Metabolic and physiological responses in tissues of the long-lived bivalve Arctica islandica to oxygen deficiency

In Arctica islandica, a long lifespan is associated with low metabolic activity, and with a pronounced tolerance to low environmental oxygen. In order to study metabolic and physiological responses to low oxygen conditions vs. no oxygen in mantle, gill, adductor muscle and hemocytes of the ocean quahog, specimens from the German Bight were maintained for 3.5 days under normoxia (21 kPa=controls), hypoxia (2 kPa) or anoxia (0 kPa). Tissue levels of anaerobic metabolites octopine, lactate and succinate as well as specific activities of octopine dehydrogenase (ODH) and lactate dehydrogenase (LDH) were unaffected by hypoxic incubation, suggesting that the metabolism of A. islandica remains fully aerobic down to environmental oxygen levels of 2 kPa. PO(2)-dependent respiration rates of isolated gills indicated the onset of metabolic rate depression (MRD) below 5 kPa in A. islandica, while anaerobiosis was switched on in bivalve tissues only at anoxia. Tissue-specific levels of glutathione (GSH), a scavenger of reactive oxygen species (ROS), indicate no anticipatory antioxidant response takes place under experimental hypoxia and anoxia exposure. Highest specific ODH activity and a mean ODH/LDH ratio of 95 in the adductor muscle contrasted with maximal specific LDH activity and a mean ODH/LDH ratio of 0.3 in hemocytes. These differences in anaerobic enzyme activity patterns indicate that LDH and ODH play specific roles in different tissues of A. islandica which are likely to economize metabolism during anoxia and reoxygenation.     

Hypoxia induces surfacing behaviour in brown-striped frog (Limnodynastes peronii) larvae

In their natural habitat, brown-striped frog (Limnodynastes peronii) larvae periodically swim rapidly from the bottom of their ponds to the water surface and then immediately dive to the bottom again. This behaviour is presumably related to air-breathing. We examined the behavioural and metabolic responses to aquatic hypoxia in L. pernoii larvae. Gas filled lungs were found in all free-swimming larval stages of L. peronii, but air-breathing occurred infrequently in normoxic water. The frequency of air-breathing at 30°C increased rapidly in hypoxic water when oxygen partial pressure (P_o2) fell below 10 kPa. Only a slight increase was observed at similar oxygen partial pressures at 20°C. The critical oxygen tension at 30°C was about 7kPa, below which, aquatic breathing larvae become metabolic oxygen conformers. In natural habitats where surfacing behaviour was observed, temperatures during summer months frequently exceed 25°C and some ponds become extremely hypoxic (po₂ < 3.0 kPa); therefore air-breathing appears to be the only way in which these larvae can maintain a fully aerobic metabolism.     

Influence of hypoxia and of hypoxemia on the development of cardiac activity in zebrafish larvae

Cardiac activity and anaerobic metabolism were analyzed in zebrafish larvae raised under normoxia (PO(2) = 20 kPa) and under chronic hypoxia (PO(2) = 10 kPa) at three different temperatures (25, 28, and 31 degrees C). Heart rate increased with development and with temperature. Under normoxia, cardiac output increased significantly at high temperature (31 degrees C), but not at 28 or at 25 degrees C. Under chronic hypoxia, however, heart rate as well as cardiac output increased at all temperatures in larvae at about hatching time or shortly thereafter. Cardiac activity of larvae raised for 2 wk after fertilization with a reduced hemoglobin oxygen-carrying capacity in their blood (hypoxemia; due to the presence of CO or of phenylhydrazine in the incubation water) was not different from control animals. Whole body lactate content of these animals did not increase. Thus there was no indication of a stimulated anaerobic energy metabolism. The increase in cardiac activity observed during hypoxia suggests that at about hatching time receptors are present that sense hypoxic conditions, and this information can be used to induce a stimulation of convective oxygen transport to compensate for a reduction in bulk oxygen diffusion in the face of a reduced oxygen gradient between environmental water and tissues. Under normoxia, however, the PO(2) gradient between environmental water and tissues and diffusional oxygen transport assure sufficient oxygen supply even if hemoglobin oxygen transport in the blood is severely impaired. Thus, under normoxic conditions and with a normal metabolic rate of the tissues, convective oxygen transport is not required until approximately 2 wk after fertilization.     

