desert (Argentina). Variables measured were: selected body temperature (T_sel), critical thermal maximum (CT_max) and thermal critical minimum (CT_min). The tadpoles were acclimated to 15±2 °C for 15 days, and they were divided in three experimental groups: 24 h light, 24 h dark and 12 h/12 h light/dark. Data indicate that the photoperiod had an important effect upon the thermal biology of the Odontophrynus occidentalis tadpoles. The treatment group exposed to 24 h of light showed the highest selected temperature and thermal extremes. We suggest that changes in photoperiod may allow these organisms to anticipate the future changes in their thermal environment, as longer days usually involve higher temperatures.     

Evaporative water loss and energy metabolic in two small mammals,voles (Eothenomys miletus) and mice (Apodemus chevrieri), in Hengduan mountains region

Evaporative water loss (EWL) and energy metabolism were measured at different temperatures in Eothenomys miletus and Apodemus chevrieri in dry air. The thermal neutral zone (TNZ) of E. miletus was 22.5–30 °C and that of A. chevrieri was 20–27.5 °C. Mean body temperatures of the two species were 35.75±0.5 and 36.54±0.61 °C. Basal metabolic rates (BMR) were 1.92±0.17 and 2.7±0.5 ml O₂/g h, respectively. Average minimum thermal conductance (C_m) were 0.23±0.08 and 0.25±0.06 ml O₂/g h °C. EWL in E. miletus and A. chevrieri increased with the increase in temperature; the maximal EWL at 35 °C was 4.78±0.6 mg H₂O/g h in E. miletus, and 5.92±0.43 mg H₂O/g h in A. chevrieri. Percentage of evaporative heat loss to total heat production (EHL/HP) increased with the increase in temperature; the maximal EHL/HP was 22.45% at 30 °C in E. miletus, and in A. chevrieri it was 19.96% at 27.5 °C. The results may reflect features of small rodents in the Hengduan mountains region: both E. miletus and A. chevrieri have high levels of BMR and high levels of total thermal conductance, compared with the predicted values based on their body masses, while their body temperatures are relatively low. EWL plays an important role in temperature regulation.     

Embryonic development rate and hatchling phenotypes in the Chinese three-keeled pond turtle (Chinemys reevesii): The influence of fluctuating temperature versus constant temperature

Although the effects of constant temperatures on hatchling traits have been extensively studied in reptiles, the effects of fluctuating temperatures remain poorly understood. Eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) were incubated at a constant temperatures (28 °C) and two fluctuating temperatures (28±3 °C and 28±6 °C) to test for the influence of thermal environment on incubation duration, hatchling traits, and post-hatching growth. Incubation duration was shorter at constant temperature than at fluctuating temperatures. The sex ratio of hatchlings varied among temperature treatments, with more females from 28±6 °C than from 28 °C. The size and mass were greater for hatchlings from a constant temperature than from fluctuating ones, but this difference in body size disappeared when the hatchlings were 3 months old. In addition, the swimming ability, survival, and growth of hatchlings from fluctuating temperatures did not differ from those of hatchlings from constant temperature, when they were kept at an artificial environment without food scarcity or predation. Therefore, the thermal environments with various temperature fluctuations used in this study do not significantly affect fitness-related hatchling traits in this species.     

Ambient temperature-dependent thermoregulatory role of REM sleep

Changes in ambient temperature produce complex effects on sleep–wakefulness. In order to find out the mechanisms involved in temperature-sensitive changes in sleep in rats, their thermal preference, body temperature and sleep were studied before and after the destruction of both peripheral and central warm receptors, by systemic administration of 375 mg/kg capsaicin. Though the pre-treated rats preferred to stay mostly at the ambient temperature of 27 °C, post-treated rats strayed freely into chambers having ambient temperature of 30 °C and 33 °C. Sleep and body temperature of these rats were studied for six hours each, when they were kept at an ambient temperature of 18–36 °C. Total sleep time, especially REM sleep, was maximum at 30 °C in pre-treated rats, but this REM sleep peak at 30 °C disappeared after capsaicin administration. Body temperature increased sharply in post-treated rats, at ambient temperatures above 30 °C. Apart from the ability to defend body temperature at high ambient temperature, avoidance of warm ambient temperature and increase in REM sleep are the behavioral measures which are lost in post-treated rats. Results of this study suggest that the ambient temperature-related increase in REM sleep at 30 °C could be part of the thermoregulatory measures.     

