The functions of belly-soaking in Kentish Plovers Charadrius alexandrinus

We tested whether belly-soaking (i.e. wetting of ventral plumage) in incubating Kentish Plovers Charadrius alexandrinus in a hot environment serves to cool overheated eggs, or whether belly-soaking would mainly serve for adult thermoregulation, and egg wetting would be a mere consequence of the ventral feathers of incubating adults being wet. When ambient temperature was high (> 30 °C), body temperature of incubating Kentish Plovers increased with ambient temperatures. When adults departed from nests to belly-soak, egg temperatures were not critical for embryos. However, eggs in exposed nests overheated to levels that may be lethal for embryos when adults left the nests to belly-soak, and adults also employed belly-soaking to cool down overheated eggs when they returned to their nests. Indeed, the cooling rate of eggs was much faster when they were wetted. We conclude that the primary function of belly-soaking in the Kentish Plover is to dissipate body heat in heat-stressed incubating adults, rather than to cool overheated eggs. Eggs overheated as a consequence of short-term interruptions in nest attendance by heat-stressed adults to belly-soak, and Plovers employed secondarily belly-soaking to cool down overheated eggs. These results indicate that adult thermoregulation and egg cooling are not mutually exclusive functions of belly-soaking.     

Determination of time of death in forensic science via a 3-D whole body heat transfer model

This study is focused on developing a whole body heat transfer model to accurately simulate temperature decay in a body postmortem. The initial steady state temperature field is simulated first and the calculated weighted average body temperature is used to determine the overall heat transfer coefficient at the skin surface, based on thermal equilibrium before death. The transient temperature field postmortem is then simulated using the same boundary condition and the temperature decay curves at several body locations are generated for a time frame of 24 h. For practical purposes, curve fitting techniques are used to replace the simulations with a proposed exponential formula with an initial time delay. It is shown that the obtained temperature field in the human body agrees very well with that in the literature. The proposed exponential formula provides an excellent fit with an R² value larger than 0.998. For the brain and internal organ sites, the initial time delay varies from 1.6 to 2.9 h, when the temperature at the measuring site does not change significantly from its original value. The curve-fitted time constant provides the measurement window after death to be between 8 h and 31 h if the brain site is used, while it increases 60–95% at the internal organ site. The time constant is larger when the body is exposed to colder air, since a person usually wears more clothing when it is cold outside to keep the body warm and comfortable. We conclude that a one-size-fits-all approach would lead to incorrect estimation of time of death and it is crucial to generate a database of cooling curves taking into consideration all the important factors such as body size and shape, environmental conditions, etc., therefore, leading to accurate determination of time of death.     

Starvation reduces the heat shock protein responses in white sturgeon larvae

This study investigates the responses of white sturgeon larvae (Acipenser transmontanus) to starvation and thermal stress, through the measurement of nutritional status (i.e. growth performances) and cellular biomarkers: heat shock proteins (Hsp) 70 and 90. White sturgeon larvae (25 day post hatch; initial weight 179.0 ± 5.1 mg) were fed (20% body weight per day) or starved for 24, 48 or 72 hrs. Every 24 hrs, five larvae from each of the starved or fed treatment replicates were exposed to heat shock resulting from an increase in water temperature from 19°C to 26°C, at a rate of 1°C per 15 min, and maintained at 26°C for 4 hrs. No mortality was observed in this study. Starvation significantly (p < 0.05) decreased the body weight and body contents of energy, protein, and lipid of the experimental larvae, compared to the fed larvae. Heat shock induced the expressions of Hsp70 and Hsp90 in both the fed and starved group; however, starvation reduced the induction at all sampling points. The current study demonstrates that poor larval nutritional status, assessed by the aforementioned parameters, reduced heat shock responses to thermal stress, as measured by heat shock protein levels. Furthermore, Hsp70 and 90 are more sensitive to heat shock and starvation, respectively. This may be, in part, a result of the different functioning of the heat shock proteins in cellular stress response and warrants further study.     

