Repeatability and correlation of swimming performances and size over varying time-scales in the guppy (Poecilia reticulata)

Parasite load, rather than parasite presence, decreases upstream movement in Trinidadian guppies Poecilia reticulata

Several factors influence whether an organism remains in its local habitat. Parasites can, for example, influence host movement by impacting their behavior, physiology, and morphology. In rivers, fish that swim efficiently against the current are able to maintain their position without being displaced downstream, a behavior referred to as positive rheotaxis. We hypothesized that both the presence and number of ectoparasites on a host would affect the ability of fish to avoid downstream displacement and thus prevent them from remaining in their habitat. We used the guppy-Gyrodactylus host-ectoparasite model to test whether parasite presence and parasite load had an effect on fish rheotaxis. We quantified rheotaxis of sham-infected and parasite-infected fish in a circular flow tank in the laboratory prior to infection and 5-6 days postinfection. Both parasite-infected and sham-infected individuals expressed similar levels of positive rheotaxis prior to infection and after infection. However, with increasing parasite numbers, guppies covered less distance in the upstream direction and spent more time in slower flow zones. These results suggest that higher numbers of Gyrodactylus ectoparasites negatively influence rheotactic movements. Further research is needed to understand the ecological and evolutionary implications of this ectoparasite on fish movement.

Maxed Out: Optimizing Accuracy, Precision, and Power for Field Measures of Maximum Metabolic Rate in Fishes

Both laboratory and field respirometry are rapidly growing techniques to determine animal performance thresholds. However, replicating protocols to estimate maximum metabolic rate (MMR) between species, populations, and individuals can be difficult, especially in the field. We therefore evaluated seven different exercise treatments-four laboratory methods involving a swim tunnel (critical swim speed [Ucrit], Ucrit postswim fatigue, maximum swim speed [Umax], and Umax postswim fatigue) and three field-based chasing methods (3-min chase with 1-min air exposure, 3-min chase with no air exposure, and chase to exhaustion)-in adult coho salmon (Oncorhynchus kisutch) as a case study to determine best general practices for measuring and quantifying MMR in fish. We found that all seven methods were highly comparable and that chase treatments represent a valuable field alternative to swim tunnels. Moreover, we caution that the type of test and duration of measurement windows used to calculate MMR can have significant effects on estimates of MMR and statistical power for each approach.

Sex-specific transgenerational plasticity: developmental temperatures of mothers and fathers have different effects on sons and daughters

Each parent can influence offspring phenotype via provisioning of the zygote or sex-specific DNA methylation. Transgenerational plasticity may therefore depend on the environmental conditions experienced by each parent. We tested this hypothesis by conducting a fully factorial experiment across three generations of guppies (Poecilia reticulata), determining the effects of warm (28°C) and cold (21°C) thermal backgrounds of mothers and fathers on mass and length, and thermal performance (sustained and sprint swimming speeds, citrate synthase and lactate dehydrogenase activities; 18, 24, 28, 32 and 36°C test temperatures) of sons and daughters. Offspring sex was significant for all traits except for sprint speed. Warmer mothers produced sons and daughters with reduced mass and length, and warmer fathers produced shorter sons. Sustained swimming speed (Ucrit) of male offspring was greatest when both parents were raised at 28°C, and warmer fathers produced daughters with greater Ucrit. Similarly, warmer fathers produced sons and daughters with greater metabolic capacity. We show that the thermal variation experienced by parents can modify offspring phenotype, and that predicting the impacts of environmental change on populations would require knowledge of the thermal background of each mother and father, particularly where sexes are spatially segregated.

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 (U_crit), but not sprint speed. In a fully factorial design, we show that living in flowing water increased U_crit compared to a still water control, and that BPS reduced U_crit 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.

Detecting behavioural lateralisation in Poecilia reticulata is strongly dependent on experimental design

Abstract

Despite the potential benefits gained from behavioural lateralisation, defined as the asymmetrical expression of cognitive functioning, this trait demonstrates widespread variation within and between populations. Numerous methodologies have been applied to investigate lateralisation, although whether different methodologies give consistent results has been relatively understudied. In this study, we assess (1) the repeatability of individual Poecilia reticulata’s lateralisation indexes between a classic detour assay (I-maze), quasi-circular mirror maze and novel detour assay (a radially symmetric Y-maze); (2) whether the methodological standard of analysing only the first ten turns in a detour assay accurately quantifies lateralisation; and (3) whether lateralisation indexes produced can be adequately explained by random chance by comparing the observed data to a novel unbiased ‘coin-toss’ randomisation model. We found (1) the two detour assays to produce generally consistent results in terms of relative lateralisation (directionality) but differed in terms of absolute laterality (intensity). The mirror assay, however, demonstrated no similarity to either assay. (2) The first ten turns were generally reflective of all turns undertaken during the 15-min trial but reducing the number of turns did exaggerate lateralisation indexes. (3) The observed laterality indexes from the assays were found to be similar to corresponding datasets produced by the randomisation model, with significant deviations likely explained by individuals’ propensity to perform consecutive turns in the same direction. These results demonstrate the need to increase the number of observed turning choices to reduce the likelihood of producing spurious or exaggerated lateralisation indexes from random chance or external influences.

Significance statement

Published studies investigating lateralisation, or ‘handedness’, in fish species have used a diverse array of methodologies. Given the variability in methodologies being employed and the widespread variation in the extent fish are lateralised and in which direction (left or right), it is important to assess whether different methods produce consistent laterality indexes. From assessing individual Poecilia reticulata in three laterality assays, the direction of lateralisation was found to correlate between the two detour assays measuring turn choice, although the absolute strength of this laterality was not consistent. There were no correlations between these assays and in an individual’s eye-use when viewing their reflection in a mirror maze assay. However, further investigation using a novel unbiased ‘coin-toss’ randomisation model to simulate replica datasets for each assay brings into question whether patterns of laterality found in the observed population differ significantly from random chance.

Effects of Aerobic Exercise Training on the Growth, Swimming Performance, Antipredation Ability and Immune Parameters of Juvenile Rock Carp (Procypris rabaudi)

Many studies have found that aerobic exercise training at a moderate water velocity can improve the growth, swimming performance and survival rate of fish. To investigate the effects of aerobic exercise training on the growth, swimming performance, antipredation ability and immune parameters of rock carp, juveniles were placed in training channels with different water velocities (i.e., 3 cm s−1, 1 (body length s−1) bl s−1, 2 bl s−1 and 4 bl s−1) for 6 weeks. Then, the specific growth rate, critical swimming speed (Ucrit) and its metabolism, constant acceleration speed (Ucat), survival rate under predation, spleen index, lysozyme (LZM) activity and immunoglobulin (IgM) level were measured. Training showed no significant effect on the length-specific growth rate, weight-specific growth rate, Ucrit, maximum metabolic rate (MMR), metabolic scope (MS), Ucat or spleen index. The resting metabolic rates (RMRs) of the 2 bl s−1 and 4 bl s−1 training groups were significantly higher than those of the control group and 1 bl s−1 training group. The survival rate of the 1 bl s−1 training group in the presence of predators was significantly higher than that of the control group but significantly lower than those of the 2 bl s−1 and 4 bl s−1 training groups. The LZM activity of the 4 bl s−1 training group was significantly higher than that of the control group. The IgM level of the 2 bl s−1 training group was significantly higher than that of the control group. These data indicate that aerobic exercise training does not improve the growth and swimming performance of juvenile rock carp but can improve their antipredation ability and immunologic function.

