How photoperiod influences body temperature selection in Lacerta viridis

Summary European green lizards, Lacerta viridis, show a distinct annual cycle in their day and nighttime selected body temperature (T _b) levels when monitored under natural photoperiod. The amplitude between daily photophase and scotophase temperatures varies throughout the year. Highest body temperatures with smallest day/night variation are selected from May through July. Throughout fall, the difference between day and nighttime selected T _b levels increases. Lizards inevitably enter a state of winter dormancy which terminates daily rhythmicity patterns. Under natural photoperiodic conditions, cessation of dormancy occurs spontaneously by mid-March, regardless whether high temperatures are available or not. Lacerta viridis respond to an artificial long photoperiod (16 h light, 8 h dark) at all times of the year with modifications in both diel patterns and levels of selected T _b to summer-like conditions. When, however, the natural photoperiod at different phases in the annual cycle is held constant for six to eight weeks, T _b selection of Lacerta viridis also remains stable at the level corresponding to the prevailing photoperiod. These results implicate that the photoperiod is a more prominent Zeitgeber for seasonal cueing of temperature selection than has been surmised in the past. Further, we suggest that the large variations recorded in daily T _b cycles do not imply that this lizard is an imprecise thermoregulator, but rather indicates an important integral process necessary for seasonal acclimatization.     

Metabolism and thermoregulation in the eastern hedgehogErinaceus concolor

Body temperature and oxygen consumption were measured in the eastern hedgehog,Erinaceus concolor Martin 1838, during summer at ambient temperatures (T _a) between-6.0 and 35.6°C.E. concolor has a relatively low basal metabolic rate (0.422 ml O₂·g^-1·h^-1), amounting to 80% of that predicted from its body mass (822.7 g). Between 26.5 and 1.2°C, the resting metabolic rate increases with decreasing ambient temperature according to the equation: RMR=1.980-0.057T _a. The minimal heat transfer coefficient (0.057 ml O₂·g^-1·h^-1·°C^-1) is higher than expected in other eutherian mammals, which may result from partial conversion of hair into spines. At lower ambient temperature (from-4.6 to-6.0° C) there is a drop in body temperature (from 35.2 to 31.4° C) and a decrease in oxygen consumption (1.530 ml O₂·g^-1·h^-1) even though the potential thermoregulation capabilities of this species are significantly higher. This is evidenced by the high maximum noradrenaline-induced non-shivering thermogenesis (2.370 ml O₂·g^-1·h^-1), amounting to 124% of the value predicted. The active metabolic rate at ambient temperatures between 31.0 and 14.5° C averages 1.064 ml O₂·g^-1·h^-1; at ambient temperatures between 14.5 and 2.0° C AMR=3.228-0.140T _a.Abbreviations AMR active metabolic rate - bm body mass - BMR basal metabolic rate - h heat transfer coefficient - NA noradrenaline - NST non-shivering thermogenesis - NST_max maximum rate of NA-induced non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - STPD standard temperature and pressure (25°C, 1 ATM) - T _a ambient temperature - T _b body temperature     

The thermal and energetic significance of clustering in the speckled mousebird,Colius striatus

Summary The effect of clustering behaviour on metabolism, body temperature, thermal conductance and evaporative water loss was investigated in speckled mousebirds at temperatures between 5 and 36°C. Within the thermal neutral zone (approximately 30–35 °C) basal metabolic rate of clusters of two birds (32.5 J·g^-1·h^-1) and four birds (28.5 J·g^-1·h^-1) was significantly lower by about 11% and 22%, respectively, than that of individuals (36.4 J·g^-1·h^-1). Similarly, below the lower critical temperature, the metabolism of clusters of two and four birds was about 14% and 31% lower, respectively, than for individual birds as a result of significantly lower total thermal conductance in clustered birds. Body temperature ranged from about 36 to 41°C and was positively correlated with ambient temperature in both individuals and clusters, but was less variable in clusters. Total evaporative water loss was similar in individuals and clusters and averaged 5–6% of body weight per day below 30°C in individuals and below 25°C in clusters. Above these temperatures total evaporative water loss increased and mousebirds could dissipate between 80 and 90% of their metabolic heat production at ambient temperatures between 36 and 39°C. Mousebirds not only clustered to sleep between sunset and sunrise but were also observed to cluster during the day, even at high ambient temperature. Whereas clustering at night and during cold, wet weather serves a thermoregulatory function, in that it allows the brrds to maintain body temperature at a reduced metabolic cost, clustering during the day is probably related to maintenance of social bonds within the flock.Abbreviations BMR basal metabolic rate - bw body weight - C _totab total thermal conductance - EWI evaporative water loss - M metabolism - RH relative humidity - T _a ambient temperature - T _b body temperature - T _ch chamber temperature - T _cl cluster temperature - TEWL total evaporative water loss - LCT lower critical temperature - TNZ thermal neutral zone     

