Mass-specific Oxygen Consumption Rate Research Articles

Energy Metabolism in Postlarval Ontogenesis of Planorbarius corneus (Planorbidae, Gastropoda)

The change in the rate and mass-specific rate of oxygen consumption was studied during individual ontogenesis of nine Planorbarius corneus individuals starting from 3 weeks after hatching until the death of animals. It is shown that, at the initial stages of development, the mass-specific rate of oxygen consumption increases, reaching a maximum at 3–7 weeks after hatching. The rate of oxygen consumption then permanently increases, and the mass-specific rate of oxygen consumption permanently decreases. The dependences of mass-specific rate of oxygen consumption (q) on the age (t) for individual P. corneus can be described by the equation qst/(1 – exp(–k (t + t0))). The values ​​of the coefficients of this equation for different specimens do not differ significantly and are, on average, k = 0.134 ± 0.016 weeks–1; qst = 0.117 ± 0.006 mL O2/(h g). The dependence of the rate of oxygen consumption (Q, mL O2/h) on body weight (M, g) in individual development is well described by allometric equations, the power coefficients of which vary from 0.647 to 0.944 and significantly differ from each other (p < 0.001). Nevertheless, the data for all mollusks can be described by the united equation Q = 0.061 M0.795. The power coefficient of this equation does not significantly differ from the Hemmingsen constant 0.75.

Temperature-Modulated Expression of Allometric Respiration Strategies Supports a Metabolic Scaling Rule

A model based on the mass-specific oxygen consumption rate of the tolerant polychaete, Capitella telata, related meaningfully to a novel metabolic scaling rule as applied to the infaunal size spectrum. Depending on temperature, C. telata expressed divergent oxyregulating or oxyconforming strategies relative to oxygen availability. A non-linear response surface fitted to the allometric exponents of a family of VO2 curves for 12 treatment combinations of DO saturation and temperature was used to project oxygen consumption rates across the infaunal size spectrum. Plasticity in respiration strategies was evident, based on four simulated dynamic 32 d oxygen-temperature exposure scenarios and on simulated static oxygen-temperature exposures. The oxyconforming strategy of C. telata expressed under hypoxia near the upper thermal limit agreed with a hypothesized allometric scaling rule based on metabolic ecology. Conversely, an oxyregulating respiration strategy was expressed at cooler temperatures under low oxygen concentration, except organisms hyper-regulated relative to normoxic conditions. At warm temperatures, small organisms exhibited relatively greater metabolic depression than large organisms; whereas at cool temperatures, small organisms hyper-regulated relatively more than large organisms. Dichotomous shifts in respiration strategies likely reflect a breakdown in the functioning of special adaptations, and reliance on alternative coping mechanisms. Divergent temperature-dependent respiration strategies illustrate how responses to multiple stressors can be synergistic. Moreover, results imply that population responses to hypoxia may differ, depending on prevailing temperature regimes.

The dynamics of mass growth and oxygen consumption in ontogenesis of the newt Pleurodeles waltl: 3. The postlarval period

The relationship between animal growth and oxygen consumption was studied by the example of the postlarval period in ontogenesis of the newt Pleurodeles waltl. These parameters increased during the first 1.5 years after metamorphosis and then did not change. Gender differences were found for the body mass, growth rate, and rate of oxygen consumption, which in males were less than in females. The mass-specific rates of oxygen consumption in males and females were the same. The relationship between the body mass and the rate of oxygen consumption in immature and mature newts can be expressed by a common allometric equation.

Hypoxia tolerance decreases with body size in red drum Sciaenops ocellatus.

Mass-specific oxygen consumption rate, i.e. standard metabolic rate (Rs ) and critical oxygen tension (Pcrit ) of red drum Sciaenops ocellatus were measured and scaled over a 2500-fold range in mass (MF ; 0·26-686 g). Rs conformed to well established models (Rs = 3·73·91 MF (-0·21) ; r(2) = 0·86) while Pcrit increased over the size range (Pcrit = 3·15 log10 MF + 16·19; r(2) = 0·44). This relationship may be ecologically advantageous as it would allow smaller S. ocellatus to better utilize hypoxic zones as habitat and refuge from predators.

Comparison of swimming capacity and energetics of migratory European eel (Anguilla anguilla) and New Zealand short-finned eel (A. australis).

