Metabolic Scope Research Articles

Cutaneous respiration by diving beetles from underground aquifers of Western Australia (Coleoptera: Dytiscidae).

Insects have a gas-filled respiratory system, which provides a challenge for those that have become aquatic secondarily. Diving beetles (Dytiscidae) use bubbles on the surface of their bodies to supply O2 for their dives and passively gain O2 from the water. However, these bubbles usually require replenishment at the water's surface. A highly diverse assemblage of subterranean dytiscids has evolved in isolated calcrete aquifers of Western Australia with limited/no access to an air-water interface, raising the question of how they are able to respire. We explored the hypothesis that they use cutaneous respiration by studying the mode of respiration in three subterranean dytiscid species from two isolated aquifers. The three beetle species consume O2 directly from the water, but they lack structures on their bodies that could have respiratory function. They also have a lower metabolic rate than other insects. O2 boundary layers surrounding the beetles are present, indicating that O2 diffuses into the surface of their bodies via cutaneous respiration. Cuticle thickness measurements and other experimental results were incorporated into a mathematical model to understand whether cutaneous respiration limits beetle size. The model indicates that the cuticle contributes considerably to resistance in the O2 cascade. As the beetles become larger, their metabolic scope narrows, potentially limiting their ability to allocate energy to mating, foraging and development at sizes above approximately 5 mg. However, the ability of these beetles to utilise cutaneous respiration has enabled the evolution of the largest assemblage of subterranean dytiscids in the world.

Anintertidal fish shows thermal acclimation despite living in a rapidly fluctuating environment.

The co-evolution of acclimation capacity and thermal performance breadth has been a contentious issue for decades, and little is known regarding the extent to which acclimation alters the shape of acute thermal performance curves. Current acclimation theory suggests that when daily variation is large and unpredictable ectotherms should not acclimate but should evolve wide performance breadths, allowing maintenance of performance across a wide thermal range. The subtropical intertidal zone, however, experiences a large amount of daily thermal variation, but daily means and ranges shift in predictable ways with season, where daily and seasonal variation is roughly equal. We predicted that animals in this habitat would maintain their capacity to acclimate and that performance breadth would not be altered by acclimation to maintain function with rapidly fluctuating daily temperatures. We tested our prediction using a subtropical goby, Bathygobius cocosensis, which lives in tide pools that vary widely, over days and seasons. We exposed B. cocosensis to winter (12-17 °C) and summer (30-35 °C) thermal conditions for six weeks and then measured the thermal dependence of burst swimming speed, routine and maximum metabolic rate, and ventilation rate between 12and 36 °C. B. cocosensis exhibited an acclimation response for burst swimming speed, maximum metabolic rate and metabolic scope, but acclimation did not alter the shape of acute thermal performance curves. These results indicate that thermal acclimation can occur when short-term thermal variability is large and equal to seasonal variation, and wide performance breadths can be maintained with acclimation in heterogeneous environments.

Effects of acclimation temperature on the thermal tolerance, hypoxia tolerance and swimming performance of two endangered fish species in China.

