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.     

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     

Factors affecting body temperatures of toads

Summary Factors influencing levels and rates of variation of body temperature (T _b) in montane Bufo boreas boreas and in lowland Bufo boreas halophilus were investigated as an initial step toward understanding the role of natural thermal variation in the physiology and energetics of these ectothermic animals. Body temperatures of boreas can vary 25–30° C over 24-h periods. Such variation is primarily due to both nocturnal and diurnal activity and the physical characteristics of the montane environment. Bufo boreas halophilus are primarily nocturnal except during breeding and are voluntarily active at body temperatures ranging between 10 and 25° C. Despite variation in T _b encountered in the field, boreas select a narrow range of T _b in a thermal gradient, averaging 23.5 and 26.2° C for fasted individuals maintained under field conditions or acclimated to 20° C, respectively. In a thermal gradient the mean T _b of fasted halophilus acclimated to 20° C is 23.9° C. Skin color of boreas varies in the field from very dark to light. The dark skins absorb approximately 4% more radiation than the light ones. Light colored boreas should absorb approximately 5% more radiation than similarly colored halophilus. Evaporative water losses increase directly with skin temperatures and vapor pressure deficit in both subspecies. Larger individuals heat and cool more slowly than smaller ones. Calculation of an enery budget for boreal toads suggests that they could sit in direct sunlight for long periods without fatally overheating, providing the skin was continually moist.     

Standard operative temperatures and cost of thermoregulation in the arctic ground squirrel,Spermophilus undulatus

Summary Body temperatures (T _b) and daily activity patterns of free-living arctic ground squirrells (Spermophilus undulatus) were determined via telemetry at a field site in northern Alaska. Simultaneous measurements were made of ambient temperature (T _a), wind speed (V), and incident solar radiation. The operative environmental temperature (T _e) for ground squirrels was obtained from fur-covered, thin metal taxidermic models of the animals. Standard operative temperature (T _es), a comparative index of heat flow, was calculated from T _e, V, and laboratory measurements of thermal conductivity.During the period of the study (August), S. undulatus were active for about 14 h per day (06.00 to 20.00 h). T _b was high throughout the daily cycle, averaging 38–39°C. Circadian variations in T _b were slight; average T _b values dropped <1°C at night. Daytime T _b fluctuations were not closely correlated to activity or to changes in environmental conditions. Air temperatures during the study were low, usually between 10 and 15°C during the day. However, T _es in exposed areas was normally higher, even though skies were generally overcast. During periods of sunshine, T _es may be as high as 34°C. The absence of nocturnal activity may result from increased costs of thermoregulation at night, which sharply reduces foraging efficiency. The high and stable body temperatures of S. undulatus probably result from thermoneutral daytime T _es, low activity levels, and the use of well-insulated nests.     

Reduction of metabolism during hibernation and daily torpor in mammals and birds: temperature effect or physiological inhibition?

Summary The present study addresses the controversy of whether the reduction in energy metabolism during torpor in endotherms is strictly a physical effect of temperature (Q₁₀) or whether it involves an additional metabolic inhibition. Basal metabolic rates (BMR; measured as oxygen consumption, ), metabolic rates during torpor, and the corresponding body temperatures (T _b) in 68 mammalian and avian species were assembled from the literature (n=58) or determined in the present study (n=10). The Q₁₀ for change in between normothermia and torpor decreased from a mean of 4.1 to 2.8 with decreasingT _b from 30 to <10°C in hibernators (species that show prolonged torpor). In daily heterotherms (species that show shallow, daily torpor) the Q₁₀ remained at a constant value of 2.2 asT _b decreased. In hibernators with aT _b<10°C, the Q₁₀ was inversely related to body mass. The increase of mass-specific metabolic rate with decreasing body mass, observed during normothermia (BMR), was not observed during torpor in hibernators and the slope relating metabolic rate and mass was almost zero. In daily heterotherms, which had a smaller Q₁₀ than the hibernators, no inverse relationship between the Q₁₀ and body mass was observed, and consequently the metabolic rate during torpor at the sameT _b was greater than that of hibernators. These findings show that the reduction in metabolism during torpor of daily heterotherms and large hibernators can be explained largely by temperature effects, whereas a metabolic inhibition in addition to temperature effects may be used by small hibernators to reduce energy expenditure during torpor.Abbreviation BMR basal metabolic rate     

