Metabolism,thermogenesis and daily rhythm of body temperature in the wood lemming,Myopus schisticolor

Wood lemmings (Myopus schisticolor) were captured during their autumnal migration in September and October. The animals were maintained at 12°C and under 12L:12D photoperiod. Basal metabolic rate and thermogenic capacity of the wood lemming were studied. Basal metabolic rate was 3.54 ml O₂·g^-1·h^-1, which is 215–238% of the expected value. The high basal metabolic rate seems to be typical of rodents living in high latitudes. The body temperature of the wood lemming was high (38.0–38.8°C), and did not fluctuate much during the 24-h recording. The high basal metabolic rate and the high body temperature are discussed with regard to behavioural adaptation to a low-quality winter diet. Thermogenic capacity, thermal insulation and non-shivering thermogenesis of the wood lemming displayed higher values than expected: 53.0 mW·g^-1, 0.53 mW·g^-1·C^-1 and 53.2 mW·g^-1, respectively. Brown adipose tissue showed typical thermogenic properties, although its respiratory property was fairly low, but mitochondrial protein content was high compared to other small mammals. The 24-h recording of body temperature and motor activity did not reveal whether the wood lemming is a nocturnal animal. Possibly, the expression of a circadian rhythm was masked by peculiar feeding behaviour. It is concluded that the wood lemming is well adapted to living in cold-temperature climates.Abbreviations BAT brown adipose tissue; bm, body mass - BMR basal metabolic rate - C conductance - Cox cytochrome-c-oxidase - HP heat production - HP_max maximum heat production - M metabolism - NA noradrenaline - NST non-shivering thermogenesis - NST_max maximum non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a anibient temperature - T _b body temperature - T _lc lower critical temperature - UCP uncoupling protein - vO₂ oxygen consumption - vO_{2 max} maximum oxygen consumption     

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     

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     

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     

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     

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     

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)     

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     

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     

Metabolic thermogenesis and evaporative water loss in the Hwamei Garrulax canorus

Basal metabolic rate (BMR) is thought to be a major hub in the network of physiological mechanisms connecting life history traits. Evaporative water loss (EWL) is a physiological indicator that is widely used to measure water relations in inter- or intraspecific studies of birds in different environments. In this study, we examined the physiological responses of summer-acclimatized Hwamei Garrulax canorus to temperature by measuring their body temperature (T_b), metabolic rate (MR) and EWL at ambient temperatures (T_a) between 5 and 40 °C. Overall, we found that mean body temperature was 42.4 °C and average minimum thermal conductance (C) was 0.15 ml O₂ g⁻¹ h⁻¹ °C⁻¹ measured between 5 and 20 °C. The thermal neutral zone (TNZ) was 31.8–35.3 °C and BMR was 181.83 ml O₂ h⁻¹. Below the lower critical temperature, MR increased linearly with decreasing T_a according to the relationship: MR (ml O₂ h⁻¹)=266.59–2.66 T_a. At T_as above the upper critical temperature, MR increased with T_a according to the relationship: MR (ml O₂ h⁻¹)=−271.26+12.85 T_a. EWL increased with T_a according to the relationship: EWL (mg H₂O h⁻¹)=−19.16+12.64 T_a and exceeded metabolic water production at T_a>14.0 °C. The high T_b and thermal conductance, low BMR, narrow TNZ, and high evaporative water production/metabolic water production (EWP/MWP) ratio in the Hwamei are consistent with the idea that this species is adapted to warm, mesic climates, where metabolic thermogenesis and water conservation are not strong selective pressures.     