The use of small subcutaneous transponders for quantifying thermal biology and torpor in small mammals

Remote measurements of body temperature (T_b) in animals require implantation of relatively large temperature-sensitive radio-transmitters or data loggers, whereas rectal temperature (T_rec) measurements require handling and therefore may bias the results. We investigated whether ∼0.1 g temperature-sensitive subcutaneously implanted transponders can be reliably used to quantify thermal biology and torpor use in small mammals. We examined (i) the precision of transponder readings as a function of temperature and (ii) whether subcutaneous transponders can be used to remotely record subcutaneous temperature (T_sub). Five adult male dunnarts (Sminthopsis macroura, body mass 24 g) were implanted with subcutaneous transponders to determine T_sub as a function of time and ambient temperature (T_a), and in comparison to thermocouple readings of T_rec. Transponder temperature was highly correlated with water bath temperature (r²=0.96–0.99) over a range of approximately 10.0–40.0 °C. Transponders provided reliable data (±0.6 °C) over the T_sub of 21.4–36.9 °C and could be read from a distance of up to 5 cm. Below 21.4 °C, accuracy was reduced to ±2.8 °C, but individual transponder accuracy varied. Consequently, small subcutaneous transponders are useful to remotely quantify thermal physiology and torpor patterns without having to disturb the animal and disrupt torpor. Even at T_sub<21.4 °C where the accuracy of the temperature readings was reduced, transponders do provide reliable data on whether and when torpor is used.     

Thermal responses to environmental constraints in two populations of the oviparous lizard Liolaemus bibronii in Patagonia,Argentina

Ectotherms change their thermoregulation behaviour according to the available temperatures, photoperiod, and radiation present in their local environment. The influences of the abiotic environment not only affect the body temperature but also most life history traits of populations. The thermal biology of one of the southernmost oviparous lizards, Liolaemus bibronii, was studied at high- and low-latitude sites in Patagonia, Argentina, following the methodology of Hertz et al. [1993. Evaluating temperature regulation by field-active ectotherms: the fallacy of the inappropriate question. Am. Nat. 142, 796–818]. Our results show that L. bibronii lives under thermal–environmental constraints, behaves as a moderate thermoregulator, and shows the lowest body temperature (28 °C) for oviparous liolaemids.     

Effects of exposure to short-term heat stress on male reproductive fitness in a soil arthropod

Ambient temperature is a key environmental factor influencing a variety of aspects of the ecology and evolution of ectotherms. Reproductive traits have been suggested to be more sensitive to thermal stress than other life history traits. This study investigated the direct and indirect effects of heat shock on male reproductive success in the widespread springtail Orchesella cincta. Male springtails were exposed to four temperature treatments: heat hardening (35.2 °C for 1 h), heat shock (37.2 °C for 1 h), heat hardening + heat shock (35.2 °C for 1 h, followed 15 h later by 37.2 °C for 1 h), and control (20 °C). The heat shock gene Hsp70 showed high expression in all the heat treatments, indicating that the treatments indeed induced thermal stress. Significant mortality was only found in the treatment with heat shock, both with and without heat hardening. A direct effect of heat treatment was found on time to first reproduction, which was significantly longer after heat shock (with or without heat hardening) than in the control treatment. There was no difference among treatments in the number of spermatophores produced in the first reproductive instar. Heat treatment also had indirect effects on male reproductive success. Females chose significantly more spermatophores from control males than from males that received heat shock, heat hardening or both. A high percentage of spermatophores produced by heat shocked males caused reproductive failure in females, but no significant differences among treatments were found.Our results suggest that not all traits were equally affected by the heat stress. Heat hardening did not protect reproductive traits against the negative effects of heat shock. The indirect effects of heat shock on reproduction may be equally important as the direct effects.     