Behaviour during elevated water temperatures: can physiology explain movement of juvenile Atlantic salmon to cool water?

1. Temperature governs most physiological processes in animals. Ectotherms behaviourally thermoregulate by selecting habitats with temperatures regulating their body temperature for optimal physiological functioning. However, ectotherms can experience temperature extremes forcing the organisms to seek temperature refuge. 2. Fish actively avoid potentially lethal temperatures by moving to cool-water sites created by inflowing tributaries and groundwater seeps. Juvenile Atlantic salmon (Salmo salar) of different age classes exhibit different behavioural responses to elevated temperatures (>23 °C). Yearling (1+) and 2-year-old (2+) Atlantic salmon often cease feeding, abandon territorial behaviour and swim continuously in aggregations in cool-water sites; whereas young-of-the-year (0+) fish continue defending territories and foraging. 3. This study determined whether the behavioural shift in older individuals (2+) occurred when basal metabolic rate, driven by increasing water temperature, reached the maximum metabolic rate such that anaerobic pathways were recruited to provide energy to support vital processes. Behaviour (feeding and stress responses), oxygen consumption, muscle lactate and glycogen, and circulating blood lactate and glucose concentrations were measured in wild 0+ and 2+ Atlantic salmon acclimated to water temperatures between 16 and 28 °C. 4. Results indicate that oxygen consumption of the 2+ fish increased with temperature and reached a plateau at 24 °C, a temperature that corresponded to cessation of feeding and a significant increase in muscle and blood lactate levels. By contrast, oxygen consumption in 0+ fish did not reach a plateau, feeding continued and muscle lactate did not increase, even at the highest temperatures tested (28 °C). 5. To conclude, the experiment demonstrated that the 0+ and 2+ fish had different physiological responses to the elevated water temperatures. The results suggest that wild 2+ Atlantic salmon employ behavioural responses (e.g. movement to cool-water sites) at elevated temperatures in an effort to mitigate physiological imbalances associated with an inability to support basal metabolism through aerobic metabolic processes.     

Physiological ecology of aquatic overwintering in ranid frogs

In cold-temperate climates, overwintering aquatic ranid frogs must survive prolonged periods of low temperature, often accompanied by low levels of dissolved oxygen. They must do so with the energy stores acquired prior to the onset of winter. Overwintering mortality is a significant factor in their life history, occasionally reaching 100% due to freezing and/or anoxia. Many species of northern ranid frogs overwinter in the tadpole stage, which increases survival during hypoxic episodes relative to adults, as well as allowing for larger sizes at metamorphosis. At temperatures below 5 degrees C, submerged ranid frogs are capable of acquiring adequate oxygen via cutaneous gas exchange over a wide range of ambient oxygen partial pressures (PO(2)), and possess numerous physiological and behavioural mechanisms that allow them to maintain normal rates of oxygen uptake across the skin at a relatively low PO(2). At levels of oxygen near and below the critical PO(2) that allows for aerobic metabolism, frogs must adopt biochemical mechanisms that act to minimise oxygen utilisation and assist in maintaining an aerobic state to survive overwintering. These mechanisms include alterations in mitochondrial metabolism and affinity, changes in membrane permeability, alterations in water balance, and reduction in cellular electrochemical gradients, all of which lead to an overall reduction in whole-animal metabolism. Winter energetic requirements are fueled by the energy stores in liver, muscle, and fat depots, which are likely to be sufficient when the water is cold and well oxygenated. However, under hypoxic conditions fat stores cannot be utilised efficiently and glycogen stores are used up rapidly due to recruitment of anaerobiosis. Since ranid frogs have minimal tolerance to anoxia, it is untenable to suggest that they spend a significant portion of the winter buried in anoxic mud, but instead utilise a suite of behavioural and physiological mechanisms geared to optimal survival in cold, hypoxic conditions.     