The spawning migration of the European eel (Anguilla anguilla) can cover more than 6000 km, while that of the New Zealand short-finned eel (A. australis) is assumed to be approximately 3000 km. Since these species are expected to show adaptive traits to such an important lifetime event, we hypothesized differences in swimming capacity and energetics as a response to this adaptation. In an experimental swimming respirometer set-up, critical swimming speed (Ucrit), optimal swimming speed (Uopt), mass specific oxygen consumption rate (ṀO2), standard metabolic rate (SMR), active metabolic rate at Ucrit (AMRcrit) and at Uopt (AMRopt), the minimum cost of transport at Uopt (COTmin), and the scope for activity, were assessed and compared between the species. With a similar body length and mass, European eels showed ca. 25% higher values for both Ucrit and Uopt, and 23% lower values for COTmin, compared to New Zealand short-finned eels. However, SMR, AMRcrit, AMRopt, and scope for activity did not differ between the species, indicating very similar swimming physiology traits. This study discusses physiological aspects of long distance migration and provides recommendations for (a) swimming respirometry in anguilliform fish, and (b) telemetry research using externally attached pop-up tags.

Season and time of day affect the ability of accelerometry and the doubly labeled water methods to measure energy expenditure in northern fur seals (Callorhinus ursinus)

Estimates of energy expenditure for free-ranging animals are essential to answering a range of fundamental questions in animal biology, but are challenging to obtain and difficult to validate. We simultaneously employed three methods to measure the energy expenditure of 6 captive female northern fur seals (Callorhinus ursinus) during 5-day trials across 4 seasons: respirometry (oxygen consumption), doubly labeled water (DLW), and accelerometry. The DLW method estimated that the fur seals expended 13.1±16.5% more energy than indicated by the more direct measures of oxygen consumption. Accelerometry failed to predict the average mass-specific rate of oxygen consumption (V˙O2DEE) within the individual seasons over entire 5-day trials. However, on a finer time scale (15 or 60min) and adjusted for time of day, accelerometry estimated energy expenditure within an average difference of 5.4±29.3% (60min intervals) and 13.8±39.5% (15min intervals) of respirometry measured values. Our findings suggest that accelerometers have the potential to be more effective than the DLW method for measuring energy expenditure of free-ranging animals. However, rates of oxygen consumption varied with season, independent of overall activity. Seasonal effects (and time of day for accelerometry) must therefore be accounted for when estimating energy expenditure from measures of DLW and acceleration of free-swimming northern fur seals. Such corrections required for estimating energy expenditures in northern fur seals have implications for using accelerometers and DLW to estimate the energy expenditure of other species.

Linking allometric macrobenthic processes to hypoxia using the Peters mass balance model

Eutrophication alters coastal aquatic food web structure and function through effects of organic enrichment and hypoxia. Macrobenthic communities provide good ecological indicators of impacts on ecosystem function induced by eutrophication. However, effective resource management requires validation of ecological indicators through mechanistic links to specific stressors of concern. Organic enrichment along with subsequent hypoxia typically engenders depauperate macrobenthic communities consisting of small short-lived surface-dwelling organisms. Metabolic ecology theory offers great promise for understanding the role of body size within the context of the trophic dynamics of aquatic ecosystems. Body size is a fundamental ecological trait because it underpins vital rates, which can be scaled up to the ecosystem level through allometric laws. Thus, body size-dependent mechanisms can potentially be used to link macrobenthic indicators to ecosystem consequences of organic enrichment and hypoxia. The Peters mass balance model (PMBM) [Peters, R.H., 1983. The Ecological Implications of Body Size. Cambridge University Press, New York, 329 pp.] provides a platform for projecting stress-induced changes in the distribution of biomass among discrete size classes of organisms. In the PMBM, changes in the distribution of biomass ensue over time from differences between gains due to ingestion and losses due to egestion, respiration, and mortality. Production of biomass results when ingestion exceeds combined losses. In the present study, the PMBM was modified to envisage an inhibitory effect of hypoxia on ingestion by: (1) using unique size-specific mortality coefficients in order to realize target inverted biomass-size distributions during model initialization; (2) linking ingestion rate to the hyperbolic relationship between oxygen consumption rate (OCR) and ambient dissolved oxygen (DO); (3) hypothesizing how oxygen regulation ability follows an allometric scaling rule relative to the supply of DO. If food is unlimited, the most straightforward hypothetical connection between the oxygen consumption rate and ingestion assumes a direct proportional relationship under oxygen limitation. Although small organisms can attain much higher mass-specific rates of oxygen consumption than large ones, previous limited research on oxygen consumption relative to oxygen supply implies that large organisms regulate oxygen intake better than small individuals as ambient DO declines. Counterintuitively, linked ingestion deficits would be accordingly higher for small organisms than large organisms under hypoxia. In pilot simulations incorporating hypothetical ingestion deficits due to oxygen limitation within a modified PMBM, contrasting scenarios emulated continuous DO and water temperature conditions experienced at two shallow subtidal sites for 32 d in summer. Resulting ingestion deficits reduced total biomass and favored large size classes. Effects were stronger under the more hypoxic scenario: total biomass was lower and the biomass-size distribution was more uneven among the size classes. Differences were even more evident in terms of an integrative macrobenthic process indicator, the normalized biomass-size spectrum (NBSS). A realistic hypoxia mass balance model (HMBM) must incorporate various allometric effects that are not necessarily expressed in the same direction relative to body size. A useful resource management tool for anticipating effects of environmental stress on aquatic ecosystem function could be developed from the quantification of trophic transfer potential within a refined PMBM.