Relatively low upper threshold temperature in lizards from cool habitats

We used the slender forest skink (Scincella modesta) as a model animal to test for the hypothesis that the upper threshold of incubation temperature is relatively low in lizards using shaded (and thus, cool) habitats. Eight gravid females were collected in early May 2005 from a population in Hangzhou, Zhejiang (eastern China). All females laid a single clutch of 7–13 eggs between mid-May and early June. Eggs were incubated at 24, 28 and 30 (±0.2) °C. None of eggs incubated at 30 °C hatched. Eggs incubated at 24 and 28 °C differed in incubation length but not in hatching success. The incubation length at 24 and 28 °C averaged 22.3 and 20.3 days, respectively. Hatchlings from eggs incubated at 24 and 28 °C did not differ in all examined morphological traits, but hatchlings from eggs incubated at 28 °C performed apparently worse in the racetrack than did their counterparts from eggs incubated at 24 °C. The temperature of 28 °C is close to the upper thermal threshold for successful embryonic development in S. modesta. Compared to other oviparous lizards using open (and thus, warm) habitats, the upper thermal threshold and the range of optimal temperatures for embryonic development are both lower in S. modesta. Our study supports the previous conclusion that species living in thermally different habitats may differ in the upper thermal threshold and the range of optimal temperatures for embryonic development.     

Thermogenic characteristics and evaporative water loss in the tree shrew (Tupaia belangeri)

Thermogenic characteristics and evaporative water loss were measured at different temperatures in Tupaia belangeri. The thermal neutral zone (TNZ) of T. belangeri was 30–35 °C. Mean body temperature was 39.76±0.27 °C and mean body mass was 100.86±9.09 g. Basal metabolic rate (BMR) was 1.38±0.03 ml O₂/g h. Average minimum thermal conductance (C_m) was 0.13±0.01 ml O₂/g h °C. Evaporative water loss in T. belangeri increased when the temperature rose; the maximal evaporative water loss was 3.88±0.41 mg H₂O/g h at 37.5 °C. The results may reflect features of small mammals in the sub-tropical plateau region: T. belangeri had high basal metabolic rate and high total thermal conductance, compared with the predicted values based on their body mass whilst their body temperatures are relatively high; T. belangeri has high levels of evaporative water loss and poor water-retention capacity. Evaporative water loss plays an important role in temperature regulation.     

Heat tolerance, behavioural temperature selection and temperature-dependent respiration in larval Octopus huttoni

This study reports temperature effects on paralarvae from a benthic octopus species, Octopus huttoni, found throughout New Zealand and temperate Australia. We quantified the thermal tolerance, thermal preference and temperature-dependent respiration rates in 1-5 days old paralarvae. Thermal stress (1 °C increase h⁻¹) and thermal selection (∼10-24 °C vertical gradient) experiments were conducted with paralarvae reared for 4 days at 16 °C. In addition, measurement of oxygen consumption at 10, 15, 20 and 25 °C was made for paralarvae aged 1, 4 and 5 days using microrespirometry. Onset of spasms, rigour (CT_max) and mortality (upper lethal limit) occurred for 50% of experimental animals at, respectively, 26.0±0.2 °C, 27.8±0.2 °C and 31.4±0.1 °C. The upper, 23.1±0.2 °C, and lower, 15.0±1.7 °C, temperatures actively avoided by paralarvae correspond with the temperature range over which normal behaviours were observed in the thermal stress experiments. Over the temperature range of 10 °C-25 °C, respiration rates, standardized for an individual larva, increased with age, from 54.0 to 165.2 nmol larvae⁻¹ h⁻¹ in one-day old larvae to 40.1-99.4 nmol h⁻¹ at five days. Older larvae showed a lesser response to increased temperature: the effect of increasing temperature from 20 to 25 °C (Q₁₀) on 5 days old larvae (Q₁₀=1.35) was lower when compared with the 1 day old larvae (Q₁₀=1.68). The lower Q₁₀ in older larvae may reflect age-related changes in metabolic processes or a greater scope of older larvae to respond to thermal stress such as by reducing activity. Collectively, our data indicate that temperatures >25 °C may be a critical temperature. Further studies on the population-level variation in thermal tolerance in this species are warranted to predict how continued increases in ocean temperature will limit O. huttoni at early larval stages across the range of this species.     