An Automated Low-Cost Swim Tunnel for Measuring Swimming Performance in Fish

The study of swimming behavior is an important part of fish biology research and the swim tunnel is used to study swimming performance as well as metabolism of fish. In this investigation, we have developed a user-friendly, automated, modular, and low-cost swim tunnel that permits to study the performance of one or more fish separately, as well as a small group of individuals. To validate our swim tunnel, we assessed swimming activity of four different species (zebrafish, medaka, guppy, and cavefish) recording reliable data of swimming behavior and performance. Because swimming behavior has been recently used in different fields from physiology to ecotoxicology, our setup could help researchers with a low-cost solution.

Social rank and not physiological capacity determines competitive success in zebrafish (Danio rerio)

Competition for resources shapes ecological and evolutionary relationships. Physiological capacities such as in locomotor performance can influence the fitness of individuals by increasing competitive success. Social hierarchy too can affect outcomes of competition by altering locomotor behaviour or because higher ranking individuals monopolize resources. Here, we tested the hypotheses that competitive success is determined by sprint performance or by social status. We show that sprint performance of individuals measured during escape responses (fast start) or in an accelerated sprint test did not correlate with realized sprint speed while competing for food within a social group of five fish; fast start and accelerated sprint speed were higher than realized speed. Social status within the group was the best predictor of competitive success, followed by realized speed. Social hierarchies in zebrafish are established within 7 days of their first encounter, and interestingly, there was a positive correlation between social status and realized speed 1 and 4 days after fish were placed in a group, but not after 7 days. These data indicate that physiological performance decreases in importance as social relationships are established. Also, maximal physiological capacities were not important for competitive success, but swimming speed changed with social context.

One size does not fit all: inter- and intraspecific variation in the swimming performance of contrasting freshwater fish

Artificial barriers cause widespread impacts on freshwater fish. Swimming performance is often used as the key metric in assessing fishes' responses to river barriers. However, barrier mitigation is generally based on the swimming ability of salmonids and other strong swimmers because knowledge of swimming ability for most other freshwater fish is poor. Also, fish pass designs tend to adopt a 'one size fits all' approach because little is known about population or individual variability in swimming performance. Here, we assessed interspecific and intraspecific differences in the sustained swimming speed (U_sus ) of five freshwater fish with contrasting body sizes, morphologies and swimming modes: topmouth gudgeon, European minnow, stone loach, bullhead and brown trout. Significant U _sus variation was identified at three organizational levels: species, populations and individual. Interspecific differences in U_sus were as large as 64 cm s^-1, upstream populations of brown trout showed mean U _sus 27 cm s^-1 higher than downstream populations, and species exhibited high individual variation (e.g. cv = 62% in European minnow). Sustained swimming speed (U _sus) increased significantly with body size in topmouth gudgeon, European minnow and brown trout, but not in the two benthic species, bullhead and stone loach. Aerobic scope had a significant positive effect on U _sus in European minnow, stone loach and brown trout. Sustained swimming speed (U _sus) decreased with relative pectoral fin length in European minnow and brown trout, whereas body fineness was the best predictor in stone loach and bullhead. Hence, swimming performance correlated with a diverse range of traits that are rarely considered when predicting fish passage. Our study highlights the dangers of using species' average swimming speeds and illustrates why a 'one size fits all' approach often fails to mitigate for barrier effects. We call for an evidence-based approach to barrier mitigation, one that recognizes natural variability at multiple hierarchical levels.

Individual Repeatability of Locomotor Kinematics and Swimming Performance in a Gymnotiform Swimmer

AbstractGymnotiform swimming is a specialized form of swimming wherein thrust is produced by the ribbonlike motion of an elongate anal fin, while the body is held relatively stiff. This form of swimming has been extensively examined in relation to the biomechanics of thrust production, the kinematics of the anal fin, and neuromuscular control, whereas few studies have examined whole-animal performance parameters of this swimming mode. The goals of this research were to (1) assess the maximum abilities and repeatability of two swimming performance measures, sprinting and prolonged swimming, which would indicate that these performance measures in a gymnotiform swimmer may be a target for selection, similar to body-caudal fin-swimming fish; (2) examine how a gymnotiform swimmer modulates swimming speed; and (3) determine whether modulatory behavior is consistent across different-sized fish and within individuals across time. Sprinting and prolonged swimming were examined in black ghost knifefish (Apteronotus albifrons; N=15), multiple times on the same day, and were measured again 4 wk later. Sprinting ability was measured by chasing a fish down a photocell-lined racetrack and obtaining the fastest speed between any 8-cm span. Prolonged swimming abilities were measured in a constant acceleration test (U_cat) in a Brett-style swim tunnel by measuring the maximum speed the fish could attain against a steadily increasing water velocity. We determined frequency, wavelength, and amplitude of the anal fin sine wave in fish swimming at different speeds during the U_cat trials. We found repeatable measures of sprint speed and U_cat performance over short (day) and medium (4 wk) time periods for both tests. Neither sprint nor U_cat performance was significantly dependent on size, suggesting that the primary driver of performance variation was individual differences in physiology. Most modulation of swimming speed occurred through changes in the frequency of the wave train processing down the anal fin, with only modest changes to the wavelength and minimal changes to amplitude. Finally, we compare our measures of swimming performance in this gymnotiform swimmer to published values of body-caudal fin swimmers to demonstrate that this form of locomotion results in comparable sprint and constant-acceleration values.

Repeat UCrit and endurance swimming in juvenile shortnose sturgeon (Acipenser brevirostrum)

Previous results show that juvenile shortnose sturgeon are steady swimmers and, compared with salmonids, generally have low critical swimming (UCrit) and endurance swimming capacities. Most studies on swimming capacities of sturgeon, and other fishes, include those where fish have only been swum once and the metrics of swimming performance are assessed (e.g., time swum, speed achieved). Under natural conditions, there are ample instances where fish undergo multiple swimming cycles when traversing fish ways, culverts and other sources of fast water flow. While some evidence exists for salmonids, the effects of repeat swimming are not well known for sturgeon. The current study consisted of two experiments. The first examined the UCrit of juvenile shortnose sturgeon following three consecutive swimming trials with a 30 min recovery period between subsequent tests. The second examined the endurance swimming capacities of juvenile shortnose sturgeon following three consecutive swimming trials with a 60 min recovery period between subsequent tests. Our findings indicate that (i) UCrit was consistent (~2 body lengths/s) among swimming trials; (ii) significant individual variation exists between individuals in the endurance swimming trials; and (iii) consistent results exist for individuals across swimming trials in both the UCrit and the endurance swimming tests. These results suggest that juvenile shortnose sturgeon have a high recovery capacity, and their behaviour and morphology likely reflect aspects of their swimming capacities.

