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Field metabolic rate in two species of shrew-tenrec, Microgale dobsoni and M. talazaci
Abstract
Doubly labelled water (DLW) was used to determine field metabolic rate (FMR) in the shrew-tenrecs Microgale dobsoni and M. talazaci. Measures were obtained on six animals in their natural habitat and on five individuals in captivity. Mean FMR for nonreproducing M. dobsoni (mean body mass 42.6 ± 1.7 g) was 77.1 ± 3.2 kJ/d (CV = 53.7%, N = 4), 3.8 times resting metabolic rate (RMR). Mean FMR for nonreproducing M. talazaci (mean body mass 42.8 ± 4.9 g) was 66.5 ± 14.1 kJ/d (CV = 51.9%, N = 6), 3.2 times RMR. FMR within each species was not significantly correlated with body mass. This may in part reflect the large variation among individuals combined with the small sample size. FMR in shrew-tenrecs was within the range of FMR found in similar sized rodents, although variation was greater in the tenrecs. The high variability of FMR within the Tenrecidae may be a result of variations in body temperature. FMR/RMR ratios for both species fell within the range determined for other small mammals. The present study therefore offers further evidence to support a relationship between FMR and RMR.
... Tamoxifen is believed to be a partial oestrogen agonist as well as an antagonist, with studies demonstrating a range of results from complete oestrogen antagonism to oestrogen agonism, depending on the dose, sex of the animal, and the target organ examined, thus promoting a mix of body condition effects [38,39]. Administration of RU486 promotes persistent oestrus in rats [72] and more frequent LH surges in goats [71]. The effects of RU486 are believed to be on the pituitary, affecting FSH and LH production [4,71]. ...
... Administration of RU486 promotes persistent oestrus in rats [72] and more frequent LH surges in goats [71]. The effects of RU486 are believed to be on the pituitary, affecting FSH and LH production [4,71]. Commonly RU486 administration stimulates the development of follicles, without ovulatory rupture [4,71,72]. ...
... The effects of RU486 are believed to be on the pituitary, affecting FSH and LH production [4,71]. Commonly RU486 administration stimulates the development of follicles, without ovulatory rupture [4,71,72]. The effects of tamoxifen and RU486 on females are dose-dependent, with higher doses inflicting more disruption to oestrous cycles and body condition [38,39,71,73,59,74] . ...
Seasonal cycles of reproduction are common in many mammals and these are combined with the necessary energy budgeting for thermoregulatory challenges. Many mammals meet the challenge of changing environmental temperatures in winter by using torpor, a controlled reduction in body temperature and metabolic rate. We aimed to determine the effects of photoperiod and reproductive hormones on the seasonal cycles of reproduction and torpor use in a marsupial that commences reproduction in winter, the stripe-faced dunnart, Sminthopsis macroura. Males and females were placed under LD 14:10 and natural reproductive hormones blocked by either flutamide (males) or mifepristone (females) or tamoxifen (females). Reproductive parameters, metabolic rate and torpor variables were determined. The same animals were then placed under LD 10:14 and given testosterone (males) or progesterone (females) or oestrogen (females). Reproductive parameters, metabolic rate and torpor variables were measured. Body mass and tail widths (fattening indicator) in males were significantly affected by testosterone, and the effects were reversed by hormone blockers. Reproductive parameters were unaffected. Resting metabolic rate and ability to use torpor were not affected by treatment in males, however torpor characteristics, especially torpor bout duration, were affected by presence of testosterone in males. In females, body mass was unaffected by hormone presence, although tail widths were affected. Disruption of reproductive cycles occurred with hormone blockers in females, however, resting metabolic rate was not affected, and only presence of progesterone affected torpor characteristics in females. Our results differ from those found for rodents, where presence of testosterone abolishes the use of torpor in males, and oestrogen inhibits torpor use in females. Our study suggests that, in this mammal, metabolic responses to the presence or absence of reproductive hormones differs between males and females, and there is no absolute endocrinologically-driven reproductive season demarcated from the torpor season.
... physical activity levels represented by those groups (Dugas et al. 2011;Pontzer et al. 2012;Pontzer 2018). Analogously, while animals in captivity are considerably less active than their wild counterparts-as observed in, for example, macaques (Macaca nigra; Melfi and Feistner 2002), gibbons (Hylobates lar; Warren 2010), chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla; Ross and Shender 2016), and tigers (Panthera tigris; Breton and Barrot 2014)-the energy expenditures of wild and captive animal populations are similar (Stephenson et al. 1994;Munn et al. 2013;Pontzer et al. 2014;Nie et al. 2015). The findings of intervention studies concur with these observations. ...