Thermoregulatory differences in African mole-rat species from disparate habitats: Responses and limitations

Individuals and populations possess physiological adaptations to survive local environmental conditions. To occur in different regions where ambient temperature varies, animals must adopt appropriate thermoregulatory mechanisms. Failure to adjust to environmental challenges may result in species distributional range shifts or decreased viability. African mole-rats (Bathyergidae) occupy various habitats in sub-Saharan Africa from deserts to montane regions to mesic coastal areas. We examined thermoregulatory characteristics of three African mole-rat species originating from disparate (montane, savannah, and arid/semi-arid) habitats. Animals were exposed to various ambient temperatures, whilst core body temperature and the surface temperature of different body parts were measured. Oxygen consumption was determined as a measure of heat production. Core body temperatures of Natal (montane) mole-rats (Cryptomys hottentotus natalensis) increased significantly at ambient temperatures >24.5 °C, while those of the highveld (Cryptomys hottentotus pretoriae) (savannah) and Damaraland (Fukomys damarensis) (arid/semi-arid) mole-rats remained within narrower ranges. In terms of surface temperature variation, while pedal surfaces were important in regulating heat loss in Natal and Damaraland mole-rats at high ambient temperatures, the ventral surface was important for heat dissipation in Damaraland and highveld mole-rats. This study provides evidence of the variation and limitations of thermo-physiological mechanisms for three mole-rat species relative to their habitats. Information on physiological adaptations to particular habitats may inform predictive modelling of species movements, declines, and extinctions in response to a changing environment, such as climate change.     

Testosterone modifies response to chronic heat exposure in rats

Eight weeks of heat exposure (34±0.5°C) in sham-orchiectomized rats leads to an increase of body temperature, slowing of body growth rate, and decrease of serum corticosterone level, as compared with animals maintained at 21±2°C. Orchiectomy decreases body temperature, slows growth rate, and increases plasma corticosterone concentration both in control and heat exposed animals. Testosterone administration reverts these parameters to initial values. We conclude that testosterone plays a role in the regulation of heat balance in male rats.     

Supplemental ascorbic acid does not affect inferred heat loss in broiler chickens exposed to elevated temperature

The provision of supplemental ascorbic acid has been reported to lower the body temperature of chickens maintained at elevated environmental temperatures. Since body temperature is the net effect of heat production and heat loss, it is not known if the reductions in body temperature were due to a lower heat production or an increase in heat loss. The purpose of this work was to determine if supplemental ascorbic acid facilitates heat loss in chickens exposed to an elevated temperature. On day 12 post-hatch broiler chickens were implanted intra-abdominally with a thermo-sensitive radio transmitter. The following day, birds were placed inside an indirect calorimeter maintained at 34 C for 24 h and provided water containing 0 or 400 ppm ascorbic acid. Oxygen consumption, carbon dioxide production, heat production, respiratory exchange ratio, and body core temperature were measured for 3 h; beginning 21 h after the birds were placed inside the calorimeter. No differences were observed in heat production or body core temperature between birds provided or not and 400 ppm ascorbic acid. This suggests that ascorbic acid has no effect on heat loss. Birds provided ascorbic acid did exhibit a significantly lower respiratory exchange ratio suggesting a greater utilization of lipid for energy production. Although lipid has a lower heat increment compared with protein and carbohydrate, the significance of this finding to birds exposed to elevated temperature is not known. In conclusion, under the conditions of this study the provision of supplemental ascorbic acid to broiler chickens maintained at an elevated temperature did not affect heat loss as inferred from measured heat production and body core temperature.     

Nest construction by a ground-nesting bird represents a potential trade-off between egg crypticity and thermoregulation