Superfetation reduces the negative effects of pregnancy on the fast-start escape performance in live-bearing fish

Superfetation, the ability to simultaneously carry multiple litters of different developmental stages in utero, is a reproductive strategy that evolved repeatedly in viviparous animal lineages. The evolution of superfetation is hypothesized to reduce the reproductive burden and, consequently, improve the locomotor performance of the female during pregnancy. Here, we apply new computer-vision-based techniques to study changes in body shape and three-dimensional fast-start escape performance during pregnancy in three live-bearing fishes (family Poeciliidae) that exhibit different levels of superfetation. We found that superfetation correlates with a reduced abdominal distension and a more slender female body shape just before parturition. We further found that body slenderness positively correlates with maximal speeds, curvature amplitude and curvature rate, implying that superfetation improves the fast-start escape performance. Collectively, our study suggests that superfetation may have evolved in performance-demanding (e.g. high flow or high predation) environments to reduce the locomotor cost of pregnancy.

Repeatability of burst swimming performance in medaka (Oryzias latipes)

Burst swimming performance (U_burst) is a putative indicator of "success" in wild fish. In this study, thirty-five lab-reared medaka (Oryzias latipes) were tested for U_burst using a French press exercise system. Fish were tested once a week for four consecutive weeks and repeatability was estimated in several ways to allow comparisons between studies. Following the initial swimming tests, 50% of fish were either thermally stressed, or not, for 180 s prior to testing U_burst once a week for four consecutive weeks. Burst swimming performance was found to be 24.0 ± 6.7 (s.d.) cm s^-1 and repeatability prior to the thermal stress experiment was estimated to be 0.28 (intraclass correlation coefficient) with an upper and lower limit of 0.48 and 0.12, respectively. The measured U_burst and repeatability estimate in the thermal stressor experiment did not significantly differ from the first four trials. Swimming velocities observed match what is known about medaka swimming capabilities and, interestingly, are similar to maximum current velocities observed in their native habitat. Furthermore, our repeatability estimates confirm that burst swimming performance in medaka is a repeatable trait and validate the apparatus and swimming test used.

Repeatability of Hypoxia Tolerance of Individual Juvenile Striped Bass Morone saxatilis and Effects of Social Status

Chesapeake Bay is the primary nursery for striped bass (Morone saxatilis), which are increasingly being exposed to hypoxic waters. Tolerance to hypoxia in fish is generally determined by a single exposure of an isolated individual or by exposing large groups of conspecifics to hypoxia without regard to social status. The importance of social context in determining physiological responses to stressors is being increasingly recognized. To determine whether social interactions influence hypoxia tolerance (HT) in striped bass, loss of equilibrium HT was assessed in the same fish while manipulating the social environment around it. Small group settings were used to be more representative of the normal sociality experienced by this species than the paired encounters typically used. After establishing the dominance hierarchy within a group of fish, HT was determined collectively for the individuals in that group, and then new groups were constructed from the same pool of fish. Individuals could then be followed across multiple settings for both repeatability of HT and hierarchy position ( X ¯ = 4.2 ± 0.91 SD groups per individual). HT increased with repeated exposures to hypoxia ( P < 0.001 ), with a significant increase by a third exposure ( P = 0.004 ). Despite this changing HT, rank order of HT was significantly repeatable across trials for 6 mo ( P = 0.012 ). Social status was significantly repeatable across trials of different group composition ( P = 0.02 ) and unrelated to growth rate but affected HT weakly in a complex interaction with size. Final HT was significantly correlated with blood [hemoglobin] and hematocrit. The repeatability and large intraspecific variance of HT in juvenile striped bass suggest that HT is potentially an important determinant of Darwinian fitness in an increasingly hypoxic Chesapeake Bay.

Lizards at the Peak: Physiological Plasticity Does Not Maintain Performance in Lizards Transplanted to High Altitude

Warming climates are facilitating the range expansion of many taxa to habitats that were formerly thermally inhospitable, including to higher latitudes and elevations. The potential for such colonization, however, varies widely among taxa. Because environmental factors may interact to affect colonization potential, an understanding of underlying physiological and behavioral mechanisms is necessary to predict how species will respond to potentially suitable habitats. For example, temperature and oxygen availability will interact to shape physiological and performance traits. Our model species, the wall lizard, Podarcis muralis, is a widely distributed ectotherm that continues to expand its range in Europe despite being limited by cold temperatures at high elevations and latitudes. To test the potential for organisms to expand to warming high-altitude environments, we conducted a transplant experiment to quantify the within-individual effects of high-altitude hypoxia on physiological and performance traits. Transplanted lizards maintained individual differences in physiological traits related to oxygen capacity and metabolism (hemoglobin concentration, hematocrit, and peak postexhaustion metabolic rate), as well as performance traits tied to fitness (sprint speed and running endurance). Although lizards altered blood biochemistry to increase oxygen-carrying capacity, their performance was reduced at high altitude. Furthermore, lizards at high altitude suffered a rapid loss of body condition over the 6-wk experiment, suggesting an energetic cost to hypoxia. Taken together, this demonstrates a limited potential for within-individual plasticity to facilitate colonization of novel high-altitude environments.

Zebrafish (Danio rerio) as a Model for Sprint Exercise Training

Sprint performance is important ecologically and physiologically, and it can influence fitness by determining outcomes of predator-prey relationships, for example, and it can confer substantial human health benefits. In this article we test whether zebrafish (Danio rerio) are a suitable model to test hypotheses about the effects and consequences of sprint exercise training, and the physiological underpinnings of sprint performance. We show that stage 3 c-starts that capture the initial escape response of fish lasting <1 s were repeatable within individuals. In addition, somewhat longer constant acceleration protocols lasting 10 s (U_10s) or 30 s (U_30s) were highly repeatable within individuals over 3, 6, and 23 days. C-starts within individuals were not correlated with either U_10s or U_30s, indicating that these measures reflect different physiological aspects of sprinting. Stage 3 c-starts and U_10s responded positively to sprint exercise training. Our exercise training protocol (5 × 10 s sprints with 5-min rest periods on 4 days per week for 3 weeks) was based on the human sporting literature, and together, our results indicate that zebrafish are a good model to assess the physiological and behavioral consequences of sprint exercise training.

