Convergence in organ size but not energy metabolism enzyme activities among wild Lake Whitefish (Coregonus clupeaformis) species pairs.

The repeated evolution of similar phenotypes by similar mechanisms can be indicative of local adaptation, constraints or biases in the evolutionary process. Little is known about the incidence of physiological convergence in natural populations, so here we test whether energy metabolism in 'dwarf' and 'normal' Lake Whitefish evolves by similar mechanisms. Prior genomic and transcriptomic studies have found that divergence in energy metabolism is key to local adaptation in whitefish species pairs, but that distinct genetic and transcriptomic changes often underlie phenotypic evolution among lakes. Here, we predicted that traits at higher levels of biological organization, including the activities of energy metabolism enzymes (the product of enzyme concentration and turnover rate) and the relative proportions of metabolically active tissues (heart, liver, skeletal muscle), would show greater convergence than genetic and transcriptomic variation. We compared four whitefish species pairs and found convergence in organ size whereby all dwarf whitefish populations have a higher proportion of red skeletal muscle, three have relatively larger livers and two have relatively larger ventricles than normal fish. On the other hand, hepatic and muscle enzyme activities showed little convergence and were largely dependent on lake of origin. Only the most genetically divergent species pair (Cliff Lake) displayed white muscle enzyme activities matching results from laboratory-reared normal and dwarf whitefish. Overall, these data show convergence in the evolution of organ size, but not in the activities of candidate enzymes of energy metabolism, which may have evolved mainly as a consequence of demographic or ecological differences among lakes.

Platelets release mitochondria serving as substrate for bactericidal group IIA-secreted phospholipase A2 to promote inflammation.

Mitochondrial DNA (mtDNA) is a highly potent inflammatory trigger and is reportedly found outside the cells in blood in various pathologies. Platelets are abundant in blood where they promote hemostasis. Although lacking a nucleus, platelets contain functional mitochondria. On activation, platelets produce extracellular vesicles known as microparticles. We hypothesized that activated platelets could also release their mitochondria. We show that activated platelets release respiratory-competent mitochondria, both within membrane-encapsulated microparticles and as free organelles. Extracellular mitochondria are found in platelet concentrates used for transfusion and are present at higher levels in those that induced acute reactions (febrile nonhemolytic reactions, skin manifestations, and cardiovascular events) in transfused patients. We establish that the mitochondrion is an endogenous substrate of secreted phospholipase A2 IIA (sPLA2-IIA), a phospholipase otherwise specific for bacteria, likely reflecting the ancestral proteobacteria origin of mitochondria. The hydrolysis of the mitochondrial membrane by sPLA2-IIA yields inflammatory mediators (ie, lysophospholipids, fatty acids, and mtDNA) that promote leukocyte activation. Two-photon microscopy in live transfused animals revealed that extracellular mitochondria interact with neutrophils in vivo, triggering neutrophil adhesion to the endothelial wall. Our findings identify extracellular mitochondria, produced by platelets, at the midpoint of a potent mechanism leading to inflammatory responses.

Swimming away or clamming up: the use of phasic and tonic adductor muscles during escape responses varies with shell morphology in scallops.

The simple locomotor system of scallops facilitates the study of muscle use during locomotion. We compared five species of scallops with different shell morphologies to see whether shell morphology and muscle use change in parallel or whether muscle use can compensate for morphological constraints. Force recordings during escape responses revealed that the use of tonic and phasic contractions varied markedly among species. The active species, Amusium balloti, Placopecten magellanicus and Pecten fumatus, made more phasic contractions than the more sedentary species, Mimachlamys asperrima and Crassadoma gigantea. Tonic contractions varied considerably among these species, with the two more sedentary species often starting their response to the predator with a tonic contraction and the more active species using shorter tonic contractions between series of phasic contractions. Placopecten magellanicus made extensive use of short tonic contractions. Pecten fumatus mounted an intense series of phasic contractions at the start of its response, perhaps to overcome the constraints of its unfavourable shell morphology. Valve closure by the more sedentary species suggests that their shell morphology protects them against predation, whereas swimming by the more active species relies upon intense phasic contractions together with favourable shell characteristics.

Antioxidant defenses of flame scallop Ctenoides scaber (Born, 1778) exposed to the water-soluble fraction of used vehicle crankcase oils.