Seasonal changes in daily metabolic patterns of Lacerta viridis

Summary Lacerta viridis maintained under natural photoperiodic conditions show daily and seasonal changes in metabolic rates and body temperature (T _b) as well as seasonal differences in sensitivity to temperature change. At all times of the year lizards have a daily fluctuation in oxygen consumption, with higher metabolic rates during the light phase of the day when tested at a constant ambient temperature (T _a) of 30°C. Rhythmicity of metabolic rate persists under constant darkness, but there is a decrease in the amplitude of the rhythm.Oxygen consumption measured at various T_as shows significant seasonal differences at T _as above 20°C. Expressed as the Arrhenius activation energy, metabolic sensitivity of Lacerta viridis shows temperature dependence in autumn, which changes to metabolic temperature independence in spring at T _as above 20°C. The results indicate a synergic relationship between changing photoperiod and body temperature selection, resulting in seasonal metabolic adjustment and seasonal adaptation.Abbreviations ANOVA analysis of variance - LD long day (16 h light) - SD short day (8 h light) - T _a ambient temperature - T _b body temperature     

Metabolic and cardiovascular adaptations in the western chipmunks, genusEutamias

Summary The metabolic and cardiac responses to temperature were studied in two species (four subspecies) of western chipmunks (genusEutamias), inhabiting boreal and alpine environments. A specially designed (Fig. 1) implantable biopential radiotransmitter was used to measure heart rate in unrestrained animals. The estimated basal metabolic rates (EBMR) were 1.78 (E. minimus borealis), 1.64 (E. m. oreocetes), 1.50 (E. m. operarius), and 1.69 ml O₂ g^–1 h^–1 (E. amoenus luteiventris), or 839, 752, 698, and 628 ml O₂ kg^–0.75 h^–1, respectively, for the four subspecies (Table 1). The two alpine species (E.m.or. andE.m.op.) had significantly lower EBMR than both of their boreal counterparts. The EBMR from all animals are 120–135% of the predicted values based on body weights of the animals. The thermal neutral zone for the four subspecies ranged from 23.5 to 32°C and the minimum thermal conductances were 0.113, 0.111, 0.112 and 0.112 ml O₂ g^–1 h^–1 °C^–1, respectively, or 54.4, 54.0, 50.4 and 52.1 ml O₂ kg^–0.75 h^–1 °C^–1, respectively (Fig. 2). No interspecific diffence in conductance was observed. These values are 72 to 85% of their weight specific values. The body temperature ranged between 35.0 and 39.5°C and was usually maintained between 36 and 38°C in all subspecies between ambient temperatures of 3 and 32°C. The estimated basal heart rates were 273, 296, 273 and 264 beats/min, respectively, for the four subspecies, 49–55% of their predicted weight specific values. The resultant oxygen pulses (metabolic rate/heart rate) were 5.49, 4.50, 4.48 and 5.56×10^–3 ml O₂/beat, respectively, which are 2 to 2.4 times their weight specific values (Table 2).The observed reduction of basal heart rate without the corresponding decreases of basal metabolic rate and body temperature indicate sufficient compensatory increases in stroke volume and/or A-V oxygen difference at rest. Such cardiovascular modifications provide extra reserves when demand for aerobic metabolism rises during bursts of activity typically observed in the western chipmunk.Abbreviations A-V arterio-venous - EBMR estimated basal metabolic rate (ml O₂ g^–1 h^–1) - HR heart rate (beats/min) - MR metabolic rate (ml O₂ g^–1 h^–1) - OP oxygen pulse (ml O₂/heart beat) - T_a, T_b ambient and body temperature (°C)     

