Average Daily Metabolic Rate Research Articles

The Rate of Cooling during Torpor Entry Drives Torpor Patterns in a Small Marsupial.

AbstractTo maximize energy savings, entry into torpor should involve a fast reduction of metabolic rate and body temperature (Tb); that is, animals should thermoconform. However, animals often defend against the decrease in Tb via a temporary increase in thermoregulatory heat production, slowing the cooling process. We investigated how thermoregulating or thermoconforming during torpor entry affects temporal and thermoenergetic aspects in relation to body mass and age in juvenile and adult fat-tailed dunnarts (Sminthopsis crassicaudata; Marsupialia: Dasyuridae). During torpor entry, juvenile thermoconformers cooled twice as fast as and used less energy during cooling than juvenile thermoregulators. While both juvenile and adult thermoconformers had a lower minimum Tb, a lower torpor metabolic rate, and longer torpor bouts than thermoregulators, these differences were more pronounced in the juveniles. Rewarming from torpor took approximately twice as long for juvenile thermoconformers, and the costs of rewarming were greater. To determine the difference in average daily metabolic rate between thermoconformers and thermoregulators independent of body mass, we compared juveniles of a similar size (∼13 g) and similarly sized adults (∼17 g). The average daily metabolic rate was 7% (juveniles) and 17% (adults) less in thermoconformers than in thermoregulators, even though thermoconformers were active for longer. Our data suggest that thermoconforming during torpor entry provides an energetic advantage for both juvenile and adult dunnarts and may aid growth for juveniles. While thermoregulation during torpor entry is more costly, it still saves energy, and the higher Tb permits greater alertness and mobility and reduces the energetic cost of endogenous rewarming.

How much do large whales eat?

Estimates of the amount of prey consumed by cetaceans have been used in ecological models and also directly compared to human fisheries yields. Most of these estimates have been based on assumptions about energy requirements. However, the lack of direct measurements for large whales has necessitated extrapolation beyond the data points available from smaller species. A number of different parameterisations of general regressions in which energy requirements or consumption are estimated as proportional to body mass raised to some power B, were compared with estimates of Basal Metabolic Rate (BMR) from the widely used Kleiber equation. The choice of values has a large impact on estimates, which can differ by an order of magnitude, but modellers are frequently forced to make rather arbitrary decisions due to lack of data. Nevertheless, neither data nor theory appear to support values of B >0.75. Although some parameter values have obtained status through common usage, these have not always been based on actual data and estimates of consumption by whales need to reflect this uncertainty. Comparison of generalised relationships with data from other sources, including rates of filter feeding, oxygen consumption and seasonal changes in energy stores, suggest upper bounds on average daily metabolic rate of large whales. Estimates based on stomach contents also indicated average daily metabolic rates of less than four times the BMR from the Kleiber formula, but these are critically dependent on estimates of digestion time for which there appear to be little data. Estimates of stored energy suggest that large whales that migrate to seasonally productive feeding areas either have relatively low energy requirements for their size or need to meet a considerable proportion of their annual energy requirements outside of the feeding grounds.

Energy requirements, length of digestive tract compartments and body mass in six gerbilline rodents of the Negev Desert