Temperature is one of the most important environmental factors affecting the physiological activities and, thus, the fitness of fish, and physiological studies can help predict the effects of climate change on fish species in the field. The aim of this study was to investigate the effect of acclimation temperature on the thermal tolerance, hypoxia tolerance and swimming ability of two endangered fish species in the upper reach of the Yangtze River, namely, the Chinese sucker (Myxocyprinus asiaticus) and rock carp (Procypris rabaudi). The fish were acclimated at either 15°C or 25°C for a 3-week period. Then, thermal tolerance as indicated by the critical thermal maximum (CTmax) and critical thermal minimum (CTmin), hypoxia tolerance as indicated by the aquatic surface respiration (ASR50) and loss of equilibrium (LOE50), swimming performance as indicated by the critical swimming speed (Ucrit), aerobic capacity as indicated by the maximum metabolic rate and aerobic scope were measured. As expected, the thermal indicators of both species increased with temperature, and their values at both acclimation temperatures were similar to those of fish living in the Yangtze River. However, both species showed poor hypoxia tolerance compared to most fish species in the Yangtze River, according to previous studies. In particular, Chinese sucker acclimated at a low temperature exhibited an unusually strong decrease in hypoxia tolerance with decreasing temperature (fish usually showed high hypoxia tolerance due to decreased oxygen demand and high environmental oxygen tension at low temperature). Furthermore, Chinese sucker exhibited poorer swimming performance than rock carp (which is also a relatively poor swimmer among the fish species in the Yangtze River) when maintained at a high temperature due to low swimming efficiency, possibly as a consequence of its deep body shape. The difference in Ucrit was magnified at low temperature due to the more profound decrease in metabolic scope in Chinese sucker than in rock carp (55% vs 20%), but Chinese sucker showed a higher resting metabolic rate than rock carp at a low temperature, which is difficult to explain. This result suggested that low hypoxia tolerance and poor swimming performance due to the low cardiorespiratory capacity and (or) non-streamlined body shape of both fish species, especially Chinese sucker, reared at low temperature might be two of the reasons why they are not well adjusted to the change in their natural habitat and have thus declined in recent decades. The underlying physiological and biochemical mechanisms involved in the unusual adjustment of the physiological function of Chinese sucker and its ecological relevance must be investigated further. The present study provides a good example of a physiological investigation yielding very interesting and useful data for species conservation in a changing world.

Thermal performance of fish is explained by an interplay between physiology, behaviour and ecology.

Increasing temperatures under climate change are thought to affect individual physiology of fish and other ectotherms through increases in metabolic demands, leading to changes in species performance with concomitant effects on species ecology. Although intuitively appealing, the driving mechanism behind thermal performance is contested; thermal performance (e.g. growth) appears correlated with metabolic scope (i.e. oxygen availability for activity) for a number of species, but a substantial number of datasets do not support oxygen limitation of long-term performance. Whether or not oxygen limitations via the metabolic scope, or a lack thereof, have major ecological consequences remains a highly contested question. size and trait-based model of energy and oxygen budgets to determine the relative influence of metabolic rates, oxygen limitation and environmental conditions on ectotherm performance. We show that oxygen limitation is not necessary to explain performance variation with temperature. Oxygen can drastically limit performance and fitness, especially at temperature extremes, but changes in thermal performance are primarily driven by the interplay between changing metabolic rates and species ecology. Furthermore, our model reveals that fitness trends with temperature can oppose trends in growth, suggesting a potential explanation for the paradox that species often occur at lower temperatures than their growth optimum. Our model provides a mechanistic underpinning that can provide general and realistic predictions about temperature impacts on the performance of fish and other ectotherms and function as a null model for contrasting temperature impacts on species with different metabolic and ecological traits.

Influence of a dynamic rearing environment on development of metabolic phenotypes in age-0 Lake Sturgeon, Acipenser fulvescens.

Environment–phenotype interactions are the most pronounced during early life stages and can strongly influence metabolism and ultimately ecological fitness. In the present study, we examined the effect of temperature [ambient river temperature (ART) vs ART+2°C], dissolved oxygen (DO; 100% vs 80%) and substrate (presence vs absence) on standard metabolic rate, forced maximum metabolic rate and metabolic scope with Fulton’s condition factor (K), energy density (ED) and critical thermal maximum (CTmax) in age-0 Lake Sturgeon, Acipenser fulvescens, before and after a simulated overwintering event. We found that all the environmental variables strongly influenced survival, K, ED and CTmax. Fish reared in elevated temperature showed higher mortality and reduced K pre-winter at 127 days post-hatch (dph). Interestingly, we did not find any significant difference in terms of metabolic rate between treatments at both sampling points of pre- and post-winter. Long-term exposure to 80% DO reduced ED in Lake Sturgeon post-winter at 272 dph. Our data suggest that substrate should be removed at the onset of exogenous feeding to enhance the survival rate of age-0 Lake Sturgeon in the first year of life. Effects of early rearing environment during larval development on survival over winter are discussed with respect to successful recruitment of stock enhanced Lake Sturgeon, a species that is at risk throughout its natural range.

