Variation In Metabolic Rate Research Articles

Cardiovascular Demands and Adaptations from Practicing Hot Yoga

Background: Hatha yoga has become a popular form of exercise that has demonstrated to elicit marked increases in muscular strength and muscular flexibility. However, minimal inquiry towards its influence on cardiovascular health and performance is available. Methods: Published investigations including and preceding December 2016 were systematically reviewed and appraised. The terms, “Yoga”, “Yoga AND Exercise”, “Yoga AND Exercise Test” identified 337 articles, 6 of these articles were relevant and utilized in this review. Results: The cardiovascular demands on a Bikram yoga class appear to be light in nature while further demonstrating individual variation in metabolic cost and heart rate. The variations observed may have been a result of a diverse sample size with age, sex and fitness. Short term (ie. 8 wks) adaptions failed to demonstrate a significant difference in resting cardiovascular measurements with minimal support for enhancing aerobic power. Long term (ie. 1yr) Bikram yoga practice may elicit position adaptions in resting heart rate, systolic and diastolic blood pressure in obese individuals. There remained a lack of significant difference when examining cardiovascular performance measures between long term and novice Bikram yoga practitioners. Conclusions: Bikram yoga continues to increase in popularity as an alternative exercise option; however minimal evidence exists demonstrating its positive impact on cardiovascular health and performance. It appears this form of light exercise may be an effective and exciting means of activity for individuals looking to start an exercise program. Individuals wishing to pursue this form of exercise are encouraged to acquire approval and consent from a medical doctor and a certified exercise professional prior to starting

Complex mitonuclear interactions and metabolic costs of mating in male seed beetles.

The lack of evolutionary response to selection on mitochondrial genes through males predicts the evolution of nuclear genetic influence on male-specific mitochondrial function, for example by gene duplication and evolution of sex-specific expression of paralogs involved in metabolic pathways. Intergenomic epistasis may therefore be a prevalent feature of the genetic architecture of male-specific organismal function. Here, we assess the role of mitonuclear genetic variation for male metabolic phenotypes [metabolic rate and respiratory quotient (RQ)] associated with ejaculate renewal, in the seed beetle Callosobruchus maculatus, by assaying lines with crossed combinations of distinct mitochondrial haplotypes and nuclear lineages. We found a significant increase in metabolic rate following mating relative to virgin males. Moreover, processes associated with ejaculate renewal showed variation in metabolic rate that was affected by mitonuclear interactions. Mitochondrial haplotype influenced mating-related changes in RQ, but this pattern varied over time. Mitonuclear genotype and the energy spent during ejaculate production affected the weight of the ejaculate, but the strength of this effect varied across mitochondrial haplotypes showing that the genetic architecture of male-specific reproductive function is complex. Our findings unveil hitherto underappreciated metabolic costs of mating and ejaculate renewal, and provide the first empirical demonstration of mitonuclear epistasis on male reproductive metabolic processes.

Does individual variation in metabolic phenotype predict fish behaviour and performance?

There is increasing interest in documenting and explaining the existence of marked intraspecific variation in metabolic rate in animals, with fishes providing some of the best‐studied examples. After accounting for variation due to other factors, there can typically be a two to three‐fold variation among individual fishes for both standard and maximum metabolic rate (SMR and MMR). This variation is reasonably consistent over time (provided that conditions remain stable), and its underlying causes may be influenced by both genes and developmental conditions. In this paper, current knowledge of the extent and causes of individual variation in SMR, MMR and aerobic scope (AS), collectively its metabolic phenotype, is reviewed and potential links among metabolism, behaviour and performance are described. Intraspecific variation in metabolism has been found to be related to other traits: fishes with a relatively high SMR tend to be more dominant and grow faster in high food environments, but may lose their advantage and are more prone to risk‐taking when conditions deteriorate. In contrast to the wide body of research examining links between SMR and behavioural traits, very little work has been directed towards understanding the ecological consequences of individual variation in MMR and AS. Although AS can differ among populations of the same species in response to performance demands, virtually nothing is known about the effects of AS on individual behaviours such as those associated with foraging or predator avoidance. Further, while factors such as food availability, temperature, hypoxia and the fish's social environment are known to alter resting and MMRs in fishes, there is a paucity of studies examining how these effects vary among individuals, and how this variation relates to behaviour. Given the observed links between metabolism and measures of performance, understanding the metabolic responses of individuals to changing environments will be a key area for future research because the environment will have a strong influence on which animals survive predation, become dominant and ultimately have the highest reproductive success. Although current evidence suggests that variation in SMR may be maintained within populations via context‐dependent fitness benefits, it is suggested that a more integrative approach is now required to fully understand how the environment can modulate individual performance via effects on metabolic phenotypes encompassing SMR, MMR and AS.

