Variation In Basal Metabolic Rate Research Articles

The Sex Specific Genetic Variation of Energetics in Bank Voles, Consequences of Introgression?

Interaction between mitochondrial and nuclear genomes is expected to affect energetic phenotypes of traits linked to mitochondrial physiology, further influencing the fitness. A rodent, the bank vole (Myodes glareolus), has a population structure completely or partially introgressed with mitochondria from its relative, the red vole (M. rutilus). Females that carried either bank vole mitochondria or mitochondria from the introgressed species were repeatedly mated with males of both mtDNA types. We found that in males, but not in females, morpho-physiological phenotypes are affected by sire type, causing decreases in body mass (BM) and basal metabolic rate (BMR; including BM corrected, rBMR) in individuals sired by fathers carrying introgressed mitochondria. Higher effect sizes for the proportion of additive genetic variation (and 5.6, 1.9 and 3.6 times higher narrow sense heritability for BM, BMR and rBMR, respectively), and lower for proportion of environmental variation were detected in progeny of non-introgressed males. Our data indicate that co-adapted and possibly co-introgressed nuclear genes related to energetic physiology have an important role in adaptation to the northern conditions in bank voles, and that sex linked nuclear genes are a potential source for variation in basal metabolic rate.

Evolution of basal metabolic rate in bank voles from a multidirectional selection experiment.

A major theme in evolutionary and ecological physiology of terrestrial vertebrates encompasses the factors underlying the evolution of endothermy in birds and mammals and interspecific variation of basal metabolic rate (BMR). Here, we applied the experimental evolution approach and compared BMR in lines of a wild rodent, the bank vole (Myodes glareolus), selected for 11 generations for: high swim-induced aerobic metabolism (A), ability to maintain body mass on a low-quality herbivorous diet (H) and intensity of predatory behaviour towards crickets (P). Four replicate lines were maintained for each of the selection directions and an unselected control (C). In comparison to C lines, A lines achieved a 49% higher maximum rate of oxygen consumption during swimming, H lines lost 1.3 g less mass in the test with low-quality diet and P lines attacked crickets five times more frequently. BMR was significantly higher in A lines than in C or H lines (60.8, 56.6 and 54.4 ml O2 h(-1), respectively), and the values were intermediate in P lines (59.0 ml O2 h(-1)). Results of the selection experiment provide support for the hypothesis of a positive association between BMR and aerobic exercise performance, but not for the association of adaptation to herbivorous diet with either a high or low BMR.

Global patterns of seasonal acclimatization in avian resting metabolic rates

The adjustment of resting metabolic rates represents an important component of avian seasonal acclimatization, with recent studies revealing substantial differences between summer and winter in birds from a wide range of latitudes. We compared seasonal variation in basal metabolic rate (BMR) and summit metabolism (M sum) between temperate and tropical/subtropical latitudes, and examined correlations with latitude and temperature. The direction and magnitude of seasonal adjustments in BMR are broadly related to temperature and latitude, but are significantly more variable among tropical and subtropical species compared to those inhabiting temperate zones. Winter adjustments in BMR among subtropical species, when expressed relative to summer values, range from decreases of approximately 35 % to increases of more than 60 %, whereas the majority of temperate-zone species show increases in BMR during winter. Relatively few seasonal M sum data exist for tropical/subtropical species, but those that are available involve responses ranging from winter decreases to increases of similar magnitude to those characteristic of many temperate-zone species. Recent studies also highlight the substantial variation in seasonal adjustments that may occur within species, and reiterate the need for further investigations of the relative roles of environmental variables such as temperature and food availability as determinants of seasonal metabolic variation.

Global variation in avian metabolic rates and the slow pace of life of tropical birds

Global variation in avian metabolic rates and the slow pace of life of tropical birds

Effect of reproduction on the consistency of the between-line type divergence in laboratory mice selected on Basal metabolic rate.

