Sustained Swimming Performance Research Articles

Bisphenol S reduces locomotor performance and modifies muscle protein levels but not mitochondrial bioenergetics in adult zebrafish

Human activity has now introduced novel chemicals into most aquatic ecosystems. Endocrine-disrupting compounds originating from plastic pollution and manufacture can have pronounced biological effects by disrupting hormone-mediated processes. Bisphenol A (BPA) is one of the most commonly produced endocrine-disrupting compounds, which interferes with signalling by a broad range of hormones. In recognition of its potentially harmful effects, BPA is being replaced by substitutes such as bisphenol S (BPS). However, toxicological studies revealed that BPS too can bind to hormone receptors and disrupt signalling, particularly of thyroid hormone. The aim of this study was to test whether BPS exposure impacts locomotor performance and muscle function in zebrafish (Danio rerio). Locomotor performance depends on thyroid hormone signalling, and it is closely related to fitness so that its disruption can have negative ecological and evolutionary consequences. BPS exposure of 15 μg l−1 [∼60 nM] and 30 μg l−1 (but not 60 μg l−1) decreased sustained swimming performance (Ucrit), but not sprint speed. In a fully factorial design, we show that living in flowing water increased Ucrit compared to a still water control, and that BPS reduced Ucrit under both conditions but did not eliminate the training effect. In a second factorial experiment, we show that BPS did not affect mitochondrial bioenergetics in skeletal muscle (state 3 and 4 rates, respiratory control ratios, ROS production), but that induced hypothyroidism decreased state 3 and 4 rates of respiration. However, both hypothyroidism and BPS exposure decreased activity of AMP-activated protein kinase (pAMPK:total AMPK) but increased protein levels of myocyte enhancer factor 2, and slow and fast myosin heavy chains. Our data indicate that BPS is not a safe alternative for BPA and that exposure to BPS can have ecological consequences, which are likely to be at least partly mediated via thyroid hormone disruption.

Two Locomotor Traits Show Different Patterns of Developmental Plasticity Between Closely Related Clonal and Sexual Fish.

The capacity to compensate for environmental change determines population persistence and biogeography. In ectothermic organisms, performance at different temperatures can be strongly affected by temperatures experienced during early development. Such developmental plasticity is mediated through epigenetic mechanisms that induce phenotypic changes within the animal’s lifetime. However, epigenetic modifiers themselves are encoded by DNA so that developmental plasticity could itself be contingent on genetic diversity. In this study, we test the hypothesis that the capacity for developmental plasticity depends on a species’ among-individual genetic diversity. To test this, we exploited a unique species complex that contains both the clonal, genetically identical Amazon molly (Poecilia formosa), and the sexual, genetically diverse Atlantic molly (Poecilia mexicana). We predicted that the greater among-individual genetic diversity in the Atlantic molly may increase their capacity for developmental plasticity. We raised both clonal and sexual mollies at either warm (28°C) or cool (22°C) temperatures and then measured locomotor capacity (critical sustained swimming performance) and unforced movement in an open field across a temperature gradient that simulated environmental conditions often experienced by these species in the wild. In the clonal Amazon molly, differences in the developmental environment led to a shift in the thermal performance curve of unforced movement patterns, but much less so in maximal locomotor capacity. In contrast, the sexual Atlantic mollies exhibited the opposite pattern: developmental plasticity was present in maximal locomotor capacity, but not in unforced movement. Thus our data show that developmental plasticity in clones and their sexual, genetically more diverse sister species is trait dependent. This points toward mechanistic differences in how genetic diversity mediates plastic responses exhibited in different traits.

Incubation and water temperatures influence the performances of loggerhead sea turtle hatchlings during the dispersal phase

Artificial manipulation of incubation temperature has been proposed as a potential strategy for mitigating the effects of climate change on sea turtles for which sex determination is temperature-dependent, but thermal manipulation may also affect hatchling survival. Here, we demonstrated that incubation and water temperatures influenced several performance traits that contribute to the survival of loggerhead sea turtles (Caretta caretta) during the post-hatchling dispersal phase. Hatchlings from warm incubation temperatures (31 °C) had significantly shorter incubation periods, higher initial swimming performance, lower sustained swimming performance, and lower growth rates during the first three weeks post-hatching, as well as higher blood glucose concentrations, than those from cool incubation temperatures (27.5 °C). Hatchlings in warm water temperatures (30 °C) exhibited significantly greater swimming performance than those in cool water temperatures (27 °C). Our results indicated that altering incubation temperatures indirectly influences the survival of loggerhead hatchlings by modifying their swimming performance and growth rates, which may affect hatchling predator-avoidance capability. Moreover, thermal manipulation may alter the incubation period, exposing hatchling to water temperatures that they would not otherwise normally experience, which may affect swimming performance. Our results suggest that such conservation strategies may influence their survival, and thus should be carefully considered.