The effect of temperature and salinity on oxygen consumption in the brachyuran crab Cyclograpsus punctatus (Crustacea: Decapoda: Grapsidae)

The aquatic oxygen consumption of the estuarine brachyuran crab, Cyclograpsus punctatus, was investigated after a 24-hour acclimation period at different temperature (12.5, 20, 30°C) and salinity (9, 17.5, 35, and 44°) combinations . Salinity had no significant effect on oxygen consumption at 12.5 and 20°C in both large and small crabs. At 30°C and 44°, however, the rate of oxygen consumption declined in large crabs (from 0.233 to 0.176 mg O2 g wwt/h) and increased in small crabs (0.300 to 0.469 mg O2 g wwt/h). There was also a significant increase in the oxygen consumption (0.300 to 0.536 mg O2 g wwt/h) of small crabs at the high temperature/low salinity combination. Temperature had a significant effect on the rate of oxygen consumption at all salinities, with Q10 values ranging from 1.16 to 2.85. In all cases the mass-specific oxygen consumption rate of small crabs was higher than that of large crabs. The results suggest that the confinement of this species to the lower reaches of estuaries may, in part, be due to physiological constraints on juveniles and small individuals.

The effect of temperature and salinity on oxygen consumption in the brachyuran crab Cyclograpsus punctatus (Crustacea: Decapoda: Grapsidae)

ABSTRACT The aquatic oxygen consumption of the estuarine brachyuran crab, Cyclograpsus punctatus, was investigated after a 24-hour acclimation period at different temperature (12.5, 20, 30°C) and salinity (9, 17.5, 35, and 44‰) combinations. Salinity had no significant effect on oxygen consumption at 12.5 and 20°C in both large and small crabs. At 30°C and 44‰, however, the rate of oxygen consumption declined in large crabs (from 0.233 to 0.176 mg O2 g wwt/h) and increased in small crabs (0.300 to 0.469 mg O2 g wwt/h). There was also a significant increase in the oxygen consumption (0.300 to 0.536 mg O2 g wwt/h) of small crabs at the high temperature/low salinity combination. Temperature had a significant effect on the rate of oxygen consumption at all salinities, with Q10 values ranging from 1.16 to 2.85. In all cases the mass-specific oxygen consumption rate of small crabs was higher than that of large crabs. The results suggest that the confinement of this species to the lower reaches of estuaries may,...