The received wisdom on how activity affects energy expenditure is that the more activity is undertaken, the more calories will have been burned by the end of the day. Yet traditional hunter-gatherers, who lead physically hard lives, burn no more calories each day than Western populations living in labor-saving environments. Indeed, there is now a wealth of data, both for humans and other animals, demonstrating that long-term lifestyle changes involving increases in exercise or other physical activities do not result in commensurate increases in daily energy expenditure (DEE). This is because humans and other animals exhibit a degree of energy compensation at the organismal level, ameliorating some of the increases in DEE that would occur from the increased activity by decreasing the energy expended on other biological processes. And energy compensation can be sizable, reaching many hundreds of calories in humans. But the processes that are downregulated in the long-term to achieve energy compensation are far from clear, particularly in humans-we do not know how energy compensation is achieved. My review here of the literature on relevant exercise intervention studies, for both humans and other species, indicates conflict regarding the role, if any, of basal metabolic rate (BMR) or low-level activity such as fidgeting play, particularly once changes in body composition are factored out. In situations where BMR and low-level activity are not major components of energy compensation, what then drives it? I discuss how changes in mitochondrial efficiency and changes in circadian fluctuations in BMR may contribute to our understanding of energy management. Currently unexplored, these mechanisms and others may provide important insights into the mystery of how energy compensation is achieved.
... Evidence for the existence of energy compensation DEE adjusted for weight and age is similar between human populations of developing and industrialised nations around the world despite the diversity of lifestyles and wide range of physical activity levels represented by those groups (Dugas et al. 2011;Pontzer 2018;Pontzer et al. 2012). Analogously, while animals in captivity are considerably less active than their wild counterparts as observed in, for example, macaques (Macaca nigra; Melfi and Feistner 2002), gibbons (Hylobates lar; Warren 2010), chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla) (Ross and Shender 2016), and tigers (Panthera tigris; Breton and Barrot 2014), the energy expenditures of wild and captive animal populations are similar (Munn et al. 2013;Nie et al. 2015;Pontzer et al. 2014;Stephenson et al. 1994). The findings of intervention studies concur with these observations. ...
The received wisdom on how activity affects energy expenditure is that the more activity is undertaken, the more calories will have been burned by the end of the day. Yet traditional hunter-gatherers, who lead physically hard lives, burn no more calories each day than western populations living in labour-saving environments. Indeed, there is now a wealth of data, both for humans and other animals, demonstrating that long-term lifestyle changes involving increases in exercise or other physical activities do not result in commensurate increases in daily energy expenditure (DEE). This is because humans and other animals exhibit a degree of energy compensation at the organismal level, ameliorating some of the increases in DEE that would occur from the increased activity by decreasing the energy expended on other biological processes. And energy compensation can be sizable, reaching many hundreds of calories in humans. But the processes that are downregulated in the long-term to achieve energy compensation are far from clear, particularly in humans. We do not know how energy compensation is achieved. My review here of the literature on relevant exercise intervention studies, for both humans and other species, indicates conflict regarding the role that basal metabolic rate (BMR) or low level activity such as fidgeting play, if any, particularly once changes in body composition are factored out. In situations where BMR and low-level activity are not major components of energy compensation, what then drives it? I discuss how changes in mitochondrial efficiency and changes in circadian fluctuations in BMR may contribute to our understanding of energy management. Currently unexplored, these mechanisms and others may provide important insights into the mystery of how energy compensation is achieved.
Significance
Measurements of daily energy expenditure indicate that primates, including humans, expend only half of the calories expected for mammals of similar body size. As energy expenditure is central to organismal biology, these results hold important implications for life history, evolutionary biology, and foraging ecology for primates and other mammals. Specifically, we show that primates’ remarkably low metabolic rates account for their distinctively slow rates of growth, reproduction, and aging.
Field metabolic rate (FMR) is a measure of daily energy expenditure under field conditions. Results of various studies on FMR have been used to calculate allometric equations that can predict FMR from body weight. One of the problems in calculating these regression equations lies in the treatment of the available FMR and body weight data. However, with the tool of mixed model analysis, it is possible to account for the effect of the study as a random effect in this kind of meta-analysis. The present study is the first that has included the study as a random effect in an FMR meta-analysis. Prediction equations were derived, allowing the estimation of FMR based on body weight. Including all available single animal data on FMR and body mass in a mixed model analysis with the study as a random effect yielded the equation: FMR in kJ day−1=6.68 ± 1.21 (body weight in g)0.67 ± 0.03 (P<0.001) that had a mean error rate of 21.5% (sd 29.0%, minimum 0, maximum 236%) and a coefficient of variation of 98%. This was c. 2.7 times more precise than not including the study effect (mean error rate 58.4%). Thus, the present investigation showed that including the effect of the study in FMR meta-analysis changes not only the predictive values of the equation but also the exponent (slope).