Used vehicle crankcase oils are a source of contamination in Caribbean marine environments and may alter the oxidative balance of organism that inhabiting coastal ecosystems. This paper aims to evaluate effects of a water-soluble fraction of used vehicle crankcase oils (WSF-UVCO) on the antioxidant responses of the flame scallop Ctenoides scaber. The organisms were exposed to ascending sublethal concentrations 0, 0.001, 0.01 and 0.1 % of WSF-UVCO in a static system of aquaria during one week. Subsequently activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST) as well as concentrations of reduced glutathione (GSH) and thiobarbituric acid reactive substances (TBARS) were determined in the digestive gland, adductor muscle and gills. SOD, CAT, GST and TBARS increased in digestive gland of organisms exposed to WSF-UVCO at medium and highest concentrations, with a concomitant decrease in GPX and GR activities. In adductor muscle CAT decreased, but GR rose with exposure to 0.01 and 0.1 % WSF-UVCO; in gills, GST rose through all WSF-UVCO concentrations, and SOD, CAT and GR increased only at 0.1 %. The fluctuations in antioxidant enzymes and GST activities point out possible adjustments to control ROS production and detoxification of xenobiotics. These biochemical responses may guarantee the oxidative balance in flame scallop during short term exposure to low concentrations of WSF-UVCO. C. scaber appears suitable as an experimental organism for evaluating biological risks of sublethal exposure to hazardous xenobiotics in tropical marine environments.

Effect of day length on oxidative capacities of mitochondria from red muscle of rainbow trout (Oncorhynchus mykiss).

In nature, seasons may be more reliably announced by changes in photoperiod than in temperature. To evaluate the role of day length in setting oxidative capacities of trout muscle mitochondria, we acclimated trout to summer (15 degrees C, 16L:8D), winter (5 degrees C, 8L:16D) and mixed conditions (15 degrees C, 8L:16D). Maximal oxidative capacities of isolated mitochondria at 5 and 15 degrees C were higher in mixed than summer conditions and higher again in winter conditions. At 5 degrees C, state 4 rates changed little with acclimation state whereas at 15 degrees C state 4 rates were lower in summer than in mixed or winter conditions. Using concentrations of the adenylate nucleotide translocase as the denominator for these rates gave much the same conclusions. By using inhibitors to block flux at specific points in the electron transport chain, we found that flux through Complexes II-IV was lowest in summer acclimated trout, increased upon acclimation to mixed and to winter conditions. Flux through complex IV was similar in trout acclimated to summer and mixed conditions, but increased significantly with acclimation to winter conditions. Flux through complex IV was 1.5 fold higher than state 3 rates for summer-acclimated trout but was similar to state 3 rates in trout acclimated to mixed or winter conditions. Our results indicate that a reduction in day length initiates increases in mitochondrial oxidative capacity typically associated with cold acclimation and that acclimation to both cold temperatures and short day lengths enhanced these changes. The overall similarity of the responses of state 3, of flux through complexes II-IV and of flux through complex IV suggests that a generalised mechanism such as changes in the phospholipid composition of the inner mitochondrial membrane may coordinate these changes.

Altered fibre types in gastrocnemius muscle of high wheel-running selected mice with mini-muscle phenotypes.

Selective breeding of mice for high voluntary wheel running has favoured characteristics that facilitate sustained, aerobically supported activity, including a "mini-muscle" phenotype with markedly reduced hind limb muscle mass, increased mass-specific activities of oxidative enzymes, decreased % myosin heavy chain IIb, and, in the medial gastrocnemius, reduced twitch speed, reduced mass-specific isotonic power, and increased fatigue resistance. To evaluate whether selection has altered fibre type expression in mice with either "mini" or normal muscle phenotypes, we examined fibre types of red and white gastrocnemius. In both the medial and lateral gastrocnemius, the mini-phenotype increased activities of oxidative enzymes and decreased activities of glycolytic enzymes. In red muscle samples, the mini-phenotype markedly changed fibre types, with the % type I and type IIA fibres and the surface area of type IIA fibres increasing; in addition, mice from selected lines in general had an increased % type IIA fibres and larger type I fibres as compared with mice from control lines. White muscle samples from mini-mice showed dramatic structural alterations, with an atypical distribution of extremely small, unidentifiable fibres surrounded by larger, more oxidative fibres than normally present in white muscle. The increased proportion of oxidative fibres and these atypical small fibres together may explain the reduced mass and increased mitochondrial enzyme activities in mini-muscles. These and previous results demonstrate that extension of selective breeding beyond the time when the response of the selected trait (i.e. distance run) has levelled off can still modify the mechanistic underpinnings of this behaviour.