Energy requirements of an animal are size dependent and, in this study, the average daily metabolic rate (ADMR) of six Negev Desert gerbilline rodents, ranging in body mass (mb) from 10g to over 200g, scaled to mb0.57. Although gerbilline rodents are considered ‘granivores’, these rodents consume substantial amounts of green vegetation and the largest gerbil is a strict herbivore. We predicted that the lengths of the compartments of the digestive tract would scale allometrically to mb0.33 and that ADMR would scale allometrically to the lengths of the compartments to the exponent of 1.73. Using log-transformed data, the length of the colon scaled to mb0.50 (r2adj = 0.74; p= 0.02), of the caecum to mb0.45 (r2adj=0.80; p= 0.01) and of the small intestine to mb0.30 (r2adj=0.59; p < 0.05). Therefore, the exponents for the colon and caecum were higher than predicted and were close to the exponent for ADMR generated for the rodents. The absolute lengths of the colon (r2adj=0.68; p= 0.03; slope = 0.99) and of the caecum (r2adj=0.79; p= 0.01; slope = 1.19) were related significantly to ADMR, but of the small intestine was not (r2adj=0.04; p=0.33; slope = 0.85). The exponents implied that the relationships were isometric and not allometric as predicted and that the rates of increase of the lengths of the intestine compartments were at the same rate as the increase in ADMR. The lengths of the colon and caecum were highly correlated between each other (r2adj=0.98; p< 0.001; slope = 1.12) and explained most of the variation in ADMR. Green vegetation could be a nutritional bottleneck for rodents as it is bulky and, consequently, limits the dietary intake, and fermentation occurs in the caecum and colon, whereas seeds, which are compact and are digested in the small intestine, would limit intake to a much lesser degree. However, when the effect of body mass was eliminated by using residuals of the variables on body mass, only the length of the small intestine was significant (r2adj=0.86; p< 0.005; slope = -1.33) and was related negatively to ADMR. Therefore, when effects of body size were removed, most of the variation in ADMR was explained by the length of the small intestine and implied that the length of the small intestine increased with a decrease in ADMR. A higher energy expenditure was related to a shorter small intestine and, therefore, by implication, a higher concentration of metabolizable energy yield of the diet. We also questioned whether there are differences in the morphology of the digestive tract due to differences in dietary consumption. The digestive tracts of the gerbils were not diverse and could be characterized as structurally homogenous. All the gerbils had a uni-locular, hemi-glandular stomach and the differences in the digestive tract among species did not seem to be of functional importance, but rather were related to the taxon. However, some important morpho-functional characteristics of the digestive tract emerged that apply to the whole group.

Testosterone does not mediate variation in basal metabolic rate and activity in relation to reproductive condition and photoperiod in white-footed mice (Peromyscus leucopus).

The photoperiodic response of many temperate zone rodents, including white-footed mice (Peromyscus leucopus), is a heritable life-history trait with underlying physiological variation. Previous studies of intact male P. leucopus utilized two wild-derived bidirectional selection lines, a short photoperiod responsive (R) line selected for reproductive suppression in short-day conditions (SD) and a nonresponsive (NR) line selected for reproductive maturity in SD. NR mice in SD had greater food intake, but also higher levels of locomotor activity, and basal metabolic rate (BMR) than R mice. We hypothesized that testosterone may be a key mediator of this metabolic difference, as it is likely to be significantly reduced in R SD mice. Male P. leucopus from either line in SD were castrated and given either an implant containing testosterone (T) or a sham control (C). They were then tested for variation in metabolic rate and activity in SD, thermoneutral conditions. T mice had significantly higher levels of food intake, testosterone, and seminal vesicle dry weight than C mice. Seminal vesicle dry weight was significantly and positively correlated with average testosterone level, indicating an effect of the T implants. There was no statistically significant difference among treatment groups in BMR and average daily metabolic rate, suggesting that differences in testosterone alone are not the cause of differences in metabolic rate between selection lines.

Swimming speeds and metabolic rates of semi-captive juvenile lemon sharks (Negaprion brevirostris, Poey) estimated with acceleration biologgers

There is much interest in being able to quantify the swimming speeds and metabolic rates of wild aquatic animals such as sharks to develop bioenergetics models and evaluate the metabolic consequences of different stressors. This study sought to calibrate tri-axial acceleration biologgers (accelerometers) such that it would be possible to estimate swimming speeds and metabolic rates of semi-captive sharks in an enclosed natural mesocosm. Juvenile lemon sharks (Negaprion brevirostris, Poey; 60–75cm total length, 1–2kg) were equipped with accelerometers and swum at stepwise velocity increments in a Blazka-style swim tunnel respirometer using a critical swimming speed protocol. Metabolic rates and acceleration-derived metrics (overall dynamic body acceleration and tailbeat frequency) were measured concurrently during forced swimming, and accelerometer-equipped sharks were released to an enclosed mesocosm habitat to estimate average daily metabolic rate (ADMR) and swimming velocities across diel and tidal cycles. Acceleration-derived tailbeat frequency was a stronger predictor of metabolic rate than overall dynamic body action, and predicted an active metabolic rate of 249.7±1.9mg O2 kg−1h−1 and an ADMR of 88.7±0.7kJkg−1d−1 at 30°C. Following exhaustive exercise a maximum metabolic rate of 398.0±19.6mg O2 kg−1h−1 was achieved and over the subsequent 55-minute recovery period excess post-exercise oxygen consumption was 31.2mg O2 kg−1. The critical swimming speed of the sharks was 0.71±0.03 body lengths per second (BL s−1), and swimming speed in the mesocosm was 0.19±0.01 BL s−1. Locomotor activity levels of semi-captive sharks in the mesocosm were influenced by tide state and diel period, with sharks having highest swimming velocities during diurnal periods and flooding tides. Overall, accelerometry is a suitable means for estimating swimming speed and metabolic rate in this species, and additional research to address anaerobic energy expenditure of wild sharks is warranted.