Effects of acclimation and egg-incubation temperature on selected temperature by hatchling western painted turtles (Chrysemys picta bellii)

The ability of hatchling turtles to detect environmental temperature differences and to effectively select preferred temperature is a function that critically impacts survival. In some turtle species, temperature preference may be influenced by embryonic and post-hatching conditions, such as egg-incubation and acclimation temperature. We tested for effects of embryonic incubation temperature (27.5 °C, 30 °C) and acclimation temperature (20 °C, 25 °C) on the selected temperature and movement patterns of 32 Chrysemys picta bellii (Reptilia: Emydidae) hatchlings in an aquatic thermal gradient of 14-34 °C and in single-temperature (20 °C, 25 °C) control tests. Among 10-11 month old hatchlings, acclimation temperature and egg-incubation temperature influenced temperature selection and movement patterns. Acclimation temperature affected activity and movement: in thermal gradient and single-temperature control tests, 25 °C-acclimated turtles relocated between chambers significantly more frequently than individuals acclimated to 20 °C. Acclimation temperature also affected temperature selection: 20 °C-acclimated turtles selected a specific temperature during gradient tests, but 25 °C-acclimated turtles did not. Among 20 °C-acclimated turtles, egg-incubation temperature was inversely related to selected temperature: hatchling turtles incubated at 27.5 °C selected the warmest temperature available (34 °C); individuals incubated at 30 °C selected the coldest temperature (14 °C). These results suggest that interactions of environmental conditions may influence post-hatching thermoregulatory behavior in C. picta bellii, a factor that ultimately affects fitness.     

Response of juvenile diamond-backed terrapins (Malaclemys terrapin) to an aquatic thermal gradient

In many ectotherms, selection of environmental thermal niches may positively affect growth, nutrient assimilation rates, immune system function, and ultimately survival. Temperature preference in some turtle species may be influenced by environmental conditions, including acclimation temperature. We tested for effects of acclimation temperature (22 °C, 27 °C) on the selected temperature and movement patterns of 14 juvenile Malaclemys terrapin (Reptilia: Emydidae) in an aquatic thermal gradient of 14–34 °C and in single-temperature (22 °C, 27 °C) control tests. Among 8–10 month old terrapins, acclimation temperature influenced activity and movement patterns but did not affect temperature selection. In thermal gradient and single-temperature control tests, turtles acclimated to 27 °C used more tank chambers and relocated between chambers significantly more frequently than individuals acclimated to 22 °C. However, acclimation temperature did not affect temperature selection: both 22- and 27 °C-acclimated turtles selected the warmest temperature (34 °C), and avoided the other temperatures available, during thermal gradient tests. These results suggest that young M. terrapin are capable of detecting small temperature increments and prefer warm temperatures that may positively influence growth and metabolism.     

Time-course for attainment and reversal of acclimation to constant temperature in two Ceratitis species

