A preliminary study on the seasonal body temperature rhythms of the captive mountain hare (Lepus timidus)

The mountain hare (Lepus timidus) is a year-round active herbivore adapted to survive the boreal winter. Captive mountain hares (N = 4) were implanted with intraabdominal thermosensitive loggers to record their core body temperature (T_b) for a year and during food deprivation (8–48 h) in summer and winter. The average T_b was 38.7 ± 0.01 °C in summer and 38.3 ± 0.01 °C in winter. The yearly T_b correlated positively with the ambient temperature. The 24-h T_b was the highest from late scotophase to early photophase in summer and winter and the lowest during middle-late photophase in summer or during early-middle scotophase in winter. The range of the 24-h oscillations in T_b increased in three animals in winter. Food deprivation did not induce hypothermia in summer or winter. These preliminary data suggest that the mountain hare can spare a modest amount of energy with the wintertime reduction in T_b.     

Daily rhythm of oxygen consumption and thermoregulatory responses in some European winter- or summer-acclimatized finches at different ambient temperatures

The oxygen consumption of European finches, the siskin (Carduelis spinus), the brambling (Fringilla montifringilla), the bullfinch (Pyrhulla pyrhulla), the greenfinch (Carduelis chloris) and the hawfinch (Coccothraustes coccothraustes), was recorded continuously while ambient temperature was decreased stepwise from +30 down to-75°C. The oxygen consumption, body temperature (telemetrically), and shivering (integrated pectoral electromyography) of greenfinches were measured simultaneously at ambient temperatures between +30 and-75°C. Maximum heat production, cold limit, lower critical temperature, basal metabolic rate and thermal conductance (of the greenfinch) were determined. The diurnal variation of oxygen consumption of siskins and greenfinches was recorded at thermoneutrality and below the thermoneutral zone in winter- and summer-acclimatized birds. The diurnal variation of body temperature and thermal conductance of greenfinches were also determined. The diurnal variation of heat production was not seasonal or temperature dependent in the siskin and in the greenfinch. Nocturnal reduction of oxygen consumption saved 15–33% energy in the siskin and greenfinch. Body temperature of the greenfinch was lowered by 2.5–3.4°C. The nocturnal reduction of thermal conductance in the greenfinch was 39–48%. The basal metabolic rate was lowest in the largest bird (hawfinch) and highest in the smallest bird (siskin). The values were in the expected range. The heat production capacity of finches in winter was 4.7 times basal metabolic rate in the siskin, 4.2 times in the brambling, 3.5 times in the greenfinch and 2.9 times in the bullfinch and hawfinch. The heat production capacity of the siskin and greenfinch was not significantly lower in summer. The cold limit temperatures (°C) in winter were-61.2 in the siskin,-41.3 in the greenfinch,-37.0 in the bullfinch,-35.7 in the brambling and-28.9 in the hawfinch. The cold limit was 14.3°C higher in summer than in winter in the siskin and 8.7°C in the greenfinch. Thermal insulation of the greenfinch was significantly better in winter than in summer. The shivering of the greenfinch increased linearly when ambient temperature was decreased down to-40°C. Maintenance of shivering was coincident with season. In severe cold integrated pectoral electromyography did not correlate with oxygen consumption as expected. The possible existence of non-shivering thermogenesis in birds is discussed. It is concluded that the acclimatization of European finches is primarily metabolic and only secondly affected by insulation.Abbreviations AAT avian adipose tissue - bm body mass - BMR basal metabolic rate - C _t thermal conductance - EMG electromyogram - HP heat production - HP _max maximum heat production - MR metabolic rate - NST non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a ambient temperature - T _b body temperature - T _c colonic temperature - T _1c lower critical temperature - TNZ thermoneutral zone - T _st shivering threshold temperature - V oxygen consumption     

Seasonal effects on thermoregulatory responses of the Rock Kestrel, Falco rupicolis