Genome-wide survey of the gene expression response to saprolegniasis in Atlantic salmon.

Pathogenic saprolegniaceae species are among the major disease-causing agents in farmed salmonids and in freshwater fish in general. Recent studies have used high-throughput cDNA-based methods to identify new potential actors of fish defence systems against various bacteria and viruses. However, the response of fish to fungal or fungus-like pathogens is still poorly documented. Here, we used a 16,006-gene salmonid cDNA microarray to identify genes which transcription levels are modified in juvenile Atlantic salmon (Salmo salar) affected with saprolegniasis compared to healthy fish from the same families. Our results confirmed the importance of non-specific immunity in the response of fish to saprolegniaceae infections and identified both similarities and differences in their genome-wide transcriptional response to oomycetes compared with their responses to bacterial or viral infections. Moreover, several clones with no known homologues were shown to be over-transcribed in infected fish. These may represent as yet unidentified immune-relevant genes in fish.

Do differences in the activities of carbohydrate metabolism enzymes between Lake Whitefish ecotypes match predictions from transcriptomic studies?

Transcriptomic studies are facilitating the search for the molecular bases of adaptation in natural populations, but the impact of these differences in mRNA content on animal physiology are often unknown. One way to determine if molecular changes have the potential to influence animal physiology and performance is to test for correlated changes at higher levels of biological organization, including enzyme activity. Here, we measure the activities of carbohydrate metabolism enzymes to test if previously documented genetic and transcriptomic variation between 'dwarf' and 'normal' Lake Whitefish ecotypes are associated with corresponding changes in enzyme activity (measured as maximal rate, Vmax) in liver and skeletal muscle. We use laboratory-reared fish from the same populations as prior transcriptomic studies and find that white muscle mRNA content is a good predictor of glycolytic and glycogen metabolism enzyme activity, and dwarf whitefish have evolved higher activities than normal whitefish. However, the differences in hepatic mRNA content found between ecotypes in prior studies are not associated with comparable changes in enzyme activity. For example, dwarf whitefish have lower enzyme activities, but higher transcript abundances for two glycolytic enzymes compared to normal whitefish. Overall, we find that transcriptomic studies successfully highlight evolutionary variation in enzyme activities, but not always in the direction predicted, indicating that a variety of tissue-specific regulatory mechanisms contributed to the evolution of energy metabolism in Lake Whitefish.

Morphometry, ultrastructure, myosin isoforms, and metabolic capacities of the "mini muscles" favoured by selection for high activity in house mice.

Prolonged selective breeding of mice (Mus musculus) for high levels of voluntary wheel running has favoured an unusual phenotype ("mini muscles"), apparently caused by a single Mendelian recessive allele, in which most hind-limb muscles are markedly reduced in mass, but have increased mass-specific activities of mitochondrial enzymes. We examined whether these changes reflect changes in fibre size, number or ultrastructure in normal and "mini-muscle" mice within the two (of four) selectively bred lines (lab designations L3 and L6) that exhibit the phenotype at generations 26 and 27. In both lines, the gastrocnemius and plantaris muscles are smaller in mass (by >50% and 20%, respectively) in affected individuals. The mass-specific activities of mitochondrial enzymes in the gastrocnemius and plantaris muscles were increased in the mini phenotype in both lines, with stronger effects in the gastrocnemius muscle. In the gastrocnemius, the % myosin heavy chain (MHC) IIb was reduced by 50% in L3 and by 30% in L6, whereas the % MHC IIa and I were higher, particularly in L3. Fibre number in the plantaris muscle did not significantly differ between mini and normal muscles, although muscle mass was a significant positive correlate of fibre number. Small fibres were more abundant in mini than normal muscles in L3. Mitochondrial volume density was significantly higher in mini than normal muscle fibres in L3, but not in L6. Microscopy revealed a surprising attribute of the mini muscles: an abundance of small, minimally differentiated, myofibril-containing cells positioned in a disorderly fashion, particularly in the surface layer. We hypothesise that these unusual cells may be satellite cells or type IIb fibres that did not complete their differentiation. Together, these observations suggest that mice with the mini phenotype have reduced numbers of type IIb fibres in many of their hind-limb muscles, leading to a decrease in mass and an increase in mass-specific aerobic capacity in muscles that typically have a high proportion of type IIb fibres. Moreover, the several statistically significant interactions between muscle phenotype and line indicate that the effect of the underlying allele is altered by genetic background.