Acclimation in the thermal tolerance range of insects occurs when they are exposed to novel temperatures in the laboratory. In contrast to the large number of studies that have tested for the ability of insects to acclimate, relatively few have sought to determine the time-course for attainment and reversal of thermal acclimation. In this study the time required for the Mediterranean fruit fly, Ceratitis capitata Wiedemann, and the Natal fruit fly, Ceratitis rosa Karsch, to acclimate to a range of constant temperatures was tested by determining the chill-coma recovery time and heat knock-down time of flies that had been exposed to novel benign temperatures for different durations. The time required for reversal of acclimation for both Ceratitis species was also determined after flies had been returned to the control temperature. Acclimation to 31 °C for only one day significantly improved the heat knock-down time of C. capitata, but also led to slower recovery from chill-coma. Heat knock-down time indicated that acclimation was achieved after only one day in C. rosa, but it took three days for C. rosa to exhibit a significant acclimation response to a novel temperature of 33 °C when measured using chill-coma recovery time. Reversal of acclimation after return to initial temperature conditions was achieved after only one day in both C. capitata and C. rosa. Adult C. capitata held at 31.5 °C initially exhibited improved heat knock-down times but after 9 days the heat knock-down time of these flies had declined to levels not significantly different from that of control flies held at the baseline temperature of 24 °C. In both Ceratitis species, heat knock-down time declined with age whereas chill-coma recovery time increased with age, indicating an increased susceptibility to high and low temperatures, respectively.     

Effects of low-intensity microwave radiation on Tribolium castaneum physiological and biochemical characteristics and survival

The red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae) is a widespread pest that lives in, and feeds on, wheat flour. Here, we studied the effects of low-intensity microwave radiation (LIMR; ≤2.0 kW/kg) on physiological and biochemical characteristics of T. castaneum, and compared them to the effects of heat conduction treatment, to provide a theoretical basis for using LIMR for pest control. Lethal model equations with respect to temperature were shown to provide acceptable fitting accuracy for the effects of LIMR treatment. Semi-lethal and lethal temperatures induced through LIMR (48 °C and 50 °C, respectively) for T. castaneum were lower than those induced through heat conduction (50 °C and 52 °C). When T. castaneum were subjected to LIMR, the insects’ moisture content, pH values, alkaline phosphatase and acetyl cholinesterase activity were all lower than when the insects were subjected to heat conduction. Peroxide values and total free amino acid content were higher, and protein subunits molecular weights were lower when T. castaneum were exposed to LIMR than to heat; moreover, after LIMR exposure, the amino acid composition of T. castaneum was changed and the insect's DNA was damaged.     

Thermal tolerance,net CO2 exchange and growth of a tropical tree species, Ficus insipida, cultivated at elevated daytime and nighttime temperatures

Global warming and associated increases in the frequency and amplitude of extreme weather events, such as heat waves, may adversely affect tropical rainforest plants via significantly increased tissue temperatures. In this study, the response to two temperature regimes was assessed in seedlings of the neotropical pioneer tree species, Ficus insipida. Plants were cultivated in growth chambers at strongly elevated daytime temperature (39 °C), combined with either close to natural (22 °C) or elevated (32 °C) nighttime temperatures. Under both growth regimes, the critical temperature for irreversible leaf damage, determined by changes in chlorophyll a fluorescence, was approximately 51 °C. This is comparable to values found in F. insipida growing under natural ambient conditions and indicates a limited potential for heat tolerance acclimation of this tropical forest tree species. Yet, under high nighttime temperature, growth was strongly enhanced, accompanied by increased rates of net photosynthetic CO₂ uptake and diminished temperature dependence of leaf-level dark respiration, consistent with thermal acclimation of these key physiological parameters.     

Depth gradients in shell morphology correlate with thermal limits for activity and ice disturbance in Antarctic limpets

To fully understand how species distributions will respond to changing environments it is essential to understand the mechanisms underlying variation in animal performance and the relative importance of different ecological and environmental factors. A performance measure that has previously been used as an indicator of thermal capacity of the Antarctic limpet (Nacella concinna) to cope with regional warming is the ability to right if removed from the substratum and turned upside down. As part of an on-going study into limpet genetics and phenotypic plasticity, we tested the temperature limits for 50% righting of limpets from 6 and 30 m depth. The 50% threshold for limpets collected from 6 m (4.7 °C) was higher than for those collected from 30 m (0.7 °C). This compares with a previously published limit of 2.2 °C for limpets collected from 12-15 m at the same location. These thermal limits positively correlated with a depth gradient in shell height to length ratio; thickness and strength. Flatter limpets, had a reduced thermal limit for righting than taller limpets which we hypothesise is related to increased energy requirements of flat limpets, which have to turn through a greater angle to right than tall limpets. Of the factors that cause morphological plasticity of gastropod shells, iceberg disturbance is the most likely cause of the sub-tidal gradient in N. concinna shell shape, and therefore the thermal limit for righting of limpets from 6 to 30 m depth, rather than environmental temperature.     