Variation and repeatability of cutaneous water loss and skin resistance in relation to temperature and diel variation in the lizard Sceloporus consobrinus

Variation in rates of water loss has been proposed to be an important mechanism in the survival of terrestrial organisms, as high rates of water loss in desiccating environments may lead to hydric stress and death. Vapor density deficit, the driving force for evaporative water loss, increases exponentially as temperature increases. Acute temperature changes may be the result of daily behavioral thermoregulation of ectotherms, which may influence the among individual variation rates of water loss. The goals of this study were to determine (1) how rates of cutaneous water loss (CWL) and skin resistance (R_s) are affected by acute temperature acclimation, (2) how rates of CWL and R_s vary throughout the day allowing behavioral thermoregulation and (3) the repeatability of CWL and R_s within and among sampling periods. We measured CWL and calculated skin resistance (R_s) of 30 male Sceloporus consobrinus lizards across three summers. We measured CWL on the dorsal and ventral surface of each lizard at 23 °C followed by measurements at 35 °C, and three separate times throughout the day. We found a significant increase in R_s and decrease in CWL at increased acclimation temperatures (35 °C), a significant difference in CWL and R_s throughout the day allowing behavioral thermoregulation, and support for the repeatability of CWL and R_s. Our results demonstrate variability in CWL and R_s in relation to temperature acclimation and thermoregulation, but mixed evidence for repeatability across treatments. Our results suggest other factors, such as peripheral blood flow, may be influencing the inter-individual variation in CWL and R_s.

Environmental calcium and variation in yolk sac size influence swimming performance in larval lake sturgeon (Acipenser fulvescens)

In many animal species, performance in the early life stages strongly affects recruitment to the adult population; however, factors that influence early life history stages are often the least understood. This is particularly relevant for lake sturgeon, Acipenser fulvescens, living in areas where environmental calcium concentrations are declining, partly due to anthropogenic activity. As calcium is important for muscle contraction and fatigue resistance, declining calcium levels could constrain swimming performance. Similarly, swimming performance could be influenced by variation in yolk sac volume, because the yolk sac is likely to affect drag forces during swimming. Testing swimming performance of larval A. fulvescens reared in four different calcium treatments spanning the range of 4-132 mg l^-1 [Ca²⁺], this study found no treatment effects on the sprint swimming speed. A novel test of volitional swimming performance, however, revealed reduced swimming performance in the low calcium environment. Specifically, volitionally swimming larvae covered a shorter distance before swimming cessation in the low calcium environment compared with the other treatments. Moreover, sprint swimming speed in larvae with a large yolk sac was significantly slower than in larvae with a small yolk sac, regardless of body length variation. Thus, elevated maternal allocation (i.e. more yolk) was associated with reduced swimming performance. Data suggest that larvae in low calcium environments or with a large yolk sac exhibit reduced swimming performance and could be more susceptible to predation or premature downstream drift. Our study reveals how environmental factors and phenotypic variation influence locomotor performance in a larval fish.

Hypoxia and Sprint Swimming Performance of Juvenile Striped Bass, Morone saxatilis

Annual hypoxia in the Chesapeake Bay has expanded to the point where Darwinian fitness of juvenile striped bass (Morone saxatilis) may depend on their ability to perform in low-oxygen environments. The locomotion they use in predator/prey dynamics relies primarily on white (type II) muscle that is powered by anaerobic metabolic pathways and has generally been thought to be immune to aquatic hypoxia. We tested the sprint performance of 15 juvenile striped bass twice under acute hypoxia (20% air saturation [AS]) 5 wk apart and once under normoxia (>85% AS) in between. Average sprint performance was lower under the first hypoxia exposure than in normoxia and increased in the second hypoxia test relative to the first. The rank order of individual sprint performance was significantly repeatable when comparing the two hypoxia tests but not when compared with sprint performance measured under normoxic conditions. The maximum sprint performance of each individual was also significantly repeatable within a given day. Thus, sprint performance of striped bass is reduced under hypoxia, is phenotypically plastic, and improves with repetitive hypoxia exposures but is unrelated to relative sprint performance under normoxia. Since energy to fuel a sprint comes from existing ATP and creatine phosphate stores, the decline in sprint performance probably reflects reduced function of a part of the reflex chain leading from detection of aversive stimuli to activation of the muscle used to power the escape response.

Physiological determinants of individual variation in sensitivity to an organophosphate pesticide in Nile tilapia Oreochromis niloticus

Individual variation in sub-lethal sensitivity to the organophosphate pesticide trichlorfon was investigated in Nile tilapia, using critical swimming speed (U_crit) as an indicator. Tilapia exposed for 96h to 500μgl^-1 trichlorfon at 26°C (Tcfn group, n=27) showed a significant decline in mean U_crit, compared to their own control (pre-exposure) performance in clean water (-14.5±2.3%, mean±SEM), but also compared to a Sham group (n=10) maintained for 96h in clean water. Individuals varied in their relative sensitivity to the pesticide, with the decline in U_crit after exposure varying from 1 to 41%. The U_crit of the Tcfn group did not recover completely after 96h in clean water, remaining 9.4±3.2% below their own control performance. The decline in performance was associated with a significant increase in net cost of aerobic swimming, of +28.4±6.5% at a sustained speed of 2bodylengthss^-1, which translated into a significant decline in swimming efficiency (E_swim) of -17.6±4.0% at that speed. Within the Tcfn group, individual E_swim was a strong positive determinant of individual U_crit across all trials, and a strong negative determinant of individual% decline in U_crit after pesticide exposure (P<0.001, linear mixed effect models). Trichlorfon had no effects on standard metabolic rate or active metabolic rate (AMR) but, nonetheless, individual U_crit in all trials, and% decline in U_crit after exposure, were strongly associated with individual AMR (positively and negatively, respectively, P<0.001). Individual U_crit under control conditions was also a strong positive determinant of U_crit after trichlorfon exposure (P<0.001), but not of the% decline in U_crit performance. In conclusion, the OP pesticide impaired U_crit performance by reducing E_swim but individual tilapia varied widely in their relative sensitivity. Intrinsic individual physiology determined effects of the pesticide on performance and, in particular, good swimmers remained better swimmers after exposure.

Differences in swimming ability and its response to starvation among male and female Gambusia affinis

To explore the differences in the swimming ability and environmental adaptive abilities between male and female Gambusia affinis, we assessed the differences in burst swimming speeds (U_burst), critical swimming speeds (U_crit) and their related fin areas, and consumption of energy substances after starvation at 0 (control group), 15, 30, 45, and 60 days, respectively. The results showed that the pectoral and caudal fin areas did not differ significantly between male and female G. affinis. However, the dry mass, condition factors, and absolute contents of glycogen, lipids, and proteins were significantly elevated in females in the control group (P<0.05), whereas U_burst and U_crit were significantly low (P<0.05). After starvation of 60 days, the rate of consumption of lipids was significantly low in the females (P<0.05). Although U_burst and U_crit decreased linearly with increased duration of starvation, the coefficient of linear equation between U_crit and starvation time was significantly lower in females than males (P<0.05). These findings indicated that low body mass and condition factors reduce the relative bear load and moving resistance that causes high swimming performance in male G. affinis. High contents of energy substances and low rate of consumption of lipids result in stable U_crit in females during hunger.