Swimming performance, metabolic rates, and their correlates in the Iceland scallop Chlamys islandica.

The dramatic escape response of some scallops is modified by reproductive investment and by acclimation temperature. Despite considerable knowledge of the physiology of the escape response, functional links between escape response performance, organismal rates of oxygen uptake, and tissue metabolic capacities are little known. We measured oxygen consumption rates (standard, maximal, and aerobic scope), escape behavior (initial and repeat performance), tissue mass, condition index, protein content, and tissue metabolic capacities in the Iceland scallop Chlamys islandica to examine links between these parameters. Postexercise oxygen consumption rates were positively linked to contraction rate (repeat test) and to pyruvate kinase activity in the adductor muscle but negatively linked to digestive gland wet mass. Swimming behavior was mainly related to activity of glycolytic enzymes, and enzymatic activities were related to anatomic parameters. Scallop behavior and physiology change with size, both within our samples and on a larger scale. Small scallops showed more intense swimming activity and had higher arginine kinase activities but lower glycolytic enzyme activities in their adductor muscle than larger scallops. This corresponds to the ontogenetic change in susceptibility to predation and in habitat use observed in C. islandica.

Changes in the condition factor have an impact on metabolic rate and swimming performance relationships in Atlantic cod (Gadus morhua L.).

In the field, Atlantic cod face seasonal changes in food availability that in turn lead to changes in condition. To examine the physiological consequences of these changes in condition, we measured routine metabolic rate (RMR) to estimate standard metabolic rate (SMR), active metabolic rate (AMR), aerobic scope, critical swimming speed (Ucrit), cost of transport, sprint performance, time to exhaustion, and postexhaustion metabolic rate (EMR) for 24 Atlantic cod from the Gulf of St. Lawrence. Cod were measured at their initial condition (condition factor of 0.676+/-0.076) and after 9 wk of feeding (condition factor of 0.923+/-0.096). These levels of condition are representative of wild cod in the Gulf of St. Lawrence during the spring and during the fall-early winter, respectively. The improved condition did not change mass-specific SMR. However, mass-specific AMR, aerobic scope, and EMR decreased with the improvement in condition. The various measures of swimming performance were affected differently. Ucrit increased and cost of transport at 1.3 and 1.5 body lengths s(-1) decreased with improved condition, but the cost of transport at 0.3, 0.9, 1.1, 1.7, and 1.9 body lengths s(-1), sprint performance, and time to exhaustion did not change. Hierarchies for the speed at first burst-coast, the proportion of Ucrit supported by burst-coasts, and time to exhaustion were maintained with the improvement in condition. The relationships between metabolic rates and swimming performance differed with condition level, with stronger correlations apparent in the cod at their initial condition. Given the low condition of wild cod stocks, these responses indicate that reduced performance, due to both maintenance of metabolic expenditures and modified swimming capacities, may impair survival under conditions of reduced food availability.

Coadaptation: a unifying principle in evolutionary thermal biology.

Over the last 50 yr, thermal biology has shifted from a largely physiological science to a more integrated science of behavior, physiology, ecology, and evolution. Today, the mechanisms that underlie responses to environmental temperature are being scrutinized at levels ranging from genes to organisms. From these investigations, a theory of thermal adaptation has emerged that describes the evolution of thermoregulation, thermal sensitivity, and thermal acclimation. We review and integrate current models to form a conceptual model of coadaptation. We argue that major advances will require a quantitative theory of coadaptation that predicts which strategies should evolve in specific thermal environments. Simply combining current models, however, is insufficient to understand the responses of organisms to thermal heterogeneity; a theory of coadaptation must also consider the biotic interactions that influence the net benefits of behavioral and physiological strategies. Such a theory will be challenging to develop because each organism's perception of and response to thermal heterogeneity depends on its size, mobility, and life span. Despite the challenges facing thermal biologists, we have never been more pressed to explain the diversity of strategies that organisms use to cope with thermal heterogeneity and to predict the consequences of thermal change for the diversity of communities.