Dermal gland secretion improves the heat tolerance of the brown dog tick, Rhipicephalus sanguineus, allowing for their prolonged exposure to host body temperature

Dermal glands (sensilla sagittiformia) secrete when brown dog ticks, Rhipicephalus sanguineus, are mechanically disturbed, presumably as a defensive mechanism. Recently, we observed that these glands secrete due to the pressure stimulation of engorgement. In this study, we examine how dermal gland secretion alters the physiology of R. sanguineus, particularly if this secretion is an important mechanism during blood feeding. The ability of ticks to retain water was not modified by dermal gland secretion, but heat tolerance was enhanced. Short-term heat shock was improved slightly (1 h at 50 °C to 1 h at 56 °C) and featured reduced injury responses and greater recovery after heat shock. When exposed to their host body temperature (37 °C) for prolonged periods, individuals that had secreted survived over 1 week longer than individuals that did not secrete. Dorsal application of squalene, the main component of dermal gland secretion, did not increase temperature tolerance, suggesting that the act of secreting rather than the physical properties of the secretion itself is responsible for the increase in heat tolerance. Based on our results, dermal gland secretion may be an essential mechanism in certain tick species (Amblyomma, Dermacentor, Hyalomma, Rhipicephalus, but not Ixodes) for tolerating body temperature and not succumbing to heat stress during the extended time periods of feeding on a mammalian host, serving as a mechanism to prevent heat damage from the host during feeding.     

Seasonal changes in the thermal tolerances of the toad Rhinella arenarum (Bufonidae) in the Monte Desert of Argentina

We studied the thermal tolerances of Rhinella arenarum during the dry and wet seasons of the Monte Desert in San Juan Province, Argentina. This toad had differences in CT_max between dry and wet seasons, and the CT_max values were higher in the wet season (Austral summer). Operative temperature, body temperature, environmental maximal temperature, and relative humidity were related to CT_max, suggesting seasonal acclimatization of R. arenarum. Additionally, the CT_max recorded for R. arenarum was 36.2 °C, and the maximum ambient temperature recorded during the toads' activity time was 37 °C. Also, the CT_min recorded for R. arenarum was 5.3 °C and the minimum environmental temperature recorded was 7.2 °C. The wide thermal tolerance range recorded and the relationship between tolerance limits and the environmental extremes indicate that seasonal acclimatization is an effective mechanism by which toads can raise their thermal tolerance, allowing them to survive in the challenging conditions of the Monte Desert. Additional studies are needed to understand the relationship between the thermal tolerance of this desert amphibian and the environmental parameters that influence its thermal physiology.     

A study of human skin and surface temperatures in stable and unstable thermal environments

Skin temperature is a common physiological parameter that reflects human thermal responses. The purpose of this research was to investigate the effects of radiant temperature on human skin temperature and surface temperature in stable and unstable thermal environments. For a clothed human body, the skin temperature is the surface temperature of the skin, while the surface temperature is the outer surface temperature of the clothes. For this aim, the radiant temperature from 26 to 38 °C and then from 38 to 26 °C was controlled in three different ways; in stable condition keeping stable above 40 min, in unstable condition at a rate of 2 °C/5 min, and in another unstable condition at a rate of 2 °C/10 min. Experimental data showed that at the same radiant temperature, the local skin/surface temperatures during the radiant temperature decrease were higher compared to those during the radiant temperature increase. During the radiant temperature increase/decrease, the increments/decrements of the mean skin temperature and the mean surface temperature decreased gradually from the stable condition, 2 °C/10 min to 2 °C/5 min. Compared to surface temperature, the faster the radiant temperature changed, the more obviously the change in skin temperature was delayed. These data demonstrated that the human body has physiological adaptability to unstable thermal environments.