This paper investigates the relationship between body mass, resting metabolic rate (RMR) and life history in the insectivore families Tenrecidae and Soricidae. RMR and a number of life history variables scale to body mass within both families. Residuals from least squares regression analysis produced relative or mass-independent values which were used to determine the relationship between RMR and reproduction. Within the Tenrecidae, RMR was not correlated with any of eight reproductive variables when the effect of mass was removed. The failure of species in this family to gain a reproductive advantage from elevated RMR may be due to phylogenetic constraints on reproduction. Species with elevated RMR may benefit from improved homeothermy rather than increased reproductive output. In the Soricidae, an increase in relative RMR was associated with a decrease in gestation length, an increase in specific foetal growth velocity and an increase in liter size. The possiblity that energetic and reproductive strategies in the Soricidae may have evolved under separate constraints is discussed. It is condluded that RMR is sometimes associated with life histories in the Insectivora, but its effect varies significantly between families.
The chapter begins with an overview of cost of living based on field metabolic rates of small mammals. The chapter then goes on to discuss the importance of energy in living systems, limitations on animal energy expenditure, the extrinsic limitation hypothesis, the intrinsic limitation hypothesis, experimental studies of the limitation hypotheses, the central limitation hypothesis and links between field metabolic rate (FMR) and resting metabolic rate (RMR), interspecific reviews of the link between daily energy expenditure (DEE) and RMR, and also gives summary and aims of the chapter. Methods section proposes to review the methods available for measurement of energy expenditure by mammals, in particular, the method of indirect calorimetry and the field techniques of time and energy budgeting and doubly labelled water, and also direct measurements of free-living energy expenditure. It also gives summary and data inclusion criteria for the present review. The chapter has also discussed results and provided an overview of database studied and has described factors influencing daily energy expenditure in mammals. The chapter closes with discussion about links between FMR and RMR and sustainable metabolic scope.
The evolution of endothermy in birds and mammals was one of the most important events in the evolution of the vertebrates. Past tests of hypotheses on the evolution of endothermy in mammals have relied largely on analyses of the relationship between basal and maximum metabolic rate, and artificial selection experiments. I argue that components of existing hypotheses, as well as new hypotheses, can be tested using an alternative macrophysiological modeling approach by examining the development of endothermy during the Cenozoic. Recent mammals display a 10°C range in body temperature which is sufficiently large to identify the selective forces that have driven the development of endothermy from a plesiomorphic (ancestral) Cretaceous or Jurassic condition. A model is presented (the Plesiomorphic-Apomorphic Endothermy Model, PAE Model) which proposes that heterothermy, i.e. bouts of normothermy (constant body temperature) interspersed with adaptive heterothermy (e.g. daily torpor and/or hibernation), was the ancestral condition from which apomorphic (derived), rigid homeothermy evolved. All terrestrial mammal lineages are examined for existing data to test the model, as well as for missing data that could be used to test the model.
We summarize the recent information on field metabolic rates (FMR) of wild terrestrial vertebrates as determined by the doubly labeled water technique. Allometric (scaling) relationships are calculated for mammals (79 species), reptiles (55 species), and birds (95 species) and for various taxonomic, dietary, and habitat groups within these categories. Exponential equations based on body mass are offered for predicting rates of daily energy expenditure and daily food requirements of free-ranging mammals, reptiles, and birds. Significant scaling differences between various taxa, dietary, and habitat groups (detected by analysis of covariance with P < or = 0.05) include the following: (a) The allometric slope for reptiles (0.889) is greater than that for mammals (0.734), which is greater than that for birds (0.681); (b) the slope for eutherian mammals (0.772) is greater than that for marsupial mammals (0.590); (c) among families of birds, slopes do not differ but elevations (intercepts) do, with passerine and procellariid birds having relatively high FMRs and gallinaceous birds having low FMRs; (d) Scleroglossan lizards have a higher slope (0.949) than do Iguanian lizards (0.793); (e) desert mammals have a higher slope (0.785) than do nondesert mammals; (f) marine birds have relatively high FMRs and desert birds have low FMRs; and (g) carnivorous mammals have a relatively high slope and carnivorous, insectivorous, and nectarivorous birds have relatively higher FMRs than do omnivores and granivores. The difference detected between passerine and nonpasserine birds reported in earlier reviews is not evident in the larger data set analyzed here. When the results are adjusted for phylogenetic effects using independent contrasts analysis, the difference between allometric slopes for marsupials and eutherians is no longer significant and the slope difference between Scleroglossan and Iguanian lizards disappears as well, but other taxonomic differences remain significant. Possible causes of the unexplained variations in FMR that could improve our currently inaccurate FMR prediction capabilities should be evaluated, including many important groups of terrestrial vertebrates that remain under- or unstudied and such factors as reproductive, thermoregulatory, social, and predator-avoidance behavior.
Daily energy expenditure (DEE) was measured in sympatric populations of red and grey squirrels using the doubly labelled water technique. Grey squirrels had significantly higher DEEs than red squirrels. However, the difference between the species was not separable from the effects of body mass on DEE. The DEEs of both species were in accordance with published allometric predictions incorporating body mass and ambient temperature. The differences in energetic requirements and social dominance, both consequences of body size, may represent means by which grey squirrels exert more interspecific competition on red squirrels than do conspecifics, potentially driving populations below viable levels in some sites.