Living in flowing water increases resistance to ultraviolet B radiation.

Ultraviolet B radiation (UV-B) is an important environmental driver that can affect locomotor performance negatively by inducing production of reactive oxygen species (ROS). Prolonged regular exercise increases antioxidant activities, which may alleviate the negative effects of UV-B-induced ROS. Animals naturally performing exercise, such as humans performing regular exercise or fish living in flowing water, may therefore be more resilient to the negative effects of UV-B. We tested this hypothesis in a fully factorial experiment, where we exposed mosquitofish (Gambusia holbrooki) to UV-B and control (no UV-B) conditions in flowing and still water. We show that fish exposed to UV-B and kept in flowing water had increased sustained swimming performance (Ucrit), increased antioxidant defences (catalase activity and glutathione concentrations) and reduced cellular damage (lipid peroxidation and protein carbonyl concentrations) compared with fish in still water. There was no effect of UV-B or water flow on resting or maximal rates of oxygen consumption. Our results show that environmental water flow can alleviate the negative effects of UV-B-induced ROS by increasing defence mechanisms. The resultant reduction in ROS-induced damage may contribute to maintain locomotor performance. Hence, the benefits of regular exercise are 'transferred' to improve resilience to the negative impacts of UV-B. Ecologically, the mechanistic link between responses to different habitat characteristics can determine the success of animals. These dynamics have important ecological connotations when river or stream flow changes as a result of weather patterns, climate or human modifications.

Parental exposure modulates the effects of UV‐B on offspring in guppies

Summary The environment experienced by parents can alter offspring phenotypes. Such developmental plasticity is beneficial when it optimises offspring responses to their prevailing environment. Plasticity may be detrimental, however, if there is a mismatch between parental and offspring environments, although reversible acclimation within individuals could counteract a developmental mismatch. UV‐B radiation damages cells directly and by increasing reactive oxygen species (ROS) formation. There are indications that the developmental environment can influence ROS defences, which could enhance performance and fitness. In addition, animals exposed to UV‐B can acclimate to increase their antioxidant defences and thereby reduce ROS‐induced damage. Our aim was to test experimentally whether there are transgenerational effects of UV‐B exposure. We tested the hypothesis that parental exposure to UV‐B modulates offspring ROS defence mechanisms to reduce the negative effects of UV‐B in offspring. In a fully factorial experiment, we show that exposing guppies (Poecilia reticulata) to UV‐B increased the resilience of their offspring to the negative effects of UV‐B. When exposed to UV‐B, offspring from parents also exposed to UV‐B had significantly greater sustained swimming performance compared to controls. Higher swimming performance was paralleled by increased catalase activity and glutathione concentrations, and reduced ROS‐induced damage to membranes and proteins. There was no effect of parental exposure to UV‐B on offspring superoxide dismutase activity, resting and active metabolic rates or offspring size. However, parental exposure to UV‐B increased damage to proteins and infection rates by white spot fungus in control (no UV‐B) offspring. Our results showed that UV‐B acts as a signal that can induce developmental modification of phenotypes. Transgenerational matching of offspring phenotypes is likely to have a fitness advantage in environments exposed to UV‐B. However, the trade‐off between the beneficial effects of parental UV‐B exposure on offspring performance when exposed to UV‐B, and the increased susceptibility to infection and protein damage when offspring are not exposed to UV‐B can be important in determining the resilience of populations in variable and modified environments. A lay summary is available for this article.