Metabolism correlates with variation in post‐natal growth rate among songbirds at three latitudes

Summary Variation in post‐natal growth rates is substantial among organisms and especially strong among latitudes because tropical and south temperate species typically have slower growth than north temperate relatives. Metabolic rate is thought to be a critical mechanism underlying growth rates after accounting for allometric effects of body mass. However, comparative tests on a large spatial scale are lacking, and the importance of metabolism for growth rates remains unclear both within and particularly across latitudes. Songbirds exhibit strong interspecific variation in growth rates across geographic space, although within latitudes an association between metabolic rate and growth rate has not always been observed. Moreover, the hypothesis that differences in growth rates across latitudes reflect underlying differences in metabolism is untested. Here, we investigate these possibilities across north temperate, south temperate and tropical study sites. Phylogenetic analyses showed that, for a given body mass, metabolic rates of north temperate nestlings were higher than tropical and south temperate species. Metabolic rates controlled for body mass correlated with post‐natal growth rates both within and among latitudes. Offspring body mass explained substantial residual variation in growth rates as expected under classic allometric theory. Our results suggest that variation in metabolic rates has an important influence on broad patterns of avian growth rates at a global scale. We suggest further studies that address the ecological and physiological costs and consequences of variation in metabolism and growth rates.

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.

Metabolism at the Max: How Vertebrate Organisms Respond to Physical Activity.

Activity metabolism is supported by phosphorylated reserves (adenosine triphosphate, creatine phosphate), glycolytic, and aerobic metabolism. Because there is no apparent variation between vertebrate groups in phosphorylated reserves or glycolytic potential of skeletal muscle, variation in maximal metabolic rate between major vertebrate groups represents selection operating on aerobic mechanisms. Maximal rates of oxygen consumption in vertebrates are supported by increased conductive and diffusive fluxes of oxygen from the environment to the mitochondria. Maximal CO2 efflux from the mitochondria to the environment must be matched to oxygen flux, or imbalances in pH will occur. Among vertebrates, there are a variety of modes of locomotion and vastly different rates of metabolism supported by a variety of cardiorespiratory architectures. However, interclass comparisons strongly implicate systemic oxygen transport as the rate-limiting step to maximal oxygen consumption for all vertebrate groups. The key evolutionary step that accounts for the approximately 10-fold increase in maximal oxygen flux in endotherms versus ectotherms appears to be maximal heart rate. Other variables such as ventilation, pulmonary/gill, and tissue diffusing capacity, have excess capacity and thus are not limiting to maximal oxygen consumption. During maximal activity, the ratio of ventilation to respiratory system blood flow is remarkably similar among vertebrates, and CO2 extraction efficiency increases while oxygen extraction efficiency decreases, suggesting that the respiratory system provides the largest resistance to maximal CO2 flux. Despite the large variation in modes of activity and rates of metabolism, maximal rates of oxygen and CO2 flux appear to be limited by the cardiovascular and respiratory systems, respectively.

Effects of parasites and antigenic challenge on metabolic rates and thermoregulation in northern red-backed voles (Myodes rutilus).