Seasonal thermogenic capacity in a hibernator,Spermophilus richardsonii

Summary The maximum thermogenic capacity (HPmax) and the maximum capacity for non-shivering thermogenesis (NSTmax) were assessed in a hibernator, the Richardson's ground squirrel at different times of year. The HPmax was elicited by exposing animals to He–O₂ (21% oxygen, balance helium) at –10 to –25°C. The NSTmax was estimated by i.v. infusion of isoproterenol in anesthetized animals at thermoneutrality. Non-hibernating phase adults were collected and tested in April and June, and youngs in June and August for effects of seasonal acclimatization; animals were also tested after acclimation to cold (5°C) or warm (20°C). Hibernating phase animals were tested both shortly after the onset of hibernation season and after several months into the hibernation season. Although HPmax differed significantly between the lowest [101 cal (wt^0.73·h)^–1 in the June-Young group] and the highest [142 cal (wt^0.73·h)^–1 in the June-Adult group], it was not significantly different between other groups regardless of hibernation status or temperature acclimation (Fig. 4). The NSTmax, however, increased from 40–50 cal (wt^0.73·h)^–1 in the Warm-Acclimated, August-Young, June-Adult, and April-Adult to 66.5 and 79.2 cal (wt^0.73·h)^–1 in the two hibernating groups (Fig. 3). No significant difference in NSTmax was observed between Cold- and Warm-Acclimated groups. Since HPmax was maintained essentially constant at different times of year or after temperature acclimation, the increase of NSTmax during the hibernating phase can best be viewed as an adjustment for facilitation of periodic rewarmings from depressed body temperature during hibernation rather than to counter cold.Abbreviations HP heat production - HPmax maximum heat production - NST non-shivering thermogenesis - NSTmax maximum non-shivering thermogenesis - ST shivering thermogenesis - T _a ambient temperature - T _b body temperature     

Metabolic rate, maximum metabolism, and advantages of torpor in the fat mouse Steatomys pratensis natalensis Roberts, 1921 (Dendeomurinae)

1. The fat mouse Steatomys pratensis natalensis (mean body mass 37.4±0.43 (se)) has a low euthermic body temperature T_b=30.1–33.8 °C and a low basal metabolic rate (BMR)=0.50 ml O₂ g⁻¹ h⁻¹.

2. Below an ambient temperature (T_a)=15 °C, the mice were hypothermic.

3. The lowest survivable T_a=10 °C.

4. Torpor is efficient in conserving energy between T_a=15–30 °C, below T_a=15 °C, the mice arouse.

5. Euthermic and torpid mice were hyperthermic at T_a=35 °C.

6. Thermal conductance was 0.159 ml O₂ g⁻¹ h⁻¹ °C⁻¹, 98.8% of the expected value.

7. Non-shivering thermogenesis (NST) was 2.196 ml O² g⁻¹ h⁻¹ (3.69×BMR).

8. Maximal oxygen consumption, however, was 3.83 ml O₂ g⁻¹ h⁻¹ (6.44×BMR), indicating that other methods of heat production are additive.

9. Because fat mice conserve energy by torpor only between T_a=15–30 °C, we suggest that torpor may be a more important mechanism for surviving food shortages than for surviving cold weather.

Bioenergetics and thermal physiology of American water shrews (<Emphasis Type="Italic">Sorex palustris</Emphasis>)

Rates of O₂ consumption and CO₂ production, telemetered body temperature (T_b) and activity level were recorded from adult and subadult water shrews (Sorex palustris) over an air temperature (T_a) range of 3–32°C. Digesta passage rate trials were conducted before metabolic testing to estimate the minimum fasting time required for water shrews to achieve a postabsorptive state. Of the 228 metabolic trials conducted on 15 water shrews, 146 (64%) were discarded because the criteria for inactivity were not met. Abdominal T_b of S. palustris was independent of T_a and averaged 38.64±0.07°C. The thermoneutral zone extended from 21.2°C to at least 32°C. Our estimate of the basal metabolic rate for resting, postabsorptive water shrews (96.88±2.93 J g^–1 h^–1 or 4.84±0.14 ml O₂ g^–1 h^–1) was three times the mass-predicted value, while their minimum thermal conductance in air (0.282±0.013 ml O₂ g^–1 h^–1) concurred with allometric predictions. The mean digesta throughput time of water shrews fed mealworms (Tenebrio molitor) or ground meat was 50–55 min. The digestibility coefficients for metabolizable energy (ME) of water shrews fed stickleback minnows (Culaea inconstans) and dragonfly nymphs (Anax spp. and Libellula spp.) were 85.4±1.3% and 82.8±1.1%, respectively. The average metabolic rate (AMR) calculated from the gas exchange of six water shrews at 19–22°C (208.0±17.0 J g^–1 h^–1) was nearly identical to the estimate of energy intake (202.9±12.9 J g^–1 h^–1) measured for these same animals during digestibility trials (20°C). Based on 24-h activity trials and our derived ME coefficients, the minimum daily energy requirement of an adult (14.4 g) water shrew at T_a = 20°C is 54.0 kJ, or the energetic equivalent of 14.7 stickleback minnows.     