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     

Cardiac responses to stress and activity in the armoured legless lizard Ophisaurus apodus: Comparison with snake and tortoise

• 1.1. Heart rate (HR) was measured during and after stress and activity in the armoured legless lizard Ophisaurus apodus, the snake Natrix natrix and the tortoise Testudo hermanni, at different body temperatures T_b. These are discussed in relation to field T_b, defensive behaviour and published V́O₂.
• 2.2. Ophisaurus apodus used passive defence, including hemipenis or cloacal sac eversion and prolonged immobility after release. This was correlated with a low degree of tachycardia, bradycardia at low T_b, low metabolism and armour.
• 3.3. Defence behaviour was T_b-dependent in wild T. hermanni, with passive withdrawal into the shell at low T_b, and active struggling at high T_b. The degree of tachycardia was lower at low T_b.
• 4.4. Standard and active oxygen pulse OP were insensitive to T_b in O. apodus and N. natrix, and their SOP was lower than tetrapod lizards. Factorial scope of HR was reduced at 35°C, just above the activity T_b range of these species.
• 5.5. Recovery of HR after activity in T. hermanni was much more rapid than in the squamates, and of similar duration to recovery after stress. It is suggested that tortoises do not utilize anaerobic metabolism during activity.

     

Oxygen consumption rates of adults and chicks during brooding in king quail (Coturnix chinensis)

Oxygen consumption rates were measured in chicks (0–7 days of age), and in non-brooding and brooding adults. Brooded chicks maintained a constant oxygen consumption rate at a chamber ambient temperature of 10–35°C (0–5 days of age: 2.95ml O₂·g^-1·h^-1 and 6–17 days of age: 5.80 ml O₂·g^-1·h^-1) while unbrooded chicks increased oxygen consumption rate at ambient temperature below 30°C to double the brooded oxygen consumption rate at 25 and 15°C for chicks < 5 days of age and>5 days of age, respectively. The massspecific oxygen consumption rate of breeding male and females (non-brooding) were significantly elevated within the thermoneutral zone thermal neutral zone (28–35°C) in comparison to non-breeding adults. Below the thermal neutral zone, oxygen consumption rate was not significantly different. The elevation in oxygen consumption rate of breeding quail was not correlated with the presence of broodpatches, which developed only in females, but is a seasonal adjustment in metabolism. Male and females that actively brooded one to five chicks had significantly higher oxygen consumption rate than non-brooding quail at ambient temperature below 30°C. Brooding oxygen consumption rate was constant during day and night, indicating a temporary suppression of the circadian rhythm of metabolism. Brooding oxygen consumption rate increased significantly with brood number, but neither adult body mass nor adult sex were significant factors in the relationship between brooding oxygen consumption rate and ambient temperature. The proportion of daylight hours that chicks were brooded by parents was negatively correlated with ambient temperature. After chicks were 5 days old brooding time was reduced but brooding oxygen consumption rate was unchanged. Heat from the brooding parent appeared to originate mainly from the apteria under the wings and legs rather than the broodpatch. The parental heat contribution to chick temperature regulation below the chicks' thermal neutral zone is achieved by increasing parental thermal conductance by a feedback control similar to that suggested for the control of egg temperature via the brood-patch. It is concluded that the brooding period is an energetic burden to parent quail, and the magnitude of the cost increases directly with brood number and inversely with ambient temperature during this period. The oxygen consumption rate of brooding parents was 5.80–6.90 ml O₂·g^-1·h^-1 (ambient temperature 10–15°C) at night and up to 5.10 ml O₂·g^-1·h^-1 (ambient temperature 18°C) during the day, which are 100 and 40% higher than non-brooding birds, respectively.Abbreviations bm body mass - SMR standard metabolic rate - T _a ambient temperature - T _b body temperature - I/O₂ oxygen consumption rate - C _wet wet thermal conductance - TNZ thermal neutral zone - ANOVA analysis of variance - ANCOVA analysis of covariance     