Impact of exposure to bacteria on metabolism in the penaeid shrimp Litopenaeus vannamei

We hypothesized that aggregation of bacteria and hemocytes at the gill, which occurs as part of the shrimp's antibacterial immune defenses, would impair normal respiratory function and thereby disrupt aerobic metabolism. Changes in oxygen uptake and lactate accumulation were determined in Litopenaeus vannamei, the Pacific white shrimp, following injection with either saline (control) or a strain of the gram-negative bacterium Vibrio campbellii that is pathogenic in crustaceans. The rate of oxygen uptake was determined during the first 4 h after injection and after 24 h. Injection of bacteria decreased oxygen uptake by 27% (from 11.0 to 8.2 micromol g-1 h-1) after 4 h, while saline-injected shrimp showed no change. Decreased oxygen uptake persisted 24 h after Vibrio injection. In well-aerated water, resting whole-animal lactic acid levels increased in shrimp injected with bacteria (mean=2.59 micromol lactate g-1+/-0.39 SEM, n=8) compared to saline-injected control shrimp, but this difference did not persist at 24 h. Exposure to hypercapnic hypoxia (PCO2=1.8 kPa, PO2=6.7 kPa) also resulted in significant whole-body lactic acid differences (mean=3.99 and 1.8 micromol g-1 tissue in Vibrio and saline-injected shrimp, respectively). Our results support the hypothesis that the crustacean immune response against invading bacteria impairs normal metabolic function, resulting in depression of oxygen uptake and slightly increased anaerobic metabolism.     

Oxygen-limited thermal tolerance in Antarctic fish investigated by MRI and (31)P-MRS

The hypothesis of an oxygen-limited thermal tolerance was tested in the Antarctic teleost Pachycara brachycephalum. With the use of flow-through respirometry, in vivo (31)P-NMR spectroscopy, and MRI, we studied energy metabolism, intracellular pH (pH(i)), blood flow, and oxygenation between 0 and 13 degrees C under normoxia (PO(2): 20.3 to 21.3 kPa) and hyperoxia (PO(2): 45 kPa). Hyperoxia reduced the metabolic increment and the rise in arterial blood flow observed under normoxia. The normoxic increase of blood flow leveled off beyond 7 degrees C, indicating a cardiovascular capacity limitation. Ventilatory effort displayed an exponential rise in both groups. In the liver, blood oxygenation increased, whereas in white muscle it remained unaltered (normoxia) or declined (hyperoxia). In both groups, the slope of pH(i) changes followed the alpha-stat pattern below 6 degrees C, whereas it decreased above. In conclusion, aerobic scope declines around 6 degrees C under normoxia, marking the pejus temperature. By reducing circulatory costs, hyperoxia improves aerobic scope but is unable to shift the breakpoint in pH regulation or lethal limits. Hyperoxia appears beneficial at sublethal temperatures, but no longer beyond when cellular or molecular functions become disturbed.     

Physiology of common map turtles (Graptemys geographica) hibernating in the Lamoille river, Vermont