Daily energy metabolism of Peromyscus leucopus and Tamias striatus was measured in three natural seasonal temperature regimes by gas analysis. Average daily metabolic rates (ADMR) were calculated from these daily metabolic patterns. Polynomial multiple regression analyses were conducted to examine the relative influence of body mass, ambient temperature, and time of day on metabolic rates. Several predictive equations are derived from regression analyses which are compared with both the observed data and similar predictive equations of other authors. In both species, ADMRs are approximately double the estimated resting metabolic rates under the same environmental conditions. The $D_{2}^{18}O$ method was used to estimate free-living daily energy metabolism of these species in their natural environment. Based on results of the $D_{2}^{18}O$ method, there is no significant difference in either species in the metabolic rates of free-living animals and animals living in large, field-located metabolism chambers...
We combined field measurements of metabolic rate, made with doubly labeled water, with data from our previous studies to examine reproductive energetics in 24 female little brown bats (Myotis lucifugus). Including estimates of tissue or milk production, M. lucifugus required an average of 33.7 kJ d⁻¹ of assimilated energy in pregnancy compared to 41.3 kJ d⁻¹ during lactation. Predicted insect consumption was 5.5 g d⁻¹ for a 9-g pregnant female and 6.7g d⁻¹ for a 7.9-g lactating female. About 2% of total energy assimilated during pregnancy was stored as new tissue, whereas lactating females exported 32% as milk. Estimated assimilated energy demand on the first day of lactation was 33.8 kJ d⁻¹ and increased to 60.3 kJ d⁻¹ at peak lactation. By subtracting laboratory measurements of roosting costs from observed metabolized energy expenditure, we calculated that foraging flight by 9-g pregnant M. lucifugus required 4.46 kJ h⁻¹; this was 13% less than allometric predictions. Foraging fight accounted for the largest proportion of the daily metabolized energy budget during pregnancy (61%) and lactation (66%). The large amount of energy devoted to foraging by this aerial-feeding bat may partially explain the low proportion of energy it allocates to tissue production and milk export.
Body mass, body temperature ( $T_{b}$ ), and oxygen consumption were measured in male and female large-eared tenrecs (Geogale aurita) during the breeding season. Body temperature paralleled ambient temperature ( $T_{a}$ ) in all individuals, though $T_{b}$ was more elevated above $T_{a}$ in pregnancy and lactation, especially if these events occurred concurrently. Resting metabolic rate (RMR) in nonreproducing adults at 30°C was 7. 73 mL $O_{2}\centerdot h^{-1}$ (53% of the value expected from body mass). It did not significantly increase with body mass, except in some pregnant individuals (or those concurrently pregnant and lactating). Resting metabolic rate increased during reproduction and reached peak levels during gestation. The energy cost of gestation with simultaneous lactation was not additive and represents an energy saving. Resting metabolic rate in pregnancy and lactation was not influenced by litter size, and this implies there is no fixed minimum energy requirement for reproduction in this species. Mean daily energy expenditure of nonreproducing G. aurita was $9.67 kJ\centerdotd^{-1}$ (2.6 X RMR). Daily energy expenditure during gestation attained higher levels than those attained in nonreproducing individuals and gradually decreased during lactation. It is proposed that an increased level of RMR may be essential for reproduction in G. aurita. However, the cost of reproduction is often reduced by conception at postpartum estrus and concurrent pregnancy and lactation.
Resting metabolic rate (RMR) and body temperature ( $T_{b}$ ) were measured in the shrew-tenrecs Microgale dobsoni and Microgale talazaci during reproduction. Limited data are also presented for Microgale cowani and Microgale melanorrhachis. Resting metabolic rate and $T_{b}$ fluctuated with ambient temperature ( $T_{a}$ ) so that metabolic rate in nonbreeding animals could not be termed "basal." Resting metabolic rate in nonreproducing adults of all four species at 30°C was higher than levels previously recorded in the Tenrecidae. The smaller species had RMR higher than predicted by the Kleiber curve. During pregnancy and lactation, elevated levels of RMR were attained in M. dobsoni, M. talazaci, and M. cowani, but there was no evidence that the level of RMR attained was influenced by litter size. All three species demonstrated improved thermoregulation during pregnancy. It is concluded that a high level of RMR is advantageous, and possibly essential, for reproduction in the Tenrecidae. Elevated RMR may be associated with an improvement in homeothermy.