Respiration and heat production by the inflorescence of Philodendron selloum Koch

During a 2-d sequence of anthesis, the spadices of the thermogenic arum lily, Philodendron selloum, regulated maximum temperature within a small range (37–44°C) by reversible thermal inhibition of respiratory heat production. This response protects the inflorescence and the attracted insects from thermal damage. Heat production by whole spadices, measured by O₂ respirometry, equalled heat loss, measured by gradient layer calorimetry, which confirmed the heat equivalence of O₂ consumption (20.4 J ml^-1). This also indicated that there was no net phosphorylation during thermogenesis, heat production being the primary function of high rates of respiration. The sterile male florets consumed about 30 ml g^-1 h^-1 and the average 124-g spadix produced about 7 W to maintain a 30°C difference between spadix and ambient temperature. Most of the energy for thermogenesis is present in the florets before anthesis. Despite high respiratory rates, thermogenesis is an energetically inexpensive component of the reproductive process.     

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     

Life in extreme environments: Investigations on the ecophysiology of a desert bird,the Australian Diamond Dove (Geopelia cuneata Latham)

Summary The Diamond Dove, Geopelia cuneata, is the world's second smallest (ca. 35 g) species of the columbid order. The Diamond Dove is endemic in the arid and semiarid Mulga and Spinifex regions of Central and Western Australia. It regularly encounters ambient temperatures (T _a ) in its habitat above +40° C, especially when foraging for seeds on bare ground cover, and may be found at up to 40 km from water. This entails extreme thermal stress, with evaporative cooling constrained by limited water supply. Energy metabolism (M), respiration, body temperature (T _a ) and water budget were examined with regard to physiological adaptations to these extreme environmental conditions. The zone of thermal neutrality (TNZ) extended from +34° C to at least +45° C. Basal metabolic rate (BMR) was 34.10±4.19 J g^–1h^–1, corresponding to the values predicted for a typical columbid bird. Thermal conductance (C) was higher than predicted. Geopelia cuneata showed the typical breathing pattern of doves, a combination of normal breathing at a stable frequency (ca. 60 min^–1) at low T _a and panting followed by gular flutter (up to 960 min^–1) at high T _a . At T _a > +36° C, T _a increased to considerably higher levels without increasing metabolic rate, i.e. Q₁₀=1. This enabled the doves not only to store heat but also to save the amout of water that would have been required for evaporative cooling if T _a had remained constant. The birds were able to dissipate more than 100% of the metabolic heat by evaporation at T _a +44° C. This was achieved by gular flutter (an extremely effective mechanism for evaporation), and also by a low metabolic rate due to the low Q₁₀ value for metabolism during increased T _b . At lower T _a , Geopelia cuneata predominantly relied on non-evaporative mechanisms during heat stress, to save water. Total evaporative water loss over the whole T _a range was 19–33% lower than expected. In this respect, their small body size proved to be an important advantage for successful survival in hot and arid environments.Abbreviations and units Body Mass W (g) - Ambient Temperature T _a (°C) - Body Temperature T _b (°C) - Thermoneutral Zone (TNZ) - Metabolism M (J g^–1 h^–1) - Thermal Conductance C - wet Thermal Conductance C _wet (J g^–1 h^–1 °C^–1) - Evaporative Water Loss EWL (mg H₂O g^–1 h^–1) - Evaporative Heat Loss EHL (J g^–1 h^–1) - Breathing Frequency F (breaths min^–1) - Tidal Volume V _t (ml breath^–1) - Standard Temperature Pressure Dry STPD - Body Temperature Pressure Saturated BTPS - Respiratory Quotient RQ - n.s. not significant (P>0.05) - n number of experiments     

Adaptive mechanisms during food restriction in <Emphasis Type="Italic">Acomys russatus</Emphasis>: the use of torpor for desert survival