Heritable variation in reaction norms of metabolism and activity across temperatures in a wild-derived population of white-footed mice (Peromyscus leucopus)

Heritable variation in metabolic traits is likely to affect fitness. In this study, white-footed mice from wild-derived photoresponsive [R, infertile in short day length (SD)] and non-photoresponsive (NR, fertile in SD) selection lines were maintained under short-day (SD 8Light:16Dark), sub-thermoneutral conditions (22 or 12°C). Mice had significantly higher levels of food intake and resting metabolic rates (RMR) at low temperature. RMR differed significantly between lines (greater in NR mice). In contrast to previous work under thermoneutral conditions, there was no significant difference in overall activity or average daily metabolic rates (ADMR) of mice from the two lines. Reduced activity may reflect behavioral changes under cooler conditions (e.g., nest building) reducing the overall energetic cost of fertility (for NR mice). There was no significant difference in maximal rate of oxygen consumption ([Formula: see text]) between lines. R mice had significantly greater brown adipose tissue and white abdominal fat mass due to both line and temperature. Reaction norms for intake, resting metabolism (RMR/BMR) and level of activity from current (12 and 22°C) and previously published data (28°C) demonstrate independent effects of genetics (line) and environment (temperature) for resting metabolism, but a clear interaction between these for activity. The results suggest that fertility under winter conditions imposes metabolic costs that are related to the level of reproductive development. Under the coldest conditions tested, however, mice that remained fertile in SD reduced activity, ADMR and food requirements, decreasing the differential between selection lines. Heritable variation in reaction norms suggests a genetic by environment effect that could be subject to selection.

Variation in basal metabolic rate and activity in relation to reproductive condition and photoperiod in white-footed mice (Peromyscus leucopus)

A naturally variable life-history trait with underlying physiological variation is the photoperiodic response of many temperate-zone rodents, including white-footed mice (Peromyscus leucopus (Rafinesque, 1818)). Male P. leucopus were obtained from a short photoperiod responsive (R) line, artificially selected for reproductive suppression in short-day conditions (SD) and a nonresponsive (NR) line selected for reproductive maturity in SD. We tested for variation in metabolic rate between lines in SD and long-day conditions (LD). NR mice consumed 34% more food than R mice, without concomitant increase in body mass in SD. Basal metabolic rate (BMR) was found to be significantly greater in NR than R mice, and NR mice were found to engage in significantly more spontaneous (daily) locomotor activity. Energy-use estimates based on 24 h respirometry matched closely the level of intake reported for individual mice. The increased BMR and average daily metabolic rate in NR mice was correlated with testis size, but not with major central organs or digestibility. No significant difference in BMR or activity was found in mice from the same lines held in LD. Elevated intake in SD mice appears to be associated with differences in fertility and not other aspects of physiology in the respective lines.