Predation selects against conspicuous colors in bird eggs and nests, while thermoregulatory constraints select for nest-building behavior that regulates incubation temperatures. We present results that suggest a trade-off between nest crypticity and thermoregulation of eggs based on selection of nest materials by piping plovers (Charadrius melodus), a ground-nesting bird that constructs simple, pebble-lined nests highly vulnerable to predators and exposed to temperature extremes. Piping plovers selected pebbles that were whiter and appeared closer in color to eggs than randomly available pebbles, suggesting a crypsis function. However, nests that were more contrasting in color to surrounding substrates were at greater risk of predation, suggesting an alternate strategy driving selection of white rocks. Near-infrared reflectance of nest pebbles was higher than randomly available pebbles, indicating a direct physical mechanism for heat control through pebble selection. Artificial nests constructed of randomly available pebbles heated more quickly and conferred heat to model eggs, causing eggs to heat more rapidly than in nests constructed from piping plover nest pebbles. Thermal models and field data indicated that temperatures inside nests may remain up to 2–6°C cooler than surrounding substrates. Thermal models indicated that nests heat especially rapidly if not incubated, suggesting that nest construction behavior may serve to keep eggs cooler during the unattended laying period. Thus, pebble selection suggests a potential trade-off between maximizing heat reflectance to improve egg microclimate and minimizing conspicuous contrast of nests with the surrounding substrate to conceal eggs from predators. Nest construction behavior that employs light-colored, thermally reflective materials may represent an evolutionary response by birds and other egg-laying organisms to egg predation and heat stress. An erratum to this article can be found at     

The cranial arterio-venous temperature difference is related to respiratory evaporative heat loss in a panting species,the sheep (<Emphasis Type="Italic">Ovis aries</Emphasis>)

Panting is a mechanism that increases respiratory evaporative heat loss (REHL) under heat load. Because REHL uses body water, it is physiologically and ecologically relevant to know under what conditions free-ranging animals use panting. We investigated whether the cranial arterio-venous temperature difference could provide information about REHL. We exposed sheep to environments varying in ambient dry bulb temperatures (Env 1: ~15°C, Env 2: ~25°C, Env 3: ~40°C, Env 4: ~40°C + infrared radiation) and measured REHL simultaneously with carotid arterial (T _car) and jugular venous (T _jug) blood temperatures, as well as brain (T _brain) and rectal (T _rec) temperatures. REHL increased significantly with ambient temperature, from 18.4 ± 4.5 W at Env 1 to 79.5 ± 12.6 W at Env 4 (P < 10⁻⁶). While there was no effect of environment on T _car (P = 0.7) or T _jug (P = 0.09), the difference between them (T _a-v = T _car − T _jug) increased from Env 1 to Env 2 (P = 0.04) and from Env 3 to Env 4 (P = 0.008). T _a-v reached a maximum of 0.7 ± 0.2°C at Env 4 and was positively correlated with REHL across environments (r ² = 0.78, F = 34.7, P < 10⁻³). Calculated cranial blood flow changed only from Env 2 to Env 3 (P = 0.002). The increase in REHL maintained homeothermy when dry heat loss decreased. While REHL could increase without generating an increase in T _a-v, any increase in T _a-v was always associated with an increase in REHL. We conclude that the cranial T _a-v provides useful information about REHL in panting animals.     

Taking the heat: thermoregulation in Asian elephants under different climatic conditions

Some mammals indigenous to desert environments, such as camels, cope with high heat load by tolerating an increase in body temperature (T _b) during the hot day, and by dissipating excess heat during the cooler night hours, i.e., heterothermy. Because diurnal heat storage mechanisms should be favoured by large body size, we investigated whether this response also exists in Asian elephants when exposed to warm environmental conditions of their natural habitat. We compared daily cycles of intestinal T _b of 11 adult Asian elephants living under natural ambient temperatures (T _a) in Thailand (mean T _a ~ 30°C) and in 6 Asian elephants exposed to cooler conditions (mean T _a ~ 21°C) in Germany. Elephants in Thailand had mean daily ranges of T _b oscillations (1.15°C) that were significantly larger than in animals kept in Germany (0.51°C). This was due to both increased maximum T _b during the day and decreased minimum T _b at late night. Elephant’s minimum T _b lowered daily as T _a increased and hence entered the day with a thermal reserve for additional heat storage, very similar to arid-zone ungulates. We conclude that these responses show all characteristics of heterothermy, and that this thermoregulatory strategy is not restricted to desert mammals, but is also employed by Asian elephants.     