Artificial selection experiments are an effective tool for testing evolutionary hypotheses, because they allow one to separate genetic and environmental variances of the phenotype. However, it is unclear whether trait divergence typically selected early in life persists over an animal's life and altered physiological states, such as reproduction. Here we analyzed the long-term consistency of the between-line type divergence in basal metabolic rate (BMR) selected at 12 wk of age in laboratory mice. We measured BMR in nonreproducing and reproducing females at the age of 22 wk and then at 27 wk of age. Our results show that within both the reproducing group and the control group, the between-line type separation in BMR is consistently retained over time and reproductive status. Metabolically active internal organs (heart, liver, kidneys, and small intestine) also consistently differed in size between the two line types with no significant long-term effect of reproduction. The observed consistency of the between-line type divergence in BMR suggests the existence of the persistent effect of the selection on metabolic traits applied early in life. Moreover, BMR variation achieved by means of artificial selection is considerably higher than that found in natural/unmanipulated populations. The latter may therefore be characterized by insufficient variance to statistically resolve correlations involving BMR.

Basal metabolism in tropical birds: latitude, altitude, and the ‘pace of life’

Summary Life history varies across latitudes, with the ‘pace of life’ being ‘slower’ in tropical regions. Because life history is coupled to energy metabolism via allocation tradeoffs and links between performance capacity and energy use, low metabolic intensity is expected in tropical animals. Low metabolism has been reported for lowland tropical birds, but it is unclear if this is due to ‘slow’ life history or to a warm, stable environment. We measured basal metabolic rates (BMR) of 253 bird species across a 2·6 km altitude gradient in Peru. We predicted higher BMR at high altitude due to lower temperatures leading to elevated thermoregulatory costs. We also tested for BMR differences between widely separated tropical regions (Peru and Panama), and between tropical‐ and temperate‐breeding birds. We found no effect of altitude on BMR in Peruvian species and no difference in BMR between Peruvian and Panamanian birds, suggesting that BMR in Neotropical birds is consistent and independent of environmental temperature. In a data set encompassing more than 500 species, tropical birds had significantly lower BMR than temperate‐breeding birds. In contrast to several recent analyses, we found higher BMR in passerine birds than in non‐passerines, independent of breeding latitude. Breeding latitude affects BMR, but diversity in avian life history within and between temperate and tropical regions may explain some of the residual variation in BMR after accounting for body mass and breeding latitude. Future studies of links between life history, metabolism and environmental factors might benefit from examining these variables within individual species as well as across broad geographic contrasts.

Sources of Variation in the Basal Metabolic Rate of Laughing DovesSpilopelia senegalensis

Although avian basal metabolic rate (BMR) has been widely used in interspecific comparative studies, the sources of within-species variation in this parameter are still relatively poorly understood. Individually differing levels of activity and stress responsiveness have been proposed as potential sources for such variation in BMR. Here, I used an open flow-through respirometry system to examine the possible correlates of the time it takes individual Laughing Doves Spilopelia senegalensis to reach lowest oxygen consumption level in a metabolic chamber (‘BMR time’). Also, the association between individual response to handling stress and BMR was studied. Breath rate, measured while holding the bird in hand, was used as a measure of stress response to handling. It was found that ‘BMR time’ was not related to BMR or breath rate. However, its values were positively predicted by individuals' hematocrit. This indicates the potential importance of ‘BMR time’ as an indicator of activity. It was also found that breath rate was individually repeatable when two measurements were taken 12 hours apart. Breath rate was also positively related to BMR; however, the effect disappeared when mass-specific residuals of BMR were used. These results suggest that individual differences in response to standard handling stress probably do not affect BMR measurements.