Effects of high altitude in pregnancy: an opportunity of research in KAHS

Pregnancy is a special condition in a women’s life with unique physiological changes. There has been some research on physiological changes in human body in high altitude; however, there are many things still unknown about pregnancy at high altitude. It is an estimation that about 140 million people worldwide live in high altitude of above 2500 m, and it is believed that the hypobaric hypoxia of pregnancy at high altitude is the most common cause for maternofetal hypoxia. It has been seen that the babies born at high altitude are smaller, and the degree of smallness is inversely correlated with the number of generations of ancestors of high-altitude residence. Some studies show that women in populations with high-altitude ancestry, such as the Aymaras or Quechuas in South America and Tibetans in Asia, deliver heavier babies than women from European ancestry in South America or Han women in China living at high altitude. A study by Jensen and Moore shows that in Colorado, altitude acts as an independent factor in determining birth weight, with a reduction in birth weight of 100 g per 1000 m elevation gain.
 Studies have shown that low birth weight at high altitude has no association with socioeconomic status. Hence, it may reflect either hypoxia-induced intrauterine growth restriction or genetic adaptation. The latter implies a strong fetomaternal interaction involving adaptation to hypoxia on several levels. It also reflects the importance of interaction between the mother and the fetus which is stressed by the fact that better maternal ventilator response to hypoxic stress at high altitude correlates positively with birth weight. Another study shows that people living at altitudes of 4000 m and above have an arterial partial pressure of oxygen of 50 mmHg and an arterial oxygen saturation of just above 80%.
 There has been many studies on populations living in high-altitude regions for many generations, like Quechuas and Tibetans, which show many functional and structural adaptations in high altitude. This adaptation helps to allow for a way out for the main metabolic problem they face: maintaining an acceptably high scope for sustained aerobic metabolism despite reduced availability of oxygen in the inspired air. The functional adaptation to high altitude is measured indirectly by determining aerobic capacity, which reflects not only the maximum work performance but also the success of the individual’s biological oxygen transport system.

Environmentally relevant methylmercury exposure reduces the metabolic scope of a model songbird

For most birds, energy efficiency and conservation are paramount to balancing the competing demands of self-maintenance, reproduction, and other demanding life history stages. Yet the ability to maximize energy output for behaviors like predator escape and migration is often also critical. Environmental perturbations that affect energy metabolism may therefore have important consequences for fitness and survival. Methylmercury (MeHg) is a global pollutant that has wide-ranging impacts on physiological systems, but its effects on the metabolism of birds and other vertebrates are poorly understood. We investigated dose-dependent effects of dietary MeHg on the body composition, basal and peak metabolic rates (BMR, PMR), and respiratory quotients (RQ) of zebra finches (Taeniopygia guttata). Dietary exposure levels (0.0, 0.1, or 0.6 ppm wet weight) were intended to reflect a range of mercury concentrations found in invertebrate prey of songbirds in areas contaminated by atmospheric deposition or point-source pollution. We found adiposity increased with MeHg exposure. BMR also increased with exposure while PMR decreased, together resulting in reduced metabolic scope in both MeHg-exposed treatments. There were differences in RQ among treatments that suggested a compromised ability of exposed birds to rapidly metabolize carbohydrates during exercise in a hop-hover wheel. The elevated BMR of exposed birds may have been due to energetic costs of depurating MeHg, whereas the reduced PMR could have been due to reduced oxygen carrying capacity and/or reduced glycolytic capacity. Our results suggest that environmentally relevant mercury exposure is capable of compromising the ability of songbirds to both budget and rapidly exert energy.

Body size and temperature effects on standard metabolic rate for determining metabolic scope for activity of the polychaete Hediste (Nereis) diversicolor.