Predation risk on incubating adults constrains the choice of thermally favourable nest sites in a plover

Birds are thought to choose nest sites that meet two main functions: providing security to both nest contents and incubating adults, and providing an appropriate microclimate for incubation. Many shorebirds nest in sites with no or little cover. In a lake in southern Spain, nearly 70% of the nests of Kentish plovers, Charadrius alexandrinus, were in sites with little or no cover, where ambient temperatures might be more than 50°C during very hot days, thus causing the incubating adults to suffer from heat stress. We tested the hypothesis that Kentish plovers nest mainly in exposed sites because this may allow the incubating birds to detect approaching predators early, and thus to reduce predation risk. When we occluded the view that incubating adults had from their nests, they took longer to detect approaching predators than when the view was unrestricted. Incubating adults were also more frequently killed by mammals in covered than in exposed nests. Females that nested in covered sites were in lower body condition than those nesting in exposed sites, possibly because they were unable to withstand the high ambient temperatures in exposed sites. Thus, the benefits of thermally favourable nest sites are reduced by the constraints of predation risk.     

Experimental drought and heat can delay phenological development and reduce foliar and shoot growth in semiarid trees

Higher temperatures associated with climate change are anticipated to trigger an earlier start to the growing season, which could increase the terrestrial C sink strength. Greater variability in the amount and timing of precipitation is also expected with higher temperatures, bringing increased drought stress to many ecosystems. We experimentally assessed the effects of higher temperature and drought on the foliar phenology and shoot growth of mature trees of two semiarid conifer species. We exposed field‐grown trees to a ~45% reduction in precipitation with a rain‐out structure (‘drought’), a ~4.8 °C temperature increase with open‐top chambers (‘heat’), and a combination of both simultaneously (‘drought + heat’). Over the 2013 growing season, drought, heat, and drought + heat treatments reduced shoot and needle growth in piñon pine (Pinus edulis) by ≥39%, while juniper (Juniperus monosperma) had low growth and little response to these treatments. Needle emergence on primary axis branches of piñon pine was delayed in heat, drought, and drought + heat treatments by 19–57 days, while secondary axis branches were less likely to produce needles in the heat treatment, and produced no needles at all in the drought + heat treatment. Growth of shoots and needles, and the timing of needle emergence correlated inversely with xylem water tension and positively with nonstructural carbohydrate concentrations. Our findings demonstrate the potential for delayed phenological development and reduced growth with higher temperatures and drought in tree species that are vulnerable to drought and reveal potential mechanistic links to physiological stress responses. Climate change projections of an earlier and longer growing season with higher temperatures, and consequent increases in terrestrial C sink strength, may be incorrect for regions where plants will face increased drought stress with climate change.     

Deep body and surface temperature responses to hot and cold environments in the zebra finch

Global warming increasingly challenges thermoregulation in endothermic animals, particularly in hot and dry environments where low water availability and high temperature increase the risk of hyperthermia. In birds, un-feathered body parts such as the head and bill work as ‘thermal windows’, because heat flux is higher compared to more insulated body regions. We studied how such structures were used in different thermal environments, and if heat flux properties change with time in a given temperature. We acclimated zebra finches (Taeniopygia guttata) to two different ambient temperatures, ‘cold’ (5 °C) and ‘hot’ (35 °C), and measured the response in core body temperature using a thermometer, and head surface temperature using thermal imaging. Birds in the hot treatment had 10.3 °C higher head temperature than those in the cold treatment. Thermal acclimation also resulted in heat storage in the hot group: core body temperature was 1.1 °C higher in the 35 °C group compared to the 5 °C group. Hence, the thermal gradient from core to shell was 9.03 °C smaller in the hot treatment. Dry heat transfer rate from the head was significantly lower in the hot compared to the cold treatment after four weeks of thermal acclimation. This reflects constraints on changes to peripheral circulation and maximum body temperature. Heat dissipation capacity from the head region increased with acclimation time in the hot treatment, perhaps because angiogenesis was required to reach peak heat transfer rate. We have shown that zebra finches meet high environmental temperature by heat storage, which saves water and energy, and by peripheral vasodilation in the head, which facilitates dry heat loss. These responses will not exclude the need for evaporative cooling, but will lessen the amount of energy expend on body temperature reduction in hot environments.     