Swimming performance and behaviour of bighead carp (Hypophthalmichthys nobilis): Application to fish passage and exclusion criteria

The bighead carp (Hypophthalmichthys nobilis) is one of the most commercially important freshwater fish species in China, but their abundance has declined considerably in recent decades, partly due to river regulation. In other countries it is invasive, posing an ecological and economic threat. To improve fish pass effectiveness at impediments to migration in its native range, and create velocity barriers to reduce range expansion where it is invasive, an improved understanding of swimming ability and behaviour is needed. The burst, prolonged, and sustained swimming performance of juvenile bighead carp were quantified experimentally through constant acceleration trials (Umax), fixed velocity tests, and volitional passage efficiency trials through three consecutive constrictions. The effects of fork length (FL), temperature, swimming speed and method (swim chamber/open channel flume section) on endurance in fixed velocity trials were evaluated. The utilisation of low velocity areas close to the flume edge and floor at different mid-channel velocities was also explored. The mean sustained swimming speed in endurance tests was 3.84 FLs−1 (range equivalent to 0.37–0.78ms−1), and burst speeds reached 12.78FLs−1 (up to 1.22ms−1 for larger fish). The meanUmax was 6.81FLs −1 (0.51ms−1). In fixed velocity trials, method did not influence endurance and fish rarely utilised low velocity areas in the corners of the flume when water velocity exceeded sustained swimming ability. Passage efficiency decreased at successive flume constrictions, possibly indicating a poor repeat burst swimming performance. Field validation is required to verify wild bighead carp behaviour and passage in the hydraulic conditions created by fish passes.

Energetic cost determines voluntary movement speed only in familiar environments

Locomotor performance is closely related to fitness. However, in many ecological contexts, animals do not move at their maximal locomotor capacity, but adopt a voluntary speed that is lower than maximal. It is important to understand the mechanisms that underlie voluntary speed, because these determine movement patterns of animals across natural environments. We show that voluntary speed is a stable trait in zebrafish (Danio rerio), but there were pronounced differences between individuals in maximal sustained speed, voluntary speed and metabolic cost of locomotion. We accept the hypothesis that voluntary speed scales positively with maximal sustained swimming performance (Ucrit), but only in unfamiliar environments (1st minute in an open-field arena versus 10th minute) at high temperature (30°C). There was no significant effect of metabolic scope on Ucrit Contrary to expectation, we rejected the hypothesis that voluntary speed decreases with increasing metabolic cost of movement, except in familiar spatial (after 10 min of exploration) and thermal (24°C but not 18 or 30°C) environments. The implications of these data are that the energetic costs of exploration and dispersal in novel environments are higher than those for movement within familiar home ranges.

Skeletal muscle contractile function predicts activity and behaviour in zebrafish.

Locomotion facilitates behaviour and its underlying physiological mechanisms may therefore impact behavioural phenotypes. Metabolism is often thought to modulate locomotion and behaviour, but empirical support for this suggestion is equivocal. Muscle contractile function is directly associated with locomotion. Here, we test the hypotheses that muscle mechanics determine locomotor performance and activity in zebrafish (Danio rerio) and thereby also affect risk-taking behaviour. We show that there is a mechanistic link between muscle performance and behaviour by manipulating muscle contractile properties, which caused proportional changes in critical sustained swimming performance and, in an open arena, voluntary swimming speed, the proportion of time fish were active, and the latency to move. We modelled the relationships between muscle contractile properties, swimming performance, activity and behaviour with a partial least-squares path model. The latent variable 'muscle', formed by isolated muscle force production, stress, fatigue resistance and activation and relaxation rates, had a significant positive effect on swimming performance ('swim' reflected in sustained and sprint speeds). Together, muscle and swim had a significant positive effect on activity, and explained 71.8% of variation in the distance moved, time active and maximum voluntary speed in an open field. Activity had a significant positive effect on boldness, explaining 76.0% of variation in latencies to move and to approach a novel object. Muscle contractile function determines voluntary movement and we suggest that exploration and dispersal are functions of physiological and mechanical optimisation. Boldness therefore may be partly explained by the greater likelihood of faster fish to move further and encounter novel objects and conspecifics more quickly as a result.

Physiological plasticity to water flow habitat in the damselfish, Acanthochromis polyacanthus: linking phenotype to performance.

The relationships among animal form, function and performance are complex, and vary across environments. Therefore, it can be difficult to identify morphological and/or physiological traits responsible for enhancing performance in a given habitat. In fishes, differences in swimming performance across water flow gradients are related to morphological variation among and within species. However, physiological traits related to performance have been less well studied. We experimentally reared juvenile damselfish, Acanthochromis polyacanthus, under different water flow regimes to test 1) whether aspects of swimming physiology and morphology show plastic responses to water flow, 2) whether trait divergence correlates with swimming performance and 3) whether flow environment relates to performance differences observed in wild fish. We found that maximum metabolic rate, aerobic scope and blood haematocrit were higher in wave-reared fish compared to fish reared in low water flow. However, pectoral fin shape, which tends to correlate with sustained swimming performance, did not differ between rearing treatments or collection sites. Maximum metabolic rate was the best overall predictor of individual swimming performance; fin shape and fish total length were 3.3 and 3.7 times less likely than maximum metabolic rate to explain differences in critical swimming speed. Performance differences induced in fish reared in different flow environments were less pronounced than in wild fish but similar in direction. Our results suggest that exposure to water motion induces plastic physiological changes which enhance swimming performance in A. polyacanthus. Thus, functional relationships between fish morphology and performance across flow habitats should also consider differences in physiology.