Developmental phenotypic plasticity in a marsupial

Climate change is likely to substantially affect the distribution ranges of species. However, little is known about how different mammalian taxa respond morphologically and physiologically to a rapid change of climate. Our objective was to provide the first quantitative data on the effect of continuous cold exposure during development on morphological and functional variables of a marsupial. Fat-tailed dunnarts (Sminthopsis crassicaudata, Dasyuridae) were reared at an ambient temperature (T(a)) of 16°C [cold-reared (CR)] or 22°C [warm-reared (WR)] until they reached adult age (>200 days). Body and head length of CR animals were significantly longer than in WR animals (mean ± s.e.m.; body: CR 80.8±6 mm, WR 76.4±5 mm; head: CR 29.4±3 mm, WR 27.5±2 mm), but other body attributes were not significantly different. Use of torpor was more frequent, torpor bout duration was longer and average daily metabolic rate and percentage of savings when using torpor were significantly higher (P<0.01) in CR than in WR animals at 16°C T(a) but not at 24°C. Furthermore, resting metabolic rates measured at 16°C T(a) were significantly lower in CR than WR animals; at 30°C T(a) values were similar. Our results do not conform to Allen's rule, but to some extent they do conform to Bergmann's rule. However, the data demonstrate that a relatively moderate cold exposure from birth until adulthood induces marked changes in the morphology and thermal energetics of small marsupials. Such short-term phenotypic responses without the need for long-term selection are likely important for the ability to cope with different climates over a wide range of distribution, but will also play a crucial role in enhancing the survival of species during climate change.

Flea infestation does not cause a long-term increase in energy metabolism in Gerbillus nanus

Fleas can increase the metabolic rate of their hosts. It has been suggested that a constitutive response, in which the host constantly maintains a relatively high level of energy metabolism to combat the parasite, is advantageous for hosts with high parasite infestation, while an induced response, in which the host increases energy metabolism in response to a parasite attack, is advantageous with low parasite infestation. As free-living Gerbillus nanus show a relatively low flea infestation, we hypothesized that this host uses an induced strategy and, consequently, flea infestation would not impose a long-term effect on energy metabolism. In a previous study in spring, higher field metabolic rate (FMR) was found in free-living parasitized than in non-parasitized G. nanus. In this study, G. nanus were captured at Hazeva in spring; some had fleas (N=14) and some did not (N=10). We brought them to the laboratory, removed the fleas from those that were infested and, after 3 weeks, measured average daily metabolic rate (ADMR) of all rodents. ADMR averaged 8.68±0.95 kJ g(-0.54) day(-1) for all rodents and was similar between previously parasitized and non-parasitized G. nanus while free living. Thus, the hypothesis that flea infestation does not have a long-term effect on energy metabolism was supported, as was the idea of an induced over a constitutive immune response by G. nanus in combating parasites.

Determinants of energy expenditure and energy balance.

Energy metabolism of an individual is a function of body size, body composition, behaviour including food intake and physical activity, and health status. The analysis of determinants of energy expenditure is illustrated in relation to gender differences. Women have on average a lower energy intake and a lower average daily metabolic rate due to a lower body mass, fat-free mass, and a higher % body fat. Activity-induced energy expenditure, the energy expenditure associated with muscular contractions to perform body postures and—movements excluding exercise, is the most variable component of total energy expenditure. Determinants of activity-induced energy expenditure are presented to get a view whether it is an obligatory or a facultative phenomenon. Twin studies showed that most of the between subject variation in activity-induced energy expenditure is explained by genetic factors. Activity-induced energy expenditure of subjects in the confined environment of a respiration chamber was on average halve the value as observed in the same subjects in free-living conditions with doubly labeled water. In young adults, exercise training does not affect non-training activity. However, in elderly subjects, exercise training induced an equivalent compensatory decline in non-training activity. Similarly, activity-induced energy expenditure is reduced during energy restriction and in patients with chronic disease increasing resting energy expenditure. Studies with exercise training showed the reduction is difficult to overcome. There is little evidence for a compensatory increase in activity-induced energy expenditure during overfeeding.