Different requirements for physical dormancy release in two populations of <Emphasis Type="Italic">Sophora alopecuroides</Emphasis> relation to burial depth

Most species of Fabaceae produce seeds with physical dormancy which was broken by some environmental factors in the field, yet for the mechanism of physical dormancy release in the natural condition is still poorly understood. In present study, seeds of Sophora alopecuroides from two populations were placed on the soil surface or buried at depths of 2 and 7 cm in the field and were exhumed at time intervals to assess the changes of dormancy. Also, microenvironments were simulated in the laboratory to determine the possible components (temperature, temperature fluctuation, and moisture) involved in physical dormancy release. The laboratory work indicated that wet heat is an important dormancy release mechanism for both populations; and dry heat for one of them, but showed no effects on the other one. Consistent with that, burial experiment showed seeds of two populations had two contrasting-dormancy release patterns in the field. Most seeds of the dry heat sensitive population released dormancy but the other one remained dormant when seeds placed on the soil surface for 11 months (where seeds were exposed to dry heat but not wet heat). The difference of physical dormancy release pattern response to burial depth and simulated condition may attribute to seed coat color and hilum thickness which showed significantly different between two populations. This conclusion may improve understanding of physical dormancy release mechanism among populations and have a practical use for grassland management and weed control.     

Regulation of autophagy following ex vivo heating in peripheral blood mononuclear cells from young adults

Under conditions of extreme heat stress, the process of autophagy has previously been shown to protect human cells, but the exact body temperature at which autophagic activation occurs is largely unknown. Further, the interplay between autophagy, the heat shock response (HSR), inflammation, and apoptosis have yet to be examined together under temperature conditions representative of human internal body temperatures at rest (37 °C) or under severe heat stress conditions (41 °C). Thus, the purpose of this study was to examine threshold changes in autophagy, the HSR, inflammation, and apoptosis to increasing levels of ex vivo heat stress. Whole blood was collected from 20 young (23 ± 4 years; 10 men, 10 women) physically active participants. Peripheral blood mononuclear cells (PBMCs) were isolated immediately (baseline) and after 90-min of whole blood heating in 37, 39, and 41 °C water baths, representative of normal resting (non-heat stress) as well as moderate and severe heat stress conditions in humans, respectively. At 37 °C, increased autophagic activity was demonstrated, with no change in the HSR, and inflammation. Subsequently, responses of autophagy, the HSR, and inflammation increased with a moderate heat stress (39 °C), with further increases in only autophagy and the HSR under a severe heat stress of 41 °C. We observed no increase in apoptosis under any temperature condition. Our findings show that in human PBMCs, the autophagy and HSR systems may act cooperatively to suppress apoptotic signaling following heat stress, which may in part be mediated by an acute inflammatory response.     

Bison body size and climate change

The relationship between body size and temperature of mammals is poorly resolved, especially for large keystone species such as bison (Bison bison). Bison are well represented in the fossil record across North America, which provides an opportunity to relate body size to climate within a species. We measured the length of a leg bone (calcaneal tuber, DstL) in 849 specimens from 60 localities that were dated by stratigraphy and ¹⁴C decay. We estimated body mass (M) as M = (DstL/11.49)³. Average annual temperature was estimated from δ¹⁸O values in the ice cores from Greenland. Calcaneal tuber length of Bison declined over the last 40,000 years, that is, average body mass was 37% larger (910 ± 50 kg) than today (665 ± 21 kg). Average annual temperature has warmed by 6°C since the Last Glacial Maximum (~24–18 kya) and is predicted to further increase by 4°C by the end of the 21st century. If body size continues to linearly respond to global temperature, Bison body mass will likely decline by an additional 46%, to 357 ± 54 kg, with an increase of 4°C globally. The rate of mass loss is 41 ± 10 kg per°C increase in global temperature. Changes in body size of Bison may be a result of migration, disease, or human harvest but those effects are likely to be local and short‐term and not likely to persist over the long time scale of the fossil record. The strong correspondence between body size of bison and air temperature is more likely the result of persistent effects on the ability to grow and the consequences of sustaining a large body mass in a warming environment. Continuing rises in global temperature will likely depress body sizes of bison, and perhaps other large grazers, without human intervention.     