Considering the ecological importance and potential value of Hediste diversicolor, a better understanding of its metabolic rate and potential growth rates is required. The aims of this study are: (i) to describe key biometric relationships; (ii) to test the effects of temperature and body size on standard metabolic rate (as measure by oxygen consumption) to determine critical parameters, namely Arrhenius temperature (TA), allometric coefficient (b) and reaction rate; and (iii) to determine the metabolic scope for activity (MSA) of H. diversicolor for further comparison with published specific growth rates. Individuals were collected in a Mediterranean lagoon (France). After 10 days of acclimatization, 7 days at a fixed temperature and 24 h of fasting, resting oxygen consumption rates (VO2) were individually measured in the dark at four different temperatures (11, 17, 22 and 27 °C) in worms weighing from 4 to 94 mgDW (n = 27 per temperature). Results showed that DW and L3 were the most accurate measurements of weight and length, respectively, among all the metrics tested. Conversion of WW (mg), DW (mg) and L3 (mm) were quantified with the following equations: DW = 0.15 × WW, L3 = 0.025 × TL(mm) + 1.44 and DW = 0.8 × L33.68. Using an equation based on temperature and allometric effects, the allometric coefficient (b) was estimated at 0.8 for DW and at 2.83 for L3. The reaction rate (VO2) equaled to 12.33 µmol gDW−1 h−1 and 0.05 µmol mm L3−1 h−1 at the reference temperature (20 °C, 293.15 K). Arrhenius temperature (TA) was 5,707 and 5,664 K (for DW and L3, respectively). Metabolic scope for activity ranged from 120.1 to 627.6 J gDW−1 d−1. Predicted maximum growth rate increased with temperature, with expected values of 7–10% in the range of 15–20 °C. MSA was then used to evaluate specific growth rates (SGR) in several experiments. This paper may be used as a reference and could have interesting applications in the fields of aquaculture, ecology and biogeochemical processes.

Comparison of Aerobic Scope for Metabolic Activity in Aquatic Ectotherms With Temperature Related Metabolic Stimulation: A Novel Approach for Aerobic Power Budget.

Considering that swim-flume or chasing methods fail in the estimation of maximum metabolic rate and in the estimation of Aerobic Scope (AS) of sedentary or sluggish aquatic ectotherms, we propose a novel conceptual approach in which high metabolic rates can be obtained through stimulation of organism metabolic activity using high and low non-lethal temperatures that induce high (HMR) and low metabolic rates (LMR), This method was defined as TIMR: Temperature Induced Metabolic Rate, designed to obtain an aerobic power budget based on temperature-induced metabolic scope which may mirror thermal metabolic scope (TMS = HMR—LMR). Prior to use, the researcher should know the critical thermal maximum (CT max) and minimum (CT min) of animals, and calculate temperature TIMR max (at temperatures −5–10% below CT max) and TIMR min (at temperatures +5–10% above CT min), or choose a high and low non-lethal temperature that provoke a higher and lower metabolic rate than observed in routine conditions. Two sets of experiments were carried out. The first compared swim-flume open respirometry and the TIMR protocol using Centropomus undecimalis (snook), an endurance swimmer, acclimated at different temperatures. Results showed that independent of the method used and of the magnitude of the metabolic response, a similar relationship between maximum metabolic budget and acclimation temperature was observed, demonstrating that the TIMR method allows the identification of TMS. The second evaluated the effect of acclimation temperature in snook, semi-sedentary yellow tail (Ocyurus chrysurus), and sedentary clownfish (Amphiprion ocellaris), using TIMR and the chasing method. Both methods produced similar maximum metabolic rates in snook and yellowtail fish, but strong differences became visible in clownfish. In clownfish, the TIMR method led to a significantly higher TMS than the chasing method indicating that chasing may not fully exploit the aerobic power budget in sedentary species. Thus, the TIMR method provides an alternative way to estimate the difference between high and low metabolic activity under different acclimation conditions that, although not equivalent to AS may allow the standardized estimation of TMS that is relevant for sedentary species where measurement of AS via maximal swimming is inappropriate.