Responses to heat stress in two species of Australian quail,Coturnix pectoralis andCoturnix chinensis

Summary Stubble quail and King quail are both native to Australia although Stubble quail extend into more arid environments than do King quail. In this study, the responses of body temperature (T _b), heart rate (f _h), respiration rate (f _r) and rates of gular flutter (f _g) were measured in response to ambient temperatures (T _a) ranging from 20 °C to 50 °C. Both species exhibited hyperthermia atT _a in excess of 38–39 °C although both species maintainedT _b lower thanT _a atT _a above 42 °C. Respiration rate remained relatively constant until the onset of panting, just prior to the commencement of gular flutter. The onset of panting and gular flutter in both species was relatively sudden and occurred at a meanT _a of 38.1 °C for Stubble quail (meanT _b of 42.5 °C) and a significantly higherT _a of 40.9 °C but similar meanT _b of 42.1 °C for King quail. Gular flutter appeared to occur synchronously with respiration and showed some tendency to increase withT _b. The percentage of time spent in gular flutter showed a direct increase withT _b. Heart rate tended to decrease with increasingT _a in King quail while remaining relatively constant in Stubble quail. However, the relationship was not consistent and a great deal of variability existed between individuals. The two species are similar in their responses to heat stress and in general these responses do not reflect their different natural habitats.Symbols f _h heart rate - f _r respiratory rate - f _g rate of gular fluttering     

Effects of temperature and dissolved oxygen on heart rate,ventilation rate and oxygen consumption of spangled perch,Leiopotherapon unicolor (Günther 1859), (Percoidei,Teraponidae)

Summary Heart, ventilation and oxygen consumption rates ofLeiopotherapon unicolor were studied at temperatures ranging from 5 to 35°C, and during progressive hypoxia from 100% to 5% oxygen saturation. Biopotentials recorded from the water surrounding the fish corresponded to ventilation movements, and are thought to originate from the ventilatory musculature. Cardio-respiratory responses to temperature and dissolved oxygen follow the typical teleost pattern, with bradycardia, increased ventilation rate and reduced oxygen consumption occurring during hypoxia. However, ventilation rate did not increase at 15°C and below. Ventilation rate showed a slower response to increasing temperature (normoxic Q₁₀=1.39) than heart rate and oxygen consumption (normoxic Q₁₀=2.85 and 2.38).L. unicolor is unable to survive prolonged hypoxia by utilising anaerobic metabolism, but has a large gill surface area which presumably facilitates oxygen uptake in hypoxic environments. Periodic ventilation during normoxia in restingL. unicolor may improve ventilation efficiency by increasing the oxygen diffusion gradient across the gills.Abbreviations EBG electrobranchiogram - ECG electrocardiogram     

Evaluating thermal resource partitioning

Summary The field thermal biology of sympatric Anolis cooki and A. cristatellus were evaluated in January and in August in desert scrub forest at Playa de Tamarindo near Guanica, Puerto Rico. Data on randomly positioned copper models of lizards, each equipped with a built-in thermocouple, established null hypotheses about basking frequency and operative temperatures (T _e) against which the behavior and body temperatures (T _b) of live lizards were evaluated. Both species exhibited non-random hourly basking rates (more marked in cristatellus than in cooki), and cristatellus was virtually inactive during the warm mid-day hours. The relationship between lizards' T _b and randomly sampled T _e differed between the species: cristatellus's mean T _b was 2° to 3° C lower than randomly sampled mean T _e in both months, whereas cooki's mean T _b was slightly higher than mean T _e in January and slightly lower in August. Although cooki's mean T _b was higher than that of cristatellus in both months, the T _b's of the two species overlapped substantially over an annual cycle. Given the similarities in their field active T _b and the low thermal heterogeneity among microsites at Playa de Tamarindo, these species appear not to partition the thermal environment there in a coarse-grained way. Instead, the relatively small differences in their field active T _b probably result from small differences in their use of similar microhabitats within their mutually exclusive territories. Thermal resource partitioning by territorial animals is unlikely unless thermal heterogeneity is coarse-grained in relation to territory size.     