Why are some mitochondria more powerful than others: insights from comparisons of muscle mitochondria from three terrestrial vertebrates.

We studied the molecular composition of muscle mitochondria to evaluate whether the contents of cytochromes or adenine nucleotide translocase (ANT) or phospholipid acyl compositions reflect differences in mitochondrial oxidative capacities. We isolated mitochondria from three vertebrates of similar size and preferred temperature, the rat (Rattus norvegicus), the cane toad (Bufo marinus) and the bearded dragon lizard (Pogona vitticeps). Mitochondrial oxidative capacities were higher in rats and cane toads than in bearded dragon, whether rates were expressed relative to protein, cytochromes or ANT. Inter-specific differences were least pronounced when rates were expressed relative to cytochrome A, a component of cytochrome C oxidase (CCO), or ANT. In mitochondria from rat and cane toad, cytochrome A was more abundant than C followed by B and then C(1), while in bearded dragon mitochondria, the cytochromes were present in roughly equal levels. Analysis of correlations between mitochondrial oxidative capacities and macromolecular components revealed that cytochrome A explained at least half of the intra- and inter-specific variability in substrate oxidation rates. ANT levels were an excellent correlate of state 3 rates while phospholipid contents were correlated with state 4 rates. As the % poly-unsaturation and the % 20:4n-6 in mitochondrial phospholipids were equivalent in toads and rats, and exceeded the levels in lizards, they may contribute to the inter-specific differences in oxidative capacities. We suggest that the numbers of CCO and ANT together with the poly-unsaturation of phospholipids explain the higher oxidative capacities in muscle mitochondria from rats and cane toads.

Stickleback fights: why do winners win? Influence of metabolic and morphometric parameters.

Pairs of reproductively mature male three-spined stickleback (Gasterosteus aculeatus) were introduced into unfamiliar aquaria and observed until one male became dominant. Skin carotenoid content, morphometric indexes, and metabolic capacities of the axial and pectoral muscles were examined to establish whether morphological or physiological parameters differentiated winners and losers. Stickleback that initiated fights typically won. Quick initiation led to quick victory. Overall, winners and losers differed in few morphological or metabolic characteristics, but these properties and the differences between these attributes for losers and winners of specific fights were linked with initiation time and fight duration. Morphometric indexes of losers were the primary determinants of initiation time and fight duration, whereas for winners muscle metabolic capacities were linked to these fight characteristics. The greater the hepatosomatic index (HSI) of losers, the longer the fight initiation times. Similarly, losers with high HSI and carotenoid levels resisted defeat longer. In winners, initiation time decreased as axial muscle phosphofructokinase levels increased and citrate synthase levels decreased, whereas the metabolic capacities of the pectoral muscle were linked with time to achieve victory. When losers had greater HSI values than the winners of a specific fight, fight initiation was delayed and fights lasted longer. When losers had higher carotenoid levels than winners, fights also lasted longer. On the other hand, when losers had more visceral fat (fat body mass over somatic mass) than winners, both initiation time and combat duration were reduced. These results suggest that male stickleback assess their physiological status and that of their opponents, in particular the HSI, and adjust their combat strategies accordingly.

Adaptation and acclimation of aerobic exercise physiology in Lake Whitefish ecotypes (Coregonus clupeaformis).

The physiological mechanisms underlying local adaptation in natural populations of animals, and whether the same mechanisms contribute to adaptation and acclimation, are largely unknown. Therefore, we tested for evolutionary divergence in aerobic exercise physiology in laboratory bred, size-matched crosses of ancestral, benthic, normal Lake Whitefish (Coregonus clupeaformis) and derived, limnetic, more actively swimming "dwarf" ecotypes. We acclimated fish to constant swimming (emulating limnetic foraging) and control conditions (emulating normal activity levels) to simultaneously study phenotypic plasticity. We found extensive divergence between ecotypes: dwarf fish generally had constitutively higher values of traits related to oxygen transport (ventricle size) and use by skeletal muscle (percent oxidative muscle, mitochondrial content), and also evolved differential plasticity of mitochondrial function (Complex I activity and flux through Complexes I-IV and IV). The effects of swim training were less pronounced than differences among ecotypes and the traits which had a significant training effect (ventricle protein content, ventricle malate dehydrogenase activity, and muscle Complex V activity) did not differ among ecotypes. Only one trait, ventricle mass, varied in a similar manner with acclimation and adaptation and followed a pattern consistent with genetic accommodation. Overall, the physiological and biochemical mechanisms underlying acclimation and adaptation to swimming activity in Lake Whitefish differ.