Perturbations in host energetics are considered to be an essential pathway for parasite impact on host fitness. However, direct estimations of parasite-induced variations in basal metabolic rates of vertebrate hosts have so far provided contradictory results. The energy requirements of immunity and other vital functions may be compromised in energy-demanding conditions in comparison to comfortable conditions; therefore, in our study performed on the wild red-backed vole, Myodes rutilus, we compared the values of indices that reflect metabolic and thermoregulatory responses to acute cooling in individuals that had been naturally infected by gut helminths or Ixodes persulcatus taiga ticks to individuals with no signs of infestation. To consider the possible effects of an acquired immune response on host energetics, we also injected some of the tested individuals with sheep red blood cells (SRBC). Red-backed voles infected by the nematode Heligmosomum mixtum injected with SRBC showed significantly lower cold-induced maximum oxygen consumption than the saline control. Additionally, individuals infected with H. mixtum showed significantly lower oxygen consumption during the final minute of the 15-min acute cooling period and a significantly greater decline in body temperature than individuals free from helminths. In individuals concurrently infected by H. mixtum and the cestodes Arostrilepis horrida, these indices did not differ from helminth-free individuals. The number of ticks simultaneously parasitizing the voles at the moment of capture correlated positively with their SMR. Our results suggest that even natural parasites produce deleterious effects on host aerobic capacity and thermoregulatory abilities, although the effects of different parasites might not be additive.

Exercise-induced metabolic fluctuations influence AMPK, p38-MAPK and CaMKII phosphorylation in human skeletal muscle.

During transition from rest to exercise, metabolic reaction rates increase substantially to sustain intracellular ATP use. These metabolic demands activate several kinases that initiate signal transduction pathways which modulate transcriptional regulation of mitochondrial biogenesis. The purpose of this study was to determine whether metabolic fluctuations per se affect the signaling cascades known to regulate peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α). On two separate occasions, nine men performed a continuous (30-min) and an intermittent exercise (30 × 1-min intervals separated by 1-min of recovery) at 70% of . Skeletal muscle biopsies from the vastus lateralis were taken at rest and at +0 h and +3 h after each exercise. Metabolic fluctuations that correspond to exercise-induced variation in metabolic rates were determined by analysis of VO2 responses. During intermittent exercise metabolic fluctuations were 2.8-fold higher despite identical total work done to continuous exercise (317 ± 41 vs. 312 ± 56 kJ after intermittent and continuous exercise, respectively). Increased phosphorylation of AMP-activated protein kinase (AMPK) (˜2.9-fold, P < 0.01), calcium/calmodulin-dependent protein kinase II (CaMKII) (˜2.7-fold, P < 0.01) and p38-mitogen-activated protein kinase (MAPK) (˜4.2-fold, P < 0.01) occurred immediately in both exercises and to a greater extent after the intermittent exercise (condition x time interaction, P < 0.05). A single bout of intermittent exercise induces a greater activation of these signaling pathways regulating PGC-1α when compared to a single bout of continuous exercise of matched work and intensity. Chronic adaptations to exercise on mitochondria biogenesis are yet to be investigated.

Individuals with higher metabolic rates have lower levels of reactive oxygen species in vivo.

There is increasing interest in the effect of energy metabolism on oxidative stress, but much ambiguity over the relationship between the rate of oxygen consumption and the generation of reactive oxygen species (ROS). Production of ROS (such as hydrogen peroxide, H2O2) in the mitochondria is primarily inferred indirectly from measurements in vitro, which may not reflect actual ROS production in living animals. Here, we measured in vivo H2O2 content using the recently developed MitoB probe that becomes concentrated in the mitochondria of living organisms, where it is converted by H2O2 into an alternative form termed MitoP; the ratio of MitoP/MitoB indicates the level of mitochondrial H2O2 in vivo. Using the brown trout Salmo trutta, we tested whether this measurement of in vivo H2O2 content over a 24 h-period was related to interindividual variation in standard metabolic rate (SMR). We showed that the H2O2 content varied up to 26-fold among fish of the same age and under identical environmental conditions and nutritional states. Interindividual variation in H2O2 content was unrelated to mitochondrial density but was significantly associated with SMR: fish with a higher mass-independent SMR had a lower level of H2O2. The mechanism underlying this observed relationship between SMR and in vivo H2O2 content requires further investigation, but may implicate mitochondrial uncoupling which can simultaneously increase SMR but reduce ROS production. To our knowledge, this is the first study in living organisms to show that individuals with higher oxygen consumption rates can actually have lower levels of H2O2.