Interactive effects of temperature and photoperiod on the daily activity and energy metabolism of pouched mice (Saccostomus campestris: Cricetidae) from southern Africa

The daily activity and energy metabolism of pouched mice (Saccostomus campestris) from two localities in southern Africa was examined following warm (25 °C) and cold (10 °C) acclimation under long (LD 14:10) and short (LD 10:14) photoperiol. There was no differential effect of photoperiod on the daily activity or metabolism of pouched mice from the two localities examined, which suggests that reported differences in photoresponsivity between these two populations were not the result of differences in daily organisation. Neverthe-less, there was a significant increase in metabolism at 10 °C, irrespective of photoperiod, even though seven cold-acclimated animals displayed bouts of spontaneous torpor and saved 16.4–36.2% of their daily energy expenditure. All but one of these bouts occurred under short photoperiod, which suggests that short photoperiod facilitated the expression of torpor and influenced the daily energy metabolism of these individuals. As expected for a noctureal species, the amount of time spent active increased following acclimation to short photoperiod at 25 °C. However, there was a reduction in mean activity levels under short photoperiod at 10 °C, possibly because the stimulation of activity by short photoperiod was masked by a reduction in activity during bouts of spontaneous torpor. Cold temperature clearly had an overriding effect on the daily activity and metabolism of this species by necessitating an increase in metabolic heat production and eliciting spontaneous torpor which overrode the effect of short photoperiod on activity at an ambient temperature of 10 °C.Abbreviations 3-ANOVA three-way analysis of variance - %ACT percentage of time spent active - ADMR average daily metabolic rate - M _b body mass - MR metabolic rate - MR_dark metabolic rate recorded during the dark phase - MR_light metabolic rate recorded during the light phase - NST non-shivering thermogenesis - RQ respiratory quotient - STPD standard temperature and pressure, dry - T _a ambient temperature - T _b body temperature - VO₂ oxygen consumption     

Ventilatory accommodation of oxygen demand and respiratory water loss in a large bird,the emu (Dromaius novaehollandiae), and a re-examination of ventilatory allometry for birds

Ventilation was studied in the emu, a large flightless bird of mass 40kg, within the range of ambient temperatures from-5 to 45°C. Data for the emu and 21 other species were used to calculate allometric relationships for resting ventilatory parameters in birds (breath frequency=13.5 mass^-0.314; tidal volume=20.7 mass^1.0). At low ambient temperatures the ventilatory system must accommodate the increased metabolic demand for oxygen. In the emu this was achieved by a combination of increased tidal volume and increased oxygen extraction. Data from emus sitting and standing at-5°C, when metabolism is 1.5x and 2.6x basal metabolic rate, respectively, indicate that at least in the emu an increase in oxygen extraction can be stimulated by low temperature independent of oxygen demand. At higher ambient temperatures ventilation was increased to facilitate respiratory water loss. The emu achieved this by increased respiratory frequency. At moderate heat loads (30–35°C) tidal volume fell. This is usually interpreted as a mechanism whereby respiratory water loss can be increased without increasing parabronchial ventilation. At 45°C tidal volume increased; however, past studies have shown that CO₂ washout is minimal under these conditions. The mechanism whereby this is possible is discussed.Abbreviations BMR basal metabolic rate - BTPS body temperature, ambient pressure, saturated - EO ₂ oxygen extraction - EWL evaporative water loss - f _R ventilation frequency - RH relative humidity - RHL respiratory heat loss - SEM standard error of the mean - SNK student-Newman-Keuls multiple range test - STPD standard temperature and pressure, dry - T _a ambient temperatures(s) - T _b body temperature(s) - T _ex expired air temperature(s) - T _rh chamber excurrent air temperature - V _J ventilation - VO₂ oxygen consumption - V _T tidal volume - V/Q air ventilation to blood perfusion ratio     