Dietary fatty acid composition and the homeostatic regulation of mitochondrial phospholipid classes in red muscle of rainbow trout (Oncorhynchus mykiss).

Although dietary lipid quality markedly affects fatty acid (FA) composition of mitochondrial membranes from rainbow trout red muscle (Oncorhynchus mykiss), mitochondrial processes are relatively unchanged. As certain classes of phospholipids interact more intimately with membrane proteins than others, we examined whether specific phospholipid classes from these muscle mitochondria were more affected by dietary FA composition than others. To test this hypothesis, we fed trout with two diets differing only in their FA composition: Diet 1 had higher levels of 18:1n-9 and 18:2n-6 than Diet 2, while 22:6n-3 and 22:5n-6 were virtually absent from Diet 1 and high in Diet 2. After 5 months, trout fed Diet 2 had higher proportions of phosphatidylcholine (PC) and less phosphatidylethanolamine (PE) in mitochondrial membranes than those fed Diet 1. The FA composition of PC, PE and cardiolipin (CL) showed clear evidence of regulated incorporation of dietary FA. For trout fed Diet 2, 22:6n-3 was the most abundant FA in PC, PE and CL. The n-6 FA were consistently higher in all phospholipid classes of trout fed Diet 1, with shorter n-6 FA being favoured in CL than in PC and PE. Despite these marked changes in individual FA levels with diet, general characteristics such as total polyunsaturated FA, total monounsaturated FA and total saturated FA were conserved in PE and CL, confirming differential regulation of the FA composition of PC, PE and CL. The regulated changes of phospholipid classes presumably maintain critical membrane characteristics despite varying nutritional quality. We postulate that these changes aim to protect mitochondrial function.

Locomotor performance and muscle metabolic capacities: impact of temperature and energetic status.

In aquatic ectotherms, muscle metabolic capacities are strongly influenced by exogenous factors, principally temperature and food availability. Seasonal changes in temperature lead many organisms to modify their metabolic machinery so as to maintain capacity even in "slower" cold habitats. Modifications of mitochondrial capacities are central in this response. The increases in protein-specific oxidative capacities of mitochondria during cold acclimation of temperate fishes do not occur during the evolutionary adaptation to cold in Antarctic species. Instead, Antarctic fishes tend to increase the proportion of fibre volume devoted to mitochondria, perhaps to facilitate intracellular distribution of oxygen and metabolites. Variation in energetic status can drastically modify muscle metabolic status, with glycolytic muscle changing more than oxidative muscle. This in turn impacts swimming performance. A decrease in the condition of cod leads endurance at speeds above Ucrit to drop by 70%. Sprint swimming is less affected, perhaps as it does not exhaust glycolytic muscle. We used interindividual variation in muscle metabolic capacities to identify correlates of swimming performance in stickleback and cod. Activities of cytochrome c oxidase in glycolytic muscle are a correlate of sprint swimming in stickleback (Gasterosteus aculeatus) and cod (Gadus morhua), whereas lactate dehydrogenase activities in glycolytic muscle are a correlate of cod endurance swimming. In scallops, gonadal maturation leads to virtually complete mobilisation of glycogen from muscle. This does not reduce the capacity of the scallops, Chlamys islandica and Euvola ziczac, to mount escape responses, but significantly slows their recuperation from exhaustive exercise. Muscle metabolic capacities fall in parallel with glycogen mobilisation. In the compromise between muscles' dual roles as a motor and a macromolecular reserve, a significant loss in locomotory ability occurs during gametogenesis and spawning. Reproductive fitness takes the upper hand over maintenance of performance.

Scallops show that muscle metabolic capacities reflect locomotor style and morphology.

