Contribution of aerobic and anaerobic scope to the total metabolic scope of the desert skink,Chalcides ocellatus (Forskal)

• 1.1. Measurements of aerobic scope (resting and active oxygen consumption rates) and anaerobic scope (resting and active production of lactate rates in the whole body homogenates) were carried out on the desert skink, Chalcides ocellatus at temperatures between 10 and 40°C.
• 2.2. The aerobic scope was maximal around the preferred body temperature with a low thermal temperature dependence above the preferred levels.
• 3.3. During initial stages of forced activity, C. ocellatus employed anaerobic metabolism as its major energy source.

     

Metabolism of the spade-headed Amphisbaenian worm lizard,Diplometopon zarudnyi (Nikolsky, 1907), in Saudi Arabia (Reptilia: Trogonophidae)

The oxygen consumption rate $\stackrel{?}{V}O2$ and lactate production of the Amphisbaenian worm lizard Diplometopon zarudnyi were measured at temperatures ranging from 15?°C to 35?°C at 5?°C intervals. The $\stackrel{?}{V}O2$ was significantly different between resting and active states at any specified temperature, while the average value at the resting state generally rose with increased temperature from 15?°C (0.05?ml O₂/g/h) to 25?°C (0.111?ml O₂/g/h). The aerobic respiration scopes at resting and active states were also significantly different. The highest Q10 values (3.24 and 1.69) were obtained at 15?°C–20?°C and 30?°C–35?°C during resting and active states, respectively, with these values being significantly different. Lactate concentrations were significantly higher during active states than when resting, and the anaerobic scope was found to increase with increased temperature. There was a proportional increase in ATP molecules (μmoles/g/2?min) during aerobic or anaerobic respiration, as well as in total metabolic scope, with increasing temperature, and the anaerobic scope showed significantly higher values than the aerobic scope, confirming the importance of anaerobic behavior for this species.     

The combined effect of body size and temperature on oxygen consumption rates and the size-dependency of preferred temperature in European perch Perca fluviatilis

The present study determined the effect of body mass and acclimation temperature (15–28°C) on oxygen consumption rate (ṀO₂) and the size dependency of preferred temperature in European perch Perca fluviatilis. Standard metabolic rate (SMR) scaled allometrically with body mass by an exponent of 0.86, and temperature influenced SMR with a Q₁₀ of 1.9 regardless of size. Maximum metabolic rate (MMR) and aerobic scope (MMR-SMR) scaled allometrically with body mass by exponents of 0.75–0.88. The mass scaling exponents of MMR and aerobic scope changed with temperature and were lowest at the highest temperature. Consequently, the optimal temperature for aerobic scope decreased with increasing body mass. Notably, fish <40 g did not show a decrease aerobic scope with increasing temperature. Factorial aerobic scope (MMR × SMR⁻¹) generally decreased with increasing temperatures, was unaffected by size at the lower temperatures, and scaled negatively with body mass at the highest temperature. Similar to the optimal temperature for aerobic scope, preferred temperature declined with increasing body mass, unaffectedly by acclimation temperature. The present study indicates a limitation in the capacity for oxygen uptake in larger fish at high temperatures. A constraint in oxygen uptake at high temperature may restrict the growth of larger fish with environmental warming, at least if food availability is not limited. Furthermore, behavioural thermoregulation may be contributing to regional changes in the size distribution of fish in the wild caused by global warming as larger individuals will prefer colder water at higher latitudes and at larger depths than smaller conspecifics with increasing environmental temperatures.     