Thermoregulatory responses are known to differ seasonally in endotherms and this is often dependent on the environment and region they are resident. Holarctic animals are exposed to severe winters and substantial seasonal variation in ambient temperature. In contrast, those in the Afrotropics have less severe winters, but greater variation in temperature, rainfall and net primary production. These environmental factors place different selection pressures on physiological responses in endotherms. In this study, metabolic rate (VO₂) and body temperature (T_b) were measured in captive bred Rock Kestrels (Falco rupicolus) from the Afrotropics after a period of summer and winter acclimatisation. Resting metabolic rate was significantly lower after the winter acclimatisation period than after the summer acclimatisation period, and there was a shift in the thermoneutral zone from 20–33 °C in summer to 15–30 °C in winter. However, no significant difference in basal metabolic rate between summer and winter was found. The results show that Rock Kestrels reduce energy expenditure at low ambient temperatures in winter as expected in an Afrotropical species.     

On the low viscosity blood of two cold water,marine sculpins

Summary The viscosities of blood from shorthorn sculpin (Myoxocephalus scorpius), longhorn sculpin (Myoxocephalus octodecemspinosus) and winter flounder (Pseudopleuronectes americanus) were compared using a cone-plate viscometer. Both species of sculpin were almost identical with respect to blood and plasma viscosity at the temperatures (0 and 15°C) and shear rates (2.3–90/s) examined. In contrast, the viscosities of winter flounder blood and plasma were considerably greater than those observed in the sculpins. This difference in blood viscosity between the shorthorn sculpin and the winter flounder persisted over the hematocrit range of 0 to 40% red blood cells. The viscosity of the plasma and the interactions between plasma proteins and red blood cells appeared to be the major reasons for the relatively high viscosity of the flounder blood. Although a proportion of the flounder blood viscosity was attributable to fibrinogen, other plasma proteins also appeared to play a significant role. The relatively low blood viscosity of the sculpin species may confer a circulatory advantage during periods of low water temperatures.     

Preferred ambient temperature for old and young men in summer and winter

To investigate the effects of age on thermal sensitivity, preferred ambient temperature (T _pref) was compared between old (71–76 years) and young (21–30 years) groups, each consisting of six male subjects in summer and winter. The air temperature (T _a) was set at either 20° C or 40° C at commencement. The subject was directed to adjust theT _a for 45 min by manipulating a remote control switch to the level at which he felt most comfortable. In the older group, theT _pref was significantly lower in trials starting at 20° C than that starting at 40° C in summer. The fluctuation ofT _pref (temperature difference between maximum and minimumT _a during the last 10 min) was significantly wider in the older group in both summer and winter. Repetition of the same experiment on each subject showed a poorer reproducibility ofT _pref in the older group than in the younger group in summer. Tympanic and esophageal temperatures of the older group kept falling throughout the trial starting at 20° C in summer. These results suggest that thermal sensitivity is decreased with advancing age and that thermal perception in the elderly, especially to cold, is less sensitive in summer.     

Seasonal adaptation of thermal and metabolic responses in men wearing different clothing at 10° C

Thermoregulatory responses at ambient temperatures of 20 and 10° C in six male subjects wearing two different kinds of clothing were compared between summer and winter. The two different kinds of clothing were one insulating the upper half of the body lightly and the lower half of the body heavily (clothing A, the weight in the upper and lower halves of the body being, respectively, 489 g and 1278 g) and the other insulating the upper half of the body heavily and the lower half of the body lightly (clothing B: 1212 g and 559 g). The major findings are summarized as follow. (i) Rectal temperature was kept significantly higher in clothing B than in clothing A both in summer and winter. (ii) The fall of rectal temperature was significantly greater in summer than in winter in both types of clothing. (iii) Mean skin temperatures and skin temperatures in the face, chest, thigh and leg were significantly lower atT _a of 10° C in summer than in winter in clothing A, while skin temperatures in the face and thigh were also significantly lower atT _a of 10° C in summer than in winter in clothing B. (iv) Metabolic heat production was higher in summer than in winter at 20 and 10° C in both types of clothing. (v) The subjects felt cooler and colder toT _a of 10° C in summer than in winter in both types of clothing. These different responses occurring between summer and winter are discussed mainly in terms of total conductance and dry heat loss.     