Seasonal variation in basal metabolic rates among the yakut (Sakha) of Northeastern Siberia

Previous research has shown that indigenous circumpolar populations have elevated basal metabolic rates (BMRs), yet few studies have explored whether metabolic rates increase during the winter. This study addresses this gap by examining seasonal variation in BMR and its associations with thyroid function and lifestyle factors among the Yakut (Sakha) of Siberia. Anthropometric dimensions, BMR, and thyroid hormone levels (free triiodothyronine [fT3], free thyroxine [fT4], thyroid-stimulating hormone [TSH]) were measured on two occasions (July/August, 2009 and January 2011) on a sample of 94 Yakut (Sakha) adults (35 men, 59 women) from the rural village of Berdygestiakh, Sakha Republic, Russia. Seasonal changes in BMR varied by age. Younger Yakut adults (19-49 years) showed significant elevations in winter-time BMR of 6% (P < 0.05), whereas older individuals (≥50 years) showed modest declines (2%; n.s.). Both younger and older Yakut men and women showed increased respiratory quotients during the winter. FT3 and fT4 levels significantly declined during the winter in both younger and older Yakut men and women (P < 0.05). Lifestyle factors were significant predictors of BMR variation, particularly among older men and women. Among the Yakut, increased wintertime BMR was observed among younger but not older adults, whereas all adults showed sharp reductions in free thyroid hormone levels during the winter. Among men, greater participation in subsistence activities was associated with increased BMRs and greater fat oxidation. Among women, variation in food use had the strongest impact on metabolic function.

High basal metabolic rate does not elevate oxidative stress during reproduction in laboratory mice

Increased oxidative stress (OS) has been suggested as a physiological cost of reproduction. However, previous studies reported ambiguous results, with some even showing a reduction of oxidative damage during reproduction. We tested whether the link between reproduction and OS is mediated by basal metabolic rate (BMR), which has been hypothesized to affect both the rate of radical oxygen species production and antioxidative capacity. We studied the effect of reproduction on OS in females of laboratory mice divergently selected for high (H-BMR) and low (L-BMR) BMR, previously shown to differ with respect to parental investment. Non-reproducing L-BMR females showed higher oxidative damage to lipids (quantified as the level of malondialdehyde in internal organ tissues) and DNA (quantified as the level of 8-oxodG in blood serum) than H-BMR females. Reproduction did not affect oxidative damage to lipids in either line; however, it reduced damage to DNA in L-BMR females. Reproduction increased catalase activity in liver (significantly stronger in L-BMR females) and decreased it in kidneys. We conclude that the effect of reproduction on OS depends on the initial variation in BMR and varies between studied internal organs and markers of OS.

A macrophysiological analysis of energetic constraints on geographic range size in mammals.

Physiological processes are essential for understanding the distribution and abundance of organisms, and recently, with widespread attention to climate change, physiology has been ushered back to the forefront of ecological thinking. We present a macrophysiological analysis of the energetics of geographic range size using combined data on body size, basal metabolic rate (BMR), phylogeny and range properties for 574 species of mammals. We propose three mechanisms by which interspecific variation in BMR should relate positively to geographic range size: (i) Thermal Plasticity Hypothesis, (ii) Activity Levels/Dispersal Hypothesis, and (iii) Energy Constraint Hypothesis. Although each mechanism predicts a positive correlation between BMR and range size, they can be further distinguished based on the shape of the relationship they predict. We found evidence for the predicted positive relationship in two dimensions of energetics: (i) the absolute, mass-dependent dimension (BMR) and (ii) the relative, mass-independent dimension (MIBMR). The shapes of both relationships were similar and most consistent with that expected from the Energy Constraint Hypothesis, which was proposed previously to explain the classic macroecological relationship between range size and body size in mammals and birds. The fact that this pattern holds in the MIBMR dimension indicates that species with supra-allometric metabolic rates require among the largest ranges, above and beyond the increasing energy demands that accrue as an allometric consequence of large body size. The relationship is most evident at high latitudes north of the Tropics, where large ranges and elevated MIBMR are most common. Our results suggest that species that are most vulnerable to extinction from range size reductions are both large-bodied and have elevated MIBMR, but also, that smaller species with elevated MIBMR are at heightened risk. We also provide insights into the global latitudinal trends in range size and MIBMR and more general issues of phylogenetic and geographic scale.

