Maximum Aerobic Metabolic Rate Research Articles

Plasticity in Standard and Maximum Aerobic Metabolic Rates in Two Populations of an Estuarine Dependent Teleost, Spotted Seatrout (Cynoscion nebulosus).

We studied the effects of metabolic cold adaptation (MCA) in two populations of a eurythermal species, spotted seatrout (Cynoscion nebulosus) along the U.S. East Coast. Fish were captured from their natural environment and acclimated at control temperatures 15 °C or 20 °C. Their oxygen consumption rates, a proxy for metabolic rates, were measured using intermittent flow respirometry during acute temperature decrease or increase (2.5 °C per hour). Mass-specific standard metabolic rates (SMR) were higher in fish from the northern population across an ecologically relevant temperature gradient (5 °C to 30 °C). SMR were up to 37% higher in the northern population at 25 °C and maximum metabolic rates (MMR) were up to 20% higher at 20 °C. We found evidence of active metabolic compensation in the southern population from 5 °C to 15 °C (Q10 < 2), but not in the northern population. Taken together, our results indicate differences in metabolic plasticity between the northern and southern populations of spotted seatrout and provide a mechanistic basis for predicting population-specific responses to climate change.

Do the high energy lifestyles of shorebirds result in high maximal metabolic rates? Basal and maximal metabolic rates in least and pectoral sandpipers during migration

Shorebirds have high resting and field metabolic rates relative to many other bird groups, and this is posited to be related to their high‐energy lifestyle. Maximum metabolic outputs for cold or exercise are also often high for bird groups with energetically demanding lifestyles. Moreover, shorebirds demonstrate flexible basal and maximal metabolic rates, which vary with changing energy demands throughout the annual cycle. Consequently, shorebirds might be expected to have high maximum metabolic rates, especially during migration periods. We captured least Calidris minutilla and pectoral C. melanotos sandpipers during spring and fall migration in southeastern South Dakota and measured maximal exercise metabolic rate (MMR; least sandpipers only), summit metabolic rate (Msum, maximal cold‐induced metabolic rate) and basal metabolic rate (BMR, minimum maintenance metabolic rate) with open‐circuit respirometry. BMR for both least and pectoral sandpipers exceeded allometric predictions by 3–14%, similar to other shorebirds, but Msum and MMR for both species were either similar to or lower than allometric predictions, suggesting that the elevated BMR in shorebirds does not extend to maximal metabolic capacities. Old World shorebirds show the highest BMR during the annual cycle on the Arctic breeding grounds. Similarly, least sandpiper BMR during migration was lower than on the Arctic breeding grounds, but this was not the case for pectoral sandpipers, so our data only partially support the idea of similar seasonal patterns of BMR variation in New World and Old World shorebirds. We found no correlations of BMR with either Msum or MMR for either raw or mass‐independent data, suggesting that basal and maximum aerobic metabolic rates are modulated independently in these species.

Hypoxia during incubation does not affect aerobic performance or haematology of Atlantic salmon (Salmo salar) when re-exposed in later life.

Hypoxia in aquatic ecosystems is becoming increasingly prevalent, potentially reducing fish performance and survival by limiting the oxygen available for aerobic activities. Hypoxia is a challenge for conserving and managing fish populations and demands a better understanding of the short- and long-term impacts of hypoxic environments on fish performance. Fish acclimate to hypoxia via a variety of short- and long-term physiological modifications in an attempt to maintain aerobic performance. In particular, hypoxia exposure during early development may result in enduring cardio-respiratory modifications that affect future hypoxia acclimation capacity, yet this possibility remains poorly investigated. We incubated Atlantic salmon (Salmo salar) in normoxia (~100% dissolved oxygen [DO, as percent air saturation]), moderate hypoxia (~63% DO) or cyclical hypoxia (100–25% DO daily) from fertilization until 113 days post-fertilization prior to rearing all groups in normoxia for a further 8 months. At ~11 months of age, subsets of each group were acclimated to hypoxia (50% DO) for up to 44 days prior to haematology, aerobic metabolic rate and hypoxia tolerance measurements. Hypoxia exposure during incubation (fertilization to 113 days post-fertilization) did not affect the haematology, aerobic performance or hypoxia tolerance of juvenile salmon in later life. Juveniles acclimated to hypoxia increased maximum aerobic metabolic rate and aerobic scope by ~23 and ~52%, respectively, when measured at 50% DO but not at 100% DO. Hypoxia-incubated juveniles also increased haematocrit and haemoglobin concentration but did not affect acute hypoxia tolerance (critical oxygen level and DO at LOE). Thus, while Atlantic salmon possess a considerable capacity to physiologically acclimate to hypoxia by improving aerobic performance in low oxygen conditions, we found no evidence that this capacity is influenced by early-life hypoxia exposure.