Seasonal and daily rhythms of body temperature in the European hamster (Cricetus cricetus) under semi-natural conditions

Body temperature of five European hamsters exposed to semi-natural environmental conditions at 47° N in Southern Germany was recorded over a 1.5-year period using intraperitoneal temperature-sensitive radio transmitters. The animals showed pronounced seasonal changes in body weight and reproductive status. Euthermic body temperature changed significantly throughout the year reaching its maximum of 37.9±0.2°C in April and its minimum of 36.1±0.4°C in December. Between November and March the hamsters showed regular bouts of hibernation and a few bouts of shallow torpor. During hibernation body temperature correlated with ambient temperature. Monthly means of body temperature during hibernation were highest in November (7.9±0.8°C) and March (8.2±0.5°C) and lowest in January (4.4±0.7°C). Using periodogram analysis methods, a clear diurnal rhythm of euthermic body temperature could be detected between March and August, whereas no such rhythm could be found during fall and winter. During hibernation bouts, no circadian rhythmicity was evident for body temperature apart from body temperature following ambient temperature with a time lag of 3–5 h. On average, hibernation bouts lasted 104.2±23.8 h with body temperature falling to 6.0±1.7°C. When entering hibernation the animals cooled at a rate of -0.8±0.2°C·h^-1; when arousing from hibernation they warmed at a rate of 9.9±2.4°C·h^-1. Warming rates were significantly lower in November and December than in January and February, and correlated with ambient temperature (r=-0.46, P<0.01) and hibernating body temperature (r=-0.47, P<0.01). Entry into hibrnation occured mostly in the middle of the night (mean time of day 0148 hours ±3.4 h), while spontaneous arousals were widely scattered across day and night. For all animals regression analysis revealed free-running circadian rhythms for the timing of arousal. These results suggest that entry into hibernation is either induced by environmental effects or by a circadian clock with a period of 24 h, whereas arousal from hibernation is controlled by an endogenous rhythm with a period different from 24 h.Abbreviations bw body weight - CET central European time - T _a ambient temperature - T _b body temperature - TTL transistor-transistor logic     

Comparative thermoregulatory adaptations of field mice of the genus Apodemus to habitat challenges

Thermoregulatory abilities, which may play a role in physiological adaptations, were compared between two field mouse species (Apodemus mystacinus and A. hermonensis) from Mount Hermon. While A. hermonensis is common at altitudes above 2100 m, A. mystacinus is common at 1650 m. The following variables were compared in mice acclimated to an ambient temperature of 24°C with a photoperiod of 12L:12D, body temperature during exposure to 4°C for 6 h, O₂ consumption and body temperature at various ambient temperature, non-shivering thermogenesis measured as a response to a noradrenaline injection, and the daily rhythm of body temperature. Both species could regulate their body temperature at ambient temperatures between 6 and 34°C. The thermoneutral zone for A. mystacinus lies between 28 and 32°C, while for A. hermonensis a thermoneutral point is noted at 28°C. Both species increased O₂ consumption and body temperature as a response to noradrenalin. However, maximal VO ₂ consumption as an response to noradrenaline and non-shivering thermogenesis capacity were higher in A. mystacinus, even though A. hermonensis is half the size of A. mystacinus. The body temperature rhythm in A. hermonensis has a clear daily pattern, while A. mystacinus can be considered arhythmic. The results suggest that A. hermonensis is adapted to its environment by an increase in resting metabolic rate but also depends on behavioural thermoregulation. A. mystacinus depends more on an increased non-shivering thermogenesis capacity.Abbreviations C thermal conductance - NA noradrenaline - NST non-shivering thermogenesis - OTC overall thermal conductance - RMR resting metabolic rate - STPD standard temperature and pressure dry - T _a ambient temperature - T _b body temperature - I _b Min minimal T _b , measured before NA iniection - T _b NA maximal - T _b as a response to NA injection - T _lc lower critical point - TNP thermoneutral point - TNZ thermoneutral zone - VO₂ O₂ consumption - VO₂ Min minimal VO₂ measured before NA injection - VO₂NA maximal VO₂, as a response to NA injection     

A radio-telemetric study of the thermoregulation of free living water monitor lizards,Varanus S. salvator