Equations describing changes in weight and mass-specific rate of oxygen consumption in animals during postembryonic development

Equations describing growth and respiration rate of animals during postembryonic development have been derived on the basis of thermodynamics of linear irreversible processes. The conditions for equation application are specified as well as the conditions when growth equation can be reduced to the von Bertalanffy equation and when the relationship between the mass-specific rate of oxygen consumption and body weight becomes an allometric relationship. DOI: 10.1134/S1062359006040029

Energy budget of juvenile fat snook Centropomus parallelus fed live food

The fat snook Centropomus parallelus is a tropical estuarine species with importance for recreational and commercial fisheries and further aquaculture potential. Considering ingested energy ( C) is channeled into growth ( P), metabolic expenditure ( R), excretion ( U) and feces ( F), a balanced energy budget was established for isolated and grouped juvenile C. parallelus (5.18 to 10.25 g wet mass) by experimental quantification of each of these parameters. Fish were fed live prawn ( Macrobrachium sp.) at 25 °C and 20‰ for 19 days and daily energy budgets could be calculated. Energy content of food (live prawn), fish whole body and feces were 17.7, 14.5 and 6.1 KJ g − 1 dry mass (DW), respectively. Mass-specific rates of oxygen consumption and ammonia-N excretion were 0.271 and 0.0082 mg of O 2 or NH 3–N g − 1 wet mass (WW) h − 1 , respectively, resulting in O : N = 23.4. Daily ingestion ( C) was dependent on the amount of food offered and ranged between 4.9% to 7.4% of initial wet weight. Growth ( P) was positively correlated with initial mass varying from 0.008 to 0.104 g day − 1 . Feces release also correlated to fish mass and averaged 9.53 mg dry mass day − 1 . The components of energy budget showed mean values of 2.39 ( C), 0.24 ( P), 1.96 ( R), 0.11 ( U) and 0.06 ( F) KJ ind − 1 day − 1 . As percentage of ingested energy, C. parallelus channeled 10% in growth ( P), 82% in metabolism ( R), 4.6% in excretion ( U) and 2.5% in feces ( F). Gross ( K 1) and net ( K 2) growth efficiencies were 9.2% and 9.9%, respectively. On the course of this period of juvenile development, K 1 and K 2 increased significantly. Partitioning of ingested energy in P, R, U and F was significantly different in individually and group maintained fish ( P < 0.05). Energy budget of C. parallelus fed a highly digestible diet (live prawn) revealed poor growth and growth efficiencies ( K 1 and K 2) possibly associated with an elevated metabolic demand and a high channeling of metabolized energy ( P + R) into metabolism ( R) in both isolated and grouped fish. Data can be applied to ecosystem modeling and may contribute to identify species potential to aquaculture.

Effects of hypoxia acclimation on morpho-physiological traits over three generations of Daphnia magna

The mechanisms, dynamics and effects of hypoxia acclimation were studied in the water flea Daphnia magna over three successive generations (parental, first and second filial generation: P, F1 and F2). The P generation was raised under normoxic conditions at 20 degrees C and became exposed to environmental hypoxia (10-19% air saturation) at maturity. Their progenies (F1 and F2) experienced hypoxia from birth onwards. Controls were kept under normoxic conditions. Individuals were successively sampled in a 3-day interval from each acclimation group to determine morpho-physiological parameters relevant in oxygen transport and regulation. Hypoxia acclimation induced adjustments at the haemoglobin (Hb) and metabolic level (within 3 days) but none at the systemic level. The convective performance and oxygen-sensitive control of the ventilatory and circulatory systems were the same in both acclimation groups. The Hb concentration and oxygen affinity increased by 266% and 32%, respectively. The 22% decrease in mass-specific oxygen consumption rate reduced the energy allocation to somatic growth without greatly affecting reproduction. The onset and duration of hypoxic exposure during ontogenesis have had a significant influence on Hb oxygen affinity and body size. Transgenerational effects of hypoxia acclimation could not be observed. The adjustments at the Hb and metabolic levels in combination with the smaller body size, which is advantageous to diffusive oxygen transport, reduced the critical ambient oxygen tension by approximately 50%.