Exercise-induced maximum metabolic rate scaled to body mass by the fractal dimension of the vascular distribution network

The central postulation of the present approach to metabolic rate scaling is that exercise-induced maximum aerobic metabolic rate (MMR) is proportional to the fractal extent ( V ) of an animal. Total fractal extent can be calculated from the sum of the fractal extents of the capillary service units, as specified by the formula V ∞ N 1 L D 1 , where ∞ means 'proportional to'. Here N 1 is the number of capillaries and L 1 is capillary length, with D the fractal dimension of the vascular distribution network and with L D 1 the fractal extent of a capillary service unit. D can be any real number in the interval 2 ≤ D ≤ 3 . From dimensional considerations V scales with body mass ( M ) with power exponent D/3 , or V∞M D / 3 . Then MMR ∞ M b with b=D/3 follows from the postulate MMR ∞ V . The utility of the relationship b=D/3 depends on the feasibility of estimating D . There are two possibilities. The first is to estimate D from the scaling of aorta cross-section area with body mass. The second is from morphometric observations on various body organs. Both give estimates of b in remarkable agreement with estimates obtained by exercise induction or oxygen half-saturation pressure scaling with body mass. The predicted range 2 ≤ D ≤ 3 is experimentally observed. Likely causes of notable particular instances of the symmorphosis b=D/3 with 2 ≤ D ≤ 3 include optimal movement requirements, muscle stress limitation, and maximized oxygen delivery and metabolic rates. Lastly, it is shown that the scaling exponent of basal metabolic rate with body mass can be obtained by taking body composition into account in the product of the scaling exponents of MMR and visceral mass. Keywords: basal metabolic rate, fractal dimension, fractal extent, maximum metabolic rate, vascular distribution network

Do method and species lifestyle affect measures of maximum metabolic rate in fishes?

The rate at which active animals can expend energy is limited by their maximum aerobic metabolic rate (MMR). Two methods are commonly used to estimate MMR as oxygen uptake in fishes, namely during prolonged swimming or immediately following brief exhaustive exercise, but it is unclear whether they return different estimates of MMR or whether their effectiveness for estimating MMR varies among species with different lifestyles. A broad comparative analysis of MMR data from 121 fish species revealed little evidence of different results between the two methods, either for fishes in general or for species of benthic, benthopelagic or pelagic lifestyles.

Is reproduction costly? No increase of oxidative damage in breeding bank voles

According to life-history theory, investment in reproduction is associated with costs, which should appear as decreased survival to the next reproduction or lower future reproductive success. It has been suggested that oxidative stress may be the proximate mechanism of these trade-offs. Despite numerous studies of the defense against reactive oxygen species (ROS) during reproduction, very little is known about the damage caused by ROS to the tissues of wild breeding animals. We measured oxidative damage to lipids and proteins in breeding bank vole (Myodes glareolus) females after rearing one and two litters, and in non-breeding females. We used bank voles from lines selected for high maximum aerobic metabolic rates (which also had high resting metabolic rates and food intake) and non-selected control lines. The oxidative damage was determined in heart, kidneys and skeletal muscles by measuring the concentration of thiobarbituric acid-reactive substances, as markers of lipid peroxidation, and carbonyl groups in proteins, as markers of protein oxidation. Surprisingly, we found that the oxidative damage to lipids in kidneys and muscles was actually lower in breeding than in non-breeding voles, and it did not differ between animals from the selected and control lines. Thus, contrary to our predictions, females that bred suffered lower levels of oxidative stress than those that did not reproduce. Elevated production of antioxidant enzymes and the protective role of sex hormones may explain the results. The results of the present study do not support the hypothesis that oxidative damage to tissues is the proximate mechanism of reproduction costs.