Although all scallops swim using their adductor muscle to close their valves, scallop species differ considerably in how they use their muscle during escape responses, in parallel with the striking interspecific differences in shell morphology. This provides an excellent opportunity to study links between muscle metabolic capacities and animal performance. We found that the capacity for anaerobic glycolysis and aerobic metabolism, as well as phosphoarginine levels in the phasic adductor muscle, differ with escape response strategy. Phosphoarginine contents were high in species that rely on phasic contractions (Amusium balloti, Placopecten magellanicus, and Pecten fumatus). Arginine kinase activities reflect reliance on rapid initial bursts of phasic contractions. Scallops that maintain their valves in a closed position for prolonged periods (P. fumatus, Mimachlamys asperrima, and Crassadoma gigantea) have high activities of enzymes of anaerobic glycolysis in their phasic adductor muscle. Myosin ATPase activity was lower in the nonswimming scallop, C. gigantea, than in swimming scallops. The different patterns and roles of swimming are reflected in interspecific differences in the biochemical attributes of the phasic adductor muscle. These patterns suggest coevolution of muscle metabolic capacities, patterns of adductor muscle use, and shell morphology in scallops.

Thermal acclimation, mitochondrial capacities and organ metabolic profiles in a reptile (Alligator mississippiensis).

Reptiles thermoregulate behaviourally, but change their preferred temperature and the optimal temperature for performance seasonally. We evaluated whether the digestive and locomotor systems of the alligator show parallel metabolic adjustments during thermal acclimation. To this end, we allowed juvenile alligators to grow under thermal conditions typical of winter and summer, providing them with seasonally appropriate basking opportunities. Although mean body temperatures of alligators in these groups differed by approximately 10°C, their growth and final anatomic status was equivalent. While hepatic mitochondria isolated from cold-acclimated alligators had higher oxidative capacities at 30°C than those from warm-acclimated alligators, the capacities did not differ at 20°C. Cold acclimation decreased maximal oxidative capacities of muscle mitochondria. For mitochondria from both organs and acclimation groups, palmitate increased oligomycin-inhibited respiration. GDP addition reduced palmitate-uncoupled rates more in liver mitochondria from warm- than cold-acclimated alligators. In muscle mitochondria, carboxyatractyloside significantly reduced palmitate-uncoupled rates. This effect was not changed by thermal acclimation. The aerobic capacity of liver, skeletal muscle and duodenum, as estimated by activities of cytochrome c oxidase (COX), increased with cold acclimation. At acclimation temperatures, the activities of COX and citrate synthase (CS) in these organs were equivalent. By measuring COX and CS in isolated mitochondria and tissue extracts, we estimated that cold acclimation did not change the mitochondrial content in liver, but increased that of muscle. The thermal compensation of growth rates and of the aerobic capacity of the locomotor and digestive systems suggests that alligators optimised metabolic processes for the seasonally altered, preferred body temperature. The precision of this compensatory response exceeds that typically shown by aquatic ectotherms whose body temperatures are at the mercy of their habitat.

Enzyme activity in the aestivating green-striped burrowing frog (Cyclorana alboguttata).

Green-striped burrowing frogs (Cyclorana alboguttata) can depress their resting metabolism by more than 80% during aestivation. Previous studies have shown that this species is able to withstand long periods of immobilisation during aestivation while apparently maintaining whole muscle mass and contractile performance. The aim of this study was to determine the effect of prolonged aestivation on the levels of metabolic enzymes (CCO, LDH and CS) in functionally distinct skeletal muscles (cruralis, gastrocnemius, sartorius, iliofibularis and rectus abdominus) and liver of C. alboguttata. CS activity was significantly reduced in all tissues except for the cruralis, gastrocnemius and the liver. LDH activity was significantly reduced in the sartorius and rectus abdominus, but remained at control (active) levels in the other tissues. CCO activity was significantly reduced in the gastrocnemius and rectus abdominus, and unchanged in the remaining tissues. Muscle protein was significantly reduced in the sartorius and iliofibularis during aestivation, and unchanged in the remaining muscles. The results suggest that the energy pathways involved in the production and consumption of ATP are remodelled during prolonged aestivation but selective. Remodelling and subsequent down-regulation of metabolic activity seem to target the smaller non-jumping muscles, while the jumping muscles retain enzyme activities at control levels during aestivation. These results suggest a mechanism by which aestivating C. alboguttata are able to maintain metabolic depression while ensuring that the functional capacity of critical muscles is not compromised upon emergence from aestivation.