Factorial scopes of cardio-metabolic variables remain constant with changes in body temperature in the varanid lizard,Varanus rosenbergi

The majority of information concerning the cardio-metabolic performance of varanids during exercise is limited to a few species at their preferred body temperature (T(b)) even though, being ectotherms, varanids naturally experience rather large changes in T(b). Although it is well established that absolute aerobic scope declines with decreasing T(b), it is not known whether changes in cardiac output (V(b)) and/or tissue oxygen extraction, (Ca(O2) - Cv(O2)), are in proportion to the rate of oxygen consumption (Vo(2)). To test this, we studied six Rosenberg's goannas (Varanus rosenbergi) while at rest and while maximally exercising on a treadmill both at 25 and 36 degrees C. During maximum exercise both at 25 and 36 degrees C, mass-specific rate of oxygen consumption (Vo(2kg)) increased with an absolute scope of 8.5 ml min(-1) kg(-1) and 15.7 ml min(-1) kg(-1), respectively. Interestingly, the factorial aerobic scope was temperature-independent and remained at 7.0 which, at each T(b), was primarily the result of an increase in V(bkg), governed by approximate twofold increases both in heart rate (f(H)) and cardiac stroke volume (V(Skg)). Both at 25 degrees C and 36 degrees C, the increase in V(bkg) alone was not sufficient to provide all of the additional oxygen required to attain maximal Vo(2kg), as indicated by a decrease in the blood convection requirement V(bkg)/Vo(2kg); hence, there was a compensatory twofold increase in (Ca(O2) - Cv(O2)). Although associated with an increase in hemoglobin-oxygen affinity, a decrease in T(b) did not impair unloading of oxygen at the tissues and act to reduce (Ca(O2) - Cv(O2)); both Ca(O2)) and Cv(O2)) were maintained across T(b). The change in Vo(2kg) with T(b), therefore, is solely reliant on the thermal dependence of V(bkg). Maintaining a high factorial aerobic scope across a range of T(b) confers an advantage in that cooler animals can achieve higher absolute aerobic scopes and presumably improved aerobic performance than would otherwise be achievable.

Metabolic rate is not reduced by dietary-restriction or by lowered insulin/IGF-1 signalling and is not correlated with individual lifespan in Drosophila melanogaster

The link between resting metabolic rate and aging, measured as adult lifespan, was investigated in Drosophila melanogaster by (i) comparing lifespan and metabolic rate of individual flies, (ii) examining the effect of dietary-restriction on the metabolic rate of adult flies, and (iii) comparing the metabolic rate of wild-type and insulin/IGF-1 signalling mutant chico 1 flies. The resting oxygen consumption of 65 individually housed and fully fed Drosophila was measured weekly throughout their lifetime. There was no significant difference in the mass-specific rate of oxygen consumption between cohorts that differed in lifespan. Nor was there any statistical correlation between mass-specific oxygen consumption and lifespan of individual Drosophila. The average mass-specific rate of oxygen consumption at 25 °C was 3.52±0.07 μl O 2 mg −1 h −1. Variation in mass-specific metabolic rate explained only 4% of variation in individual life span in these flies. Contrary to predictions from the ‘rate of living’ theory of aging lifetime oxygen consumption was not constant and the lifespan of individual flies accounted for 91% of their lifetime oxygen consumption. An average Drosophila consumes about 3 ml O 2 during its adult life. Dietary-restriction had no effect on mass-specific resting metabolic rate both when measured as oxygen consumption by respirometry and when measured as heat production by microcalorimetry. The mass-specific resting heat production of fully fed adult flies at 25 °C averaged 17.3±0.3 μW mg −1. Similarly there was no difference in mass-specific metabolic rate of wild-type flies and longliving chico 1 insulin/IGF-1 signalling mutant flies, either when measured as oxygen consumption or heat production. Thus, individual variation in lifespan in wild-type flies, and life extension by dietary-restriction and reduced insulin/IGF-1 signalling is not attributable to differences in metabolic rate.

Energetics of diving in macaroni penguins.

Heart rate (fH), abdominal temperature (T(ab)) and diving depth were measured in thirteen free-ranging breeding female macaroni penguins. Measurement of these variables allowed estimation of the mass-specific rate of oxygen consumption (V(O(2))) while diving and investigation of the physiological adjustments that might facilitate the diving behaviour observed in this species. In common with other diving birds, macaroni penguins showed significant changes in fH associated with diving, and these variables accounted for 36% of the variation in dive duration. When V(O(2)) was calculated for dives of different durations, 95.3% of dives measured were within the calculated aerobic dive limit (cADL) for this species. Mean fH for all complete dive cycles was 147+/-6 beats min(-1). When this fH is used to estimate (O(2)) of 26.2+/-1.4 ml min(-1) kg(-1) then only 92.8% of dives measured were within the cADL. Significant changes in abdominal temperature were not detected within individual dives, though the time constant of the measuring device used may not have been low enough to record these changes if they were present. Abdominal temperature did decline consistently during bouts of repeated diving of all durations and the mean decrease in T(ab) during a diving bout was 2.32+/-0.2 degrees C. There was a linear relationship between bout duration and the magnitude of this temperature drop. There was no commensurate increase in dive duration during dive bouts as T(ab) declined, suggesting that macaroni penguins are diving within their physiological limits and that factors other than T(ab) are important in determining the duration of dives and dive bouts. Lowered T(ab) will in turn facilitate lower metabolic rates during diving bouts, but it was not possible in the present study to determine the importance of this energy saving and whether it is occurs actively or passively.