Estimated digestible energy intakes in moderate and overweight horses

Estimated digestible energy intakes in moderate and overweight horses

HOW DOES EVOLUTIONARY VARIATION IN BASAL METABOLIC RATES ARISE? A STATISTICAL ASSESSMENT AND A MECHANISTIC MODEL

Metabolic rates are related to the pace of life. Hence, research into their variability at global scales is of vital importance for several contemporary theories in physiology, ecology, and evolution. Here we evaluated the effect of latitude, climate, primary productivity, habitat aridity, and species trophic habits, on mass-independent basal metabolic rates (BMRs) for 195 rodent species. The aims of this article were twofold. First, we evaluated the predictive power of different statistical models (via a model selection approach), using a dimensional reduction technique on the exogenous factor matrix to achieve a clear interpretation of the selected models. Second, we evaluated three specific predictions derived from a recently proposed hypothesis, herein called the "obligatory heat" model (OHM), for the evolution of BMR. Obtained results indicate that mean/minimum environmental temperature, rainfall/primary productivity and, finally, species trophic habits are, in this order, the major determinants of mass-independent BMR. Concerning the mechanistic causes behind this variation, obtained data agree with the predictions of the OHM: (1) mean annual environmental temperature was the best single predictor of residual variation in BMR, (2) herbivorous species have greater mass-independent metabolic rates, and tend to be present at high-latitude cold environments, than species in other trophic categories.

Determinants of inter-specific variation in basal metabolic rate

Basal metabolic rate (BMR) is the rate of metabolism of a resting, postabsorptive, non-reproductive, adult bird or mammal, measured during the inactive circadian phase at a thermoneutral temperature. BMR is one of the most widely measured physiological traits, and data are available for over 1,200 species. With data available for such a wide range of species, BMR is a benchmark measurement in ecological and evolutionary physiology, and is often used as a reference against which other levels of metabolism are compared. Implicit in such comparisons is the assumption that BMR is invariant for a given species and that it therefore represents a stable point of comparison. However, BMR shows substantial variation between individuals, populations and species. Investigation of the ultimate (evolutionary) explanations for these differences remains an active area of inquiry, and explanation of size-related trends remains a contentious area. Whereas explanations for the scaling of BMR are generally mechanistic and claim ties to the first principles of chemistry and physics, investigations of mass-independent variation typically take an evolutionary perspective and have demonstrated that BMR is ultimately linked with a range of extrinsic variables including diet, habitat temperature, and net primary productivity. Here we review explanations for size-related and mass-independent variation in the BMR of animals, and suggest ways that the various explanations can be evaluated and integrated.

Determinants of intra-specific variation in basal metabolic rate

Basal metabolic rate (BMR) provides a widely accepted benchmark of metabolic expenditure for endotherms under laboratory and natural conditions. While most studies examining BMR have concentrated on inter-specific variation, relatively less attention has been paid to the determinants of within-species variation. Even fewer studies have analysed the determinants of within-species BMR variation corrected for the strong influence of body mass by appropriate means (e.g. ANCOVA). Here, we review recent advancements in studies on the quantitative genetics of BMR and organ mass variation, along with their molecular genetics. Next, we decompose BMR variation at the organ, tissue and molecular level. We conclude that within-species variation in BMR and its components have a clear genetic signature, and are functionally linked to key metabolic process at all levels of biological organization. We highlight the need to integrate molecular genetics with conventional metabolic field studies to reveal the adaptive significance of metabolic variation. Since comparing gene expressions inter-specifically is problematic, within-species studies are more likely to inform us about the genetic underpinnings of BMR. We also urge for better integration of animal and medical research on BMR; the latter is quickly advancing thanks to the application of imaging technologies and ‘omics’ studies. We also suggest that much insight on the biochemical and molecular underpinnings of BMR variation can be gained from integrating studies on the mammalian target of rapamycin (mTOR), which appears to be the major regulatory pathway influencing the key molecular components of BMR.