Eight water monitor lizards, Varanus s. salvator, were captured; four individuals from an oil palm estate on the Malayan peninsula, and four from fresh water-deficient Tulai island 65 km off-shore in the South China Sea. They were fitted with a radio transmitter attached to a thermistor which was inserted into the cloaca of the animals and released. The heating rate during basking was measured as 0.117 and 0.118 °C·min^-1 while the daily cloacal temperature fluctuated between 29.5–37.3 °C. Cloacal temperature was measured on other individuals caught at random times during the day, which revealed a considerable daily and individual variation. The average cloacal temperature during activity was 30.4 °C. The peak activity appeared when body temperature was 31 °C. Thermoregulation by behavioural means included cooling in water and reducing heat loss at night by sleeping in burrows. The cooling rate for two individuals when submerged in 29 °C water was 0.308 and 0.340 °C·min^-1. There appeared to be a strong correlation between ambient temperature and cloacal temperature.Abbreviations bw body weight - T _a ambient temperature - T _a body temperature - T _c cloacal temperature - TOP Timor Oil Palm Estate - TUL Tulai Island     

Thermoregulatory responses to egg cooling in incubating bantam hens

Summary O₂ consumption, electromyographic activity (EMG), heart rate (HR), cloacal temperature (T _b) and broodpatch temperature (T _sb) were measured in bantam hens incubating eggs of different temperatures (T _e). For comparison, the metabolic response to low ambient temperature (T _a) was measured in non-incubating hens.O₂ consumption increased nearly linearly with decreasingT _e down to 30°C. At this temperature O₂ consumption was about 3.5 x the resting level. Below 30°C O₂ consumption increased non-linearly, and reached 4.6 x the resting consumption at 15°C. Eggs of 10 and 0°C gave no further increase. Pectoral muscle EMG and HR also increased in response to egg cooling. The onset of egg cooling was associated with a decrease inT _b andT _sb. Hens exposed to lowT _a showed a lower critical temperature of about 24°C.It is concluded that heat loss from the brood-patch during incubation of cold eggs is compensated by shivering thermogenesis. AtT _e below 15°C heat production is at a maximum level, corresponding to the expected O₂ consumption at exposure to an ambient temperature of –65°C.Abbrevations EMG electromyography - T _a ambient temperature - T _b cloacal temperature - T _e egg temperature - T _sb brood-patch skin temperature     

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     

Reduction of metabolic rate and thermoregulation during daily torpor

Physiological mechanisms causing reduction of metabolic rate during torpor in heterothermic endotherms are controversial. The original view that metabolic rate is reduced below the basal metabolic rate because the lowered body temperature reduces tissue metabolism has been challenged by a recent hypothesis which claims that metabolic rate during torpor is actively downregulated and is a function of the differential between body temperature and ambient temperature, rather than body temperature per se. In the present study, both the steady-state metabolic rate and body temperature of torpid stripe-faced dunnarts, Sminthopsis macroura (Dasyuridae: Marsupialia), showed two clearly different phases in response to change of air temperature. At air temperatures between 14 and 30°C, metabolic rate and body temperature decreased with air temperature, and metabolic rate showed an exponential relationship with body temperature (r ²=0.74). The Q ₁₀ for metabolic rate was between 2 and 3 over the body temperature range of 16 to 32°C. The difference between body temperature and air temperature over this temperature range did not change significantly, and the metabolic rate was not related to the difference between body temperature and air temperature (P=0.35). However, the apparent conductance decreased with air temperature. At air temperatures below 14°C, metabolic rate increased linearly with the decrease of air temperature (r ²=0.58) and body temperature was maintained above 16°C, largely independent of air temperature. Over this air temperature range, metabolic rate was positively correlated with the difference between body temperature and air temperature (r ²=0.61). Nevertheless, the Q ₁₀ for metabolic rate between normothermic and torpid thermoregulating animals at the same air temperature was also in the range of 2–3. These results suggest that over the air temperature range in which body temperature of S. macroura was not metabolically defended, metabolic rate during daily torpor was largely a function of body temperature. At air temperatures below 14°C, at which the torpid animals showed an increase of metabolic rate to regulate body temperature, the negative relationship between metabolic rate and air temperature was a function of the differential between body temperature and air temperature as during normothermia. However, even in thermoregulating animals, the reduction of metabolic rate from normothermia to torpor at a given air temperature can also be explained by temperature effects.Abbreviations BM body mass - BMR basal metabolic rate - C apparent conductance - MR metabolic rate - RMR resting metabolic rate - RQ respiratory quotient - T _a air temperature - T _b body temperature - T _lc lower critical temperature - T _tc critical air temperature during torpor - TMR metabolic rate during torpor - TNZ thermoneutral zone - T difference between body temperature and air temperature - VO₂ rate of oxygen consumption     