Thermal performance of fish is explained by an interplay between physiology, behaviour, and ecology

Increasing temperatures under climate change are thought to affect individual physiology of fish and other ectotherms through increases in metabolic demands, leading to changes in species performance with concomitant effects on species ecology. Although intuitively appealing, the driving mechanism behind thermal performance is contested; thermal performance (e.g. growth) appears correlated with metabolic scope (i.e. oxygen availability for activity) for a number of species, but a substantial number of datasets do not support oxygen limitation of long-term performance. Whether or not oxygen limitations via the metabolic scope, or a lack thereof, have major ecological consequences remains a highly contested question. size and trait-based model of energy and oxygen budgets to determine the relative influence of metabolic rates, oxygen limitation and environmental conditions on ectotherm performance. We show that oxygen limitation is not necessary to explain performance variation with temperature. Oxygen can drastically limit performance and fitness, especially at temperature extremes, but changes in thermal performance are primarily driven by the interplay between changing metabolic rates and species ecology. Furthermore, our model reveals that fitness trends with temperature can oppose trends in growth, suggesting a potential explanation for the paradox that species often occur at lower temperatures than their growth optimum. Our model provides a mechanistic underpinning that can provide general and realistic predictions about temperature impacts on the performance of fish and other ectotherms and function as a null model for contrasting temperature impacts on species with different metabolic and ecological traits.

Thermal preference, critical thermal limits, oxygen routine consumption and active metabolic scope of Macrobrachium tenellum (Smith, 1871) maintained at different acclimation temperatures

Thermal preference, critical thermal limits, oxygen routine consumption and active metabolic scope of Macrobrachium tenellum (Smith, 1871) maintained at different acclimation temperatures

The thermal acclimation rate varied among physiological functions and temperature regimes in a common cyprinid fish

The acclimation rate of physiological functions that bear fitness costs under a changing environment is key to making predictions for fish, yet this has seldom been investigated. This study aimed to test whether there were different responses when different physiological functions reached steady states and to determine possible relationships with metabolic constraints during temperature changes in fish. Qingbo (Spinibarbus sinensis), a common cyprinid in southern China, was first pre-acclimated at either high (25 °C) or low (15 °C) temperature for eight weeks and assumed to be at thermal equilibrium. Then, the temperature was reversed, that is, the temperature was decreased from 25 °C to 15 °C in one group, defined as the cooling group, whereas the temperature of the other group was increased from 15 °C to 25 °C, defined as the warming group. The thermal tolerance, swimming performance and feeding metabolism were measured before temperature reversal as well as 1, 2, 4 and 8 weeks. The growth performance was also measured after the temperature reversal. Typical thermal compensation was suggested by a stronger heat tolerance, faster swimming speed and higher postprandial metabolic response in those acclimated at 25 °C than in those acclimated at 15 °C before temperature reversal. Cold tolerance suggested by the critical minimal temperature (CTmin) of the cooling group reached a thermal steady state within one week, whereas the adjustment of heat tolerance to the temperature increase indicated by the critical maximum temperature (CTmax) was much slower, reaching a steady state two weeks after the temperature reversal. The high flexibility of the standard metabolic rate as well as the postprandial metabolism and relatively lower feeding metabolism demonstrated that there were negligible effects at the aerobic scope for other physiological functions during digestion in qingbo, even during the temperature acclimation period. However, there was a slower adjustment of the swimming performance with the temperature decrease, which parallels the change of metabolic capacity. Furthermore, both the cooling and warming treatments had negative effects on growth performance, with the former mainly occurring through extra energy expenditure, whereas the latter mainly occurred through decreased feeding. It suggested that the slow adjustment of heat tolerance after the temperature increase compared to that of cold tolerance might be a challenge for cyprinids distributed in southern China. Furthermore, the decreased metabolic scope and hence swimming performance after the temperature decrease might have a fitness cost in qingbo and possibly other cyprinids in China.

Metabolic Scope as a Proximate Constraint on Individual Behavioral Variation: Effects on Personality, Plasticity, and Predictability.

Behavioral ecologists have hypothesized that among-individual differences in resting metabolic rate (RMR) may predict consistent individual differences in mean values for costly behaviors or for behaviors that affect energy intake rate. This hypothesis has empirical support and presently attracts considerable attention, but, notably, it does not provide predictions for individual differences in (a) behavioral plasticity or (b) unexplained variation (residual variation from mean individual behavior, here termed predictability). We outline how consideration of aerobic maximum metabolic rate (MMR) and particularly aerobic scope (= MMR - RMR) can be used to simultaneously make predictions about mean and among- and within-individual variation in behavior. We predict that while RMR should be proportional to an individual's mean level of sustained behavioral activity (one aspect of its personality), individuals with greater aerobic scope will also have greater scope to express behavioral plasticity and/or greater unpredictability in behavior (=greater residual variation). As a first step toward testing these predictions, we analyze existing activity data from selectively bred lines of mice that differ in both daily activity and aerobic scope. We find that replicate high-scope mice are more active on average and show greater among-individual variation in activity, greater among-individual variation in plasticity, and greater unpredictability. These data provide some tentative first support for our hypothesis, suggesting that further research on this topic would be valuable.