Annual variations in resting metabolic rate (RMR) and body temperature (Tb) were measured in the streaked tenrecs Hemicentetes nigiceps and H. semispinosus. RMR in non-reproducing, non-torpid adults was lower than predicted by the Kleiber (1961) curve, supporting Genoud's (1990) hypothesis on BMR in hibernating mammals. Both species demonstrated a reduction in RMR and Tb during the austral winter and these changes were independent of body mass. H. semispinosus frequently roused from torpor to forage whereas H. nigriceps remained dormant throughout the winter, This contrast in activity patterns may result from altitudinal differences in species distributions. H. nigriceps may be an obligate hibernator whereas H. semispinosus, living at lower, warmer altitudes, may be a facultative hibernator. It is proposed that the ability of H. semispinosus to remain active during favourable climatic conditions allows winter breeding and increases annual reproductive output.
Energy metabolism, thermoregulation, and water flux ofMacrotus californicus, the most northerly representative of the Phyllostomidae, were studied in the laboratory using standard methods, and energy metabolism and water fluxes were studied in the field using the doubly labelled water method together with a time budget. Daily energy expenditures of free-living bats averaged 22.8 kJ during the winter study period. Approximately 60% of this was allocated to resting metabolism costs while in the primary roosts (22 h/day).Macrotus californicus is unable to use torpor. The thermoneutral zone (TNZ) in this species is narrow (33 to 40 C) and metabolic rate increased rapidly as ambient temperature decreased below the TNZ. Basal metabolic rate was 1.25 ml O2/gh, or 24 J/gh. Total thermal conductance below the TNZ. was 1.8 mW/gC, similar to values measured for other bats. Evaporative water loss showed a hyperbolic increase with increasing ambient temperature, and was approximately 1% of total body mass/h in the TNZ. The success of these bats as year-round residents in deserts in the southwestern United States is probably not due to special physiological adaptations, but to roosting and foraging behavior. They use geothermally-heated winter roost sites (stable year-round temperatures of approximately 29 C) which minimize energy expenditures, and they have an energetically frugal pattern of foraging that relies on visual prey location. These seem to be the two major factors which have allowedM. californicus to invade the temperate zone.
A model is developed which predicts the equilibrium enrichment of 18O in body water. By setting limiting values to parameters in the model, the maximum and minimum enrichments of 18O in body water are predicted to be 0·99 and 1·02 × the enrichment of the environmental source of drinking water. Empirical tests of the model were attempted using Long-eared bats (Plecotus auritus) and Pipistrelle bats (Pipistrellus pipistrellus). In Long-eared bats the enrichment of body water relative to the local water pool always fell within the predicted limits. In Pipistrelle bats the difference in body water enrichment between pregnant and lactating bats was qualitatively in accord with the model predictions. The implications of variability in the equilibrium enrichment of 18O in body water, for the accuracy of the doubly-labelled water technique, are explored. Four levels of accuracy in evaluation of equilibrium enrichment are identified. The error in estimates of carbon dioxide production due to inaccuracy of the equilibrium enrichment rapidly becomes limiting to the potential duration of doubly-labelled water experiments. In small animals with rapid turnover different methods of evaluating equilibrium enrichment have little effect on the potential experimental duration. In large animals, however, the method of measuring equilibrium enrichment has a much greater influence on the potential duration of the measurement. It is suggested all studies on larger animals should take a blood sample, prior to injection of labels, to assess the equilibrium enrichment. Measurement of the ratio of body to environmental enrichment of 18O may provide an estimate of RQ for some animals.
Field metabolic rates (FMR) measured using doubly labeled water, of 23 species of eutherian mammals, 13 species of marsupial mammals, and 25 species of birds were summarized and analyzed allometrically. FMR is strongly correlated with body mass in each of these groups. FMR scales differently than does basal or standard metabolic rate in eutherians (FMR slope=0.81) and marsupials (0.58), but not in birds (0.64 overall, but 0.75 in passerines and 0.75 in all other birds). Medium-sized (240-550 g) eutherians, marsupials, and birds have similar FMRs; these are approx 17 times as high as FMRs of like-sized ectothermic vertebrates such as iguanid lizards. For endothermic vertebrates, the energy cost of surviving in nature is enormous compared with that for ectotherms. Within eutherians, marsupials or birds, FMR scales differently for the following subgroups: rodents, passerine birds, herbivorous eutherians, herbivorous marsupials, desert eutherians, desert birds, and seabirds. Equations are given for use in predicting daily and annual FMR and food requirement of a species of terrestrial vertebrate, given its body mass.-from Author
Laboratory validation studies indicate that doubly labeled water (3HH18O and 2HH18O measurements of CO2 production are accurate to within ±8% in nine species of mammals and reptiles, a bird, and an insect. However, in field studies, errors can be much larger under certain circumstances. Isotopic fraction of labeled water can cause large errors in animals whose evaporative water loss comprises a major proportion of total water efflux. Input of CO2 across lungs and skin caused errors exceeding +80% in kangaroo rats exposed to air containing 3.4% unlabeled CO2. Analytical errors of ±1% in isotope concentrations can cause calculated rates of CO2 production to contain errors exceeding ±70% in some circumstances. These are 1) when little decline in isotope concentrations has occurred during the measurement period, 2) when final isotope concentrations closely approach background levels, and 3) when the rate of water flux in an animal is high relative to its rate of CO2 production. The following sources of error are probably negligible in most situations: 1) use of an equation that does not correspond to the pattern of change in total body water, 2) variations in rates of water or CO2 flux through time, 3) use of H218O dilution space as a measure of body water volume, 4) exchange of 18O between water and organic compounds in animals (including excrement), 5) incomplete mixing of isotopes in the animal, and 6) input of unlabeled water via lungs and skin. Errors in field measurements of CO2 production can be reduced to acceptable levels (<10%) by appropriate selection of study subjects and recapture intervals.
