Behavioral thermoregulation in Hemigrapsus nudus,the amphibious purple shore crab

The thermoregulatory behavior of Hemigrapsus nudus, the amphibious purple shore crab, was examined in both aquatic and aerial environments. Crabs warmed and cooled more rapidly in water than in air. Acclimation in water of 16 degrees C (summer temperatures) raised the critical thermal maximum temperature (CTMax); acclimation in water of 10 degrees C (winter temperatures) lowered the critical thermal minimum temperature (CTMin). The changes occurred in both water and air. However, these survival regimes did not reflect the thermal preferences of the animals. In water, the thermal preference of crabs acclimated to 16 degrees C was 14.6 degrees C, and they avoided water warmer than 25.5 degrees C. These values were significantly lower than those of the crabs acclimated to 10 degrees C; these animals demonstrated temperature preferences for water that was 17 degrees C, and they avoided water that was warmer than 26.9 degrees C. This temperature preference was also exhibited in air, where 10 degrees C acclimated crabs exited from under rocks at a temperature that was 3.2 degrees C higher than that at which the 16 degrees C acclimated animals responded. This behavioral pattern was possibly due to a decreased thermal tolerance of 16 degrees C acclimated crabs, related with the molting process. H. nudus was better able to survive prolonged exposure to cold temperatures than to warm temperatures, and there was a trend towards lower exit temperatures with the lower acclimation (10 degrees C) temperature. Using a complex series of behaviors, the crabs were able to precisely control body temperature independent of the medium, by shuttling between air and water. The time spent in either air or water was influenced more strongly by the temperature than by the medium. In the field, this species may experience ranges in temperatures of up to 20 degrees C; however, it is able to utilize thermal microhabitats underneath rocks to maintain its body temperature within fairly narrow limits.     

Thermal, metabolic, and cardiovascular responses to various degrees of cold stress.

The metabolic, thermal, and cardiovascular responses of two male Caucasians to 1 2 h exposure to ambient temperature ranging between 28 degrees C and 5 degrees C were studied and related to the respective ambient temperatures. The metabolic heat production increased linearly with decreasing ambient temperature, where heat production (kcal times m- minus 2 times h- minus 1) = minus 2.79 Ta degrees C + 103.4, r = -0.97, P smaller than 0.001. During all exposures below 28 degrees C, the rate of decrease in mean skin temperature (Tsk) was found to be an exponential function dependent upon the ambient temperature (Ta) and the time of exposure. Reestablishment of Tsk steady state occurred at 90-120 min of exposure, and the time needed to attain steady state was linearly related to decreasing Ta. The net result was that a constant ratio of 1.5 of the external thermal gradient to the internal thermal gradient was obtained, and at all experimental temperatures, the whole body heat transfer coefficient remained constant. Cardiac output was inversely related to decreasing Ta, where cardiac output (Q) = minus 0.25 Ta degrees C + 14.0, r = minus 0.92, P smaller than 0.01. However, the primary reason for the increased Q, the stroke output, was also described as a third-order polynomial, although the increasing stroke volume throughout the Ta range (28-5 degrees C) was linearly related to decreasing ambients. The non-linear response of this parameter which occurred at 20 degrees C larger than or equal to Ta larger than or equal to 10 degrees C suggested that the organism's cardiac output response was an integration of the depressed heart rate response and the increasing stroke output at these temperatures.     