Thermal sensitivity of scope for activity in Pagothenia borchgrevinki, a cryopelagic Antarctic nototheniid fish

The thermal sensitivity of scope for activity was studied in the Antarctic nototheniid fish Pagothenia borchgrevinki. The scope for activity of P. borchgrevinki at 0°C was 189 mg O₂ kg⁻¹ h⁻¹ (factorial scope 6.8) which is similar to that of temperate and tropical species at their environmental temperatures, providing no evidence for metabolic cold adaptation of maximum activity. The scope for activity increased to a maximum value of 266 mg O₂ kg⁻¹ h⁻¹ (factorial scope 8.3) at 3°C and then decreased from 3 to 6°C. The thermal sensitivity of critical swimming speed was also investigated and followed a similar pattern to aerobic scope for activity, suggesting oxygen limitation of aerobic performance. Oxygen consumption rates and ventilation frequencies were monitored for 24 h after the swimming challenge and the recovery of both parameters to resting levels was rapid and independent of temperature.     

Modelling the future hydroclimatology of the lower Fraser River and its impacts on the spawning migration survival of sockeye salmon

Short episodic high temperature events can be lethal for migrating adult Pacific salmon (Oncorhynchus spp.). We downscaled temperatures for the Fraser River, British Columbia to evaluate the impact of climate warming on the frequency of exceeding thermal thresholds associated with salmon migratory success. Alarmingly, a modest 1.0 °C increase in average summer water temperature over 100 years (1981–2000 to 2081–2100) tripled the number of days per year exceeding critical salmonid thermal thresholds (i.e. 19.0 °C). Refined thresholds for two populations (Gates Creek and Weaver Creek) of sockeye salmon (Oncorhynchus nerka) were defined using physiological constraint models based on aerobic scope. While extreme temperatures leading to complete aerobic collapse remained unlikely under our warming scenario, both populations were increasingly forced to migrate upriver at reduced levels of aerobic performance (e.g. in 80% of future simulations, ≥90% of salmon encountered temperatures exceeding population‐specific thermal optima for maximum aerobic scope; T_opt=16.3 °C for Gates Creek and T_opt=14.5 °C for Weaver Creek). Assuming recent changes to river entry timing persist, we also predicted dramatic increases in the probability of freshwater mortality for Weaver Creek salmon due to reductions in aerobic, and general physiological, performance (e.g. in 42% of future simulations≥50% of Weaver Creek fish exceeded temperature thresholds associated with 0–60% of maximum aerobic scope). Potential for adaptation via directional selection on run‐timing was more evident for the Weaver Creek population. Early entry Weaver Creek fish experienced 25% (range: 15–31%) more suboptimal temperatures than late entrants, compared with an 8% difference (range: 0–17%) between early and late Gates Creek fish. Our results emphasize the need to consider daily temperature variability in association with population‐specific differences in behaviour and physiological constraints when forecasting impacts of climate change on migratory survival of aquatic species.     

Plasma osmolality and oxygen consumption of perch Perca fluviatilis in response to different salinities and temperatures

The present study determined the blood plasma osmolality and oxygen consumption of the perch Perca fluviatilis at different salinities (0, 10 and 15) and temperatures (5, 10 and 20° C). Blood plasma osmolality increased with salinity at all temperatures. Standard metabolic rate (SMR) increased with salinity at 10 and 20° C. Maximum metabolic rate (MMR) and aerobic scope was lowest at salinity of 15 at 5° C, yet at 20° C, they were lowest at a salinity of 0. A cost of osmoregulation (SMR at a salinity of 0 and 15 compared with SMR at a salinity of 10) could only be detected at a salinity of 15 at 20° C, where it was 28%. The results show that P. fluviatilis have capacity to osmoregulate in hyper‐osmotic environments. This contradicts previous studies and indicates intraspecific variability in osmoregulatory capabilities among P. fluviatilis populations or habitat origins. An apparent cost of osmoregulation (28%) at a salinity of 15 at 20° C indicates that the cost of osmoregulation in P. fluviatilis increases with temperature under hyperosmotic conditions and a power analysis showed that the cost of osmoregulation could be lower than 12·5% under other environmental conditions. The effect of salinity on MMR is possibly due to a reduction in gill permeability, initiated to reduce osmotic stress. An interaction between salinity and temperature on aerobic scope shows that high salinity habitats are energetically beneficial during warm periods (summer), whereas low salinity habitats are energetically beneficial during cold periods (winter). It is suggested, therefore, that the seasonal migrations of P. fluviatilis between brackish and fresh water is to select an environment that is optimal for metabolism and aerobic scope.     