Data presented in this paper suggest that a complex interaction occurs between the physiological parameters of mammals and the growth and fluctuation of their populations: The Malthusian parameter rm increases with rate of metabolism, which in turn varies with body size and food habits. It can be concluded that it behooves all mammals to have as high a rate of metabolism as can be sustained by the quantity and quality of their food resources in space and time, because this adjustment will permit them to maximize their reproductive efforts. These interactions raise many questions, one of which concerns the temporal variation in reproductive strategies. Thus, Coady (1975) showed that the basal rate in the brown lemming (Lemmus trimucronatus) may be especially high during a winter in which the snow cover is reduced. Does a seasonal variation in the rate of metabolism therefore have a significant influence on seasonal variation in reproduction and therefore in population size? Whatever the correct answer to t...
Many aspects of the study of human nutrition would benefit from the ability to measure the energy which is expended by subjects as they go about their normal activities. The doubly-labelled water technique is a method which allows such measures to be made. The technique depends on the principle that a measure of carbon dioxide production is possible from the difference in the rates at which isotopic labels of hydrogen and oxygen are eliminated from the body. This simple explanation however conceals a host of assumptions. Several issues have emerged as important in the application of the technique to humans. These issues include first, the use of two samples (an initial and final sample) or multiple samples to estimate the rates of isotope elimination, and secondly the appropriate use of dilution spaces. This paper reviews the current status of the debates concerning these two issues. Paradoxically, improvements in our understanding of the technique, in the methods for calculating carbon dioxide production and in the accuracy of mass spectrometry, have not led to improvements in the accuracy of the technique. The mean deviation of estimates of carbon dioxide production using the technique from estimates made by conventional methods averages 7 per cent.
Measurements of basal metabolic rate (BMR), body water, fat, and lean dry mass of different organs were obtained in 22 bird species, ranging from 10.8 to 1,253 g body mass. Residuals of BMR (after subtracting BMR allometrically predicted from body mass) were positively correlated with residuals of lean dry heart and kidney mass. Measurements of both BMR and the daily energy expenditure of parent birds (DEEpar) during the period of nestling care as assessed by labeled-water turnover were collected from the literature for 26 altricial bird species. The allometric relationships with body mass in this data set were: log BMR (W) = -1.385 + 0.684 log mass (g) [fraction of variance (r2) = 0.973] and log DEEpar (W) = -0.797 + 0.659 log mass (g) (r2 = 0.967). Residuals of log BMR and log DEEpar were positively correlated with each other. The parallel regressions and correlation of residuals lead to reduced variance in the ratio of BMR/DEEpar (mean 0.301; SD 0.086). We suggest that natural selection has led to an adjustment of the size of organs (such as heart and kidney) involved in sustaining energy metabolism at the DEE maximized during parental care and that size-independent variation in BMR reflects the relative size of this highly metabolically active machinery. These relationships of BMR lead to new interpretations of the decline in mass-specific BMR with increasing body size and decreasing latitude and of the difference in mass-specific BMR between birds and mammals.
The doubly-labelled water technique is a non-invasive method for direct measurement of the energy expenditure of free-living animals. This paper considers the theoretical foundation of the technique and details the simplifying assumptions. Validation studies, which compare the measurement made by the technique with simultaneous evaluations using conventional laboratory techniques, suggest the technique gives an estimate of energy expenditure with an accuracy of c50%, when applied to vertebrates. Offsetting this is the fact that the technique provides invaluable information which can be collected in no other way. -from Authors
The doubly labelled water technique is made possible by an exchange equilibrium between the oxygen of body water and the oxygen of expired CO2. If the oxygen of body water is labelled with the stable isotope oxygen-18, loss of respiratory CO2 will subsequently cause a corresponding depletion of the label, but water loss will cause the ¹⁸O label to be eliminated, making necessary a second label to quantify elimination of the oxygen label in the form of excretory or evaporative water. Deuterium and tritium are both suitable for this purpose, the former being preferable. The difference between turnover rates of the deuterium and the oxygen labels then yields an estimate of total CO2 production over the interval between an initial and final estimate of the isotopic composition of body water. The author reviews the use of this technique at ecosystem, population and individual levels. Future applications might involve measurement of energy expenditure of activities in the field; testing models in behavioural ecology; application to organisms previously unstudied in this way; multiple-labelling techniques, and life history studies. -P.J.Jarvis
W respirometrze typu zamknietego zmierzono 70 dobowych przebiegow zuzycia tlenu ryjowki aksamitnej, Sorex araneus. Ryjowki badano w pieciu grupach obejmujących pelny cykl zyciowy tych zwierząt: mlode (lato, jesien, zima), przezimki (wiosna, lato) (Ryc. 1).