Flea species richness and parameters of host body, host geography and host ‘milieu’

Summary 1 We have assessed how different host parameters affect species richness of flea assemblages using the independent contrasts method. Three groups of host parameters were examined. The first group included host body parameters (body size, basal and average daily metabolic rates), the second group included parameters of geographical range size and position of this range in relation to the equator (latitude) and the third group comprised parameters related to the number of sympatric closely related species. 2 None of the host body parameters correlated with species richness of flea assemblages. 3 Flea species richness increased with an increase in latitude of the geographical range centre of a host as well as with an increase in a composite variable that described the size of the geographical range. 4 The number of sympatric closely related species both across the entire geographical range and locally was correlated positively with species richness of fleas. 5 Our results show that species richness of ectoparasites is affected little by parameters of the host body and to a greater extent by parameters related to the host environment.

Factors affecting average daily metabolic rate of the fat mouse Steatomys pratensis (Dendromurinae)

1. Euthermic Steatomys pratensis showed a circadian rhythm in body temperature ( T b) ranging 31.1–32.6 °C throughout day and 33.2–35.0 °C at night. 2. Tb of torpid mice was close to ambient temperature ( T a) in the early hours of the morning, higher in late morning. 3. Daily torpor lasted 5.5 to 11.6 h. 4. Energy expenditure in thermoneutrality was 30.9 kJ day −1, about three times basal metabolic rate (BMR). 5. For euthermic mice at T a = 20 ° C ADMR averaged 41.4 kJ day −1 but in torpid mice it declined to 18.2 kJ day −1, an energy saving of 56%. 6. In contrast, huddling at T a = 20 ° C reduced energy expenditure by 18%.

Average daily metabolic rate, reproduction and energy allocation during lactation in the Sundevall Jird Meriones crassus

Summary Non‐reproducing Sundevall Jird (Meriones crassus) females (body mass = 84 g; n = 51), with a mean average daily metabolic rate (ADMR) of 88 kJ day−1, were divided into three groups: high (H), medium (M) and low (L) ADMR. It was hypothesized that ADMR is related to reproductive rate and predicted that the H group could support a higher reproductive rate than the L group. It was also hypothesized that allocation of energy differs with ADMR level and predicted that the H group would use mainly the reallocation of metabolizable energy to compensate for an increased energy demand for reproduction whereas the L group would increase their metabolizable energy intake markedly. To test the hypotheses, the females were mated and, in those that had litters (n = 32), changes in body mass and metabolizable energy intake were determined and milk production was estimated during 15 days of lactation. Litter size, offspring mass and growth rate were determined for pups. Body mass of dams, litter size and body mass of young at birth were similar among ADMR groups. However, milk production was 42% higher and litter mass at 15 days was significantly greater in the H than in L group, supporting our first hypothesis. All females were in negative energy balance during lactation. Mobilization of body energy reserves increased with litter size but was similar among ADMR groups. In addition, the increase in metabolizable energy intake of lactating females above that of non‐reproducing females was similar among ADMR groups and therefore the second hypothesis was rejected. ADMR was reduced by 23% during lactation and milk energy was only 30% of total metabolizable energy invested in milk production in all females. It is concluded that lactating M. crassus used a combination of reallocation of energy and increased metabolizable energy intake during lactation. The efficiency of offspring production did not differ among ADMR groups and therefore a high ADMR has an advantage when food is abundant, whereas a low ADMR has an advantage when food is sparse.

Energy cost of ectoparasitism: the fleaXenopsylla ramesison the desert gerbilGerbillus dasyurus

AbstractMetabolizable energy intake and changes in body mass was measured in the desert gerbilGerbillus dasyuruswhen parasitized by the fleaXenopsylla ramesis. We hypothesized that energy requirements for maintenance, or average daily metabolic rate, of parasitized gerbils would be higher than those of non‐parasitized gerbils. We also hypothesized that the efficiency of utilization of energy for maintenance would be the same for parasitized and non‐parasitized gerbils, as this measurement is dependent mainly on dietary quality. Fifty fleas feeding on a gerbil consumed 3.68±1.19 mg blood, in total. This amounted to 34.3±1.8% of body mass of a starving flea and only about 0.17% of the blood volume of the host. The absolute amount of blood consumed byX. ramesisis the lowest reported for fleas in other studies. This suggested that the pressure of parasitism ofX. ramesisonG. dasyurusin terms of blood consumed was relatively low. Both our hypotheses were confirmed. Average daily metabolic rate of the parasitized gerbils (7.75 kJ g−0.54d−1) was 16% higher than that of non‐parasitized gerbils (6.69 kJ g−0.54d−1). In addition, at zero metabolizable energy intake, the parasitized gerbils lost body mass at a faster rate than the non‐parasitized gerbils (4.34vs3.95% body mass d−1). The efficiency of utilization of energy in the parasitized and non‐parasitized gerbils was similar.