The effect of gravity on surface temperatures of plant leaves

A fundamental study was conducted to develop a facility having an adequate air circulation system for growing healthy plants over a long-term under microgravity conditions in space. To clarify the effects of gravity on heat exchange between plant leaves and the ambient air, surface temperatures of sweet potato and barley leaves and replica leaves made of wet paper and copper were evaluated at gravity levels of 0.01, 1.0, 1.5 and 2.0 g for 20 s each during parabolic aeroplane flights. Thermal images were captured using infrared thermography at an air temperature of 26 degrees C, a relative humidity of 18% and an irradiance of 260 W m-2. Mean leaf temperatures increased by 0.9-1.0 degrees C with decreasing gravity levels from 1.0 to 0.01 g and decreased by 0.5 degrees C with increasing gravity levels from 1.0 to 2.0 g. The increase in leaf temperatures was at most 1.9 degrees C for sweet potato leaves over 20 s as gravity decreased from 1.0 to 0.01 g. The boundary layer conductance to sensible heat exchange decreased by 5% when the gravity decreased from 1.0 to 0.01 g at the air velocity of 0.2 m s-1. The decrease in the boundary layer conductance with decrease in the gravity levels was more significant in a lower air velocity. Heat exchange between leaves and the ambient air was more retarded at lower gravity levels because of less sensible and latent heat transfers with less heat convection.     

Thermoregulatory and nonthermoregulatory heat production in burned rat

Severely burned patients are hypermetabolic within their thermoneutral zone (TNZ), where there are no thermoregulatory demands on heat production. The rat has been used as a model of postburn hypermetabolism without clear evidence that it behaves in a similar way. Male rats (400-500 g; n = 34-39) were placed as a group in a respiration chamber and metabolic rates for the average rat were determined over 3-6 h at ambient temperatures between 9 and 36 degrees C. Colonic temperatures (Tco) and body weights were measured after each run. Animals were studied sequentially as normals (N), after clipping (C) and following 50% total body surface scald burns. Clipping increased the lower critical temperature (LCT) from 27.7 to 29.1 degrees C without affecting resting heat production (N = 42.6 +/- 0.5; C = 42.0 +/- 0.8 W/m2; mean +/- S.E.) or Tco (N = 36.6 +/- 0.1; C = 36.6 +/- 0.1 degrees C) in the TNZ. Injury increased LCT to 32.8 degrees C and the burned animals were hypermetabolic (47.2 +/- 0.6 W/m2; P less than 0.05 vs. N) and febrile (36.9 +/- 0.1 degrees C; P less than 0.05 vs. N) in the elevated TNZ. These metabolic and temperature responses of burned rats are limited in magnitude but are qualitatively similar to those of patients. The extra heat production in the TNZ reflects the basic metabolic cost of injury.     

Thermogenic capabilities of the opossum Monodelphis domestica when warm and cold acclimated: similarities between American and Australian marsupials

1. Monodelphis domestica is a small marsupial mammal from South America. Its thermogenic abilities in the cold were determined when the opossums were both warm (WA) and cold (CA) acclimated. Maximum heat production of M. domestica was obtained at low temperatures in helium-oxygen. 2. Basal metabolic rate (BMR) in the WA animals was 3.2 W/kg and mean body temperature was 32.6 degrees C at 30 degrees C. These values were lower than those generally reported for marsupials. Nevertheless, these M. domestica showed considerable metabolic expansibility in response to cold. Sustained (summit) metabolism was 8-9 times BMR, while peak metabolism was 11-13 times BMR. These maximum values were equal to, or above, those expected in small placentals. 3. Cold acclimation altered the thermal responses of M. domestica, particularly in warm TaS. However, summit metabolism was not significantly increased; nor did M. domestica show a significant thermogenic response to noradrenaline, which in many small placentals elicits non-shivering thermogenesis. The thermoregulatory responses of this American marsupial were, in most aspects, similar to those of Australian marsupials. This suggests that the considerable thermoregulatory abilities of marsupials are of some antiquity.     

Body temperature and oxygen uptake in the kinkajou (Potos flavus, Schreber), a nocturnal tropical carnivore.