Common map turtles (Graptemys geographica) were collected from a natural underwater hibernaculum in Vermont at monthly intervals during the winter of 1997-1998. Blood was sampled by cardiac puncture and analyzed for pH, PCO(2), PO(2), and hematocrit; separated plasma was tested for Na(+), K(+), Cl(-), total [Ca], total [Mg], [lactate], and osmolality (mOsm kg(-1) H(2)O). Control (eupneic; 1 degrees C) values for pH, PO(2), PCO(2), [HCO(3)(-)], and [lactate] were 7.98 +/- 0.03, 47.4 +/- 18.7, 10.1 +/- 0.7 (mm Hg), 36.1 +/- 0.2 (mmol liter(-1)), and 2.1 +/- 0.1 (mmol liter(-1)), respectively. Between November 1997 and March 1998, ice covered the river and the turtles rested on the substratum, fully exposed to the water, and were apneic. Blood PO(2) was maintained at less than 3 mm Hg (range 0.9 +/- 0.2 to 2.1 +/- 0.7 mm Hg), PCO(2) decreased slightly, plasma [lactate] was <5 mmol liter(-1), and plasma [HCO(3)(-)] decreased significantly. In March [lactate] rose to 7.5 +/- 1.5 mmol liter(-l), but there was no acidemia. Map turtles meet most of their metabolic demand for O(2) via aquatic respiration and tolerate prolonged submergence at 1 degrees C with little change in acid-base or ionic status. The adaptive significance of remaining essentially aerobic during winter is to avoid the life-threatening progressive acidosis that results from anaerobic metabolism. J. Exp. Zool. 286:143-148, 2000.     

Gas exchange is essential for bioreactor cultivation of tissue engineered cartilage

Tissue engineered cartilage can be grown in vitro if the necessary physical and biochemical factors are present in the tissue culture environment. Cell metabolism and tissue composition were studied for engineered cartilage cultured for 5 weeks using bovine articular chondrocytes, polymer scaffolds (5 mm diameter x 2 mm thick fibrous discs), and rotating bioreactors. Medium pH and concentrations of oxygen, carbon dioxide, glucose, lactate, ammonia, and glycosoaminoglycan (GAG) were varied by altering the exchange rates of gas and medium in the bioreactors. Cell-polymer constructs were assessed with respect to histomorphology, biochemical composition and metabolic activity. Low oxygen tension ( approximately 40 mmHg) and low pH ( approximately 6.7) were associated with anaerobic cell metabolism (yield of lactate on glucose, YL/G, of 2.2 mol/mol) while higher oxygen tension ( approximately 80 mmHg) and higher pH ( approximately 7.0) were associated with more aerobic cell metabolism (YL/G of 1.65-1.79 mol/mol). Under conditions of infrequent medium replacement (50% once per week), cells utilized more economical pathways such that glucose consumption and lactate production both decreased, cell metabolism remained relatively aerobic (YL/G of 1.67 mol/mol) and the resulting constructs were cartilaginous. More aerobic conditions generally resulted in larger constructs containing higher amounts of cartilaginous tissue components, while anaerobic conditions suppressed chondrogenesis in 3D tissue constructs.     

Acid-base, plasma lactate and glucose changes in the rabbit following administration of Gaboon viper (Bitis gabonica) venom

The acid-base and metabolic effects of Bitis gabonica venom administered intravenously to the anaesthetised rabbit were studied. Doubling doses of venom from 0.125 mg/kg to 1.0 mg/kg were used. Venom caused progressive and significant increases in plasma glucose and plasma lactate levels although oxygen consumption only became significantly lower after the fourth dose. Standard base excess (SBE) became significantly more negative after the third dose of venom and the fall in pH became significant at the same point. The results indicate that venom induces a metabolic acidosis in the rabbit and because the acidosis occurs in the absence of any fall in arterial PO2, it cannot be considered a consequence of impaired pulmonary ventilation. The reduction in oxygen uptake is likely to occur at a cellular level with a shift from aerobic to anaerobic metabolism hence the increase in plasma lactate levels. However, the magnitude of the acidosis is unlikely to be the principal cause of death under experimental conditions.     