Energy requirements of female Macaroni Penguins breeding at South Georgia

Summary Breeding female Macaroni Penguins (Eudyptes chrysolophus) were implanted with heart rate, temperature and depth data loggers in order to estimate their rate of energy expenditure from heart rate. The estimated average daily metabolic rates (ADMR) of birds during the brood and crèche phases of the breeding season were 8·17 ± 0·44 W kg−1 and 8·24 ± 0·41 W kg−1, respectively. There was no significant difference between these estimates and the pooled ADMR for all birds was 8·22 ± 0·38 W kg−1. Metabolic rate while the penguins were at‐sea was 9·03 ± 0·39 W kg−1 and this was significantly greater than the metabolic rate of 6·27 ± 0·38 W kg−1 while they were on‐shore. Females undertook shorter foraging trips during the crèche phase than during the brood phase. When considered as a breeding pair, Macaroni Penguins expend more energy in raising their chick during the crèche phase of the breeding season as the male assists in provisioning the chick only at this time.

The energetics of Gentoo Penguins, Pygoscelis papua, during the breeding season

Summary The food consumption of an animal, both at the individual and the population level, is an essential component for assessing the impact of that animal on its ecosystem. As such, measurements of the energy requirements of marine top‐predators are extremely valuable as they can be used to estimate these food requirements. The present study used heart rate to estimate the rate of energy expenditure of gentoo penguins during the breeding season. The average daily metabolic rate (ADMR) of penguins when one adult was necessarily present at the nest (incubating eggs or guarding small chicks; IG; 4·76 W kg−1) was significantly lower than that when both parents forage concurrently during the major period of chick growth (CR; 6·88 W kg−1). The ADMR of a bird was found to be dependent on a number of factors, including the day within the breeding season and the percentage time that the bird spent foraging during that day. When they were ashore, the estimated metabolic rate of IG birds (3·94 W kg−1) was significantly lower than that of CR birds (5·93 W kg−1). However, the estimated metabolic rates when the birds were at sea during these periods were essentially the same (8·58 W kg−1). The heart rate recorded when the penguins were submerged (128 beats min−1) was significantly higher than that recorded from resting animals when ashore (89 beats min−1). However, it was lower than that recorded from birds that were swimming in a water channel (177 beats min−1). This might indicate that, although primarily aerobic in nature, there was an anaerobic component to metabolism during diving. An alternative interpretation is that the metabolic requirement during diving was lower than when the birds were swimming with access to air. There was a significant decline in abdominal temperature, from 38·8 °C at the start of a diving bout to 36·2 °C at the end, which may indicate a reduction in overall metabolic rate during submersion. This in turn may explain the lowered heart rate. In the present study, we have shown that the metabolic rate of the gentoo penguin varies during the breeding season. The relatively constant metabolic rate of the birds when at sea could represent an upper physiological limit that the birds are unable to exceed. If so, it will only be possible for the birds to increase foraging effort by diving more frequently and/or for longer periods thus reducing their foraging efficiency (the energy gained during foraging vs. energy spent gaining that food). During years when food is scarce, this reduction in foraging efficiency may have a profound influence on the reproductive productivity of the gentoo penguin.

Limits to sustainable human metabolic rate.

There is a limit to the performance of an organism set by energy intake and energy mobilization. Here, the focus is on humans with unlimited access to food and for whom physical activity can be limited by energy mobilization. The physical activity level (PAL) in the general population, calculated as doubly-labelled-water-assessed average daily metabolic rate as a multiple of basal metabolic rate, has an upper limit of 2.2-2.5. The upper limit of sustainable metabolic rate is approximately twice as high in endurance athletes, mainly because of long-term exercise training with simultaneous consumption of carbohydrate-rich food during exercise. Endurance athletes have an increased fat-free mass and can maintain energy balance at a PAL value of 4.0-5.0. High altitude limits exercise performance as a result of combined effects on nutrient supply and the capacity to process nutrients. Thus, trained subjects climbing Mount Everest reached PAL values of 2.0-2.7, well below the observed upper limit at sea level.