Energy metabolism of Chironomus anthracinus (Diptera: Chironomidae) from the profundal zone of Lake Esrom,Denmark, as a function of body size,temperature and oxygen concentration

The profundal zone of Lake Esrom, Denmark has a dense population of Chironomus anthracinus, which survives 2–4 months of oxygen depletion each summer during stratification. The metabolism of 3rd and 4th instar larvae was examined in regard to variation in biomass and temperature. Respiration at air saturation was described by a curvilinear multiple regression relating oxygen consumption to individual AFDW and temperature. At 10 °C and varying oxygen regimes the O₂ consumption and CO₂ production of 4th instar larvae were almost unaltered from saturation to about 3 mg O₂ l^–1, but decreased steeply below this level. The respiratory quotient increased from 0.82 at saturation to about 3.4 at oxygen concentrations near 0.5 mg O₂ l^–1. This implied a shift from aerobic to partially anaerobic metabolism. At 0.5 mg O₂ l^–1 the total energy production equalled 20% of the rate at saturation of which more than one third was accounted for by anaerobic degradation of glycogen. This corresponded to a daily loss of 12 µg mg AFDW^–1 or approximately 5% of the body reserves. At unchanged metabolic rate the glycogen store would last three weeks, but long term oxygen deficiency causes a further suppression of the energy metabolism in C. anthracinus.     

Factors affecting the daily rhythm of body temperature of captive mouse lemurs (<Emphasis Type="Italic">Microcebus murinus</Emphasis>)

Microcebus murinus, a small nocturnal Malagasy primate, exhibits adaptive energy-saving strategies such as daily hypothermia and gregarious patterns during diurnal rest. To determine whether ambient temperature (T_a), food restriction and nest sharing can modify the daily body temperature (T_b) rhythm, T_b was recorded by telemetry during winter in six males exposed to different ambient temperatures (T_a=25, 20, 15°C) and/or to a total food restriction for 3 days depending on social condition (isolated versus pair-grouped). At 25°C, the daily rhythm of T_b was characterized by high T_b values during the night and lower values during the day. Exposure to cold significantly decreased minimal T_b values and lengthened the daily hypothermia. Under food restriction, minimal T_b values were also markedly lowered. The combination of food restriction and cold induced further increases in duration and depth of torpor bouts, minimal T_b reaching a level just above T_a. Although it influenced daily hypothermia less than environmental factors, nest sharing modified effects of cold and food restriction previously observed by lengthening duration of torpor but without increasing its depth. In response to external conditions, mouse lemurs may thus adjust their energy expenditures through daily modifications of both the duration and the depth of torpor.     

Aerobic and anaerobic metabolism during activity in snakes

Summary Oxygen consumption and blood lactate concentration in the snakesColuber constrictor, Crotalus viridis, Lichanura roseofusca andMasticophis flagellum and whole body lactate concentration inCrotalus viridis andMasticophis flagellum were determined under standard conditions and after a bout of maximal activity induced by a 5 min period of mechanical stimulation. Observations were made atT _b=35°C inColuber, Crotalus, andMasticophis and 32°C inLichanura. Maximal oxygen consumption inColuber andMasticophis was twice that ofCrotalus and 4 x that ofLichanura (Fig. 1). Post-active whole body lactate concentration inMasticophis was twice that ofCrotalus (Fig. 2). Immediately post-active and 30 min post-active blood lactate concentration inColuber andMasticophis was 1.5 x and 3.5 x that ofCrotalus andLichanura, respectively (Fig. 3). These data support conclusions that: (a) maximal energy production by these snakes correlates well with their respective modes of predation and defense, the highly active predatorsColuber andMasticophis being capable of the greatest net energy production during activity; (b)Coluber andMasticophis exhibit aerobic scopes as high or higher than any other comparably sized reptile heretofore investigated; (c) weight specific anaerobic metabolism probably does not decrease with increasing body size in reptiles; (d) anaerobic metabolism provides >50% of net energy production during five minutes of activity in all species examined (Table 1).     