Q10 measures of metabolic performance and critical swimming speed in King George whiting Sillaginodes punctatus

This study examined thermally driven changes in swimming performance and aerobic metabolism (Q₁₀ and aerobic scope of activity) of adult King George whiting Sillaginodes punctatus to the coldest (16° C) and the warmest (26° C) temperature encountered by this species. Compensation of aerobic scope, higher maximal swimming speeds and a maintained capacity to repay oxygen debt indicate that this species is capable of thermal acclimation to conditions expected under global warming.     

Counter-Gradient Variation in Respiratory Performance of Coral Reef Fishes at Elevated Temperatures

The response of species to global warming depends on how different populations are affected by increasing temperature throughout the species'' geographic range. Local adaptation to thermal gradients could cause populations in different parts of the range to respond differently. In aquatic systems, keeping pace with increased oxygen demand is the key parameter affecting species'' response to higher temperatures. Therefore, respiratory performance is expected to vary between populations at different latitudes because they experience different thermal environments. We tested for geographical variation in respiratory performance of tropical marine fishes by comparing thermal effects on resting and maximum rates of oxygen uptake for six species of coral reef fish at two locations on the Great Barrier Reef (GBR), Australia. The two locations, Heron Island and Lizard Island, are separated by approximately 1200 km along a latitudinal gradient. We found strong counter-gradient variation in aerobic scope between locations in four species from two families (Pomacentridae and Apogonidae). High-latitude populations (Heron Island, southern GBR) performed significantly better than low-latitude populations (Lizard Island, northern GBR) at temperatures up to 5°C above average summer surface-water temperature. The other two species showed no difference in aerobic scope between locations. Latitudinal variation in aerobic scope was primarily driven by up to 80% higher maximum rates of oxygen uptake in the higher latitude populations. Our findings suggest that compensatory mechanisms in high-latitude populations enhance their performance at extreme temperatures, and consequently, that high-latitude populations of reef fishes will be less impacted by ocean warming than will low-latitude populations.     

Energetic costs of prey ingestion in a scincid lizard,Scincella lateralis

Summary The relative importance of aerobic and anaerobic metabolism during feeding was investigated in the ground skink, Scincella lateralis. Animals were fed crickets of three different sizes relative to body mass (5, 10, and 15% of body mass). Oxygen consumption and lactic acid production of animals during feeding were compared with those of animals at rest and when exercising intensely. Oxygen consumption was higher in feeding and exercising animals than in those at rest. Rates of oxygen consumption of animals consuming prey of 5 and 10% of body mass were not significantly different from each other, but were lower than rates of animals consuming prey of 15% of body mass. Lactic acid concentrations in feeding animals increased with increasing prey size. Concentrations in resting and feeding animals were not different, but those of exercising animals were significantly higher. These data suggest that, despite a positive correlation between prey size and lactic acid concentration, anaerobiosis is relatively unimportant in the support of prey handling for Scincella lateralis. The energetic requirements of feeding in this species are met largely by increased aerobic metabolism.     