Axenic growth up-regulates mass-specific metabolic rate, stress resistance, and extends life span in Caenorhabditis elegans

Culture in axenic medium causes two-fold increases in the length of development and adult life span in Caenorhabditis elegans. We asked whether axenic medium imposes dietary restriction (ADR), and causes changes in metabolic activity and stress resistance. Eat mutants, which have a reduced food intake, were studied in parallel with wild-type worms to assess potential synergistic actions of axenic culture and food restriction. We found that axenic culture enhances metabolic activity as assessed by mass-specific oxygen consumption rate and heat production. Axenic culture also caused higher activities of the antioxidant enzymes superoxide dismutase and catalase, and led to increased resistance to high temperature, which was further exacerbated by mutation in eat-2. These results show that axenic medium up-regulates a variety of somatic maintenance functions including oxidative and thermal stress resistance and that food restriction due to axenic growth and to mutation in eat-2 are very similar but not identical.

The relationship between heart rate and rate of oxygen consumption in Galapagos marine iguanas (Amblyrhynchus cristatus) at two different temperatures.

To enable the use of heart rate (fH) for estimating field metabolic rate (FMR) in free-ranging Galapagos marine iguanas Amblyrhynchus cristatus, we determined the relationships between fH and mass-specific rate of oxygen consumption (sVO2) in seven iguanas before and during exercise on a treadmill and during the post-exercise period. The experiments were conducted at 27 and 35 degrees C, which are the temperatures that represent the lowest and highest average body temperatures of these animals in the field during summer. There were linear and significant relationships between fH and sVO2 at both temperatures (r(2)=0.86 and 0.91 at 27 degrees C and 36 degrees C, respectively). The slopes of the two regression lines did not differ, but there were significant differences in their intercepts. Thus, while heart rate can be used to predict FMR, the effects of temperature on the intercept of the regression must be taken into account when converting fH to sVO2. On the basis of our data, this can be achieved by applying the following formula: sVO2=0.0113fH-0.2983Q(10)((T(b)-27)/10). The increase in sVO2 with elevated body temperature results from an increase in fH, with no significant change in mass-specific oxygen pulse (sO(2) pulse; cardiac stroke volume times the difference in oxygen content between arterial and mixed venous blood). However, during exercise at both temperatures, increases in fH are insufficient to provide all of the additional O(2) required and there are also significant increases in the sO(2) pulses. This creates the situation whereby the same fH at the two temperatures can represent different values of sVO2.

Efficiency as a foraging currency in animals attaining a gain below the energetic ceiling

Previous research has found that efficiency, or, more precisely, the foraging gain ratio (FGR), is a valid currency in foraging theory when (1) there is a limit to the energy that can be assimilated by the forager and (2) a forager is trying to meet an energy requirement. The FGR is b/ (c — cr), where b is the rate of metabolizable energy intake, and c and cr are the rates of energy expenditure while foraging and resting, respectively. Here I show that, when energy expenditure has a cost besides energy, animals should also choose the option with the highest FGR when they are aiming at a given positive daily gain. The next question is which gain they should aim for? Researchers have shown that observed intake levels of growing ruminants are close to the levels predicted by maximization of the efficiency of oxygen utilization. This currency can be approximated by (B — C + Cr) / C, where B is the daily metabolizable energy intake, and C and Cr are the total and basal daily energy expenditures, respectively. By simulating growth at different intake levels, I found that mass-specific oxygen consumption rate is indeed minimal at the observed intake levels. This is the first study in which these efficiency measures (FGR and the efficiency of oxygen utilization) are combined. [KEYWORDS: energy balance, feed intake regulation, foraging gain ratio, growth, optimal foraging theory, oxygen utilization]

Oxygen uptake by embryos and ovigerous females of two intertidal crabs, Heterozius rotundifrons (Belliidae) and Cyclograpsus lavauxi (Grapsidae): scaling and the metabolic costs of reproduction.