Increasing ocean temperature reduces the metabolic performance and swimming ability of coral reef damselfishes

AbstractTropical coral reef teleosts are exclusively ectotherms and their capacity for physical and physiological performance is therefore directly influenced by ambient temperature. This study examined the effect of increased water temperature to 3 °C above ambient on the swimming and metabolic performance of 10 species of damselfishes (Pomacentridae) representing evolutionary lineages from two subfamilies and four genera. Five distinct performance measures were tested: (a) maximum swimming speed (Ucrit), (b) gait‐transition speed (the speed at which they change from strictly pectoral to pectoral‐and‐caudal swimming, Up−c), (c) maximum aerobic metabolic rate (MO2−MAX), (d) resting metabolic rate (MO2−REST), and (e) aerobic scope (ratio of MO2−MAX to MO2−REST, ASC). Relative to the control (29 °C), increased temperature (32 °C) had a significant negative effect across all performance measures examined, with the magnitude of the effect varying greatly among closely related species and genera. Specifically, five species spanning three genera (Dascyllus, Neopomacentrus and Pomacentrus) showed severe reductions in swimming performance with Ucrit reduced in these species by 21.3–27.9% and Up−c by 32.6–51.3%. Furthermore, five species spanning all four genera showed significant reductions in metabolic performance with aerobic scope reduced by 24.3–64.9%. Comparisons of remaining performance capacities with field conditions indicate that 32 °C water temperatures will leave multiple species with less swimming capacity than required to overcome the water flows commonly found in their respective coral reef habitats. Consequently, unless adaptation is possible, significant loss of species may occur if ocean warming of ≥3 °C arises.

An Investigation of Metabolic Prioritization in the European Sea Bass,Dicentrarchus labrax

We investigated the ability of European sea bass (Dicentrarchus labrax) to respond simultaneously to the metabolic demands of specific dynamic action (SDA) and aerobic exercise and how this was influenced by moderate hypoxia (50% air saturation). At 3 h after feeding in normoxia at 20 degrees C, SDA raised the instantaneous oxygen uptake (Mo(2)) of sea bass by 47% +/- 18% (mean +/- SEM, N = 7) above their standard metabolic rate (SMR) when fasted. This metabolic load was sustained throughout an incremental exercise protocol until fatigue, with a 14% +/- 3% increase in their maximum aerobic metabolic rate (MMR) relative to their fasted rate. Their incremental critical swimming speed (U(crit)) did not differ between fasted and fed states. Thus, in normoxia, the bass were able to meet the combined oxygen demands of SDA and aerobic exercise. In hypoxia, the sea bass suffered a significant decline in MMR and U(crit) relative to their normoxic performance. The SDA response was similar to normoxia (84% +/- 24% above fasted SMR at 3 h after feeding), but although this load was sustained at low swimming speeds, it gradually disappeared as swimming speed increased. As a result, the hypoxic sea bass exhibited no difference in their fasted versus fed MMR. Hypoxic U(crit) did not, however, differ between fasted and fed states, indicating that the sea bass deferred their SDA to maintain exercise performance. The results demonstrate that, in normoxia, the sea bass possesses excess cardiorespiratory capacity beyond that required for maximal aerobic exercise. The excess capacity is lost when oxygen availability is limited in hypoxia, and, under these conditions, the sea bass prioritize exercise performance. Thus, environmental conditions (oxygen availability) had a significant effect on patterns of oxygen allocation in sea bass and revealed intrinsic prioritization among conflicting metabolic demands.