Metabolic Costs of Feeding Predictively Alter the Spatial Distribution of Individuals in Fish Schools

Group living is ubiquitous among animals [1, 2], but the exact benefits of group living experienced by individual groupmates is related to their spatial location within the overall group [3-5]. Individual variation in behavioral traits and nutritional state is known to affect interactions between individuals and their social group [6, 7], but physiological mechanisms underpinning collective animal behavior remain largely unexplored [8]. Here, we show that while fish at the front of moving groups are most successful at capturing food items, these individuals then show a systematic, post-feeding movement toward the rear of groups. Using observations of fish feeding in groups coupled with estimates of metabolic rate in fish consuming different meal sizes, we demonstrate that the magnitude of this shift in spatial position is directly related to the aerobic metabolic scope remaining after accounting for energetic costs of digestion. While previous work has shown that hungry individuals occupy anterior positions in moving groups [9, 10], our results show that the metabolic demand of food processing reduces the aerobic capacity available for locomotion in individuals that eat most, thus preventing them from maintaining leading positions. This basic trade-off between feeding and locomotor capacity could fundamentally dictate the spatial position of individuals within groups, perhaps obviating the role of individual traits in determining spatial preferences over shorter timescales (e.g., hours to days). This may be a general constraint for individuals within animal collectives, representing a key, yet overlooked, mediator of group functioning that could affect leadership, social information transfer, and group decision making.

Energy allocation and behaviour in the growing broiler chicken

Broiler chickens are increasingly at the forefront of global meat production but the consequences of fast growth and selection for an increase in body mass on bird health are an ongoing concern for industry and consumers. To better understand the implications of selection we evaluated energetics and behaviour over the 6-week hatch-to-slaughter developmental period in a commercial broiler. The effect of posture on resting metabolic rate becomes increasingly significant as broilers grow, as standing became more energetically expensive than sitting. The proportion of overall metabolic rate accounted for by locomotor behaviour decreased over development, corresponding to declining activity levels, mean and peak walking speeds. These data are consistent with the inference that broilers allocate energy to activity within a constrained metabolic budget and that there is a reducing metabolic scope for exercise throughout their development. Comparison with similarly sized galliforms reveals that locomotion is relatively energetically expensive in broilers.

Casual movement speed but not maximal locomotor capacity predicts mate searching success.

Maximal locomotor performance is often used as a proxy for fitness. Maximal speed may be important under high-threat conditions, such as during predator escape. However, animals do not always move at a speed that reflects their maximal physiological capacities when undisturbed. The physiological factors that determine the movement speed chosen by animals, such as minimization of energy use, may be independent from maximal performance. As a result, the casual speed at which individuals move when undisturbed in a given context may better represent an individual's motivation to move. The casual speed may therefore be a better predictor of fitness in natural contexts than maximal performance capacity. We tested the hypothesis that casual movement speed rather than maximal speed predicts fitness in the golden orb-web spider, Nephila plumipes. We measured fitness in two separate contexts, mate-searching success and the positional rank near a female. We show that casual but not maximal locomotor speed predicted both aspects of fitness. Casual speed was linearly related to maximal speed, indicating that casual speed is determined by physiological optimization. Size and metabolic scope were not related to either maximal or chosen speeds, indicating that the supply of ATP does not limit locomotor performance in this species. Overall, our results demonstrate that locomotor performance is related to fitness, but suggest that different types of performance and not necessarily maximal physiological capacities are most relevant for particular ecologically relevant tasks.