Seasonal variation on metabolism and thermoregulation in Chinese bulbul

1

Seasonal changes in a bird's physiology and behavior are considered to be a part of an adaptive strategy for survival and reproductive success. To understand modes of metabolic adaptations, the metabolic rate (Vo₂), body temperature (T_b), and thermal conductance (C) of the Chinese bulbul (Pycnonotus sinensis) in the Zhejiang Province of China were determined in the summer and the winter at a temperature range from 5 to 35 °C, respectively.     

The effect of temperature on the pattern of torpor in a marsupial hibernator

Physiological variables of torpor are strongly temperature dependent in placental hibernators. This study investigated how changes in air temperature affect the duration of torpor bouts, metabolic rate, body temperature and weight loss of the marsupial hibernator Burramys parvus (50 g) in comparison to a control group held at a constant air temperature of 2°C. The duration of torpor bouts was longest (14.0±1.0 days) and metabolic rate was lowest (0.033±0.001 ml O₂·g^-1·h^-1) at2°C. At higher air temperatures torpor bouts were significantly shorter and the metabolic rate was higher. When air temperature was reduced to 0°C, torpor bouts also shortened to 6.4±2.9 days, metabolic rate increased to about eight-fold the values at 2°C, and body temperature was maintained at the regulated minimum of 2.1±0.2°C. Because air temperature had such a strong effect on hibernation, and in particular energy expenditure, a change in climate would most likely increase winter mortality of this endangered species.Abbreviationst STP standard temperature and pressure - T _a air temperature - T _b body temperature - VO₂ rate of oxygen consumption     

Aerobic and anaerobic energy expenditure during rest and activity in montane Bufo b. boreas and Rana pipiens

Summary The relations of standard and active aerobic and anaerobic metabolism and heart rate to body temperature (T _b) were measured in montane groups of Bufo b. boreas and Rana pipiens maintained under field conditions. These amphibians experience daily variation of T _b over 30°C and 23°C, respectively (Carey, 1978). Standard and active aerobic and anaerobic metabolism, heart rate, aerobic and anaerobic scope are markedly temperature-dependent with no broad plateaus of thermal independence. Heart rate increments provide little augmentation of oxygen transport during activity; increased extraction of oxygen from the blood probably contributes importantly to oxygen supply during activity. Development of extensive aerobic capacities in Bufo may be related to aggressive behavior of males during breeding. Standard metabolic rates of both species are more thermally dependent than comparable values for lowland relatives. Thermal sensitivity of physiological functions may have distinct advantages over thermally compensated rates in the short growing season and daily thermal fluctuations of the montane environment.     

Daily and seasonal cycles of body temperature and aspects of heterothermy in the hedgehog Erinaceus europaeus