Sub-tropical seagrass ecosystem metabolism measured by eddy covariance

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 529:75-90 (2015) - DOI: https://doi.org/10.3354/meps11314 Sub-tropical seagrass ecosystem metabolism measured by eddy covariance Matthew H. Long1,2,*, Peter Berg1, Karen J. McGlathery1, Joseph C. Zieman1 1Department of Environmental Sciences, University of Virginia, 291 McCormick Rd, Charlottesville, Virginia 22904, USA 2Present address: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, USA *Corresponding author: mlong@whoi.edu ABSTRACT: The metabolism of seagrass ecosystems was examined at 4 sites in south Florida, USA, using the eddy covariance technique under in situ conditions. Three sites were located across a phosphorus-driven productivity gradient to examine the combined effects of dynamic variables (irradiance, flow velocity) and state variables (sediment phosphorus and organic content, seagrass biomass) on ecosystem metabolism and trophic status. Gross primary production and respiration rates varied significantly across Florida Bay in the summer of 2012 with the lowest rates (64 and –53 mmol O2 m–2 d–1, respectively) in low-phosphorus sediments in the northeast and the highest (287 and –212 mmol O2 m–2 d–1, respectively) in the southwest where sediment phosphorus, organic matter, and seagrass biomass are higher. Seagrass ecosystems offshore of the Florida Keys had similar large daily production and respiration rates (397 and –17 mmol O2 m–2 d–1, respectively) and were influenced by flow through the permeable offshore sediments. Across all sites, net ecosystem metabolism rates indicated that the seagrass ecosystems were autotrophic in the summertime. Substantial day-to-day variability in metabolic rates was found due to variations in irradiance and flow velocity. At all sites the relationship between photosynthesis and irradiance was linear and did not show any sign of saturation over the entire irradiance range (up to 1400 µmol photons m–2 s–1). This was likely due to the efficient use of light by the large photosynthetic surface area of the seagrass canopy, an effect which can only be examined by in situ measurements that integrate across all autotrophs in the seagrass ecosystem. KEY WORDS: Seagrass · Eddy covariance · Metabolism · Carbon cycling Full text in pdf format PreviousNextCite this article as: Long MH, Berg P, McGlathery KJ, Zieman JC (2015) Sub-tropical seagrass ecosystem metabolism measured by eddy covariance. Mar Ecol Prog Ser 529:75-90. https://doi.org/10.3354/meps11314 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 529. Online publication date: June 08, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Field Metabolic Rate Is Dependent on Time-Activity Budget in Ring-Billed Gulls (Larus delawarensis) Breeding in an Anthropogenic Environment.

Environmental and behavioral factors have long been assumed to affect variation in avian field metabolic rate (FMR). However, due to the difficulties in measuring continuous behavior of birds over prolonged periods of time, complete time-activity budgets have rarely been examined in relation to FMR. Our objective was to determine the effect of activity (measured by detailed time-activity budgets) and a series of extrinsic and intrinsic factors on FMR of the omnivorous ring-billed gull (Larus delawarensis). The experiment was conducted during the incubation period when both members of the pair alternate between attending the nest-site and leaving the colony to forage in aquatic and anthropogenic environments (city, agricultural). FMR was determined using the doubly labeled water method. Time-activity budgets were extrapolated from spatio-temporal data (2-5 days) obtained from bird-borne GPS data loggers. Gulls had low FMRs compared to those predicted by allometric equations based on recorded FMRs from several seabird species. Gulls proportioned their time mainly to nest-site attendance (71% of total tracking time), which reduced FMR/g body mass, and was the best variable explaining energy expenditure. The next best variable was the duration of foraging trips, which increased FMR/g; FMR/g was also elevated by the proportion of time spent foraging or flying (17% and 8% of tracking time respectively). Most environmental variables measured did not impact FMR/g, however, the percent of time birds were subjected to temperatures below their lower critical temperature increased FMR. Time-activity budgets varied between the sexes, and with temperature and capture date suggesting that these variables indirectly affected FMR/g. The gulls foraged preferentially in anthropogenic-related habitats, which may have contributed to their low FMR/g due to the high availability of protein- and lipid-rich foods. This study demonstrates that activities were the best predictors of FMR/g in ring-billed gulls, thus providing strong support for this long-standing theory in bioenergetics.