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     

Capacity for sustained terrestrial locomotion in an insect: Energetics,thermal dependence,and kinematics

Summary The capacity for sustained, terrestrial locomotion in the cockroach. Blaberus discoidalis, was determined in relation to running speed, metabolic cost, aerobic capacity, and ambient temperature (T _a=15, 23, and 34°C; acclimation temperature=24°C). Steady-state thoracic temperature (T _tss) increased linearly with speed at each T _a.The difference between T _tss and T _awas similar at each experimental temperature with a maximum increase of 7°C. Steady-state oxygen consumption (VO_2ss) increased linearly with speed at each T _aand had a low thermal dependence (Q₁₀=1.0-1.4). The minimum cost of locomotion (the slope of the VO_2ss versus speed function) was independent of T _a.Cockroaches attained a maximal oxygen consumption (VO_2max). increased with T _afrom 2.1 ml O₂·g^-1·h^-1 at 15°C to 4.9 ml O₂·g^-1·h^-1 at 23°C, but showed no further increase at 34°C, VO_2max increased 23-fold over resting VO₂ at 23°C, 10-fold at 34°C, and 15-fold at 15°C. Endurance correlated with the speed at which VO_2max was attained (MAS, maximal aerobic speed). Temperature affected the kinematics of locomotion. compared to cockroaches running at the same speed, but higher temperatures (23–34°C), low temperature (15°C) increased protraction time, reduced stride frequency, and reduced stability by increasing body pitching. The thermal independence of the minimum cost of locomotion (C_min), the low thermal dependence of VO_2ss (i.e., y-intercept of the VO_2ss versus speed function), and a typical Q₁₀ of 2.0 for VO_2max combined to increase MAS and endurance in B. discoidalis when T _awas increased from 15 to 23°C. Exerciserelated endothermy enabled running cockroaches to attain a greater VO_2max, metabolic scope, and endurance capacity at 23°C than would be possible if T _tss remained equal to T _a. The MAS of B. discoidalis was similar to that of other arthropods that use trachea, but was 2-fold greater than ectotherms, such as salamanders, frogs, and crabs of a comparable body mass.Abbreviations T _a ambient temperature - T _t thoracic temperature - T _tss steady state thoracic temperature during exercise - T _trest thoracic temperature during rest - VO₂ oxygen consumption - VO_2rest oxygen consumption during rest - VO_2ss steady-state oxygen consumption during exercise - VO_2max maximal oxygen consumption; MAS maximum aerobic speed - C _min minimum cost of locomotion - t _end endurance time     

Thermoregulatory and metabolic responses of Japanese quail to hypoxia

Common responses to hypoxia include decreased body temperature (T_b) and decreased energy metabolism. In this study, the effects of hypoxia and hypercapnia on T_b and metabolic oxygen consumption (V.O₂) were investigated in Japanese quail (Coturnix japonica). When exposed to hypoxia (15, 13, 11 and 9% O₂), T_b decreased only at 11% and 9% O₂ compared to normoxia; quail were better able to maintain T_b during acute hypoxia after a one-week acclimation to 10% O₂. V.O₂ also decreased during hypoxia, but at 9% O₂ this was partially offset by increased anaerobic metabolism. T_b and V.O₂ responses to 9% O₂ were exaggerated at lower ambient temperature (T_a), reflecting a decreased lower critical temperature during hypoxia. Conversely, hypoxia had little effect on T_b or V.O₂ at higher T_a (36 °C). We conclude that Japanese quail respond to hypoxia in much the same way as mammals, by reducing both T_b and V.O₂. No relationship was found between the magnitudes of decreases in T_b and V.O₂ during 9% O₂, however. Since metabolism is the source of heat generation, this suggests that Japanese quail increase thermolysis to reduce T_b. During hypercapnia (3, 6 and 9% CO₂), T_b was reduced only at 9% CO₂ while V.O₂ was unchanged.