The association between body mass, metabolic rates and survival of bank voles

Summary 1Many studies have been performed in an attempt to explain physiological, ecological and evolutionary factors behind inter- and intraspecific variation in basal metabolic rate (BMR) and maximum aerobic metabolic rate (VO2max). However, very little is known about the association between the traits and fitness components in populations of free-living animals. 2We studied the association between body size and the metabolic rates of bank voles Myodes (= Clethrionomys) glareolus and their survival, measured by repeated trappings across 2 years in an isolated, island population. All measured traits (body mass, BM; head width, HW; VO2max and BMR) were significantly repeatable over short (mean 5·4 days) and long (mean 56·4 days) intervals. 3Logistic regression analyses showed no consistent relationship between the measured traits and survival until the next trapping session. The correlations, if present, differed in direction between sessions and sexes. Survival over winters was negatively correlated with BM in males (P = 0·001) but not in females (P = 0·43). The logistic regression with quadratic effects revealed stabilizing selection on VO2max in males (across all sessions: P = 0·010; in breeding seasons only: P = 0·001). 4Both the presence of stabilizing selection and the opposite direction of the selection between sexes and/or seasons could contribute to the relatively high additive genetic variance of metabolic rates, reported earlier in the bank voles. 5The results indicate that the maximum rather than the basal rate of metabolism is important to individual fitness of the voles. However, lack of consistency in the association between survival and the metabolic traits casts doubt on previous assumptions regarding the importance of the level of metabolism to an individual's fitness.

Allometric scaling of maximum metabolic rate: the influence of temperature

1 Maximum aerobic metabolic rate, measured in terms of rate of oxygen consumption during exercise (), is well known to scale to body mass (M) with an exponent greater than the value of 0·75 predicted by models based on the geometry of systems that supply nutrients. 2 Recently, the observed scaling for (∝M0·872) has been hypothesized to arise because of the temperature dependence of biological processes, and because large species show a greater increase in muscle temperature when exercising than do small species. 3 Based on this hypothesis, we predicted that will be positively related to ambient temperature, because heat loss is restricted at high temperatures and body temperature is likely to be elevated to a greater extent than during exercise in the cold. 4 This prediction was tested using a comparative phylogenetic generalized least-squares (PGLS) approach, and 34 measurements of six species of rodent (20·5–939 g) maximally exercising at temperatures from –16 to 30 °C. 5 is unrelated to testing temperature, but is negatively related to acclimation temperature. We conclude that prolonged cold exposure increases exercise-induced by acting as a form of aerobic training in mammals, and that elevated muscle temperatures of large species do not explain the scaling of across taxa.

Maximal metabolic rates during voluntary exercise, forced exercise, and cold exposure in house mice selectively bred for high wheel-running

Selective breeding for high wheel-running activity has generated four lines of laboratory house mice (S lines) that run about 170% more than their control counterparts (C lines) on a daily basis, mostly because they run faster. We tested whether maximum aerobic metabolic rates (V(O2max)) have evolved in concert with wheel-running, using 48 females from generation 35. Voluntary activity and metabolic rates were measured on days 5+6 of wheel access (mimicking conditions during selection), using wheels enclosed in metabolic chambers. Following this, V(O2max) was measured twice on a motorized treadmill and twice during cold-exposure in a heliox atmosphere (HeO2). Almost all measurements, except heliox V(O2max), were significantly repeatable. After accounting for differences in body mass (S < C) and variation in age at testing, S and C did not differ in V(O2max) during forced exercise or in heliox, nor in maximal running speeds on the treadmill. However, running speeds and V(O2max) during voluntary exercise were significantly higher in S lines. Nevertheless, S mice never voluntarily achieved the V(O2max) elicited during their forced treadmill trials, suggesting that aerobic capacity per se is not limiting the evolution of even higher wheel-running speeds in these lines. Our results support the hypothesis that S mice have genetically higher motivation for wheel-running and they demonstrate that behavior can sometimes evolve independently of performance capacities. We also discuss the possible importance of domestication as a confounding factor to extrapolate results from this animal model to natural populations.