不同适应条件对细鳞鲑幼鱼游泳能力的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同适应条件对细鳞鲑幼鱼游泳能力的影响 DOI: 10.5846/stxb201305241165 作者: 作者单位: 中国水产科学研究院黑龙江水产研究所,黑龙江水产研究所,东北农业大学动物科技学院,东北农业大学动物科技学院,中国水产科学研究院黑龙江水产研究所,中国水产科学研究院黑龙江水产研究所,中国水产科学研究院黑龙江水产研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 中央级公益性科研院所基本科研业务费专项(HSY201312);国家"十二五"农村领域科技计划(2012BAD26B05) Effects of different acclimation conditions on sustainable swimming performance of juvenile lenok, Brachymystax lenok (Pallas) Author: Affiliation: Heilongjiang River Fisheries Research Institute,Chinese Academy of Fishery Sciences,,College of Animal Science and Technology,Northeast Agricultural University,College of Animal Science and Technology,Northeast Agricultural University,Heilongjiang River Fisheries Research Institute,Chinese Academy of Fishery Sciences,Heilongjiang River Fisheries Research Institute,Chinese Academy of Fishery Sciences,Heilongjiang River Fisheries Research Institute,Chinese Academy of Fishery Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了研究适应条件对鲑科鱼类幼鱼续航游泳能力的影响,在(16.0±0.2)℃和8 mg/L溶解氧条件下,以续航时间作为评定游泳能力的关键指标,通过适应时间、适应流速、加速时间以及测试流速对细鳞鲑幼鱼的续航游泳时间的影响进行了研究, 试验采用4因素8水平的均匀设计方案。结果表明,最大适应流速应控制在1-1.5 BL/s为宜,相应的最佳适应时间应为1 h,在合理条件下适应流速和适应时间对续航游泳能力的影响可忽略不计;加速时间只在大流速条件下(> 0.5 m/s)对续航时间有极显著影响,其他情况的影响可以忽略不计;尽管长时间适应环境更有利于鱼类身体机能的充分调整,但适应时间仍建议控制在1-2 h以内,且受试鱼类要经过试验前的适应能力筛选;测试流速建议控制在3-4 BL/s以内,以避免超过鱼类的最大游泳耐受范围。测试流速对细鳞鲑幼鱼的续航时间有极为显著的影响,其续航时间随测试流速的增加呈幂函数规律衰减。 Abstract:Swimming performance is considered a critical factor in determining the survival of many fish species under natural conditions. Flume experimentation, which is visible, measurable, and repeatable for the adjustment and control of environmental factors, is a basic and effective method for the study of swimming performance and behavior in fish. However, many current studies of fish behavior have focused solely on the process of adaptation, while other influencing factors such as temperature, light, dissolved oxygen, velocity, and time have been generally ignored. In addition, maximal sustained swimming time and maximal sustained swimming speed are accepted as key indicators for determining swimming performance in fish. Swimming performance is assessed by determining the maximum sustained swimming performance at a given time and constant speed, and maximal sustained swimming speed is used as the base-line reference when fish become fatigued. The lenok, Brachymystax lenok (Pallas), is one of the rare and valuable salmonid species found in the northeast of China. In recent years, the biology, ecology, reproduction success, disease prevention, and culture techniques of this species have been extensively studied and reported. However, to the best of our knowledge, there have been very few studies on the behavioral ecology of this species. In this report, the effects of acclimation time, acclimation flow velocity, acceleration time, and tested flow velocity on the sustained swimming time of juvenile lenok were investigated at a water temperature of 16.0 ± 0.2 ℃ and dissolved oxygen level of 8 mg/L. The observed results served as reference data on the ethology, kinematics, energetics, and behavioral ecology of this species. Uniform experimental design was used with four factors and eight levels being applied to all tests. The results revealed that the maximal acclimation flow velocity (AFVmax) should be limited to 1.0-1.5 (body lengths) BL/s, with a corresponding optimum acclimation time (AT) of 1 h. Under reasonable conditions (AFVmax≤ 1.0-1.5 BL/s, AT ≤ 1 h), the influence of acclimation flow velocity and acclimation time on sustainable swimming performance was negligible. Acceleration time significantly affected sustained swimming time under stronger flow velocities (> 0.5 m/s) (P < 0.05). Although a longer time period may be favorable in allowing fish to adjust to a new environment, an acclimation time of 1-2 h is recommended; screening for a suitable acclimation time should be performed before trials. It is recommended that the tested flow velocity be limited to 3-4 BL/s to avoid the maximum swimming tolerance range. Sustained swimming time was significantly affected by the tested flow velocities: sustained swimming time decreased significantly with an increase in flow velocity (P < 0.05). The energy loss in fish was also affected by tested flow velocity, acceleration time, and acclimation time. Under the maximal tested flow velocity (> 0.5 m/s), the maximal acclimation time and the acceleration time should be limited to 60 and 4 min, respectively. In conclusion, this study provides a scientific baseline for the behavioral ecology, kinematic theory, and energetics of B. lenok, which will prove valuable for the design and construction of fish-pass facilities. 参考文献 相似文献 引证文献