Two kinkajous (Potos flavus, Procyonidae) showed marked nycthemeral variations in their rectal temperature. The mean Tr at night was 38.1 +/- 0.4 degrees C SD and 36.0 +/- 0.6 degrees C SD while resting during the day. Body temperature and O2-consumption were measured at ambient temperatures from 5-35 degrees C. With one exception at 35 degrees C, hypo- or hyperthermia was never observed. At air temperatures above 30 degrees C the bears reacted with behavioural responses. O2-consumption was minimal at Ta's from 23-30 degrees C. The mean basal metabolic rate was 0.316 ml O2 g-1 h-1 which is only 65% of the expected value according to the Kleiber formula. Below 23 degrees C heat production followed the equation : y (ml O2 g-1 h-1) = 0.727--0.018 Ta. The minimal thermal conductance was 90% of the predicted value according to the formula : C (ml O2 g-1 h-1 degrees C-1) = 1.02 W-0.505 (HERREID & KESSEL, 1967). Kinkajous are another distinct exception to the mouse to elephant curve.     

Heat loss regulation: role of appendages and torso in the deer mouse and the white rabbit

Thermal conductance was subdivided into the component conductances of the appendages and torso using a heat transfer analysis for the deer mouse, Peromyscus maniculatus, and the white rabbit, Oryctolagus cuniculus. Our analysis was based on laboratory measurements of skin temperature and respiratory gas exchange made between air temperatures of 8 and 34 degrees C for the deer mouse, and from published data for the white rabbit. Two series conductances to heat transfer for each appendage and torso were evaluated: internal (hin), for blood flow and tissue conduction to the skin surface, and external (hex), for heat loss from the skin surface to the environment. These two series conductances were represented in a single, total conductance (htot). The limit to htot was set by hex and was reached by the torso htot of both animals. The increase in torso htot observed with air temperature for the mouse suggests that a pilomotor change in fur depth occurred. A control of htot below the limit set by hex was achieved by the hin of each appendage. Elevation of mouse thermal conductance (C) resulted from increases in feet, tail, and torso htot. In contrast, the rabbit showed no change in torso htot between 5 and 30 degrees C and ear htot exclusively increased C over these air temperatures. We suggest that the hyperthermia reported for the rabbit at 35 degrees C resulted from C reaching the physical limit set by torso and near hex. Thus the ear alone adjusted rabbit C, whereas the feet, tail, and the torso contributed to the adjustment of mouse C.     

Involvement of basal metabolic rate in determination of type of cold tolerance

This study aimed to assess the relationship between basal metabolic rate (BMR) and metabolic heat production, and to clarify the involvement of BMR in determining the phenotype of cold tolerance. Measurements of BMR, maximum oxygen uptake, and cold exposure test were conducted on ten males. In the cold exposure test, rectal (T(rec)) and mean skin temperatures (T(ms)), oxygen uptake, and blood flow at forearm (BF(arm)) were measured during exposure to cold (10 degrees C) for 90 min. Significant correlations were observed between BMR and increasing rate of oxygen uptake, as well as between decreasing rate of BF(arm) and increasing rate of oxygen uptake at the end of cold exposure. These findings suggested that individuals with a lower BMR were required to increase their metabolic heat production during cold exposure, and that those with a higher BMR were able to moderate increased metabolic heat production during cold exposure because they were able to reduce heat loss. This study showed that BMR is an important factor in determining the phenotype of cold tolerance, and that individuals with a low BMR showed calorigenic-type cold adaptation, whereas subjects with a high BMR exhibited adiabatic-type cold adaptation by peripheral vasoconstriction.     

Thermoregulation during cold exposure: effects of prior exercise.

This study examined whether acute exercise would impair the body's capability to maintain thermal balance during a subsequent cold exposure. Ten men rested for 2 h during a standardized cold-air test (4.6 degrees C) after two treatments: 1) 60 min of cycle exercise (Ex) at 55% peak O(2) uptake and 2) passive heating (Heat). Ex was performed during a 35 degrees C water immersion (WI), and Heat was conducted during a 38.2 degrees C WI. The duration of Heat was individually adjusted (mean = 53 min) so that rectal temperature was similar at the end of WI in both Ex (38.2 degrees C) and Heat (38.1 degrees C). During the cold-air test after Ex, relative to Heat 1) rectal temperature was lower (P < 0.05) from minutes 40-120, 2) mean weighted heat flow was higher (P < 0.05), 3) insulation was lower (P < 0.05), and 4) metabolic heat production was not different. These results suggest that prior physical exercise may predispose a person to greater heat loss and to experience a larger decline in core temperature when subsequently exposed to cold air. The combination of exercise intensity and duration studied in these experiments did not fatigue the shivering response to cold exposure.     