Temperature dependence and ontogenetic changes of metabolic rate of an endemic earthworm <Emphasis Type="Italic">Dendrobaena mrazeki</Emphasis>

Ontogenetic changes and temperature dependency of respiration rate were studied in Dendrobaena mrazeki, an earthworm species inhabiting relatively warm and dry habitats in Central Europe. D. mrazeki showed respiration rate lower than in other earthworm species, < 70 μl O₂ g⁻¹ h⁻¹, within the temperature range of 5–35°C. The difference of respiration rate between juveniles and adults was insignificant at 20°C. The response of oxygen consumption to sudden temperature changes was compared with the temperature dependence of respiratory activity in animals pre-acclimated to temperature of measurement. No significant impact of acclimation on the temperature response of oxygen consumption was found. The body mass-adjusted respiration rate increased slowly with increasing temperature from 5 to 25°C (Q₁₀ from 1.2 to 1.7) independently on acclimation history of earthworms. Oxygen consumption decreased above 25°C up to upper lethal limit (about 35°C). Temperature dependence of metabolic rate is smaller than in other earthworm species. The relationships between low metabolic sensitivity to temperature, slow locomotion and reactivity to touching as observed in this species are discussed.     

Disentangling environmental drivers of metabolic flexibility in birds: the importance of temperature extremes versus temperature variability

Examining physiological traits across large spatial scales can shed light on the environmental factors driving physiological variation. For endotherms, flexibility in aerobic metabolism is especially important for coping with thermally challenging environments and recent research has shown that aerobic metabolic scope [the difference between maximum thermogenic capacity (M_sum) and basal metabolic rate (BMR)] increases with latitude in mammals. One explanation for this pattern is the climatic variability hypothesis, which predicts that flexibility in aerobic metabolism should increase as a function of local temperature variability. An alternative explanation is the cold adaptation hypothesis, which predicts that cold temperature extremes may also be an important driver of variation in metabolic scope. To determine the thermal drivers of aerobic metabolic flexibility in birds, we combined data on metabolic scope from 40 bird species sampled across a range of environments with several indices of local ambient temperature. Using phylogenetically‐informed analyses, we found that minimum winter temperature was the best predictor of variation in avian metabolic scope, outperforming all other thermal variables. Additionally, M_sum was a better predictor of latitudinal patterns of metabolic scope than BMR, with species inhabiting colder environments exhibiting increased M_sum over their counterparts in warmer environments. Taken together, these results suggest that cold temperature extremes drive latitudinal patterns of metabolic scope via selection for enhanced thermogenic performance in cold environments, supporting the cold adaptation hypothesis. Temperature extremes may therefore be an important selective pressure driving macrophysiological trends of aerobic performance in endotherms.     

Life on the edge: thermal optima for aerobic scope of equatorial reef fishes are close to current day temperatures

Equatorial populations of marine species are predicted to be most impacted by global warming because they could be adapted to a narrow range of temperatures in their local environment. We investigated the thermal range at which aerobic metabolic performance is optimum in equatorial populations of coral reef fish in northern Papua New Guinea. Four species of damselfishes and two species of cardinal fishes were held for 14 days at 29, 31, 33, and 34 °C, which incorporated their existing thermal range (29–31 °C) as well as projected increases in ocean surface temperatures of up to 3 °C by the end of this century. Resting and maximum oxygen consumption rates were measured for each species at each temperature and used to calculate the thermal reaction norm of aerobic scope. Our results indicate that one of the six species, Chromis atripectoralis, is already living above its thermal optimum of 29 °C. The other five species appeared to be living close to their thermal optima (ca. 31 °C). Aerobic scope was significantly reduced in all species, and approached zero for two species at 3 °C above current‐day temperatures. One species was unable to survive even short‐term exposure to 34 °C. Our results indicate that low‐latitude reef fish populations are living close to their thermal optima and may be more sensitive to ocean warming than higher‐latitude populations. Even relatively small temperature increases (2–3 °C) could result in population declines and potentially redistribution of equatorial species to higher latitudes if adaptation cannot keep pace.     