UV-B exposure reduces locomotor performance by impairing muscle function but not mitochondrial ATP production.

Ultraviolet B radiation (UV-B) can reduce swimming performance by increasing reactive oxygen species (ROS) formation. High concentrations of ROS can damage mitochondria, resulting in reduced ATP production. ROS can also damage muscle proteins, thereby leading to impaired muscle contractile function. We have shown previously that UV-B exposure reduces locomotor performance in mosquitofish (Gambusia holbrooki) without affecting metabolic scope. Our aim was therefore to test whether UV-B influences swimming performance of mosquitofish by ROS-induced damage to muscle proteins without affecting mitochondrial function. In a fully factorial design, we exposed mosquitofish to UV-B and no-UV-B controls in combination with exposure to N-acetylcysteine (NAC) plus no-NAC controls. We used NAC, a precursor of glutathione, as an antioxidant to test whether any effects of UV-B on swimming performance were at least partly due to UV-B-induced ROS. UV-B significantly reduced critical sustained swimming performance and tail beat frequencies, and it increased ROS-induced damage (protein carbonyl concentrations and lipid peroxidation) in muscle. However, UV-B did not affect the activity of sarco-endoplasmic reticulum ATPase (SERCA), an enzyme associated with muscle calcium cycling and muscle relaxation. UV-B did not affect ADP phosphorylation (state 3) rates of mitochondrial respiration, and it did not alter the amount of ATP produced per atom of oxygen consumed (P:O ratio). However, UV-B reduced the mitochondrial respiratory control ratio. Under UV-B exposure, fish treated with NAC showed greater swimming performance and tail beat frequencies, higher glutathione concentrations, and lower protein carbonyl concentrations and lipid peroxidation than untreated fish. Tail beat amplitude was not affected by any treatment. Our results showed, firstly, that the effects of UV-B on locomotor performance were mediated by ROS and, secondly, that reduced swimming performance was not caused by impaired mitochondrial ATP production. Instead, reduced tail beat frequencies indicate that muscle of UV-B exposed fish were slower, which was likely to have been caused by slower contraction rates, because SERCA activities remained unaffected.

Exercise changes behaviour

Summary Exercise, which may be defined as bodily movement produced by the contraction of skeletal muscle and which increases energy expenditure above basal levels, is essential for fitness‐related activities such as foraging, migration and dispersal. The frequency with which individuals engage in exercise depends on a range of intrinsic and environmental factors. Exercise itself can modify behaviour by inducing endocrine changes and by a training effect that increases physiological capacities. Here, we test the hypothesis that exercise changes behaviour and that there is positive feedback so that performing exercise increases the likelihood of performing exercise‐related behaviours. We show that there was a training effect that improved sustained swimming performance of mosquitofish (Gambusia holbrooki) exposed to chronic exercise in flowing water for 4 weeks compared to sedentary controls. Exercised fish also became bolder and were quicker to leave a refuge, showed an increasing tendency to explore unfamiliar environments, and were more aggressive than sedentary fish. These physiological and behavioural changes reverted back to control levels when exercised fish assumed a sedentary lifestyle again. We used the calcium channel blocker nifedipine to decrease swimming performance of exercised fish to control levels, which allowed us to determine whether increased locomotor capacity per se influences behaviour. We show that reducing the swimming performance of exercised fish also reduced exploration and aggression, but it did not affect the latency to leave a refuge (boldness). Our data show that behavioural phenotypes are not fixed. Exercise changes behaviour and may thereby alter interactions between individuals and dispersal. Environmental changes that demand increased levels of exercise induce behavioural responses that are likely to increase the success of individuals under these changed conditions.