Summary: The study explored the causes of variation in swimming performance with respect to morphological and physiological characteristics, which provides further information about environmental adaptive ability in Gambusia affinis.

A comparison of constant acceleration swimming speeds when acceleration rates are different with critical swimming speeds in Chinese bream under two oxygen tensions

To investigate the effect of acceleration rates on the constant acceleration test speed (U cat) and to compare U cat with the critical swimming speed (U crit) in Chinese bream (Parabramis pekinensis), the U cat test at acceleration rates of 0.05, 0.1, 0.2, 0.4 and 0.8 cm s(-2) and the U crit test in juvenile fish at 20 °C in either normoxia (>90 % saturation oxygen tension) or hypoxia (30 % saturation) were compared. The lactate concentration ([lactate]) of white muscle, liver and plasma and the glycogen concentration ([glycogen]) of white muscle and liver were also measured to identify whether tissue substrate depletion or tissue lactate accumulation correlated with exhaustion. The U cat decreased with the acceleration rate, and there was no significant difference between U crit and U cat at lower acceleration rates. Hypoxia resulted in lower U cat and U crit, and the difference increased with decreased acceleration rates of the U cat test, possibly due to the increased contribution of aerobic components in U crit or U cat at low acceleration rates. Hypoxia elicited a significant decrease in muscle [glycogen] and an increase in muscle and liver [lactate] in resting fish. All post-exercise fish had similar muscle [lactate], suggesting that tissue lactate accumulation may correlate with exercise exhaustion. Unlike hypoxia, exercise induced an increase in muscle [lactate] and a significant increase in plasma [lactate], which were worthy of further investigation. The similar swimming speed and biochemical indicators after exercise in the U crit and U cat groups at low acceleration rates suggested that U cat can be an alternative for the more frequently adopted protocols in U crit in Chinese bream and possibly in other cyprinid fish species.

The effects of starvation and re-feeding on growth and swimming performance of juvenile black carp (Mylopharyngodon piceus)

We investigated the effects of starvation and re-feeding on growth and swimming performance and their relationship in juvenile black carp (Mylopharyngodon piceus). We measured the specific growth rate (SGR), resting metabolic rate (RMR) and constant acceleration test speed (U CAT, the maximum swimming speed at exhaustion by constant acceleration test with 0.1667 cm s(-2) rate) in a treatment group (21 days of starvation then 21 days of re-feeding) and control group (routine feeding) (n = 20). Starvation resulted in a 17 % decrease in body mass of black carp (P < 0.05). After 21 days of re-feeding, body mass was greater than that of pre-starvation but still less than that of the control group at 42 days. During the re-feeding phase, the SGR of the treatment group was higher than that of the control group (P < 0.05). Starvation resulted in a significant decrease in the RMR and U CAT. After 21 days of re-feeding, both the RMR and U CAT recovered to the pre-starvation levels. In the control group, individual juvenile black carp displayed strong repeatability of the RMR and U CAT across the measurement periods (P ≤ 0.002). In the treatment group, RMR showed significant repeatability between pre-starvation and re-feeding (P = 0.007), but not between pre-starvation and starvation or between starvation and re-feeding. U CAT showed significant repeatability between pre-starvation and starvation (P = 0.006) and between pre-starvation and re-feeding (P = 0.001), but not between starvation and re-feeding. No correlation or only a weak correlation was found between any two variables of RMR, U CAT and SGR, whereas the increment of the U CAT (ΔU CAT) was negatively correlated with that of SGR during the starvation phase (r = -0.581, n = 20, P = 0.007) and re-feeding phase (r = -0.568, n = 20, P = 0.009). This suggested that within individual black carp, there is a trade-off between growth and maintenance (or development) of swimming performance under food-limited conditions.

Scaling of the fast-start escape response of juvenile bluegills

Morphology, size and physiological properties change markedly across fish ontogeny. This impacts locomotor performance and organismal fitness, although the effects are unpredictable due to the complexity of phenotype-function relationships. Morphological and behavioral changes with growth are often paralleled by changes in habitat use, diet and vulnerability to predators. Our goal was to quantify the changes in external morphology and escape performance throughout post-larval development in bluegill sunfish (Lepomis macrochirus), and place these changes in context with known changes in habitat use in the field. Development into adult ecomorphs is associated with phenotypic plasticity in response to habitat-specific differences in diet. On this basis, we hypothesized that variation in morphology and performance would increase during bluegill ontogeny as diversification of adult ecomorphs occurred. However, we found that variation in phenotype and escape performance decreased during early ontogeny. Phenotypic variation expanded later in development, after fish gained access to the variety of habitats and food types that may favor phenotypic plasticity. Performance is predicted to decline with growth due to the differential scaling of inertia and cross-sectional area, a major determinant of muscle force. In contrast, acceleration increased with size, and velocity and acceleration increased more rapidly with size than predicted. Post-larval maturation in bluegill featured a shift to a deeper body shape, and an increase in the relative size of the anal and caudal fins. This was a likely factor in the deviation of escape performance scaling relationships from predictions based on geometric similarity.

Partitioning the metabolic scope: the importance of anaerobic metabolism and implications for the oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis

Ongoing climate change is predicted to affect the distribution and abundance of aquatic ectotherms owing to increasing constraints on organismal physiology, in particular involving the metabolic scope (MS) available for performance and fitness. The oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis prescribes MS as an overarching benchmark for fitness-related performance and assumes that any anaerobic contribution within the MS is insignificant. The MS is typically derived from respirometry by subtracting standard metabolic rate from the maximal metabolic rate; however, the methodology rarely accounts for anaerobic metabolism within the MS. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), this study tested for trade-offs (i) between aerobic and anaerobic components of locomotor performance; and (ii) between the corresponding components of the MS. Data collection involved measuring oxygen consumption rate at increasing swimming speeds, using the gait transition from steady to unsteady (burst-assisted) swimming to detect the onset of anaerobic metabolism. Results provided evidence of the locomotor performance trade-off, but only in S. aurata. In contrast, both species revealed significant negative correlations between aerobic and anaerobic components of the MS, indicating a trade-off where both components of the MS cannot be optimized simultaneously. Importantly, the fraction of the MS influenced by anaerobic metabolism was on average 24.3 and 26.1% in S. aurata and P. reticulata, respectively. These data highlight the importance of taking anaerobic metabolism into account when assessing effects of environmental variation on the MS, because the fraction where anaerobic metabolism occurs is a poor indicator of sustainable aerobic performance. Our results suggest that without accounting for anaerobic metabolism within the MS, studies involving the OCLTT hypothesis could overestimate the metabolic scope available for sustainable activities and the ability of individuals and species to cope with climate change.