Effect of thermal stress on physiological parameters, feed intake and plasma thyroid hormones concentration in Alentejana, Mertolenga, Frisian and Limousine cattle breeds

The aim of the present study was to assess the heat tolerance of animals of two Portuguese (Alentejana and Mertolenga) and two exotic (Frisian and Limousine) cattle breeds, through the monitoring of physiological acclimatization reactions in different thermal situations characterized by alternate periods of thermoneutrality and heat stress simulated in climatic chambers. In the experiment, six heifers of the Alentejana, Frisian and Mertolenga breeds and four heifers of the Limousine breed were used. The increase in chamber temperatures had different consequences on the animals of each breed. When submitted to heat stress, the Frisian animals developed high thermal polypnea (more than 105 breath movements per minute), which did not prevent an increase in the rectal temperature (from 38.7°C to 40.0°C). However, only a slight depression in food intake and in blood thyroid hormone concentrations was observed under thermal stressful conditions. Under the thermal stressful conditions, Limousine animals decreased food intake by 11.4% and blood triiodothyronine (T3) hormone concentration decreased to 76% of the level observed in thermoneutral conditions. Alentejana animals had similar reactions. The Mertolenga cattle exhibited the highest capacity for maintaining homeothermy: under heat stressful conditions, the mean thermal polypnea increased twofold, but mean rectal temperature did not increase. Mean food intake decreased by only 2% and mean T3 blood concentration was lowered to 85,6% of the concentration observed under thermoneutral conditions. These results lead to the conclusion that the Frisian animals had more difficulty in tolerating high temperatures, the Limousine and Alentejana ones had an intermediate difficulty, and the Mertolenga animals were by far the most heat tolerant.     

Temperature regulation in adult quail (Colinus virginianus) during acute thermal stress

1. Evaporative heat loss, O2 consumption, CO2 production, and internal body temperature were measured in unanesthetized, unrestrained bobwhite (Colinus virginianus) at specific ambient temperatures (Ta). 2. No significant change in body temperature occurred at any Ta tested, but metabolic heat production (H) increased from 42.17 W/m2 at Ta 35 degrees C to 102.89 W/m2 at Ta 10 degrees C. 3. Evaporative heat loss (E) increased approximately two-fold from Ta 10-35 degrees C, with E/H increasing exponentially over the same temperature range. 4. No significant change in thermal insulation occurred from Ta 10-30 degrees C. 5. Combined convective and radiative heat transfer for the bobwhite was 2.96 W/m2 X C from Ta 10-35 degrees C.     

Thermal balance and survival time prediction of man in cold water.

Metabolic rates and rectal temperatures were continuously monitored for humans immersed in cold ocean water (4.6--18.2 degrees C) under stimulated accident conditions. The subjects wore only light clothing and a kapok lifejacket while either holding-still or swimming. While holding-still, metabolic heat production (Hm,kcal-min--1) was inversely related to water temperature (Tw, degrees C) according to the equation Hm equals 4.19 minus-0.117 Tw. This temperature response pattern is shown to be similar to that for exposure to air of the same temperature when air velocity is just over 5 m.p.h. (2.24 m/s). The thermogenic response was one-third efficient in balancing the calculated heat loss in cold water, resulting in hypothermia at a rectal temperature cooling rate (C, degrees C-min--1) dependent on water temperature (Tw, degrees C) according to the relation C equal 0.0785 - 0.0034Tw. Although swimming increased heat production to 2.5 times that of holding-still at 10.5 degrees C water temperature, cooling rate was 35% greater while swimming. A prediction equation for survival time (ts, min) of persons accidentally immersed in cold water (Tw, degrees C) has the form ts equal 15 + 7.2/(0.0785-0.0034Tw), based on the findings of this study, and it is compared to pre-existing models.     