Postexercise physiology and repeat performance behaviour of free-swimming smallmouth bass in an experimental raceway

We studied postexercise physiology and behaviour of smallmouth bass (Micropterus dolomieu) that voluntarily ascended experimental raceways of varying length (20-50 m) against water velocities ranging from 8 to 120 cm/s. Our first objective was to link mean swimming speed to metabolism using patterns in postexercise muscle glycogen, muscle lactate, and plasma lactate. Our second objective was to examine several behavioural indices (attempt rate, success rate, and recovery time between an ascent and a subsequent attempt) and determine whether patterns in these data reflected those from the physiological measurements. Postexercise muscle glycogen and plasma lactate data suggest that smallmouth bass powered swimming speeds up to 70-80 cm/s using energy from aerobic processes. However, lactate did not begin to accumulate in the white muscle until speeds in excess of 120-130 cm/s were reached. The behavioural parameters measured did not indicate the presence of a physiological threshold at 70-80 cm/s; however, patterns in all factors changed appreciably when fish maintained speeds in excess of 120-130 cm/s. Therefore, it is clear that behaviour and physiology are tightly linked in this species and that maximum aerobic swimming capacity may not limit performance (or re-performance) during short-duration swims.     

Aerobic performance: role of oxygen delivery and utilization, glycolytic flux

Oxygen delivery to muscle, its consumption and glycolytic flux, all of each affect and restrict aerobic performance, are discussed. Energy supply of intensive exercise till exhaustion lasting 3 to 4 min is provided mainly by oxidative metabolism, simultaneously glycolytic flux may be increased considerably. Other conditions being equal, capacity of oxygen delivery determines oxygen partial pressure in myoplasm of exercising/contracting muscle. With PO2 in myoplasm increasing from 0 to 1-2 mm Hg oxygen consumption (VO2) in mitochondria enhances dramatically, with further increase of PO2 its rise slows down. At the ascending part of VO2-PO2 relationship for mitochondria the increase of VO2 is noticeably restricted by oxygen delivery to contracting muscle. When PO2 approaches plateau of the VO2-PO2 relationship, an increase of VO2 is restricted by mitochondria capacity to accumulate oxygen and augmented oxygen delivery will not lead to a significant increase of muscle VO2. On the other hand considerable accumulation of glycolytic metabolites in contracting muscle causes a decrease of contractility which in its turn may restrict aerobic performance. Noteworthy no strict relationship between glycolytic flux and PO2 in myoplasm exists. That is why correct evaluation of factors limiting aerobic performance presupposes simultaneous evaluation of both glycolytic flux and oxygen consumption in muscle which in its turn depends on oxygen delivery to mitochondria and its utilization.     

Mitochondrial dysfunction in chronic ischemia and peripheral vascular disease

In peripheral vascular disease, impaired muscle energy metabolism is assumed to be due mainly to defective vascular O2 supply, the resulting cellular hypoxia inhibiting oxidative ATP synthesis. Older work suggested a compensatory increase in muscle aerobic enzymes, but more recent studies suggest a relative decrease in some mitochondrial components and an accumulation of damage in mitochondrial DNA, perhaps due to reactive oxygen species. However, to establish whether in vivo muscle mitochondria suffer from anything other than a low concentration of O2 will require more knowledge of the mitochondrial behaviour at low PO2, and the actual cell PO2 during exercise.     

Profiles of enzyme activity in larvae of two cyprinid species with contrasting life styles (Cyprinidae; Teleostei)

Growth and the development of gills, muscle fibres and 10 enzymes serving different metabolic functions were studied in larvae of Rutilus rutilus (L.) and Chalcalburnus chalcoides (Agassiz, 1832). R. rutilus starts swimming and feeding one to three days after hatching, whereas in C. chalcoides this process is delayed by about 10 days. This difference in behaviour is reflected in the time-course of growth, the differentiation of the red muscle fibres and the activity of the enzymes of aerobic energy metabolism. On the other hand, the activity of the enzymes of anaerobic energy metabolism increases steadily throughout the period of observation (up to 60 days post-hatch), this trend being more pronounced in C. chalcoides than in R. rutilus . A weight-independent and a weight-dependent phase of development can be distinguished in the enzymes of aerobic energy metabolism. It is suggested that, in accord with previous findings, the early phase of locomotor activity of cyprinid larvae is fuelled mainly by aerobic processes, and that the central muscle mass of the larvae is more aerobic than the white muscle fibres of the adults. The delayed development of aerobic enzyme activity in C. chalcoides is compensated by the accelerated development of anaerobic enzyme activity, particularly of creatine kinase and lactate dehydrogenase. This difference between the two species studied suggests differences in the metabolic basis of burst activity.     