Patterns of variation in feeding strike kinematics of juvenile ghost praying mantis (Phyllocrania paradoxa): are components of the strike stereotypic?

Functional systems, such as feeding mechanics, often involve the evolution of several components of the musculoskeletal system that are moved in coordination to capture prey. Because these systems often involve the quick movement of several structures, some feeding systems have been hypothesized to be stereotypic. While the motor activity patterns are often stereotyped, the subsequent kinematics can be variable, many times in response to variation in prey stimulus (e.g., prey position). Patterns of feeding kinematics have been well studied among vertebrates, with less attention on invertebrate systems. The goal of this study was to examine the amount of stereotypy in the feeding strike kinematics of praying mantises. We filmed 8 juvenile ghost praying mantises (Phyllocrania paradox) at 1000 Hz, across several days within instar 7. We digitized several points that represent the movement of the coxa, trochanter-femur and tibia of the raptorial foreleg to obtain a set of kinematics including angles and angular velocities of the joint, as well as body lunge. Using the coefficient of variation, we found less stereotypy in the approach stage of the strike compared to the sweep. Using Bonferroni corrected Pearson's correlations of kinematics with prey position we found few traits related to prey position with the exception of some kinematics of the coxa joint and the amount of lunge used during the strike. Our results suggest that several components of the praying mantis strike are stereotypic, while others exhibit flexibility to ensure successful capture of the prey.

Understanding the individual to implement the ecosystem approach to fisheries management

Ecosystem-based approaches to fisheries management (EAFMs) have emerged as requisite for sustainable use of fisheries resources. At the same time, however, there is a growing recognition of the degree of variation among individuals within a population, as well as the ecological consequences of this variation. Managing resources at an ecosystem level calls on practitioners to consider evolutionary processes, and ample evidence from the realm of fisheries science indicates that anthropogenic disturbance can drive changes in predominant character traits (e.g. size at maturity). Eco-evolutionary theory suggests that human-induced trait change and the modification of selective regimens might contribute to ecosystem dynamics at a similar magnitude to species extirpation, extinction and ecological dysfunction. Given the dynamic interaction between fisheries and target species via harvest and subsequent ecosystem consequences, we argue that individual diversity in genetic, physiological and behavioural traits are important considerations under EAFMs. Here, we examine the role of individual variation in a number of contexts relevant to fisheries management, including the potential ecological effects of rapid trait change. Using select examples, we highlight the extent of phenotypic diversity of individuals, as well as the ecological constraints on such diversity. We conclude that individual phenotypic diversity is a complex phenomenon that needs to be considered in EAFMs, with the ultimate realization that maintaining or increasing individual trait diversity may afford not only species, but also entire ecosystems, with enhanced resilience to environmental perturbations. Put simply, individuals are the foundation from which population- and ecosystem-level traits emerge and are therefore of central importance for the ecosystem-based approaches to fisheries management.

Repeatability of locomotor performance and of morphology – locomotor performance relationships

There is good evidence that natural selection drives the evolution of locomotor performance, but the processes that generate among individual variation in locomotion, the substrate upon which selection acts, are relatively poorly understood. We measured prolonged swimming performance, Ucrit, and morphology in a large cohort (n=461) of wildtype zebrafish, Danio rerio, at ∼6 months and again at ∼9 months. Using mixed model analyses to estimate repeatability as the intraclass correlation coefficient, we determined that Ucrit was significantly repeatable (r = 0.55; 95% CI: 0.45 -0.64). Performance differences between the sexes (males 12% faster than females) and changes with age (decreasing 0.07% per day) both contributed to variation in Ucrit and, therefore, the repeatability estimate. Accounting for mean differences between sexes within the model decreased the estimate of Ucrit repeatability to 21% below the naïve estimate, while fitting age in the models increased the estimate to 14% above the naïve estimate. Greater consideration of factors such as age and sex is therefore necessary for the interpretation of performance repeatability in wild populations. Body shape significantly predicted Ucrit in both sexes in both assays, with the morphology – performance relationship significantly repeatable at the population level. However, morphology was more strongly predicative of performance in older fish, suggesting a change in the contribution of morphology relative to other factors such as physiology and behaviour. The morphology – performance relationship changed with age to a greater extent in males than females.

Body size, swimming speed, or thermal sensitivity? Predator-imposed selection on amphibian larvae

Background

Many animals rely on their escape performance during predator encounters. Because of its dependence on body size and temperature, escape velocity is fully characterized by three measures, absolute value, size-corrected value, and its response to temperature (thermal sensitivity). The primary target of the selection imposed by predators is poorly understood. We examined predator (dragonfly larva)-imposed selection on prey (newt larvae) body size and characteristics of escape velocity using replicated and controlled predation experiments under seminatural conditions. Specifically, because these species experience a wide range of temperatures throughout their larval phases, we predict that larvae achieving high swimming velocities across temperatures will have a selective advantage over more thermally sensitive individuals.

Results

Nonzero selection differentials indicated that predators selected for prey body size and both absolute and size-corrected maximum swimming velocity. Comparison of selection differentials with control confirmed selection only on body size, i.e., dragonfly larvae preferably preyed on small newt larvae. Maximum swimming velocity and its thermal sensitivity showed low group repeatability, which contributed to non-detectable selection on both characteristics of escape performance.

Conclusions

In the newt-dragonfly larvae interaction, body size plays a more important role than maximum values and thermal sensitivity of swimming velocity during predator escape. This corroborates the general importance of body size in predator–prey interactions. The absence of an appropriate control in predation experiments may lead to potentially misleading conclusions about the primary target of predator-imposed selection. Insights from predation experiments contribute to our understanding of the link between performance and fitness, and further improve mechanistic models of predator–prey interactions and food web dynamics.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0522-y) contains supplementary material, which is available to authorized users.

Sex-specific genetic differences in endurance swimming of Trinidadian guppies

Swim performance is considered a main fitness-determining trait in many aquatic organisms. Swimming is generally the only way most aquatic prey can escape predation, and swimming capacity is directly linked to food capture, habitat shifts, and reproduction. Therefore, evolutionary studies of swim performance are important to understand adaptation to aquatic environments. Most studies, however, concentrate on the importance of burst-swim responses to predators, and little is known about its effect on endurance. Even fewer studies associate differences in organism swim capabilities to key gender-specific responses. In this experiment, we assess the gender-specific genetic basis of swimming endurance among four different populations of Trinidadian guppies adapted to different predation regimes. Our results show that second-generation common-garden females adapted to a low-predation environment show longer swim endurance than fish adapted to a high-predation environment. We also find an expected effect of lowered swimming endurance during pregnancy, but interestingly, it did not matter whether the females were in advanced stages of pregnancy, which severely changes body morphology, versus mid-pregnancy. Males did not show the same trends across populations, and overall had lower swim endurances than female fish combined even when accounting for size differences. Populations recently transplanted from high- to low-predation environments showed similar endurance to natural low-predation environments in one population but not the other. This study highlights the importance of endurance in the adaptation of aquatic organisms to different predation regimes.