Heterozius rotundifrons and Cyclograpsus lavauxi are crabs of similar size, whose intertidal habitats overlap. They differ in the number and size of their eggs. A 2 g ovigerous H. rotundifrons incubates 675 large yolky eggs (mean single-egg mass 269 microg; egg clutch 9.15 % of mass of female crab; increasing to 435 microg and 13.4 % at hatching). The egg clutch of a 2 g C. lavauxi is larger (15.4 % of crab mass increasing to 18.9 % at hatching) and contains more numerous (28 000), smaller (10.9 microg increasing to 20.3 microg) eggs. The longer development time of the larger eggs (194 days versus 56 days at 15 degrees C) results from a delayed increase in metabolic rate (diapause) and not metabolic scaling. On the basis of the total mass of single eggs, the mass-specific metabolic rates of early embryonic stages of H. rotundifrons (0.72 micromol g(-1 )h(-1) for the blastula stage at 15 degrees C) and C. lavauxi (1.13 micromol g(-1 )h(-1)) were similar to those of the adult female crabs (0.70 micromol g(-1 )h(-1) for H. rotundifrons and 0.91 micromol g(-1 )h(-1) for C. lavauxi) and increased 13- and 10-fold, respectively, by the time of hatching. Thus, early embryonic metabolic rates were much lower than expected from their mass, but the metabolic rates of pre-hatching embryos were consistent with the allometry of juveniles and adults. Possible interpretations of this apparently anomalous scaling of embryonic metabolic rates are discussed. Mass-specific rates of oxygen consumption by ovigerous females (including the eggs) of both species were higher than for non-ovigerous crabs, in water and in air, and increased greatly during the development of the eggs. This difference was attributable mainly to the increasing metabolic rates of the attached embryos, but early ovigerous crabs (blastula stage) of both species also demonstrated a small elevation in metabolic rate by the crab itself, i.e. a metabolic cost of egg-bearing. In contrast, the elevation of the rate of oxygen consumption by late ovigerous females of C. lavauxi was less than predicted from the metabolic rate of eggs in a stirred respirometer. This suggests that, towards the end of development in C. lavauxi, the oxygen supply to the eggs in situ may be diffusion-limited by unstirred layers, an effect not observed for the larger eggs and more open egg clutch of H. rotundifrons. The cost of development, in terms of total oxygen consumption of single eggs, from extrusion to hatching, was 3.34 micromol O2 (approximately 1.5 J) for H. rotundifrons and 0.105 micromol O2 (approximately 0.05 J) for C. lavauxi. This 30-fold ratio approximates the ratios of their initial masses and yolk contents but represents only approximately one-third of the initial energy contents of the eggs.

Heart rate and rate of oxygen consumption of exercising macaroni penguins.

Twenty-four macaroni penguins (Eudyptes chrysolophus) from three groups, breeding males (N=9), breeding females (N=9) and moulting females (N=6), were exercised on a variable-speed treadmill. Heart rate (fH) and mass-specific rate of oxygen consumption (sVO2) were recorded from the animals, and both fh and sVO2 were found to increase linearly with increasing treadmill speed. A linear regression equation described the relationship between fh and sVO2 for each individual. There were no significant differences in these regressions between breeding and moulting females. There were significant differences in these relationships between all females and breeding males. fH and s VO2 were recorded from five of these animals for a total of 24 h. When fh was used to predict sVO2 for the 24 h period using the derived regressions, the estimate was not significantly different from the measured values, with an average error of -2.1 %. When fh was used to predict sVO2 for the 5 min intervals used for the calibration in all 24 birds, the estimate was not significantly different from the observed values, and the average error was only +0.47 %. Since the fH/sVO2 relationship was the same during periods of the annual cycle when the animals were inactive/fasting and active/foraging, it seems reasonable that, as long as sex differences are taken into account, fh can be used to predict the metabolic rates of free-ranging macaroni penguins all year round.