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.

Effect of dietary restriction on metabolic, anatomic and molecular traits in mice depends on the initial level of basal metabolic rate (BMR)

Dietary restriction (DR)-related delay of ageing is hypothesized to be mediated by the reduction of the metabolic rate (MR). However, studies on the effect of DR on MR have produced equivocal results. We demonstrated that this lack of congruency can be due to a variation in the initial level of MR within a given pool of experimental subjects. We subjected laboratory mice from two line types divergently selected for basal MR (BMR) to 30% DR lasting 6 months to test whether the effect of DR depends on the initial variation in BMR and peak MR. BMR and peak MR were independently affected by DR. The effect of DR was stronger in line types with higher initial levels of MR. Line-type-specific changes in the proportions of body components explained contrasting effects of DR on the mass-corrected BMR, which decreased in the high-BMR line type and did not change in the low-BMR line type. We conclude that the initial variation in MR can significantly affect response to DR. However, we found no association between the level of MR and mechanisms underlying the susceptibility to or protection against oxidative stress.

Shorebirds' Seasonal Adjustments in Thermogenic Capacity Are Reflected by Changes in Body Mass: How Preprogrammed and Instantaneous Acclimation Work Together

Phenotypic flexibility in shorebirds has been studied mainly in the context of adjustments to migration and to quality of food; little is known on how birds adjust their phenotype to harsh winter conditions. We showed earlier that red knot (Calidris canutus islandica) can acclimate to cold by elevating body mass. This goes together with larger pectoral muscles, i.e., greater shivering machinery, and thus, better thermogenic capacity. Here, we present results of a yearlong experiment with indoor captive knots to determine whether this strategy is part of their natural seasonal phenotypic cycle. We maintained birds under three thermal regimes: constant cold (5 °C), constant thermoneutrality (25 °C) and natural seasonal variation between these extremes (9-22 °C). Each month we measured variables related to the birds' endurance to cold and physiological maintenance [body mass, thickness of pectoral muscles, summit metabolic rate (M(sum)), food intake, gizzard size, basal metabolic rate (BMR)]. Birds from all treatments expressed synchronized and comparable variation in body mass in spite of thermal treatments, with a 17-18% increase between the warmest and coldest months of the year; which appeared regulated by an endogenous driver. In addition, birds living in the cold exhibited a 10% higher average body mass than did those maintained at thermoneutrality. Thickness of the pectoral muscle tracked changes in body mass in all treatments and likely contributed to greater capacity for shivering in heavier birds. Consequently, M(sum) was 13% higher in cold-acclimated birds compared to those experiencing no thermoregulation costs. However, our data also suggest that part of maximal heat production comes from nonshivering processes. Birds facing cold conditions ate up to 25% more food than did birds under thermoneutral conditions, yet did not develop larger gizzards. Seasonal variation in BMR followed changes in body mass, probably reflecting changes in mass of metabolically active tissues. Just as cold-exposed birds, red knots in the variable treatment increased body mass in winter, thereby improving cold endurance. During summer, however, they maintained a lower body mass and thermogenic capacity compared to cold-exposed birds, similar to individuals kept at thermoneutrality. We conclude that red knots acclimate to seasonal variations in ambient temperature by modulating body mass, combining a preprogrammed increase in mass during winter with a capacity for fine-tuning body mass and thermogenic capacity to temperature variations.