Sexually dimorphic morphology and swimming performance relationships in wild-type zebrafish Danio rerio

This study compared prolonged swimming performance (Ucrit ) between male and female Danio rerio, and characterized how body shape was associated with this performance measure in each sex. When swimming in small (n = 6) mixed-sex groups at 28 °C, males swam, on average, over 10 cm s(-1) faster than females despite being significantly smaller. Body shape was sexually dimorphic, with males and females exhibiting small, but statistically significant differences in most aspects of body shape. Body shape explained 18 and 43% of the variation in Ucrit among males and females. In general, effects of body shape on swimming performance appeared to be sex limited, whereby different aspects of body shape affected performance in each sex, although the contribution of the distance between pelvic and anal fins to swimming performance was weakly sexually antagonistic.

Inter- vs intra-individual variation and temporal repeatability of escape responses in the coral reef fish Amblyglyphidodon curacao

Fast-start escape responses are critical behaviours used by fishes during predator-prey encounters and some interactions with hetero- and conspecifics. In experimental studies, escape responses are often measured once per individual and considered representative of maximum performance. However, few studies have compared variability and repeatability in escape performances within and among individuals. Using the tropical damselfish Amblyglyphidodon curacao, we quantified inter- and intra-individual variation in behavioural and kinematic components of escape performance during repeated presentations of a stimulus at 15 min intervals. Individual maximum escape performance was repeatable through time, but there was considerable variation in the magnitude of responses both among and within fish. We found no evidence of habituation or fatigue due to repeated stimulations, suggesting that fish can be stimulated multiple times to ensure that an accurate estimate of maximum escape performance is obtained.

Summary: Quantification of the inter- and intra-individual variation in behavioural and kinematic components of escape performance of the tropical damselfish Amblyglyphidodon curacao found no evidence of habituation or fatigue due to repeated stimulations.

Intraspecific variation in aerobic and anaerobic locomotion: gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata) do not exhibit a trade-off between maximum sustained swimming speed and minimum cost of transport

Intraspecific variation and trade-off in aerobic and anaerobic traits remain poorly understood in aquatic locomotion. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), both axial swimmers, this study tested four hypotheses: (1) gait transition from steady to unsteady (i.e., burst-assisted) swimming is associated with anaerobic metabolism evidenced as excess post exercise oxygen consumption (EPOC); (2) variation in swimming performance (critical swimming speed; U_crit) correlates with metabolic scope (MS) or anaerobic capacity (i.e., maximum EPOC); (3) there is a trade-off between maximum sustained swimming speed (U_sus) and minimum cost of transport (COT_min); and (4) variation in U_sus correlates positively with optimum swimming speed (U_opt; i.e., the speed that minimizes energy expenditure per unit of distance traveled). Data collection involved swimming respirometry and video analysis. Results showed that anaerobic swimming costs (i.e., EPOC) increase linearly with the number of bursts in S. aurata, with each burst corresponding to 0.53 mg O₂ kg⁻¹. Data are consistent with a previous study on striped surfperch (Embiotoca lateralis), a labriform swimmer, suggesting that the metabolic cost of burst swimming is similar across various types of locomotion. There was no correlation between U_crit and MS or anaerobic capacity in S. aurata indicating that other factors, including morphological or biomechanical traits, influenced U_crit. We found no evidence of a trade-off between U_sus and COT_min. In fact, data revealed significant negative correlations between U_sus and COT_min, suggesting that individuals with high U_sus also exhibit low COT_min. Finally, there were positive correlations between U_sus and U_opt. Our study demonstrates the energetic importance of anaerobic metabolism during unsteady swimming, and provides intraspecific evidence that superior maximum sustained swimming speed is associated with superior swimming economy and optimum speed.

The effect of temperature on repeat swimming performance in juvenile qingbo (Spinibarbus sinensis)

To investigate the effect of temperature on the repeat constant acceleration swimming performance and on the metabolic recovery capacity in juvenile qingbo (Spinibarbus sinensis), their constant acceleration test speed (U(CAT)) and excess post-exercise oxygen consumption (EPOC) recovery process were measured twice with 1-h intervals at different acclimation temperatures (10, 15, 20, 25 and 30 °C). Temperature significantly affected U(CAT), the pre-exercise metabolic rate (MO(2)), metabolic peak values (MO(2peak)), the metabolic scope (MS, MO(2peak)--pre-exercise MO(2)) and the magnitude of the EPOC (P < 0.05). These parameters significantly increased as the temperature increased from 15 to 25 °C and significantly decreased (U(CAT) and EPOC magnitude) or did not change (MO(2peak) and MS) when the temperature increased from 25 to 30 °C in the first test (P < 0.05). The relationships between temperature (T) and these parameters (U(CAT), MO(2peak), MS and EPOC magnitude) in the first test were as follows: U(CAT) = 62.14/{1 + [(T - 25.1)/21.1](2)} (r = 0.847, P < 0.001, n = 40); MO(2peak) = 1,052.11/{1 + [(T - 29.2)/18.9](2)} (r = 0.901, P < 0.001, n = 39); MS = 753.74/{1 + [(T - 27.1)/18.6](2)} (r = 0.768, P < 0.001, n = 39); and EPOC = 195.42/{1 + [(T - 25.6)/8.7](2)} (r = 0.752, P < 0.001, n = 39). The optimal temperatures for U(CAT), MO(2peak), MS and EPOC magnitude in juvenile qingbo were 25.1, 29.2, 27.1 and 28.6 °C, respectively. Repeat exercise had different effect on U(CAT) and EPOC magnitude at different temperature (interaction effect, P < 0.05). There was no difference in U(CAT) and in EPOC magnitude between the first and second tests at low temperatures (10-20 °C). However, both U(CAT) and EPOC magnitude decreased significantly during the second test compared with the first test at high temperatures (25 and 30 °C) (P < 0.05). The present study showed that the recovery of the constant acceleration swimming performance was poorer at higher temperatures than at low temperatures in juvenile qingbo. These differences may be related to larger anaerobic metabolism, a lower pH value in the blood, larger ionic fluids and/or higher levels of hormones present at high temperatures.