Eradication of Polymyxa betae by Thermal and Anaerobic Conditions and in the Presence of Compost Leachate

The abiotic conditions required for eradication of Polymyxa betae, the vector of Beet necrotic yellow vein virus in sugar beet, were investigated. Survival of resting spores of P. betae was determined under aerobic (30 min, 4 days and 21 days) and anaerobic (4 days) conditions under several temperature regimes in a water suspension and in leachate extracted from an aerobic compost heap. In water under aerobic conditions the lethal temperature was 60, 55 and 40°C for exposure times of 30 min, 4 days and 21 days, respectively. The effect of compost leachate and/or anaerobic conditions on survival of P. betae depended on temperature. After incubation for 4 days at 20°C, no significant effects of anaerobic conditions or leachate on the survival of P. betae were found. However, at 40°C for 4 days under anaerobic conditions, survival of P. betae was significantly lower than survival under aerobic conditions in water as well as in leachate. In leachate taken from an aerobic compost heap, aerobically incubated at 40°C for 4 days, survival of P. betae was significantly lower than survival in water at the same temperature. As anaerobic spots are prevalent in aerobic compost heaps, especially during the thermophilic phase, actual inactivation temperatures under composting conditions are likely to be lower than the temperatures we found for eradication in water under aerobic conditions.     

Intracellular pH and energy metabolism in the highly stenothermal Antarctic bivalve Limopsis marionensis as a function of ambient temperature

Changes in oxygen consumption, ammonia excretion and in the acid-base and energy status of various tissues were investigated in the cold stenothermal Antarctic bivalve, Limopsis marionensis, and compared to similar data in the limpet, Nacella concinna, for an assessment of thermal sensitivity. Oxygen consumption of L. marionensis varied between −1.5 and 2°C with a Q ₁₀ of 2.2. Ammonia excretion could only be detected in animals exposed to elevated temperature for periods in excess of 45 days and close to death and it is interpreted as the onset of protein and amino acid catabolism with starvation under temperature stress. In L. marionensis any change in temperature as well as starvation stress at constant temperature induced a decrease in phospho-l-arginine and ATP levels. However, only temperature stress resulted in a drop in the Gibb's free energy change of ATP hydrolysis. Intracellular pH rose in all tissues during upward or downward temperature changes of only 1.5 or 2°C for 24 h with a concomitant trend to accumulate succinate and acetate in the tissues. These changes are seen to reflect disturbances of the tissue acid-base and energy status with any under- or overshoot in aerobic metabolic rate during a temperature decrease or increase. Elevated temperature at 2°C during 2 weeks of incubation resulted in continued net ATP depletion, at low levels of ATP free energy. This indicates long-term stress, which was also mirrored in the inability to establish a new steady-state mean rate of oxygen consumption. Incubation at even higher temperatures of 4 and 7°C led to an aggravation of energetic stress and transition to an intracellular acidosis, as well as a fall in oxygen consumption. In N. concinna a drop in energy levels was also visible at 2°C but was compensated for during long-term incubation. In conclusion, L. marionensis will be able to compensate for a temperature change only in a very narrow range whereas the thermal tolerance window is much wider in N. concinna. The inability of the metabolic rate to rise continually and the concomitant transition to anaerobic metabolism and long-term energetic stress characterize the upper critical temperature. Stenothermality is discussed, not only as reflecting the permanent and very stable low temperature in the natural environment, but also regarding dif- ferences in the level of activity and aerobic scope. Accepted: 21 December 1998     

Walking performance and aerobic and anaerobic metabolism of Carcinus maenas (L.) in sea water at 15°C