Determination of daily water exchange between an animal and its surroundings has been technically difficult. The use of tritiated water has proved useful for estimating water turnover rate, k, where k represents the fraction of body water pool turned over per unit of time. Assuming that animals are normally in a state of dynamic equilibrium, the measurement of k should equal daily water requirements. Eight species of rodents, 3 species each of kangaroo rats and ground squirrel and one species of wood rat and chipmunk, representing 3 families, were used in this study. These species are characteristic of a range of rabbits from low desert to montane forest. Among the species studied there is approximately a 10 fold range in k/day. Species arranged in increasing order of k are as follows: Dipodomys deserti, D. merriami, D. microps, Spermophilus tereticaudus, Ammospermophilus leucurus, Neotoma lepida, Spermophilus lateralis, and Eutamius palmeri. The percentage k per day for the above ranking of species was 4.5, 4.9, 8.6, 17.1, 20.2, 21,9, 28.8, and 44.0, respectively. Differences in k among the species appear in most instances to be unrelated to phylogeny but probably influenced by ecologic distribution, diet, behavior, and metabolic rate.
Golden spiny mouse Acomys russatus (Muridae), common spiny mouse A. cahirinus and bushy-tailed jird Sekeetamys calurus (Gerbillidae) , are similar in body size and are sympatric in many rocky areas in Israeli deserts. They differ in that A. russatus and S. calurus inhabit extremely arid areas where A. cahirinus is absent, and A. russatus is diurnal, whereas the other 2 species are nocturnal. All 3 species maintained water and energy balances, and had similar mass-specific water influxes (c0.13 ml g-1 d-1), while consuming different proportions of dry, mature vegetation and insects. Insects provided 38% of the total dry matter intake for A. cahirinus, 62% for A. russatus and 87% for S. calurus. A. cahirinus (38.3 g body mass) had the highest energy flux and expended 1.35 kJ g-1 d-1 during its 10.5-h activity period. A. russatus (45.0 g) expended 1.06 kJ g-1 d-1 during its 9-h activity period and S. calurus (41.2 g) expended 1.07 kJ g-1 d-1 during its 10.5-h activity period. Water influxes of these 3 species were intermediate between those of other rodents, suggesting that behavioural diet selection can be as important as physiological water conservation in adapting to desert life. Their energy expenditures were lower than those predicted for rodents of their body mass, consistent with the notion of low energy expenditures among desert-adapted rodents. The ratio of water influx to dry matter intake (ml:g) was 1.3 in A. cahirinus, compared with 1.9 in A. russatus and 2.5 in S. calurus. Thus more water was available for evaporative cooling in the latter 2 species. This could explain, at least in part, their different geographical distributions. -from Authors
A series of six artificially enriched waters, containing between 2,500 and 6,500 ppm oxygen-18, was prepared by adding weighed portions of distilled water and highly enriched H{sub 2}{sup 18}O. These waters were analyzed by radio activation analysis (proton activation PAA) and by gas isotope ratio mass spectrometry (gIRMS) with CO{sub 2} as the analysis gas. Carbon dioxide was prepared from water samples either by using the guanidine reaction, with 3-, 5- and 10-{mu}L samples, or by isotopic equilibration, using small (10 {mu}L) and large (1.5 mL) samples. The large samples were diluted to the natural abundance range prior to analysis as were the 3-{mu}L guanidine samples. Precision was greatest with large sample CO{sub 2} equilibration (mean relative standard deviation (RSD) = 0.108%). The other gIRMS gas preparation techniques had lower precision (3 {mu}L guanidine, RSD = 0.529%, 5 {mu}L guanidine, RSD = 0.364%, 10 {mu}L guanidine, RSD = 0.48%; 10 {mu}L equilibration, RSD = 0.43%) and the lowest precision occurred with PAA (RSD = 0.58%). For all the techniques except small sample equilibration, accuracy (percent deviation of mean evaluation from expected gravimetric mean) was worse than precision (RSD).