Skinfolds and resting heat loss in cold air and water: temperature equivalence.

Fourteen male subjects with unweighted mean skinfolds (MSF) of 10.23 mm underwent several 3-h exposures to cold water and air of similar velocities in order to compare by indirect calorimetry the rate of heat loss in water and air. Measurements of heat loss (excluding the head) at each air temperature (Ta = 25, 20, 10 degrees C) and water temperature (Tw = 29-33 degrees C) were used in a linear approximation of overall heat transfer from body core (Tre) to air or water. We found the lower critical air and water temperatures to fall as a negative linear function of MSF. The slope of these lines was not significantly different in air and water with a mean of minus 0.237 degrees C/mm MSF. Overall heat conductance was 3.34 times greater in water. However, this value was not fixed but varied as an inverse curvilinear function of MSF. Thus, equivalent water-air temperatures also varied as a function of MSF. Between limits of 100-250% of resting heat loss the following relationships between MSF and equivalent water-air temperatures were found (see article).     

Metabolic response to air temperature and wind in day-old mallards and a standard operative temperature scale

Most duckling mortality occurs during the week following hatching and is often associated with cold, windy, wet weather and scattering of the brood. We estimated the thermoregulatory demands imposed by cold, windy weather on isolated 1-d-old mallard (Anas platyrhynchos) ducklings resting in cover. We measured O2 consumption and evaporative water loss at air temperatures from 5 degrees to 25 degrees C and wind speeds of 0.1, 0.2, 0.5, and 1.0 m/s. Metabolic heat production increased as wind increased or temperature decreased but was less sensitive to wind than that of either adult passerines or small mammals. Evaporative heat loss ranged from 5% to 17% of heat production. Evaporative heat loss and the ratio of evaporative heat loss to metabolic heat production was significantly lower in rest phase. These data were used to define a standard operative temperature (Tes) scale for night or heavy overcast conditions. An increase of wind speed from 0.1 to 1 m/s decreased Tes by 3 degrees -5 degrees C.     

Temperature regulation and basal metabolic rate in the spotted skunk, Spilogale putorius

1. Metabolic rate, body temperature, and evaporative water loss of six spotted skunks were measured at air temperatures between 8 and 40 degrees C. 2. The mean metabolic rate of spotted skunks at thermoneutral air temperatures was 30.5% below that predicted by body mass. 3. Thermal conductance, body temperature, and rates of evaporative water loss were like those of similar sized mammals. 4. The non-elongate body form, omnivorous diet, and low level of activity of spotted skunks distinguish them from other mustelids and may account for their lower-than-expected basal metabolism.     

Effects of temperature acclimation on maximum heat production,thermal tolerance,and torpor in a marsupial

Marsupials, unlike placental mammals, are believed to be unable to increase heat production and thermal performance after cold-acclimation. It has been suggested that this may be because marsupials lack functional brown fat, a thermogenic tissue, which proliferates during cold-acclimation in many placentals. However, arid zone marsupials have to cope with unpredictable, short-term and occasionally extreme changes in environmental conditions, and thus they would benefit from an appropriate physiological response. We therefore investigated whether a sequential two to four week acclimation in Sminthopsis macroura (body mass approx. 25 g) to both cold (16 degrees C) and warm (26 degrees C) ambient temperatures affects the thermal physiology of the species. Cold-acclimated S. macroura were able to significantly increase maximum heat production (by 27%) and could maintain a constant body temperature at significantly lower effective ambient temperatures (about 9 degrees C lower) than when warm-acclimated. Moreover, metabolic rates during torpor were increased following cold-acclimation in comparison to warm-acclimation. Our study shows that, despite the lack of functional brown fat, short-term acclimation can have significant effects on thermoenergetics of marsupials. It is likely that the rapid response in S. macroura reflects an adaptation to the unpredictability of the climate in their habitat.     