Walking performance of the shore crab Carcinus maenas (L.) in sea water at 15 °C was assessed. In large crabs there was an inverse relationship between fatigue time and speed; crabs ran for $\text{\$}\text{?}$10 min at 3.2 m·min^?1 and for only 2 min at 14 m·min^?1. There were linear relationships between oxygen consumption and walking speeds for small and large animals walking at up to 4 m·min^?1 Estimates of maximum oxygen consumption were proportional to W^0.13 whereas inactive consumption is proportional to W^0.44 this resulted in aerobic scope (i.e. the difference between inactive and maximal rates of oxygen consumption) remaining almost constant across a weight range of animals whereas the aerobic expansibility (maximal rates/inactive rates) declined from 7- to 4-fold with increasing size. After a 12-h period without handling (settled animals) the animals could immediately become active and reach maximal rates of oxygen consumption similar to those of animals handled 1 h before the experiment. The aerobic expansibility of these settled animals could range from 21 to 8 times their inactive rates of oxygen consumption in small and large animals respectively. After 10 min of exercise oxygen consumption and whole body lactate levels returned to pre-exercise values within 5 to 25 min. The net oxygen debts range from 16 to 64% of the net oxygen consumption increase during exercise in small and large animals respectively.Calculations of the energy gained from lactate accumulation indicated that the net aerobic energy production during walking was supplemented from 4 to 71 % by anaerobic metabolism in small and large animals respectively. With increasing animal size the decline in aerobic expansibility was offset by an increased capacity for lactate production so that the overall maximum energy production during sustained activity remained almost constant at around seven times the inactive rate. The cost of transport (the net increase in oxygen consumption per g per m) falls with increased walking speed and increased animal size.     

Comparison of oxygen consumption in drosophilid flies from different climates

Oxygen consumption at rest was studied in drosophilid species from cool‐temperate, warm‐temperate and subtropical regions to assess whether adaptations to different climates are associated with changes in metabolic rates. In experiments at 23°C using 8‐day‐old males of 28 species, body mass was revealed to be a significant predictor of oxygen consumption. No significant relation was detected between mass‐adjusted oxygen consumption and latitudinal distribution or thermal tolerance by either conventional regression analysis or a phylogenetically based method. The effect of temperature on oxygen consumption was studied with experiments at 15, 18, 23 and 28°C using 8‐ and 24‐day‐old males of four species of each of the montium species subgroup and the subgenus Drosophila. In these experiments, it was confirmed that temperature was a significant predictor of mass‐adjusted oxygen consumption. In both lineages, mass‐adjusted oxygen consumption was not higher in cool‐temperate species than in subtropical species. Thus, adaptations to colder climates are not associated with elevation of metabolic rates in these drosophilid species. The results of the present study also indicate that oxygen consumption is not related to the capacity to walk quickly.     

Individual variation in metabolism and thermal tolerance in juvenile qingbo (Spinibarbus sinensis)

Studies of individual variation in the physiological performance of animals and their relationship with metabolism may provide insight into how selection influences diversity in phenotypic traits. Thus, the aims of the present study were to investigate variation in thermal tolerance and its relationship with individual metabolism in juvenile qingbo (Spinibarbus sinensis). To fulfill our goal, we first measured the resting metabolic rate (RMR), maximum metabolic rate (MMR), metabolic scope (MS, MMR–RMR) and excess post-exercise oxygen consumption (EPOC) of 40 fish at 25 °C. We then measured the critical thermal minimum (CT_min), lethal thermal minimum (LT_min), critical thermal maximum (CT_max), and lethal thermal maximum (LT_max) of 20 fish. Both MMR and MS were positively correlated with the metabolic recovery rate (MRR) (p = 0.001), indicating that high aerobic metabolic performance individuals possessed an advantage for the recovery of anaerobic metabolism. However, the negative correlation between EPOC and MRR (p = 0.017) indicated a slow recovery of the metabolism of high anaerobic metabolic capacity individuals. The RMR was positively correlated with CT_min and LT_min, whereas all of the metabolic rate parameters (RMR, MMR, and MS) were negatively correlated with CT_max and LT_max (p < 0.05), indicating that high aerobic metabolic performance individuals have a weakened thermal tolerance. These results suggested that there is a trade-off between aerobic metabolic performance and thermal tolerance.     