Contributions to elevated metabolism during recovery: dissecting the excess postexercise oxygen consumption (EPOC) in the desert iguana (Dipsosaurus dorsalis)

The excess postexercise oxygen consumption (EPOC), a measure of recovery costs, is known to be large in ectothermic vertebrates such as the desert iguana (Dipsosaurus dorsalis), especially after vigorous activity. To analyze the cause of these large recovery costs in a terrestrial ectotherm, Dipsosaurus were run for 15 s at maximal-intensity (distance 35.0+/-1.9 m; 2.33+/-0.13 m s(-1)) while O(2) uptake was monitored via open-flow respirometry. Muscle metabolites (adenylates, phosphocreatine, and lactate) were measured at rest and after 0, 3, 10, and 60 min of recovery. Cardiac and ventilatory activity during rest and recovery were measured, as were whole-body lactate and blood lactate, which were used to estimate total muscle activity. This vigorous activity was supported primarily by glycolysis (65%) and phosphocreatine hydrolysis (29%), with only a small contribution from aerobic metabolism (2.5%). Aerobic recovery lasted 43.8+/-4.6 min, and EPOC measured 0.166+/-0.025 mL O(2) g(-1). This was a large proportion (98%) of the total suprabasal metabolic cost of the activity to the animal. The various contributions to EPOC after this short but vigorous activity were quantified, and a majority of EPOC was accounted for. The two primary causes of EPOC were phosphocreatine repletion (32%-50%) and lactate glycogenesis (30%-47%). Four other components played smaller roles: ATP repletion (8%-13%), elevated ventilatory activity (2%), elevated cardiac activity (2%), and oxygen store resaturation (1%).     

Respiratory physiology of the Oniscidea: aerobic capacity and the significance of pleopodal lungs

The radiation of the terrestrial isopods (sub-order Oniscidea) has been accompanied by evolution of pleopodal lungs in the sections Tylida and Crinocheta. To understand the significance of such lungs for aerobic respiration, comparative studies were conducted using 6 species. Ligia occidentalis, lacking lungs, behaved as a metabolic conformer in reduced PO(2), and showed decreased V(.-)O(2) in low humidity and following dehydration. In species possessing lungs, metabolism was insensitive to dehydration. However, lung development did not show a clear relationship to metabolic regulation: Porcellio dilatatus was a metabolic conformer while Tylos punctatus and Armadillidium vulgare were efficient regulators. The metabolic conformers did not accumulate lactate during moderate hypoxia (10% O(2)), indicating that reduced V(.-)O(2) is not compensated with anaerobic glycolysis. In contrast, Alloniscus perconvexus, a littoral species with limited metabolic regulation, showed the largest lactate accumulation during hypoxia and also possessed the highest tissue LDH activity. It is hypothesized that these are adaptations to periodic hypoxia in sand burrows and the high metabolic cost of burrowing. Differences in lactate accumulation during immersion were curious, with the largest increases occurring in L. occidentalis and A. perconvexus that tolerate prolonged immersion in seawater. Possible functions of this lactate accumulation may include modulation of hemocyanin oxygen affinity.     