Summary Intra-abdominal temperature-sensitive radio transmitters were used to collect more than 350 sets of body temperature (T _b ) data from 23 captive adult hedgehogs over a 3-year period. Each data set comprised measurements made every 1/2 h for 24-h periods. Between 20 and 60 such data sets were recorded every calendar month, and a total of 17400 measurements of T _b were collected. The hedgehogs were exposed to natural environmental conditions at 57°N in NE Scotland. Hedgehogs showed seasonal changes in mean daily euthermic T _b ,with a July maximum of 35.9±0.2°C, a September minimum of 34.7±0.9°C, and a marked circadian T _b cycle that correlates closely with photoperiod. Maximal T _b occurred within 2 h of midnight and this pattern of nocturnal maximum and diurnal minimum T _b was most marked between April and September. The circadian T _b cycle was least correlated with photoperiod during winter. Hibernal T _b during winter correlated with ambient temperature (T _a ),it was maximal in September (17.7±1.0°C) and minimal in December (5.2±0.9°C). Apart from the tracking of T _a and T _b during hibernal bouts, with a time-lag of 4–6 h, circadian rhythmicity of hibernal T _b was not evident. However, the T _b of hibernating hedgehogs rose significantly when T _a fell below — 5°C, although the animals did not neccessarily arouse. Although hibernal bouts occurred between September and April, 89.5% of such bouts were recorded between November and February. The mean time of entry into hibernation was 01:45±5.1 h GMT while the mean time of the start of spontaneous arousal from hibernation was 11:53±4.8 h GMT. Therefore, during hibernation hedgehogs were either fully aroused at night, when euthermic hedgehogs have maximalT _b ,or in deep hibernation around midday, when euthermic hedgehogs have minimal T _b .Since wild hedgehogs will feed during spontaneous arousal from hibernation, these timings are probably adaptive, and suggest that entry into, and arousal from, hibernation may be extensions of circadian cyclicity. Spontaneous bouts of transient shallow torpor (TST) were recorded throughout the year, with nearly 80% of observations occurring during August and September, at the start of the hibernal period. TST bouts lasted for 4.9±2.9 h, with T _b falling to 25.8±3.1 °C. Only 20% of TST bouts immediately preceded hibernation and their duration did not correlate with T _a or body mass. TST bouts started at 06:51±4.7 h GMT, significantly later than entry into hibernation, and ended at 13:04±5.4 h GMT. The function of TST bouts is unclear, but they may be preparation for the hibernation season or a further energy conservation strategy. When arousing from hibernation hedgehogs warmed at a rate of 1.9±0.4°C·h^-1, and when entering hibernation cooled at 7.9±1.9°C·h^-1. Warming rates were slightly higher during mid-winter when T _b and body mass were minimal, but cooling rates were 44% higher at the end of the hibernal period compared to the start. Cooling and warming rates were strikingly similar to those measured in hedgehogs at 31°N. These results demonstrate that thermoregulation in the hedgehog is closely regulated and changes on a seasonal basis, in meeting with requirements of surviving food shortages and low temperature during winter.Abbreviations T _a ambient temperature - T _b body temperature - CSD circular standard deviation - SWS slow wave sleep - TST transient shallow torpor     

Nest insulation: Energy savings to brown lemmings using a winter nest

Summary Energy metabolism of brown lemmings in summer pelage was measured over long periods at several air temperatures, with and without a real nest or artificial nest material. Resting metabolism of lemmings at T _a=-16°C was 43% higher than that of lemmings in nests. As T _a increased, the difference between resting metabolism of animals with and without nests decreased and was similar at T _a=20°C. The energy saved at rest is equivalent to a reduction of approximately 40% in the thermal conductance. Independent estimates of energy savings due to nest insulation by analysis of cooling curves of a lemming model with and without a nest suggest a 46% reduction in thermal conductance due to the nest. At T _a=0°C, baby lemmings huddled in a nest had equilibrium temperature excesses (T _b-T _a) four to five times higher than isolated nestlings outside the nest. These data indicate that there is a substantial energy savings at ecologically relevant air temperatures, and that energy savings increase as T _a decreases. If the insulative value of the nest is similar whether the animal is in summer or winter pelage, these data suggest that heat production of a resting lemming would be 0.88 W (about 1.6 times BMR), while in nests at subnivean air temperatures typical of Barrow, Alaska, during the winter.     

Body temperature and basking behaviour of Nile crocodiles (Crocodylus niloticus) during winter

The ability to thermoregulate in reptilians is often through behavioural modification. We investigated body temperature (T_b) patterns during winter in the amphibious Nile crocodile (Crocodylus niloticus) and its relationship to basking behaviour at the St. Lucia Crocodile Centre, St. Lucia, South Africa. It was found that crocodiles had no daily plateaus in T_b but rather continuous oscillations in T_b within a range of mean minimum T_b 18.8–19.6 °C to mean maximum T_b 26.9–29.2 °C. Crocodile T_b increased during the day, usually after 10:00 irrespective of body size. Behavioural data showed that the crocodiles usually left the water to bask around 10:00. It is suggested that basking behaviour is important for elevating T_b rather than attaining a preferred T_b. The increased T_b may allow them to perform optimally when they return to water. The basking occurrence has management implications as it suggests that the best time to conduct aerial censuses of the St. Lucia crocodiles is during winter after 10:00 when most of the individuals are basking and hence most easily seen.     