Regulation of thermal acclimation varies between generations of the short‐lived mosquitofish that developed in different environmental conditions

Summary Environmental variability and perturbations can influence population persistence. It is therefore important to understand whether and how animals can compensate for environmental variability and thereby increase resilience of natural populations. Evolutionary theory predicts that in fluctuating environments, selection should favour developmental modifiers that reduce phenotypic expression of genetic variation. The expected result is that phenotypes are buffered from environmental variation across generations. Our aim was to determine whether phenotypes of mosquitofish (Gambusia holbrooki) remain stable across generations in which individuals were born into different thermal environments. We predicted that the spring generation (cool environment) would acclimate by increasing the concentration of regulatory transcription factor mRNA and activities of rate‐limiting enzymes (hierarchical regulation) to compensate for the negative thermodynamic effects of lower temperatures on metabolic and locomotor performance. In contrast, the summer‐born generation (warm environment) would show less capacity for acclimation and hierarchical regulation. We show that fish from both generations acclimated, but that there were significant differences in the phenotypic consequences of acclimation. The overall result was that burst performance, metabolic scope, and the activities of cytochrome c oxidase and lactate dehydrogenase were buffered from environmental change and did not differ between spring and summer fish at their natural water temperatures of 15 °C and 25 °C, respectively. However, there were differences between generations in sustained swimming performance and citrate synthase activity. We used metabolic control analysis to show that modes of regulation of metabolic scope and locomotor performance differed between generations. Spring‐born fish relied to a greater extent on rate‐limiting enzymes and transcriptional regulator (PGC‐1α and β) mRNA concentrations than summer‐born fish. We suggest that developmental modifiers are favoured in fluctuating environments to maximize phenotypic fitness of each generation. We show that the interaction between developmental and reversible acclimation can increase the resilience of physiological performance in a natural population to climate variation.

Thyroid hormone regulates muscle function during cold acclimation in zebrafish (Danio rerio)

Thyroid hormone (TH) is a universal regulator of growth, development and metabolism during cold exposure in mammals. In zebrafish (Danio rerio), TH regulates locomotor performance and metabolism during cold acclimation. The influence of TH on locomotor performance may be via its effect on metabolism or, as has been shown in mammals, by modulating muscle phenotypes. Our aim was to determine whether TH influences muscle phenotypes in zebrafish, and whether this could explain changes in swimming capacity in response to thermal acclimation. We used propylthiouracil and iopanoic acid to induce hypothyroidism in zebrafish over a 3-week acclimation period to either 18 or 28°C. To verify that physiological changes following hypothyroid treatment were in fact due to the action of TH, we supplemented hypothyroid fish with 3,5-diiodothryronine (T2) or 3,5,3'-triiodothyronine (T3). Cold-acclimated fish had significantly greater sustained swimming performance (Ucrit) but not burst speed. Greater Ucrit was accompanied by increased tail beat frequency, but there was no change in tail beat amplitude. Hypothyroidism significantly decreased Ucrit and burst performance, as well as tail beat frequency and SERCA activity in cold-acclimated fish. However, myofibrillar ATPase activity increased in cold-acclimated hypothyroid fish. Hypothyroid treatment also decreased mRNA concentrations of myosin heavy chain fast isoforms and SERCA 1 isoform in cold-acclimated fish. SERCA 1 mRNA increased in warm-acclimated hypothyroid fish, and SERCA 3 mRNA decreased in both cold- and warm-acclimated hypothyroid fish. Supplementation with either T2 or T3 restored Ucrit, burst speed, tail beat frequency, SERCA activity and myosin heavy chain and SERCA 1 and 3 mRNA levels of hypothyroid fish back to control levels. We show that in addition to regulating development and metabolism in vertebrates, TH also regulates muscle physiology in ways that affect locomotor performance in fish. We suggest that the role of TH in modulating SERCA1 expression during cold exposure may have predisposed it to regulate endothermic thermogenesis.