Biochemical adaptations to training: implications for resisting muscle fatigue

Skeletal muscle activity is invariably associated with a decline in force-generating capacity (fatigue). The build-up of metabolic by-products such as intracellular H+ and inorganic phosphate (Pi) has been shown to be one of the potential mechanisms of muscle fatigue. The use of phosphorus magnetic resonance spectroscopy is a repeatable and useful tool to study the effect of pH and Pi on force development. When maximal exercise is preceded by submaximal exercise to reduce the starting muscle pH and increase Pi, the degree of muscle fatigue correlates more strongly with H2PO4- than pH or Pi alone. However, other studies in humans have found that H2PO4- does not always correlate well with fatigue. The use of ramp exercise protocols allow repeatable and sensitive measurement of changes in muscle metabolism in response to endurance training. Chronic electrical stimulation in dogs and endurance training in humans results in reduced pH and Pi changes at the same exercise intensities. This means that the effect of pH and Pi in depressing force development is reduced, which could partially explain the increased fatigue resistance seen following endurance training.     

不同游泳速度条件下瓦氏黄颡幼鱼的有氧和无氧代谢反应

在(25±1)℃的条件下,测定瓦氏黄颡(Pelteobagrus vachelli Richardson)幼鱼体重(4.34±0.13)g的临界游泳速度(Ucrit),然后分别以临界游泳速度的不同百分比(20、40、60、80、100%Ucrit)将实验鱼分为5个速度处理组,另外设置静止对照组和高速力竭对照组。处理组实验鱼在不同游泳速度下分别游泳20min,在此过程中测定并计算运动代谢率(Activity metabolic rate,AMR),随后测定肌肉、血液和肝脏中的乳酸、糖原和葡萄糖含量。结果显示:实验鱼的绝对临界游泳速度为(48.28±1.02)cm/s,相对临界游泳速度为(6.78±0.16)BL/s;随着游泳速度的提高AMR显著增加(Pcrit时肌乳酸和血乳酸含量显著高于80%Ucrit的水平(P0.05);100%Ucrit时肝糖原含量显著低于40%Ucrit的水平(P0.05)。经计算瓦氏黄颡幼鱼到达临界游泳速度时的无氧代谢功率比例仅为11.0%,表明其游泳运动主要以有氧代谢供能;实验鱼的无氧代谢大约在80%Ucrit才开始启动,与其他鱼类比较启动时间较晚,说明其游泳运动对无氧代谢的依赖程度较低。研究提示瓦氏黄颡幼鱼是一种有氧运动能力较强的鱼类,这一能量代谢特征可能与提高其生存适合度有关。       

Effects of size, sex, temperature and condition on activity metabolism and defence behaviour of the viperine snake, Natrix maura

The activity metabolism (aerobic and anaerobic), performance (burst speed and endurance) and defence behaviour (static or active) of the snake Natrix maura were investigated in relation to size, sex, temperature and fasting. Conditions which reduced performance (low temperature, fasting) promoted the use of static defensive behaviour. Aerobic scope for activity decreased with increasing size, but this was compensated for by increased capacity for anaerobic metabolism. Burst speed (as lengths time^-1) was slightly lower in large snakes; endurance was much lower in small snakes. Increased use of static defence by small snakes is related to their predators, which are likely to take occasional snakes in a diet of worms; a balled, still snake may not provide a stimulus for feeding. Large snakes have predators which feed on vertebrates and may recognize them as food in any position, and so they are better off trying to escape.
Aerobic scope was not maximal at the mean selected body temperature (25 °C), but increased right up to near lethal temperatures (> 35 °C). Anaerobic metabolism (lactate production) was less temperature-sensitive, and accounted for about 80 and 50% of the energy produced during 30 and 5 min of maximal activity, respectively. Resting and active oxygen consumption were weight-dependent, VO₂∝ W^0·75, the same exponent as that of interspecific comparisons. This exponent was independent of temperature and acclimation state. Acclimation to a variable or constant temperature regime had no effect on maximal oxygen consumption, but there was a significant effect on resting metabolic rate, possibly attributable to energy conservation when inactive. There were no differences in activity metabolism, performance or defence behaviour between similar-sized snakes of different sexes.