The effect of metabolic fuel availability on thermoregulation and torpor in a marsupial hibernator

The physiological signal for torpor initiation appears to be related to fuel availability. Studies on metabolic fuel inhibition in placental heterotherms show that glucose deprivation via the inhibitor 2-deoxy-D-glucose (2DG) initiates a torpor-like state, whereas fatty acid deprivation via mercaptoacetate (MA) does not. As previous studies using inhibitors were limited to quantifying body temperature in placentals, we investigated whether inhibition of glucose or fatty acids for cellular oxidation induces torpor in the marsupial hibernator Cercartetus nanus, and how the response of metabolic rate is related to body temperature. Glucoprivation initiated a torpor-like state in C. nanus, but animals had much higher minimum body temperatures and metabolic rates than those of torpid food-deprived animals and arousal rates were slower. Moreover, 2DG-treated animals were thermoregulating at ambient temperatures of 20 and 12 °C, whereas food-deprived torpid animals were thermo-conforming. We suggest that glucoprivation reduces the hypothalamic body temperature set point, but only by about 8 °C rather than the approximately 28 °C during natural torpor. Reduced fatty acid availability via MA also induced a torpor-like state in some C. nanus, with physiological variables that did not differ from those of torpid food-deprived animals. We conclude that reduced glucose availability forms only part of the physiological trigger for torpor initiation in C. nanus. Reduced fatty acid availability, unlike for placental heterotherms, may be an important cue for torpor initiation in C. nanus, perhaps because marsupials lack functional brown adipose tissue.Abbreviations BAT brown adipose tissue - BMR basal metabolic rate - 2DG 2-deoxy-D-glucose - FD food deprived - GLM general linear models - MA mercaptoacetate - MR metabolic rate - RQ respiratory quotient - T_a ambient temperature - T_b body temperature - T_set body temperature set pointCommunicated by I.D. Hume     

Thermoregulation in a large bird,the emu (Dromaius novaehollandiae)

The emu is a large, flightless bird native to Australia. Its habitats range from the high snow country to the arid interior of the continent. Our experiments show that the emu maintains a constant body temperature within the ambient temperature range-5 to 45°C. The males regulate their body temperature about 0.5°C lower than the females. With falling ambient temperature the emu regulates its body temperature initially by reducing conductance and then by increasing heat production. At-5°C the cost of maintaining thermal balance is 2.6 times basal metabolic rate. By sitting down and reducing heat loss from the legs the cost of homeothermy at-5°C is reduced to 1.5 times basal metabolic rate. At high ambient temperatures the emu utilises cutaneous evaporative water loss in addition to panting. At 45°C evaporation is equal to 160% of heat production. Panting accounts for 70% of total evaporation at 45°C. The cost of utilising cutaneous evaporation for the other 30% appears to be an increase in dry conductance.Abbreviations A _r Effective radiating surface area - BMR basal metabolic rate - C _dry dry conductance - CEWL cutaneous evaporative water loss - EHL evaporative heat loss - EWL evaporative water loss - FECO₂ fractional concentration of CO₂ in excurrent air - FF_H2O water content of chamber excurrent air - FEO₂ fractional concentration of O₂ in chamber excurrent air - FICO₂ fractional concentration of CO₂ in incurrent air - FIO₂ fractional concentration of O₂ in chamber incurrent air - MHP metabolic heat production - MR metabolic rate - REWL respiratory evaporative water loss - RH relative humidity - RQ respiratory quotient ; - SA surface area - SEM standard error of the mean - SNK Student-Newman-Keuls multiple range test - STPD standard temperature and pressure dry - T _a ambient temperature(s) - T _b body temperature(s) - T _e surface temperature(s) - flow rate of air into the chamber - carbon dioxide production - oxygen consumption - vapour pressure of water     