Physical activity in daily life in patients with chronic low back pain

Verbunt JA, Westerterp KR, van der Heijden GJ, Seelen HA, Vlaeyen JW, Knottnerus JA. Physical activity in daily life in patients with chronic low back pain. Arch Phys Med Rehabil 2001;82:726-30. Objectives: To evaluate disuse (ie, a decreased daily physical activity level) in patients with chronic low back pain (LBP) and to evaluate the construct validity of accelerometry for measuring physical activity in daily life. Design: Case-control study in a cross-sectional design; comparison of accelerometry to the criterion standard (doubly labeled water technique). Setting: Normal daily living (unrestricted by the measurement devices). Patients: Thirteen patients with chronic nonspecific LBP and 13 age- and gender-matched healthy controls. Main Outcome Measures: Physical activity in daily life, expressed as whole-body acceleration measured with a triaxial accelerometer (Tracmor), and as the ratio between average daily metabolic rate (ADMR), measured by the doubly labeled water technique, and resting metabolic rate (RMR), measured by the ventilated hood. Both techniques were used simultaneously for 14 days. Results: Mean physical activity level in patients and controls did not differ significantly. The correlation between the Tracmor and ADMR and RMR was.72 (p <.01). Conclusions: Decreased physical activity levels in this sample of chronic LBP patients was not confirmed. The Tracmor is a valid instrument for measuring daily activity in LBP patients.

Seasonal variations in thermal energetics of Australian silvereyes (Zosterops lateralis)

AbstractMost Australian birds do not migrate over long distances and therefore have to cope with seasonal changes in weather and food availability. We investigated whether the small (11 g) silvereye Zosterops lateralis changes its thermal tolerance from winter to summer. Body mass and body temperature of silvereyes exhibited little seasonal variability. However, metabolic rates (MR) and thermal conductance showed significant changes. Below the thermoneutral zone (TNZ), winter‐acclimatized birds had significantly lower resting MR and thermal conductance than summer‐acclimatized birds. Within the TNZ (∼27.0–33.6 °C winter; ∼25.4–33.5 °C summer) basal MR of winter‐acclimatized birds (2.30 ± 0.29 mL O2 g−1 h−1) was significantly lower than that of summer‐acclimatized birds (2.88 ± 0.43 mL O2 g−1 h−1). The average daily MR also differed significantly between summer and winter largely due to a greater reduction of MR at night and the decreased conductance. Our study shows that small passerines such as silvereyes exhibit seasonal variability in physiology and thermal energetics, even when they live in areas with a relatively mild climate, to help overcome seasonal changes in weather conditions and food availability.

Seasonal variations in thermal energetics of Australian silvereyes (Zosterops lateralis)

Most Australian birds do not migrate over long distances and therefore have to cope with seasonal changes in weather and food availability. We investigated whether the small (11 g) silvereye Zosterops lateralis changes its thermal tolerance from winter to summer. Body mass and body temperature of silvereyes exhibited little seasonal variability. However, metabolic rates (MR) and thermal conductance showed significant changes. Below the thermoneutral zone (TNZ), winter-acclimatized birds had significantly lower resting MR and thermal conductance than summer-acclimatized birds. Within the TNZ (∼27.0–33.6 °C winter; ∼25.4–33.5 °C summer) basal MR of winter-acclimatized birds (2.30 ± 0.29 mL O2 g−1 h−1) was significantly lower than that of summer-acclimatized birds (2.88 ± 0.43 mL O2 g−1 h−1). The average daily MR also differed significantly between summer and winter largely due to a greater reduction of MR at night and the decreased conductance. Our study shows that small passerines such as silvereyes exhibit seasonal variability in physiology and thermal energetics, even when they live in areas with a relatively mild climate, to help overcome seasonal changes in weather conditions and food availability.