Data on energy expenditure by 553 individuals of 28 species of small bird (10–150 g) are presented. All estimates of energy expenditure were obtained using the doubly-labelled water technique. Intraspecies variation in daily energy expenditure was found to be positively correlated with brood provisioning rates, percentage of time flying and the frequency of non-resting activity. Correlations were also shown with body-mass, body-size and several environmental factors. Published data on basal metabolic rates (BMR) sometimes differed substantially from estimates either made specifically as part of the studies considered here or calculated from allometric equations. For the purpose of interspecific comparisons, specific estimates of BMR are to be preferred. When expressed as a function of BMR, energy expenditures of free-living birds ranged from 1 + to 7 + times BMR with a mode at 3 +. Values of daily energy expenditure exceeding 4 times BMR were found in up to 48% of species and 30% of individuals, so that, contrary to earlier suggestions, 4 times BMR is not a universal upper limit to the sustained work rate of small birds. Observed upper limits tended to be higher in species with energy-expensive foraging habits. Energy expended by breeding birds is likely to involve a balance between the benefits a greater expenditure has for offspring production and any fitness penalty associated with the high level of energy expediture which nest provisioning involves.
1.1. No single equation adequately describes the allometric relation between body mass and BMR for mammals.2.2. Least squares regression of log-transformed data for 248 eutherian species results in a line with a slope (−0.30) significantly different from that of Kleiber's line (−0.25).3.3. Interordinal comparisons of least squares regressions of log-transformed BMR and mass suggest that the Insectivora have a significantly steeper slope to their allometric relationship than do most other orders, while the non-insectivore orders are statistically homogeneous with respect to slope.4.4. With respect to elevation, Edentata have the lowest BMRs; Marsupialia, Primates and Chiroptera are indistinguishable from each other but above the edentates; Primates, Chiroptera, Rodentia, Lagomorpha and Carnivora form the next highest homogeneous grouping; and Artiodactyla have the highest BMRs, significantly greater than all but Lagomorpha and Carnivora.5.5. Analysis of intraordinal variation within the Rodentia suggests significant heterogeneity among families in BMR-mass allometry.
Basal metabolic rate (BMR) is widely assumed to be an index of energy expenditure of free-living animals. However, few attempts have been made to check if the assumption is valid. In this study field metabolic rates (FMR) of 58 species of birds and mammals have been compared with their BMRs. FMR tends to increase with increasing body mass slower than BMR, but the difference was significant only in marsupials. A correlation between mass-independent FMR and BMR (residuals from regressions) is very high in eutherians (mainly rodents), but it is weak in birds and approaches zero in marsupials. The assumption of a proportionality between BMR and energy expenditure of animals does not have a sound experimental support.
Thesis (Ph. D.)--University of Aberdeen, 1991.
Sustained metabolic rates (SusMR) are time-averaged metabolic rates that are measured in free-ranging animals maintaining constant body mass over periods long enough that metabolism is fueled by food intake rather than by transient depletion of energy reserves. Many authors have suggested that SusMR of various wild animal species are only a few times resting (basal or standard) metabolic rates (RMR). We test this conclusion by analyzing all 37 species (humans, 31 other endothermic vertebrates, and 5 ectothermic vertebrates) for which SusMR and RMR had both been measured. For all species, the ratio of SusMR to RMR, which we term sustained metabolic scope, is less than 7; most values fall between 1.5 and 5. Some of these values, such as those for Tour de France cyclists and breeding birds, are surely close to sustainable metabolic ceilings for the species studied. That is, metabolic rates higher than 7 times RMR apparently cannot be sustained indefinitely. These observations pose several questions: whether the proximate physiological causes of metabolic ceilings reside in the digestive tract's ability to process food or in each tissue's metabolic capacity; whether ceiling values are independent of the mode of energy expenditure; whether ceilings are set by single limiting physiological capacities or by coadjusted clusters of capacities (symmorphosis); what the ultimate evolutionary causes of metabolic ceilings are; and how metabolic ceilings may limit animals' reproductive effort, foraging behavior, and geographic distribution.
1.1. The energy metabolism and comparative body water turnover rates of two species of kangaroo rats, Dipodomys merriami and Dipodomys microps, were measured in the natural environment over a 1-yr period with the D218O method.2.2. In addition to yielding energy metabolism data indicative of active, non-postabsorbtive animals, the results suggest that both species undergo diurnal torpor during periods of cold stress.3.3. Comparative water metabolism data indicate that D. merriami possesses a more conservative body water turnover rate than does D. microps.4.4. The D218O method of studying animal energy metabolism in the natural environment yields data not obtainable through conventional laboratory methods. It is preferable, therefore, that where practicable this method be employed in investigations of animal physiological ecology unless there is reasonable assurance that laboratory methods are adequate.
The theory is developed for the use of the isotopically determined turnover rates of the hydrogen and oxygen of body water for measurement of total energy and material balance of an animal.After a consideration of several simplifying assumptions, a summary is given of tests of the extent to which theoretical expectations are realized. The results of these appear to be in general accord with theoretical expectations.
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Energetics of Reproduction and Over-wintering in some Insectivorous Mammals (Mammalia: Insectivora)
- Poppitt
The energetics of pregnancy and lactation in brown long-eared bats (Plecotus auritus)
- Speakman
A review of techniques for the preparation of biological samples for massspectrometric measurements of hydrogen-2/hydrogen-l and oxygen-18/oxygen-16 isotope ratios
- Wong