Evidence of circadian rhythm, oxygen regulation capacity, metabolic repeatability and positive correlations between forced and spontaneous maximal metabolic rates in lake sturgeon Acipenser fulvescens

Animal metabolic rate is variable and may be affected by endogenous and exogenous factors, but such relationships remain poorly understood in many primitive fishes, including members of the family Acipenseridae (sturgeons). Using juvenile lake sturgeon (Acipenser fulvescens), the objective of this study was to test four hypotheses: 1) A. fulvescens exhibits a circadian rhythm influencing metabolic rate and behaviour; 2) A. fulvescens has the capacity to regulate metabolic rate when exposed to environmental hypoxia; 3) measurements of forced maximum metabolic rate (MMR_F) are repeatable in individual fish; and 4) MMR_F correlates positively with spontaneous maximum metabolic rate (MMR_S). Metabolic rates were measured using intermittent flow respirometry, and a standard chase protocol was employed to elicit MMR_F. Trials lasting 24 h were used to measure standard metabolic rate (SMR) and MMR_S. Repeatability and correlations between MMR_F and MMR_S were analyzed using residual body mass corrected values. Results revealed that A. fulvescens exhibit a circadian rhythm in metabolic rate, with metabolism peaking at dawn. SMR was unaffected by hypoxia (30% air saturation (O_2sat)), demonstrating oxygen regulation. In contrast, MMR_F was affected by hypoxia and decreased across the range from 100% O_2sat to 70% O_2sat. MMR_F was repeatable in individual fish, and MMR_F correlated positively with MMR_S, but the relationships between MMR_F and MMR_S were only revealed in fish exposed to hypoxia or 24 h constant light (i.e. environmental stressor). Our study provides evidence that the physiology of A. fulvescens is influenced by a circadian rhythm and suggests that A. fulvescens is an oxygen regulator, like most teleost fish. Finally, metabolic repeatability and positive correlations between MMR_F and MMR_S support the conjecture that MMR_F represents a measure of organism performance that could be a target of natural selection.

The evolution of the sexually selected sword in Xiphophorus does not compromise aerobic locomotor performance

Sexual selection can increase morphological diversity within and among species. Little is known regarding how interspecific variation produced through sexual selection affects other functional systems. Here, we examine how morphological diversity resulting from sexual selection impacts aerobic locomotor performance. Using Xiphophorus (swordtail fish) and their close relatives (N = 19 species), we examined whether the evolution of a longer sexually selected sword affects critical swimming speed. We also examined the effect of other suborganismal, physiological, and morphological traits on critical swimming speed, as well as their relationship with sword length. In correlation analyses, we found no significant relationship between sword length and critical swimming speed. Unexpectedly, we found that critical swimming speed was higher in species with longer swords, after controlling for body size in multiple regression analyses. We also found several suborganismal and morphological predictors of critical swimming speed, as well as a significant negative relationship between sword length and heart and gill mass. Our results suggest that interspecific variation in sword length is not costly for this aspect of swimming performance, but further studies should examine potential costs for other types of locomotion and other components of Darwinian fitness (e.g., survivorship, life span).

Artificial selection on relative brain size reveals a positive genetic correlation between brain size and proactive personality in the guppy

Animal personalities range from individuals that are shy, cautious, and easily stressed (a “reactive” personality type) to individuals that are bold, innovative, and quick to learn novel tasks, but also prone to routine formation (a “proactive” personality type). Although personality differences should have important consequences for fitness, their underlying mechanisms remain poorly understood. Here, we investigated how genetic variation in brain size affects personality. We put selection lines of large- and small-brained guppies (Poecilia reticulata), with known differences in cognitive ability, through three standard personality assays. First, we found that large-brained animals were faster to habituate to, and more exploratory in, open field tests. Large-brained females were also bolder. Second, large-brained animals excreted less cortisol in a stressful situation (confinement). Third, large-brained animals were slower to feed from a novel food source, which we interpret as being caused by reduced behavioral flexibility rather than lack of innovation in the large-brained lines. Overall, the results point toward a more proactive personality type in large-brained animals. Thus, this study provides the first experimental evidence linking brain size and personality, an interaction that may affect important fitness-related aspects of ecology such as dispersal and niche exploration.

Relationships among traits of aerobic and anaerobic swimming performance in individual European sea bass Dicentrarchus labrax

Teleost fishes exhibit wide and temporally stable inter-individual variation in a suite of aerobic and anaerobic locomotor traits. One mechanism that could allow such variation to persist within populations is the presence of tradeoffs between aerobic and anaerobic performance, such that individuals with a high capacity for one type of performance have a reduced capacity for the other. We investigated this possibility in European seabass Dicentrarchuslabrax, each measured for a battery of indicators of maximum locomotor performance. Aerobic traits comprised active metabolic rate, aerobic scope for activity, maximum aerobic swimming speed, and stride length, using a constant acceleration test. Anaerobic traits comprised maximum speed during an escape response, maximum sprint speed, and maximum anaerobic burst speed during constant acceleration. The data provided evidence of significant variation in performance among individuals, but there was no evidence of any trade-offs among any traits of aerobic versus anaerobic swimming performance. Furthermore, the anaerobic traits were not correlated significantly among each other, despite relying on the same muscular structures. Thus, the variation observed may reflect trade-offs with other morphological, physiological or behavioural traits.

Effects of intraspecific variation in reproductive traits, pectoral fin use and burst swimming on metabolic rates and swimming performance in the Trinidadian guppy (Poecilia reticulata)

There is considerable intraspecific variation in metabolic rates and locomotor performance in aquatic ectothermic vertebrates; however, the mechanistic basis remains poorly understood. Using pregnant Trinidadian guppies (Poecilia reticulata), a live-bearing teleost, we examined the effects of reproductive traits, pectoral fin use and burst-assisted swimming on swimming metabolic rate, standard metabolic rate (O2std) and prolonged swimming performance (Ucrit). Reproductive traits included reproductive allocation and pregnancy stage, the former defined as the mass of the reproductive tissues divided by the total body mass. Results showed that the metabolic rate increased curvilinearly with swimming speed. The slope of the relationship was used as an index of swimming cost. There was no evidence that reproductive traits correlated with swimming cost, O2std or Ucrit. In contrast, data revealed strong effects of pectoral fin use on swimming cost and Ucrit. Poecilia reticulata employed body-caudal fin (BCF) swimming at all tested swimming speeds; however, fish with a high simultaneous use of the pectoral fins exhibited increased swimming cost and decreased Ucrit. These data indicated that combining BCF swimming and pectoral fin movement over a wide speed range, presumably to support swimming stability and control, is an inefficient swimming behaviour. Finally, transition to burst-assisted swimming was associated with an increase in aerobic metabolic rate. Our study highlights factors other than swimming speed that affect swimming cost and suggests that intraspecific diversity in biomechanical performance, such as pectoral fin use, is an important source of variation in both locomotor cost and maximal performance.

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 4 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&lt;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&lt;0.016). Average clap-rate was repeatable in the short term (2 days, P&lt;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&lt;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.