Advantages of a smaller bodymass in humans when distance-running in warm, humid conditions

Using a 65-kg athlete running a 2 h 10 min marathon as an example, we estimated that imbalances between approximately 1400 W of heat production and dissipation would occur in ambient temperatures of 17 degrees C at 90% relative humidity (rh) to 37 degrees C at 50% rh. Because heat production during running depends on body mass and heat loss depends on surface area, intercepts between predicted heat production and maximal heat loss with increasing speeds depend on an athlete's body mass. At 35 degrees C and 60% rh, a 45-kg athlete could maintain thermal balance by running a 2 h 13 min marathon at 19.1 km x h(-1) but a 75-kg athlete would only be able run a 3 h 28 min marathon at 12.2 km x h(-1). In both cases, the production of 970-1020 W of heat would necessitate the evaporation of at least 1.5-1.6 l of sweat per hour. A lower metabolic heat production in lighter runners at any given speed may be one reason why smallness of stature is an asset in distance running.     

The lower and upper critical temperatures in male Japanese

Critical temperatures were determined by a new estimating system called the polynomial equation method. Its consists of polynomial regression equations of metabolic rate on ambient and body temperatures and conversion equations enable to convert metabolic rate value into temperature value. Nine young adult males were tested using the system. Metabolic rate was calculated indirectly with a reference to protein metabolism and the critical temperatures were determined as follows; the lower critical air temperature to be 26.2 C, the upper critical air temperature to be 47.0 degrees C, the lower and upper mean skin temperature to be 29.2 degrees C and 36.5 degrees C, and the lower and upper critical rectal temperature to be 35.5 degrees C and 37.9 degrees C, respectively. The polynomial equation method has an advantage over the intersect method since it allows estimation of several kinds of critical temperature.     

Temperature and humidity of expired air of sheep

The temperature and humidity of expired air from three adult Merino sheep were measured at air temperatures of 20, 30 and 40 degrees C before and after the animals were shorn. Expired air was apparently always saturated with water vapour. At the higher air temperatures the temperature of expired air was close to deep body temperature; at lower air temperatures, expired air had been significantly cooled, e.g. to 32.3 degrees C in shorn sheep at 20 degrees C air temperature. Expired air was cooler from shorn than from unshorn animals at 20 and 30 degrees C air temperature, possibly due to thermally induced vasomotor changes in the upper respiratory tract. Cooling of expired air would be expected to lead to recovery of some of the water evaporated during inspiration; at 20 degrees C air temperature, this fraction was estimated to be 25% in unshorn sheep and 36% in shorn sheep.     

Prediction of mean skin temperature in warm environments

The data collected by the authors in four experimental series have been analysed together with data from the literature, to study the relationship between mean skin temperature and climatic parameters, subject metabolic rate and clothing insulation. The subjects involved in the various studies were young male subjects, unacclimatized to heat. The range of conditions examined involved mean skin temperatures between 33 degrees C and 38 degrees C, air temperatures (Ta) between 23 degrees C and 50 degrees C, ambient water vapour pressures (Pa) between 1 and 4.8 kPa, air velocities (Va) between 0.2 and 0.9 m.s-1, metabolic rates (M) between 50 and 270 W.m-2, and Clo values between 0.1 and 0.6. In 95% of the data, mean radiant temperature was within +/- 3 degrees C of air temperature. Based on 190 data averaged over individual values, the following equation was derived by a multiple linear regression technique: Tsk = 30.0 + 0.138 Ta + 0.254 Pa-0.57 Va + 1.28.10(-3) M-0.553 Clo. This equation was used to predict mean skin temperature from 629 individual data. The difference between observed and predicted values was within +/- 0.6 degrees C in 70% of the cases and within +/- 1 degrees C in 90% of the cases. It is concluded that the proposed formula may be used to predict mean skin temperature with satisfactory accuracy in nude to lightly clad subjects exposed to warm ambient conditions with no significant radiant heat load.