Repeatability of escape response performance in the queen scallop (Aequipecten opercularis)

In order for natural selection to operate, physiological and behavioural traits must exhibit both inter-individual variability and intra-individual consistency (i.e. repeatability) in performance. In this study, we describe individual variation and temporal repeatability in the escape responses of the queen scallop, Aequipecten opercularis, and determine whether individuals exhibited consistently high or low rankings in different aspects of the escape response. Five measures of individual performance were recorded on four occasions (days 0, 2, 7 and 28), providing proxies for sensory acuity (response latency), immediate and sustained swimming performance (burst and average clap rates), and swimming endurance (total number of claps and total time spent clapping). All components of the escape response exhibited significant inter-individual variability (all P<0.0001). Escape response latency, burst clap rate, total number of claps and total duration spent clapping maintained significant repeatability over 28 days (all P<0.016). Average clap rate was repeatable in the short term (2 days, P<0.0001) but repeatability declined by 28 days (P=0.097). Concordance analysis indicated that individuals maintained the same performance rankings over time for each component of the escape response (all P<0.001). In addition, some individuals ranked as consistently high or low performers across response latency, burst and average clap rate, and total number of claps. An individual's ability to evade predators through the provision of an escape response of an appropriate magnitude, subject to physiological, behavioural and organismal constraints, will have clear fitness-related consequences.

How well do muscle biomechanics predict whole-animal locomotor performance? The role of Ca2+ handling

It is important to determine the enabling mechanisms that underlie locomotor performance to explain the evolutionary patterns and ecological success of animals. Our aim was to determine the extent to which calcium (Ca(2+)) handling dynamics modulate the contractile properties of isolated skeletal muscle, and whether the effects of changing Ca(2+) handling dynamics in skeletal muscle are paralleled by changes in whole-animal sprint and sustained swimming performance. Carp (Cyprinus carpio) increased swimming speed by concomitant increases in tail-beat amplitude and frequency. Reducing Ca(2+) release from the sarcoplasmic reticulum (SR) by blocking ryanodine receptors with dantrolene decreased isolated peak muscle force and was paralleled by a decrease in tail-beat frequency and whole-animal sprint performance. An increase in fatigue resistance following dantrolene treatment may reflect the reduced depletion of Ca(2+) stores in the SR associated with lower ryanodine receptor (RyR) activity. Blocking RyRs may be detrimental by reducing force production and beneficial by reducing SR Ca(2+) depletion so that there was no net effect on critical sustained swimming speed (U(crit)). In isolated muscle, there was no negative effect on force production of blocking Ca(2+) release via dihydropyridine receptors (DHPRs) with nifedipine. Nifedipine decreased fatigue resistance of isolated muscle, which was paralleled by decreases in tail-beat frequency and U(crit). However, sprint performance also decreased with DHPR inhibition, which may indicate a role in muscle contraction of the Ca(2+) released by DHPR into the myocyte. Inhibiting sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) activity with thapsigargin decreased fatigue resistance, suggesting that SERCA activity is important in avoiding Ca(2+) store depletion and fatigue. We have shown that different molecular mechanisms modulate the same muscle and whole-animal traits, which provides an explanatory model for the observed variations in locomotor performance within and between species.

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature-controlled, Brett-type swimming-tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L(F) ), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U(crit)) was 102·5 ± 13·7 cm s⁻¹ or 4·6 ± 0·9 L(F) s⁻¹. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U(max,c)) was 99·4 ± 14·4 cm s⁻¹ or 4·5 ± 0·9 L(F) s⁻¹. Oxygen consumption rate (M in mg O₂ min⁻¹) increased with swimming speed and with fish mass, but mass-specific M (mg O₂ kg⁻¹ h⁻¹) as a function of relative speed (L(F) s⁻¹) did not vary significantly with fish size. Mean standard metabolic rate (R(S) ) was 170 ± 38 mg O₂ kg⁻¹ h⁻¹, and the mean ratio of M at U(max,c) to R(S) , an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U(opt) ), at which the gross cost of transport was a minimum of 2·14 J kg⁻¹ m⁻¹, was 3·8 L(F) s⁻¹. In a subset of the fish studied (19·7-22·7 cm L(F) , 106-164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L(F) . The mean propulsive wavelength was 86·7 ± 5·6 %L(F) or 73·7 ± 5·2 %L(T) . Mean ±s.d. yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L(F) ; 23·4, 25·3 and 26·4 cm L(T) ), were 4·6 ± 0·1 and 17·1 ± 2·2 %L(T) , respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.