Thermal relations of large crocodiles,Crocodylus porosus,free-ranging in a naturalistic situation

We monitored behaviour and environmental and body temperatures (T_b) in summer and winter in 11 salt-water crocodiles (Crocodylus porosus), of body mass 32 to 1010kg, free-ranging in naturalistic captivity in northern Australia. We found pronounced daily cycles in air and water temperatures in both winter (16 to 33 degrees C and 20 to 31degrees C, respectively) and summer (21 to 45 degrees C and 24 to 36 degrees C, respectively). In winter, crocodiles exposed themselves to the sun during the day and stayed in the water at night. In summer, they remained in the water during the day and emerged onto land at night. Body temperature showed a daily cycle the amplitude of which decreased with increasing mass, from 3.5 degrees C (mass 32kg) to 1.0 degrees C (660kg) in summer, and from 3.5 degrees C (42kg) to 1.4 degrees C (1010kg) in winter. Underlying the daily cycles in T_b were intermediate (10 to 13 day, tidal?) and seasonal cycles. Overall, values of modal T_b ranged from 25.1 to 28.7 degrees C in winter and from 28.4 to 33.6 degrees C in summer, trending upwards with body size. This pattern of continuous oscillations in T_b, with no daily plateau, is conspicuously different from that seen in crocodilians of small sizes and from the pattern usually regarded as typical of reptiles in general.     

Cold adaptation of the terrestrial isopod,Porcellio scaber,to subnivean environments

The terrestrial isopod, Porcellio scaber, was susceptible to subzero temperature: both freezing and chilling were injurious. The level of cold hardiness against chilling and freezing showed different patterns in their seasonal variation. The lower lethal temperature causing 50% mortality, an indicator of the tolerance to chilling, ranged from-1.37°C in August to-4.58°C in December. The whole body supercooling point, the absolute limit of freeze avoidance, was kept at about-7°C throughout the year. The winter decrease in lower lethal temperature was concomitant with an accumulation of low molecular weight carbohydrates which are possible protective reagents against chilling injury, whereas the less seasonally variable supercooling point seemed to be associated with the year-round presence of gut content. Food derivatives may act as efficient ice nucleators. The different trend in seasonal changes between lower lethal temperature and supercooling point may be related to the microclimate of the hibernacula in subnivean environments, where the winter temperature became lower than the lower lethal temperature in the summer active phase, but remained higher than the summer supercooling point.Abbreviations LLT₅₀ lower lethal temperature inducing 50% mortality - SCP supercooling point - T _a ambient air temperature - T _s soil surface temperature     

Blood viscosity and optimal hematocrit in narrow tubes

Blood viscosity in normal adults was measured in glass tubes with diameters of 50, 100 and 500 microns for a wide range of adjusted feed hematocrits (15-70%). Blood viscosity decreased at each of the adjusted feed hematocrits when going from a 500-micron tube to a 50-micron tube. The viscosity reduction increased with increasing hematocrit. The steepness in the hematocrit-viscosity curves decreased with decreasing tube diameter. Erythrocyte transport efficiency (hematocrit/blood viscosity) was calculated to estimate the optimal hematocrit for oxygen transport. Optimal hematocrit averaged 38% in 500-micron tubes, 44% in 100-micron tubes and 51% in 50-micron tubes. Our results suggest that the strong F?hraeus-Lindqvist effect at high hematocrits may help to maintain oxygen transport in polycythemic patients as long as the driving pressure is sufficient.     

Effect of constant and fluctuating temperatures on resting and active oxygen consumption of toads,Bufo boreas

Summary The relations of standard and active rates of oxygen consumption to body temperature (T_b) were tested in montane Bufo b. boreas and lowland Bufo boreas halophilus acclimated to constant T _b of 10, 20, or 30° C or to a fluctuating cycle of 5–30° C. Standard metabolic rates (SMR) of boreas acclimated to 30° C and halophilus acclimated to 10° C show pronounced regions of thermal independence but all other standard and active metabolic rates of groups acclimated to other thermal regimes are thermally sensitive. The SMR of both subspecies acclimated to the 5–30° C cycle are more thermally sensitive than those of similar individuals acclimated to constant T _b. In cases where the relation between SMR and T _b is linear for both halophilus and boreas at the same acclimation temperature, the slope and Q₁₀ of the relation for boreas are significantly higher than those of halophilus. Acclimation had little or no effect on the active metabolic rates of either subspecies. The relation between SMR and T _b of boreas maintained under field conditions (Carey, 1979) is matched only by those of individuals from the same population acclimated to 20° C.     