Rapid thermal adaptation during field temperature variations in Drosophila melanogaster

Under natural conditions, the fruit fly (Drosophila melanogaster) is constantly exposed to variations in temperature and light. Laboratory investigations have demonstrated that D. melanogaster and other insects adapt quickly to temperature variations, but only few studies have investigated this ability under natural temperature variations. Here we placed laboratory raised female D. melanogaster in field cages and exposed them to natural variations in light and temperature over a 2 day period (temperature range: 12–25 °C). During this period we sampled flies every 6 h and measured their ability to survive heat and cold shock. There was a significant positive correlation between field temperature and heat shock survival and a significant negative correlation between field temperature and cold shock survival indicating that D. melanogaster are constantly adapting to their surrounding environment. The results also suggest that heat and cold resistance are obtained at a cost as these two traits were negatively correlated.     

BEHAVIORAL THERMOREGULATION OF THE NEW ZEALAND SEA LION (PHOCARCTOS HOOKERI)

Behavioral thermoregulation of New Zealand sea lions (Phocarctos hookeri) was studied at a male haul‐out ground at Papanui Beach, Otago Peninsula, New Zealand. The proportion of time spent by sea lions in each of five postures (prone, curled, oblique, ventral‐up, dorsal‐up) and also with the number of flippers exposed or tucked (hind and fore) at different black‐bulb temperature (T_bb°C) ranges was recorded. Use of prone and curled postures (0–1 flippers exposed) declined as T_bb increased, suggesting that these are adopted to conserve heat; oblique and dorsal‐up postures (3–4 flippers exposed) use increased with T_bb indicating a role in heat dissipation. The transition between heat conserving and heat dissipating postures occurred at about 14°–20°C (T_bb). Both foreflipper and hind flipper exposure increased with T_bb and the trends were similar, but overall hind flipper exposure was 89% of foreflipper exposure. The results show that surface area of flippers exposed to air is largely controlled by postural adjustment. The increase in flipper exposure with T_bb provides evidence of behavioral thermoregulation and that flippers are major sites for heat loss in the New Zealand sea lion, as observed for other otariid species. Nonpostural thermoregulatory behaviors such as flipper waving and sand flipping increased with T_bb, and may provide additional means of dissipating heat. Total body surface areas of six sea lions ranged from 1.72 to 3.39 m² (curvilinear length range from 1.60 to 2.35 m), and total flipper surface area averaged 22.7% of total body surface area. As otariids do not employ their hind limbs for aquatic propulsion, their role in behavioral thermoregulation may provide an explanation for the relatively large size of the hind flippers of the New Zealand sea lion.     

The energetics of basking behaviour and torpor in a small marsupial exposed to simulated natural conditions

Limited information is available on basking behaviour in torpid mammals and its energetic consequences. We investigated the effects of physiological and behavioural strategies on the energetics of the fat-tailed dunnart (Sminthopsis crassicaudata). Metabolic rate and body temperature during torpor, basking and rest were measured over 24 h in response to simulated environmental conditions: (a) constant ambient temperature (T _a) of 15°C, (b) constant T _a of 15°C with access to a radiant heat lamp, (c) a T _a cycle (range 15–31°C), and (d) a T _a cycle with access to a radiant heat lamp. When a radiant heat source was provided, all dunnarts (n = 16) basked during all measurements, which resulted in energy savings of up to 74% during rest. Overall, torpor was used on 59% of measurements with a maximum duration of 16.2 h and reductions in metabolic rate of 90% compared to normothermic values. Torpid dunnarts actively moved from a shaded area to position themselves under the heat lamp with body temperatures as low as 17.5°C and thereby reduced rewarming costs by 66%. We demonstrated, for the first time in the laboratory, that torpid animals actively move to a heat source to bask, and that this behaviour results in considerable energy savings. Our finding supports the view that basking during normothermia and rewarming from torpor substantially reduces energetic requirements, which may be important for the survival of small dasyurids living on limited resources in the Australian arid zone.