Hummingbirds pay a high cost for a warm drink

Endotherms must warm ingested food to body temperature. Food warming costs may be especially high for nectar-feeding birds, which can ingest prodigious volumes. We formulated a mathematical model to predict the cost of warming nectar as a function of nectar temperature and sugar concentration. This model predicts that the cost of warming nectar should: (1) decrease as a power function of nectar concentration, and (2) increase linearly with the difference between body temperature and nectar temperature. We tested our model on rufous hummingbirds (Selasphorus rufus). A typical experiment consisted of feeding birds nectar of a given concentration at 39°C (equivalent to body temperature) and then at 4°C, and vice versa. We used the percentage change in metabolic rate between the two food temperatures to estimate the cost of warming nectar. The model's predictions were accurately met. When birds had to hover rather than perch during feeding bouts, estimated food-warming costs were only slightly lower. The cost of warming nectar to body temperature appears to be an important yet overlooked aspect of the energy budgets of nectar-feeding birds. Hummingbirds feeding on 5% sucrose solutions at 4^oC have to increase their metabolic rate by an amount equivalent to that elicited by a 15°C drop in ambient temperature.Abbreviations AE assimilation efficiency - C nectar concentration - H' cost of warming food to body temperature - SDA specific dynamic action - T_a ambient temperature - T_b body temperature - T_n nectar temperatureCommunicated by: G. Heldmaier     

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     

The impact of dietary fats,photoperiod, temperature and season on morphological variables,torpor patterns,and brown adipose tissue fatty acid composition of hamsters,Phodopus sungorus

We investigated how dietary fats and oils of different fatty acid composition influence the seasonal change of body mass, fur colour, testes size and torpor in Djungarian hamsters, Phodopus sungorus, maintained from autumn to winter under different photoperiods and temperature regimes. Dietary fatty acids influenced the occurrence of spontaneous torpor (food and water ad libitum) in P. sungorus maintained at 18°C under natural and artificial short photoperiods. Torpor was most pronounced in individuals on a diet containing 10% safflower oil (rich in polyunsaturated fatty acids), intermediate in individuals on a diet containing 10% olive oil (rich in monounsaturated fatty acids) and least pronounced in individuals on a diet containing 10% coconut fat (rich in saturated fatty acids). Torpor in P. sungorus on chow containing no added fat or oil was intermediate between those on coconut fat and olive oil. Dietary fatty acids had little effect on torpor in animals maintained at 23°C. Body mass, fur colour and testes size were also little affected by dietary fatty acids. The fatty acid composition of brown fat from hamsters maintained at 18°C and under natural photoperiod strongly reflected that of the dietary fatty acids. Our study suggests that the seasonal change of body mass, fur colour and testes size are not significantly affected by dietary fatty acids. However, dietary fats influence the occurrence of torpor in individuals maintained at low temperatures and that have been photoperiodically primed for the display of torpor.Abbreviations BAT brown adipose tissue - bm body mass - FA fatty acid(s) - MR metabolic rate - MUFA monounsaturated fatty acid(s) - PUFA polyunsaturated fatty acid(s) - SFA saturated fatty acid(s) - T _a air temperature - T _b body temperature - T_s body surface temperature(s) - TNZ thermoneutral zone - UFA unsaturated fatty acid(s)     

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     

Diving metabolism and thermoregulation in common and thick-billed murres

The diving and thermoregulatory metabolic rates of two species of diving seabrid, common (Uria aalge) and thick-billed murres (U. lomvia), were studied in the laboratory. Post-absorptive resting metabolic rates were similar in both species, averaging 7.8 W·kg^-1, and were not different in air or water (15–20°C). These values were 1.5–2 times higher than values predicted from published allometric equations. Feeding led to increases of 36 and 49%, diving caused increases of 82 and 140%, and preening led to increases of 107 and 196% above measured resting metabolic rates in common and thick-billed murres, respectively. Metabolic rates of both species increased linearly with decreasing water temperature; lower critical temperature was 15°C in common murres and 16°C in thick-billed murres. Conductance (assuming a constant body temperature) did not change with decreasing temperature, and was calculated at 3.59 W·m^-2·^oC^-1 and 4.68 W·m^-2·^oC^-1 in common and thick-billed murres, respectively. Murres spend a considerable amount of time in cold water which poses a significant thermal challenge to these relatively small seabirds. If thermal conductance does not change with decreasing water temperature, murres most likely rely upon increasing metabolism to maintain body temperature. The birds probably employ activities such as preening, diving, or food-induced thermogenesis to meet this challenge.Abbreviations ADL aerobic dive limit - BMR basal metabolic rate - FIT food-induced thermogenesis - MHP metabolic heat production - MR metabolic rate - PARR post-absorption resting rate - RMR resting metabolic rate - RQ respiratory quotient - SA surface area - STPD standard temperature and pressure (25°C, 1 ATM) - T _a ambient temperature - T _b body temperature - T _IC Iower critical temperatiure - TC thermal conductance - V oxygen consumption rate - W body mass     