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.

Planktonic production and respiration in a subtropical lake dominated by Cyanobacteria.

Planktonic primary production and respiration rates were estimated in a subtropical coastal lake dominated by Cyanobacteria in order to investigate the temporal and vertical variation in this lake and to evaluate its relationships with limnological variables and phytoplankton. Light and dark bottles were incubated at four different depths in the central part of the lake and were performed bimonthly from June/2009 to December/2010. No significant difference was evident among depths in relation to phytoplankton, limnological variables and metabolic rates. However, the highest production rates were recorded at the surface, and decreased towards the bottom, coupled with phytoplanktonic photosynthetic capacity. Wind induced mixing in Peri Lake played an important role in nutrient and phytoplankton redistribution, characterizing this lake as polymictic. According to density and biovolume, the phytoplankton community was dominated by filamentous Cyanobacteria, especially Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba-Raju. This study has shown that both water temperature and nutrient availability drive phytoplankton growth and consequently the temporal variation in metabolic rates, where respiration is higher than primary production.

Circannual rhythm of resting metabolic rate of a small Afrotropical bird

Seasonal variation in avian metabolic rate is well established in Holarctic and temperate species, while trends in Afrotropical species are relatively poorly understood. Furthermore, given the paucity of data on circannual rhythm in avian metabolism, it is not known whether seasonal measurements made in summer and winter correspond with annual peaks and troughs in avian metabolic rate. Thus, we investigated how mean body mass, resting metabolic rate (RMR) and evaporative water loss (EWL) of a small Afrotropical bird, the Cape white-eye (Zosterops virens), changed monthly over the course of a year at 20°C and 25°C. Mean body mass was 12.2±1.0g throughout the study period. However, both EWL and RMR varied monthly, and peaks and troughs in RMR occurred in March and October respectively, which did not correspond to peaks and troughs in mean monthly outdoor ambient temperatures. These results suggest that measuring RMR at the height of summer and winter may underestimate the flexibility of which birds are capable in terms of their metabolic rate. We encourage further studies on this topic, to establish whether the lag between environmental temperature and RMR is consistent in other species.

Reduction of Energetic Demands through Modification of Body Size and Routine Metabolic Rates in Extremophile Fish.

Variation in energy availability or maintenance costs in extreme environments can exert selection for efficient energy use, and reductions in organismal energy demand can be achieved in two ways: reducing body mass or metabolic suppression. Whether long-term exposure to extreme environmental conditions drives adaptive shifts in body mass or metabolic rates remains an open question. We studied body size variation and variation in routine metabolic rates in locally adapted populations of extremophile fish (Poecilia mexicana) living in toxic, hydrogen sulfide-rich springs and caves. We quantified size distributions and routine metabolic rates in wild-caught individuals from four habitat types. Compared with ancestral populations in nonsulfidic surface habitats, extremophile populations were characterized by significant reductions in body size. Despite elevated metabolic rates in cave fish, the body size reduction precipitated in significantly reduced energy demands in all extremophile populations. Laboratory experiments on common garden-raised fish indicated that elevated routine metabolic rates in cave fish likely have a genetic basis. The results of this study indicate that adaptation to extreme environments directly impacts energy metabolism, with fish living in cave and sulfide spring environments expending less energy overall during routine metabolism.