In situ swimming behaviors and oxygen consumption rates of juvenile lemon sharks (Negaprion brevirostris)

Knowing how often animals engage in different behaviors and their energetic costs may explain why animals behave the way they do in the wild. This study sought to investigate the relationship between the frequency of various swimming behaviors and their associated energetic costs (oxygen consumption rates) in situ for juvenile lemon sharks (Negaprion brevirostris). Behaviors were identified for captive animals and remotely observed for animals in the wild with accelerometers, and oxygen consumption rates of behaviors were estimated using acceleration-calibrated relationships. Lemon sharks rested infrequently (4.3% of deployment), and the occurrence of active swimming behaviors was inversely related to their respective oxygen consumption rates. Furthermore, time of day and tide state influenced when lemon sharks exhibited active swimming behaviors – but not resting – such that sharks were most active during the day on flooding tides. Oxygen consumption rates also differed across and within different behaviors with time of day and tide state, although mean oxygen consumption rates were highest on daytime flooding tides and uniformly reduced across all other diel and tide combinations. Despite variation in oxygen consumption rates, however, lemon shark activity occurred at 32.3–35.6% of their aerobic metabolic scope. These data do not provide a clear oxygen consumption basis for swimming behaviors observed in situ, which may have been masked by potentially stronger ecological drivers (e.g., predator-prey dynamics). However, these data are relevant to linking behavioral modifications to changes in energy use that shows much promise for addressing conservation issues in fishes.

Metabolic activity throughout early development of dusky kob Argyrosomus japonicus (Sciaenidae)

The physiology of fishes in the early stages of development remains poorly assessed despite the importance of identifying energy bottlenecks in organisms faced with changing environmental conditions. This study describes the metabolic activity of dusky kob Argyrosomus japonicus throughout its early development, from hatchling to settlement stage. Standard, routine and active metabolic rates (SMR, RMR and AMR, respectively) were assessed to determine the species’ metabolic scope and identify how metabolism changes with growth and development. Distinct metabolic changes occurred in association with developmental changes during the early life stages, with flexion-stage larvae showing significantly reduced metabolic scope (approx. 0.30 µmol O2 ind.–1 h–1), representing an energy bottleneck. Based on these findings, it is likely that larvae of A. japonicus are most susceptible to environmental perturbations during flexion. The variability of metabolic rates during the diel cycle was also assessed and revealed that the early-stage larvae showed no preference for daylight, although settlement-stage juveniles were more active during daylight hours (RMR = 12.78 µmol O2 ind.–1 h–1) than at night (RMR = 5.87 µmol O2 ind.–1 h–1). These results suggest that metabolic measurements of the SMR of A. japonicus larvae can be taken at any time of the diel cycle until the settlement phase, when readings should take place at night.

Hyperoxia increases maximum oxygen consumption and aerobic scope of intertidal fish facing acutely high temperatures.

Daytime low tides that lead to high-temperature events in stranded rock pools often co-occur with algae-mediated hyperoxia as a result of strong solar radiation. Recent evidence shows aerobic metabolic scope (MS) can be expanded under hyperoxia in fish but so far this possibility has not been examined in intertidal species despite being an ecologically relevant scenario. Furthermore, it is unknown whether hyperoxia increases the upper thermal tolerance limits of intertidal fish and, therefore, their ability to withstand extreme high-temperature events. Therefore, we measured the metabolic response (mass-specific rate of oxygen consumption, ṀO2 ) to thermal ramping (21-29°C) and the upper thermal tolerance limit (UTL) of two intertidal triplefin fishes (Bellapiscis medius and Forsterygion lapillum) under hyperoxia and normoxia. Hyperoxia increased maximal oxygen consumption (ṀO2,max) and MS of each species at ambient temperature (21°C) but also after thermal ramping to elevated temperatures such as those observed in rock pools (29°C). While hyperoxia did not provide a biologically meaningful increase in upper thermal tolerance of either species (>31°C under all conditions), the observed expansion of MS at 29°C under hyperoxia could potentially benefit the aerobic performance, and hence the growth and feeding potential, etc., of intertidal fish at non-critical temperatures. That hyperoxia does not increase upper thermal tolerance in a meaningful way is cause for concern as climate change is expected to drive more extreme rock pool temperatures in the future and this could present a major challenge for these species.

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

The oxygen consumption rate 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 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.