The effect of photoperiod on temperature selection in the European green lizard,Lacerta viridis

Summary Voluntary body temperature selection of unrestrained Lacerta viridis revealed consistant photoperiod entrained diel patterns. Each daily cycle was characterized by an elevation in body temperature (T _b) to a high level plateau which declined at the onset of scotophase to a low level; both of which were maintained within narrow ranges.Under natural photoperiod in fall, lizards responded to shorter days by sinking low level T _b's and expanding the duration of these low levels until no rhythmicity was shown. Subsequent exposure to long day, LD 16:8, induced self-arousal and a slightly altered diel T _b selection with significantly higher T _b's being chosen at both the elevated and lower daily levels. Changes in the relations of diel T _b selection due to shift in photoperiod, suggest that photoperiod acts as a seasonal indicator for thermal adaptation.This research was carried out in partial fulfillment of a diploma degree at the J.W.G. University, Frankfurt/Main     

The energetics of the common mole rat Cryptomyś, a subterranean eusocial rodent from Zambia

Body temperature, oxygen consumption, respiratory and cardiac activity and body mass loss were measured in six females and four males of the subterranean Zambian mole rat Cryptomys sp. (karyotype 2 n=68), at ambient temperatures between 10 and 35°C. Mean body temperature ranged between 36.1 and 33.2°C at ambient temperatures of 32.5–10°C and was lower in females (32.7°C) than in males (33.9°C) at ambient temperatures of 10°C but dit not differ at thermoneutrality (32.5°C). Except for body temperature, mean values of all other parameters were lowest at thermoneutrality. Mean basal oxygen consumption of 0.76 ml O₂·g^-1· h^-1 was significantly lower than expected according to allometric equations and was different in the two sexes (females: 0.82 ml O₂·g^-1·h^-1, males: 0.68 ml O₂·g¹·h^-1) but was not correlated with body mass within the sexes. Basal respiratory rate of 74·min^-1 (females: 66·min¹, males: 87·min^-1) and basal heart rate of 200·min^-1 (females: 190·min^-1, males: 216·min^-1) were almost 30% lower than predicted, and the calculated thermal conductance of 0.144 ml O₂·g^-1·h¹·°C^-1 (females; 0.153 ml O₂·g^-1·h^-1·°C^-1, males: 0.131 ml O₂·g^-1·h^-1·°C^-1) was significantly higher than expected. The body mass loss in resting mole rats of 8.6–14.1%·day^-1 was high and in percentages higher in females than in males. Oxygen consumption and body mass loss as well as respiratory and cardiac activity increased at higher and lower than thermoneutral temperatures. The regulatory increase in O₂ demand below thermoneutrality was mainly saturated by increasing tidal volume but at ambient temperatures <15°C, the additional oxygen consumption was regulated by increasing frequency with slightly decreasing tidal volume. Likewise, the additional blood transport capacity was mainly effected by an increasing stroke volume while there was only a slight increase of heart frequency. In an additional field study, temperatures and humidity in different burrow systems have been determined and compared to environmental conditions above ground. Constant temperatures in the nest area 70 cm below ground between 26 and 28°C facilitate low resting metabolic rates, and high relative humidity minimizes evaporative water loss but both cause thermoregulatory problems such as overheating while digging. In 13–16 cm deep foraging tunnels, temperature fluctuations were higher following the above ground fluctuations with a time lag. Dominant breeding females had remarkably low body temperatures of 31.5–32.3°C at ambient temperatures of 20°C and appeared to be torpid. This reversible hypothermy and particular social structure involving division of labour are discussed as a strategy reducing energy expenditure in these eusocial subterranean animals with high foraging costs.Abbreviations BMR basal metabolic rate - br breath - C thermal conductance - HR neart rate - LD light/dark - M _b body mass - MR metabolic rate - OP oxygen pulse - PCO₂ partial pressure of carbon dioxide - PO₂ partial pressure of oxygen - RMR resting metabolic rate - RR respiratory rate - T _a ambient temperature - T _b body temperature - TNZ thermal neural zone - O₂ oxygen consumption