Metabolic rates of juvenile scalloped hammerhead sharks (Sphyrna lewini)

Oxygen consumption of juvenile scalloped hammerhead sharks, Sphyrna lewini, was measured in a Brett-type flume (volume=635 l) to quantify metabolic rates over a range of aerobic swimming speeds and water temperatures. Oxygen consumption (log transformed) increased at a linear rate with increases in tailbeat frequency and swimming speed. Estimates of standard metabolic rate ranged between 161 mg O2 kg–1 h–1 at 21°C and 203 mg O2 kg–1 h–1 at 29°C (mean±SD: 189±15 mg O2 kg–1 h–1 at 26°C). Total metabolic rates ranged from 275 mg O2 kg–1 h–1 at swimming speeds of 0.5 body lengths per second (L s–1) to a maximum aerobic metabolic rate of 501 mg O2 kg–1 h–1 at 1.4 L s–1. Net cost of transport was highest at slower swimming speeds (0.5–0.6 L s–1) and was lowest between 0.75 and 0.9 L s–1. Therefore, these sharks are most energy efficient at swimming speeds between 0.75 and 0.9 L s–1. These data indicate that tailbeat frequency and swimming speed can be used as predictors of metabolic rate of free-swimming juvenile hammerhead sharks.

Metabolic and cardiac scope of high energy demand teleosts, the tunas

The maximum aerobic metabolic rates of tunas are far above those of other fishes. In this review we attempt to define features of the cardiovascular system that may account for this extreme performance. Tuna hearts are much larger than those of most other fishes and are half the mass of those of similarly sized mammals; however, the ratio of compact to spongy myocardium is not (except for one tuna species) higher than in other active teleosts. Myocardial aerobic enzyme activity levels are not significantly elevated. The cardiac outputs of spinally blocked skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) are roughly 4 times those of other active teleosts. Ventral aortic blood pressures are the highest among all fishes (more than twice those of rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri)), and appear to be due to a high resistance to blood flow in the gills, since dorsal aortic blood pressures are not exceptional. Heart rates, cardiac output, and ventilation volume are high, but gill ventilation and perfusion appear to be well matched (i.e., gill ventilation: perfusion conductance ratios of ≈1). Blood hemoglobin concentrations of tunas are elevated, essentially identical with those of humans and twice those seen in other fishes. Because their blood oxygen carrying capacity is high and because skipjack and yellowfin tunas appear to be able to increase the minimum observed arterial to venous oxygen content differences approximately 3 times, we predict that they need to increase cardiac output only about 2 times during maximum rates of oxygen uptake. This ratio is not very different from those of other teleosts.

Energy Costs of Walking and Running Gaits and Their Aerobic Limits in Golden-Mantled Ground Squirrels

We studied locomotion of field-caught golden-mantled ground squirrels (Spermophilus saturatus) on a motorized treadmill that was incorporated into a respirometry system. The animals shifted gaits, from walking to trotting, at about 0.8 m/s and from trotting to galloping at 1.2 m/s; they ran as fast as 3 m/s (10.8 km/h) on our treadmill. Because we were able to determine oxygen consumption instantaneously, we observed rates of energy expenditure that accompany brief bouts of locomotion at speeds higher than those of previous studies. The slope of equations describing oxygen consumption ($\dot{V}O_{2}$, in ml/g· h) in relation to speed (m/s) differ significantly (P < .02) for walking and running (running = trot and gallop combined): walking ($\dot{V}O_{2}$ = 2.91 + 3.80 X speed), running (V02 = 5.76 + 1.41 X speed). The animals thereby experience less incremental increase in rate of energy expenditure with increased speed when running than when walking. We conclude that with a maximum aerobic metabolic rate...

Oxygen Consumption of Plethodontid Salamanders during Rest, Activity and Recovery

The resting, active and recovery rates of oxygen consumption for Plethodon jordani, P. glutinosus and P. yonahlossee ranging in size from 0.5 to 6 g, were strongly correlated with body mass. The absolute aerobic scope (pl 02 g-1 hr-1) increased with body mass, whereas the factorial scope (Vo2,max/Vo2,rest) was approximately constant at 4x. The resting and recovery rates of oxygen consumption were only slightly influenced by ambient Po2 whereas active rates were markedly depressed at Po2 < 110 mm Hg. Allometric analyses indicate that the cutaneous surface area of large plethodontid salamanders might limit their maximum aerobic metabolic rate and the maximum attainable body mass. However, the aerobic metabolic rate of small Plethodon (<6 g) appears to be limited by factors other than cutaneous respiratory surface area.