Ventilatory accommodation of changing oxygen demand in sciurid rodents

Summary Ventilation was measured across a range of O₂ consumption rates in four sciurid rodents: Tamias minimus (47 g), Spermophilus lateralis (189 g), S. beecheyi (531 g), and Marmota flaviventris juveniles (1054 g) and adults (2989 g). Maximum thermogenic oxygen consumption was measured for all but adult M. flaviventris. Aerobic scopes (maximum/minimum O₂ consumption rates) were 4.6, 3.8, 5.4, and 4.8 in T. minimus, S. lateralis, S. beecheyi, and juvenile M. flaviventris, respectively. Aerobic scope was at least 4.1 in adult M. flaviventris. Ventilatory accommodation of changing O₂ consumption rate was qualitatively similar in the four species, with the bulk of accommodation resulting from changes in minute volume. Nevertheless, there were significant differences in the relative importance of frequency, tidal volume, and O₂ extraction in accommodation. In all species, frequency and minute volume were strongly correlated to O₂ consumption rate. Tidal volume was significantly correlated to O₂ consumption rate in T. minimus and S. beecheyi, but not in the other species. Oxygen extraction was not significantly correlated to O₂ consumption rate in any species. Analysis of factorial ventilation changes across a standardized 3.8-fold change in O₂ consumption rate revealed significant differences among species in frequency and O₂ extraction, but not in tidal or minute volume. When compared to a generalized allometry for mammalian resting ventilation, the four sciurid species had consistently lower respiration frequency and higher O₂ extraction than predicted, perhaps because the sciurid measurements were made on unrestrained animals. There was no indication that ventilation constrained maximum O₂ consumption rate.Abbreviations BMR basal metabolic rate - BTPS body temperature and pressure saturated - EO₂ oxygen extraction - f respiration frequency - MMR minimal metabolic rate - RH relative humidity - STPD standard pressure and temperature, dry - T _a ambient temperature - T _b body temperature - minute volume - tidal volume - maximum rate of oxygen consumption     

Aerobic and anaerobic energy expenditure during rest and activity in montane Bufo b. boreas and Rana pipiens

Summary The relations of standard and active aerobic and anaerobic metabolism and heart rate to body temperature (T _b) were measured in montane groups of Bufo b. boreas and Rana pipiens maintained under field conditions. These amphibians experience daily variation of T _b over 30°C and 23°C, respectively (Carey, 1978). Standard and active aerobic and anaerobic metabolism, heart rate, aerobic and anaerobic scope are markedly temperature-dependent with no broad plateaus of thermal independence. Heart rate increments provide little augmentation of oxygen transport during activity; increased extraction of oxygen from the blood probably contributes importantly to oxygen supply during activity. Development of extensive aerobic capacities in Bufo may be related to aggressive behavior of males during breeding. Standard metabolic rates of both species are more thermally dependent than comparable values for lowland relatives. Thermal sensitivity of physiological functions may have distinct advantages over thermally compensated rates in the short growing season and daily thermal fluctuations of the montane environment.     

Activity metabolism of the toad (Bufo americanus): Ecological consequences of ontogenetic change

Summary Following metamorphosis, juvenile toads form dense, heliothermic aggregations on the margins of the ponds from which they emerge. After a period of growth and development, during which body mass increases ten-fold, the juveniles disperse from the pond and assume the solitary, nocturnal habits that characterize adult toads.The dispersal of the toads coincides with the culmination of ontogenetic changes in activity metabolism. Unlike adults, juvenile toads exhaust rapidly when exercised and exhibit a low aerobic component of total metabolic scope. Values of aerobic scope for sustained activity ranged from 0.5 ml O₂/(g·h) for the smallest juveniles to 1.0 ml O₂/(g·h) for adults. The capacity of juveniles for oxygen consumption increases rapidly with growth, reaching the level of mature animals immediately prior to dispersal.In contrast to aerobic metabolism, anaerobic scope was independent of body size. Whole body lactate content after a 1 min bout of vigorous activity was elevated above the resting level by 0.14 mg lactate/g for both juvenile and adult animals.The elevated body temperatures that are achieved by basking juvenile toads probably hasten their physiological development and increase their capacity for aerobic metabolism.