Sex cells in changing environments: can organisms adjust the physiological function of gametes to different temperatures?

AbstractOver the past decade, hundreds of studies have examined the abilities of whole organisms to modify their physiology and behaviour in response to environmental temperature changes; despite this, virtually nothing is known about the ability of sex cells to adjust to different temperature conditions. In fact, a recent meta‐analysis based on studies of 309 species and 112 physiological and ecological traits found no studies examining the influence of temperature on gamete function. Because sex cells play a critical role in the adaptation and persistence of species, this represents a severe oversight in physiological studies of thermal adaptation. Our study examines whether sex cells can respond phenotypically to variation in the thermal environment that is experienced by the whole‐organism. Specifically, we studied the thermal dependence of sperm swimming and the critical thermal limits of sperm cells in males of the poeciliid fish, Gambusia holbrooki. This species is well known for its ability to modify physiological function and maintains burst and sustained swimming performance and mating ability across a wide range of thermal conditions. In contrast, we found that sperm cells from male G. holbrooki did not adjust their physiological function as predicted by adaptive models. After acclimation of adult males to cool or warm temperatures, we found that the critical thermal limits of sperm function remained unchanged, as did the effect of temperature on sperm swimming performance. However, warm‐acclimated fish had sperm with higher swimming speeds across all temperatures. The absence of phenotypic changes in the critical thermal limits of sperm or thermal dependence of sperm swimming performance is surprising given that whole‐organism traits in G. holbrooki generally show improved performance after exposure to novel environments. As such an inability to thermally adjust gamete function may be widespread among other organisms, we urge biologists to investigate the generality of this result.

Dietary carotenoid availability and reproductive effort influence the age-related decline in performance

Elevated breeding effort is known to increase an individual’s rate of senescence, although the underlying mechanisms are not well understood. One possibility is that the ability to resist senescence is limited by the availability of antioxidants, which are necessary to mitigate the deleterious effects of oxidative stress thought to underlie the aging process. Susceptibility to oxidative stress is likely to be particularly high during reproduction, and so for a given level of reproductive effort, the rate of senescence should be fastest in those individuals with the poorest antioxidant capacity. We tested this hypothesis in an experimental study of breeding male three-spined sticklebacks (Gasterosteus aculeatus) held under a high or low reproduction regime and fed on either high or low levels of carotenoids (potentially limiting dietary compounds with antioxidant properties). Fish on the high reproduction regime and those on the low-carotenoid diet both showed an accelerated decline in sustained swimming performance (an indicator of locomotor senescence) compared with males on the low reproduction regime and high-carotenoid diet, respectively. The swimming performance of fish subjected to the high rate of reproduction, but fed a low-carotenoid diet, appeared to decline most rapidly, perhaps because of the additive effects of increased levels of reproduction-induced oxidative stress and lower antioxidant availability. These findings show that both dietary carotenoid intake and breeding effort can impact on the age-related decline in swimming performance and have important implications for female choice and the capacity of males with insufficient antioxidant defenses to adequately perform paternal care.

Can Phenotypic Plasticity Facilitate the Geographic Expansion of the TilapiaOreochromis mossambicus?

Climate influences the distribution of organisms because of the thermal sensitivity of biochemical processes. Animals may compensate for the effects of variable temperatures, and plastic responses may facilitate radiation into different climates. The tropical fish Oreochromis mossambicus has radiated into climates that were thought to be thermally unsuitable. Here, we test the hypothesis that thermal acclimation will extend the locomotory and metabolic performance range of O. mossambicus. Juvenile fish were acclimated to 14 degrees, 17 degrees, and 22 degrees C. We measured responses to acclimation at three levels of organization: whole-animal performance (sustained swimming and resting and recovery rates of oxygen consumption), mitochondrial oxygen consumption in caudal muscle, and metabolic enzyme activities in muscle and liver at 12 degrees, 14 degrees, 17 degrees, 22 degrees, and 26 degrees C. Thermal optima of sustained swimming performance (U(crit)) changed significantly with acclimation, but acclimation had no effect on either resting or recovery oxygen consumption. Fish compensated for cold temperatures by upregulating state 3 mitochondrial oxygen consumption and increasing activity of lactate dehydrogenase in the liver. The capacity for phenotypic plasticity in O. mossambicus means that the fish would not be limited by its locomotor performance or metabolic physiology to expand its range into cooler thermal environments from its current distribution.