The allometry of parrot BMR: seasonal data for the Greater Vasa Parrot, Coracopsis vasa, from Madagascar

In this study we examined the allometry of basal metabolic rate (BMR) of 31 parrot species. Unlike previous reports, we show that parrots per se do not display BMRs that are any different to other captive-raised birds of their body size. An ordinary least squares regression fitted the data best and body mass explained 95% of the variation in BMR. There was no phylogenetic signal in the BMR data. We also provide new data for the Greater Vasa Parrot (Coracopsis vasa) of Madagascar. We tested the hypotheses that C. vasa may, because of its insular existence, display conservative energetic traits (low BMR, use of adaptive heterothermy) similar to those observed in several Malagasy mammals. However, this was not the case. C. vasa had a higher BMR than other parrots, especially during summer, when BMR was up-regulated by 50.5% and was 95.7% higher than predicted from an ordinary least squares (OLS) allometry of parrots (BMR=0.042M (b) (0.649) , BMR in Watts, M (b) in grammes). Compared with BMR data for 94 captive-raised bird species, the winter and summer BMRs were, respectively, 45.5 and 117.8% higher than predicted by a phylogenetic generalised least squares (PGLS) allometry (BMR=0.030M (b) (0.687) , BMR in Watts, M (b) in grammes). The summer up-regulation of BMR is the highest recorded for a bird of any size to date. We suggest that the costs of a high summer BMR may be met by the unusual cooperative breeding system of C. vasa in which groups of males feed the female and share paternity. The potential breeding benefits of a high summer BMR are unknown.

Mitochondrial oxygen affinity predicts basal metabolic rate in humans

The basal metabolic rate (BMR) is referred to as the minimal rate of metabolism required to support basic body functions. It is well known that individual BMR varies greatly, even when correcting for body weight, fat content, and thyroid hormone levels, but the mechanistic determinants of this phenomenon remain unknown. Here, we show in humans that mass-related BMR correlates strongly to the mitochondrial oxygen affinity (p50(mito); R(2)=0.66, P=0.0004) measured in isolated skeletal muscle mitochondria. A similar relationship was found for oxygen affinity and efficiency during constant-load submaximal exercise (R(2)=0.46, P=0.007). In contrast, BMR did not correlate to overall mitochondrial density or to proton leak. Mechanistically, part of the p50(mito) seems to be controlled by the excess of cytochrome c oxidase (COX) protein and activity relative to other mitochondrial proteins. This is illustrated by the 5-fold increase in p50(mito) after partial cyanide inhibition of COX at doses that do not affect maximal mitochondrial electron flux through the ETS. These data suggest that the interindividual variation in BMR in humans is primarily explained by differences in mitochondrial oxygen affinity. The implications of these findings are discussed in terms of a trade-off between aerobic efficiency and power.

Basal metabolic rate and the rate of senescence in the great tit

1. Between-individual variation in rates of senescence has recently been found to relate to natal and early-life conditions in several natural populations. Mechanistic theories of senescence have predicted between-individual variation in basal metabolic rate (BMR) to also underlie such variation in rates of senescence. The question whether variation in BMR is linked to natal and early-life conditions with effects on senescence has, however, not yet been addressed. 2. Using cross-sectional data on winter BMR of nearly 700 individual great tits Parus major, we tested whether factors associated with individual variation in the rate of senescence were also associated with differences in BMR. 3. We found that winter BMR was a repeatable trait (36%), and that variation in winter BMR was partly explained by body mass, and interactive effects of sex, age and seasonal date with ambient temperature. 4. Our data, however, revealed that neither the level of BMR, nor its age-specific decline, was explained by three parameters previously shown to underlie variation in rates of reproductive senescence in our study population: maternal age, immigrant status and early-life reproductive performance. 5. These results therefore did not support the suggestion that variation in BMR underlies variation in rates of reproductive senescence in relation to maternal age, immigrant status and early-life reproductive performance. 6. We further found a low repeatability of BMR from winter to the subsequent breeding season (1%, n = 55), which suggested that a relationship between BMR and proxies for rates of senescence may have been absent in our data set because winter BMR did not represent year-round metabolic strategies. 7. Further study, preferably using longitudinal data, is required to resolve the link between BMR at different times of year and senescence.