The golden spiny mouse (Acomys russatus) is an omnivorous desert rodent that does not store food, but can store large amounts of body fat. Thus, it provides a good animal model to study physiological and behavioural adaptations to changes in food availability. The aim of this study was to investigate the time course of metabolic and behavioural responses to prolonged food restriction. Spiny mice were kept at an ambient temperature of 27°C and for 3 weeks their food was reduced individually to 30% of their previous ad libitum food intake. When fed ad libitum, their average metabolic rate was 82.77±3.72 ml O₂ h^–1 during the photophase and 111.19±4.30 ml O₂ h^–1 during the scotophase. During food restriction they displayed episodes of daily torpor when the minimal metabolic rate gradually decreased to 16.07±1.07 ml O₂ h^–1, i.e. a metabolic rate depression of approximately 83%. During the hypometabolic bouts the minimum average body temperature T_b, decreased gradually from 32.6±0.1°C to 29.0±0.4°C, with increasing duration of consecutive bouts. In parallel, the animals increased their activity during the remaining daytime. Torpor as well as hyperactivity was suppressed immediately by refeeding. Thus golden spiny mice used two simultaneous strategies to adapt to shortened food supply, namely energysaving torpor during their resting period and an increase in locomotor activity pattern during their activity period.     

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     

Effect of torpor on the water economy of an arid-zone marsupial,the stripe-faced dunnart (<Emphasis Type="Italic">Sminthopsis macroura</Emphasis>)

Metabolic rate and evaporative water loss (EWL) were measured for a small, arid-zone marsupial, the stripe-faced dunnart (Sminthopsis macroura), when normothermic and torpid. Metabolic rate increased linearly with decreasing ambient temperature (T_a) for normothermic dunnarts, and calculated metabolic water production (MWP) ranged from 0.85±0.05 (T_a=30°C) to 3.13±0.22 mg H₂O g^–1 h^–1 (T_a=11°C). Torpor at T_a=11 and 16°C reduced MWP to 24–36% of normothermic values. EWL increased with decreasing T_a, and ranged from 1.81±0.37 (T_a=30°C) to 5.26±0.86 mg H₂O g^–1 h^–1 (T_a=11°C). Torpor significantly reduced absolute EWL to 23.5–42.3% of normothermic values, resulting in absolute water savings of 50–55 mg H₂O h^–1. The relative water economy (EWL/MWP) of the dunnarts was unfavourable, remaining >1 at all T_a investigated, and did not improve with torpor. Thus torpor in stripe-faced dunnarts results in absolute, but not relative, water savings.     

Summer acclimatization in the short-tailed field vole,Microtus agrestis

We investigated the changes that occurred in basal and noradrenaline-induced metabolic rate, body temperature and body mass in short-tailed field voles,Microtus agrestis, during exposure to naturally increasing photoperiod and ambient temperature. These parameters were first measured in winter-acclimatized voles (n=8) and then in the same voles which had been allowed to seasonally acclimatize to photoperiod and ambient temperature (6 months later). Noradrenaline induced metabolic rate, basal metabolic rate and nonshivering thermogenesis were significantly higher in winter-acclimatized compared to summer-acclimatized voles. There was a significant positive relationship between basal metabolic rate and noradrenaline-induced metabolic rate. Body mass was significantly higher in summer-acclimatized compared to winter-acclimatized voles. There was a significant positive relationship between body mass and noradrenaline-induced metabolic rate in both winter-acclimalized and summer-acclimatized voles; however, there was no relationship between basal metabolic rate and body mass in either seasonal group of voles. Body temperature after measurements of basal metabolic rate was not significantly different in the seasonal cohorts of voles. However, body temperature was significantly higher in winter-acclimatized compared to summer-acclimatized voles after injection of noradrenaline. Previously we have found that a long photoperiod was not a sufficient stimulus to reduce thermogenic capacity in winter-acclimatized voles during cold exposure, since basal metabolic rate increased to compensate for a reduction in regulatory nonshivering thermogenesis. Here we found that a combination of increased ambient temperature and photoperiod did significantly reduce thermogenic capacity in winter-acclimatized voles. This provided evidence that the two aspects of non-shivering thermogenesis, obligatory and regulatory, are stimulated by different exogenous cues. Summer acclimatization in the shorttailed field vole is manifest as a significant decrease in both basal and noradrenaline-induced metabolic rate, combined with a significant increase in body mass.Abbreviations ANCOV A analysis of covariance - BAT brown adipose tissue - BM body mass - BMR basal metabolic rate - NST non-shivering thermogenesis - NA noradrenaline - V the maximum V recorded following mass specific injection of noradrenaline - V the maximum V recorded following mass specific injection of saline - T _a ambient temperature - T _b rectal body temperature - T _1c lower critical temperature - UCP uncoupling protein - V oxygen consumption