Telemetric field studies of body temperature and activity rhythms of Acomys russatus and A. cahirinus in the Judean Desert of Israel

Two species of the genus Acomys coexist in arid zones of southern Israel. Acomys russatus is distributed in extremely arid areas, while A. cahirinus is common in both Mediterranean and arid regions. Individuals of both species from a rodent community in the Ein Gedi Nature Reserve were implanted with temperature-sensitive transmitters. Body temperature (T _b) rhythms were recorded in free-ranging mice at four different seasons of the year. A. cahirinus (30–45 g) showed a nocturnal rhythm of T _b throughout the year. In the activity phase during the night T _b increased to 38.2°C. During the day T _b decreased to 34°C. This species displayed this pattern in summer also when ambient temperatures rose above T _b. The T _b of A. russatus (45–65 g) varied between 34.8 and 41°C during the hot season, showing a bimodal temperature rhythm with maximal values in the morning and in the evening. Measurements of activity in this species showed inactivity during the hottest period of a summer day. In winter A. russatus showed no clearly detectable diurnal or ultradian rhythm in T _b, which remained constant between narrow limits of 35.2 and 36.8°C. Received: 21 December 1998 / Accepted: 15 March 1999     

Optimal hematocrit theory during activity in the bullfrog (Rana catesbeiana).

1. There is an exponential relationship between blood viscosity (cP) and hematocrit (%) for the bullfrog; eta = 1.81 e0.033Hct. The in vitro optimal hematocrit calculated for blood flow through tubes, from this relationship for bullfrog blood, is 30%. 2. Amphibian blood is a non-Newtonian fluid with viscosity dependent on shear rate. It has a finite yield shear stress of about 1.5 dynes cm-2. 3. Hematocrit of bullfrogs was increased from 27% (control) to 57% by isovolemic erythrocythemia (constant volume blood-doping). There was a slight increase in systolic, diastolic and venous blood pressure with elevated hematocrit. 4. Systemic arch blood flow rate was inversely related to blood viscosity for erythrocythemic bullfrogs. The decrease in systemic arch blood flow at high hematocrits was due primarily to reduced pulse volume rather than reduced heart rate. 5. Systemic arch blood flow, when standardised between individuals, was inversely related to blood viscosity; Qbl = 0.185 + 3.73 eta -1. This relationship was significantly different from that predicted by the Poiseuille-Hagen flow formula. The in vivo optimal hematocrit calculated from this relationship was 41%. 6. Optimal hematocrit theory appears to be generally applicable for Rana catesbeiana in vitro and in vivo. Most individuals had an in vivo optimal hematocrit, but the absence of a clear optimal hematocrit for some individuals could reflect methodological variability, or in vivo physiological compensation for the increased blood viscosity at high hematocrit.     

Body temperature patterns in two syntopic elephant shrew species during winter

We measured body temperature (T_b) in free-ranging individuals of two species of elephant shrews, namely western rock elephant shrews (Elephantulus rupestris) and Cape rock elephant shrews (E. edwardii), during winter in a winter-rainfall region of western South Africa. These syntopic species have similar ecologies and morphologies and thus potential for large overlaps in diet and habitat use. Unexpectedly, they displayed different T_b patterns. Western rock elephant shrews were heterothermic, with all individuals decreasing T_b below 30 °C on at least 34% of nights. The level of heterothermy expressed was similar to other species traditionally defined as daily heterotherms and was inversely related to T_a, as is commonly seen in small heterothermic endotherms. In contrast, Cape rock elephant shrews rarely allowed their T_b to decrease below 30 °C. The level of heterothermy was similar to species traditionally defined as homeotherms and there was no relationship between the level of heterothermy expressed and T_a. In both species, the minimum daily T_b was recorded almost exclusively at night, often shortly before sunrise, although in some individuals minimum T_b occasionally occurred during the day. The interspecific variation in T_b patterns among Elephantulus species recorded to date reiterates the importance of ecological determinants of heterothermy that interact with factors such as body mass and phylogeny.