Daily variation in body mass and thermoregulation in male Hwamei (Garrulax canorus) at different seasons

Acclimatization to winter conditions is an essential prerequisite for survival of small passerines of the northern temperate zone. In the present study, we measured diurnal variations in body mass, body temperature and basal metabolic rate (BMR) for seasonally acclimatized Hwameis (Garrulax canorus). Body mass was determined with a Sartorius balance. Metabolic rates of Hwameis were measured with an open-circuit respirometry system. Body masses varied with time of day and were higher in daytime for Hwameis in both summer and winter, and body masses in winter were higher compared to that in summer. Body temperatures of Hwameis were higher in daytime, and the summer acclimatized birds had significantly higher body temperatures compared to the winter acclimatized birds. BMRs of Hwameis were significantly higher during the daytime compared to the nighttime of the daily cycle in both summer and winter, and Hwameis in winter had significantly higher BMRs than that in summer. This result showed that Hwameis rely mostly on metabolic capacity to maintain their body temperature in cold weathers, and Hwameis exhibited daily and seasonal flexibility in morphology and physiology which is important under changing environmental conditions.

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.

Setting the pace of life: membrane composition of flight muscle varies with metabolic rate of hovering orchid bees.

Patterns of metabolic rate variation have been documented extensively in animals, but their functional basis remains elusive. The membrane pacemaker hypothesis proposes that the relative abundance of polyunsaturated fatty acids in membrane phospholipids sets the metabolic rate of organisms. Using species of tropical orchid bees spanning a 16-fold range in body size, we show that the flight muscles of smaller bees have more linoleate (%18 : 3) and stearate (%18 : 0), but less oleate (%18 : 1). More importantly, flight metabolic rate (FlightMR) varies with the relative abundance of 18 : 3 according to the predictions of the membrane pacemaker hypothesis. Although this relationship was found across large differences in metabolic rate, a direct association could not be detected when taking phylogeny and body mass into account. Higher FlightMR, however, was related to lower %16 : 0, independent of phylogeny and body mass. Therefore, this study shows that flight muscle membrane composition plays a significant role in explaining diversity in FlightMR, but that body mass and phylogeny are other factors contributing to their variation. Multiple factors are at play to modulate metabolic capacity, and changing membrane composition can have gradual and stepwise effects to achieve a new range of metabolic rates. Orchid bees illustrate the correlated evolution between membrane composition and metabolic rate, supporting the functional link proposed in the membrane pacemaker hypothesis.

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

Variability in diel and seasonal in situ metabolism of the tropical gastropod Tectus niloticus

Researchers often use metabolic measurements in the field over narrow time periods to estimate an organism's metabolism over large time scales. Here, we measured in situ respira- tion, calcification and excretion rates of the tropical gastropod Tectus niloticus L. through benthic chamber experiments. Our samples spanned a 21 h time frame and were taken during both the warm and cool seasons. We assessed diel and seasonal variability in metabolic rates, as well as the effect of individual size and the contribution of shell epi- and endobionts. Our results show that metabolic rates vary through time at both diel and seasonal scales, as measured fluxes for respira- tion and calcification were significantly higher at night during the warm season. This nocturnal pattern was not significant in the cool season. Size effects were significant with higher respiration and calcification rates for small individuals regardless of the season, although the difference tended to be more pronounced in the warm season. We also found that shell epi- and endobionts made an important contribution to respiration, as 40 and up to 100% of total measured fluxes for night and day, respectively, could be attributed to the shell community. More importantly, the direction of the measured flux was occasionally opposite that of the individual trochus, highlight- ing that the contribution of shell epi- and endobionts must be accounted for in order to achieve an accurate understanding of individual metabolism. Lastly, depending on the time of day and season when measurements are taken, ignoring diel or seasonal variations in metabolic rates could result in important under- or overestimation of the contributions of gastropods to carbon and calcium carbonate fluxes in coastal ecosystems.