Thermal constraints on exercise and metabolic performance do not explain the use of dormancy as an overwintering strategy in the cunner (Tautogolabrus adspersus)

Winter cold slows ectotherm physiology, potentially constraining activities and ecological opportunities at poleward latitudes. Yet, many fishes are winter-active, facilitated by thermal compensation that improves cold performance. Conversely, winter-dormant fishes (e.g. cunner, Tautogolabrus adspersus) become inactive and non-feeding overwinter. Why are certain fishes winter-dormant? We hypothesized that winter dormancy is an adaptive behavioural response arising in poleward species that tolerate severe, uncompensated constraints of cold on their physiological performance. We predicted that below their dormancy threshold of 7--8°C, exercise and metabolic performance of cunner are greatly decreased, even after acclimation (i.e. shows above-normal, uncompensated thermal sensitivity, Q10>1-3). We measured multiple key performance metrics (e.g. C-start maximum velocity, chase swimming speed, aerobic scope) in cunner after acute exposure to 26-2°C (3°C intervals using 14°C-acclimated fish) or acclimation (5-8 weeks) to 14-2°C (3°C intervals bracketing the dormancy threshold). Performance declined with cooling, and the acute Q10 of all six performance rate metrics was significantly greater below the dormancy threshold temperature (Q10,acute8-2°C=1.5-4.9, mean=3.3) than above (Q10,acute14-8°C=1.1-1.9, mean=1.5), inferring a cold constraint. However, 2°C acclimation (temporally more relevant to seasonal cooling) improved performance, abolishing the acute constraint (Q10,acclimated8-2°C=1.4-3.0, mean=2.0; also cf. Q10,acclimated14-8°C=1.2-2.9, mean=1.7). Thus, dormant cunner show partial cold-compensation of exercise and metabolic performance, similar to winter-active species. However, responsiveness to C-start stimuli was greatly cold-constrained even following acclimation, suggesting dormancy involves sensory limitation. Thermal constraints on metabolic and exercise physiology are not significant drivers of winter dormancy in cunner. In fact, compensatory plasticity at frigid temperatures is retained even in a dormant fish.

The effects of temperature on elastic energy storage and release in a system with a dynamic mechanical advantage latch

Changes in temperature alter muscle kinetics and in turn affect whole-organism performance. Some organisms use the elastic recoil of biological springs, structures which are far less temperature sensitive, to power thermally robust movements. For jumping frogs, the use of elastic energy in tendons is facilitated through a geometric latching mechanism that operates through dynamic changes in the mechanical advantage (MA) of the hindlimb. Despite the well-documented use of elastic energy storage, frog jumping is a locomotor behavior that is significantly affected by changes in temperature. Here, we used an in vitro muscle preparation interacting in real time with an in silico model of a legged jumper to understand how changes in temperature affect the flow of energy in a system using a MA latch. We used the plantaris longus muscle-tendon unit (MTU) to power a virtual limb with changing MA and a mass being accelerated through a real-time feedback controller. We quantified the amount of energy stored in and recovered from elastic structures and the additional contribution of direct muscle work after unlatching. We found that temperature altered the duration of the energy loading and recovery phase of the in vitro/in silico experiments. We found that the early phase of loading was insensitive to changes in temperature. However, an increase in temperature did increase the rate of force development, which in turn allowed for increased energy storage in the second phase of loading. We also found that the contribution of direct muscle work after unlatching was substantial and increased significantly with temperature. Our results show that the thermal robustness achieved by an elastic mechanism depends strongly on the nature of the latch that mediates energy flow, and that the relative contribution of elastic and direct muscle energy likely shapes the thermal sensitivity of locomotor systems.

Habitat restoration weakens negative environmental effects on telomere dynamics

Habitat quality can have far-reaching effects on organismal fitness, an issue of concern given the current scale of habitat degradation. Many temperate upland streams have reduced nutrient levels due to human activity. Nutrient restoration confers benefits in terms of invertebrate food availability and subsequent fish growth rates. Here we test whether these mitigation measures also affect the rate of cellular ageing of the fish, measured in terms of the telomeres that cap the ends of eukaryotic chromosomes. We equally distributed Atlantic salmon eggs from the same 30 focal families into 10 human-impacted oligotrophic streams in northern Scotland. Nutrient levels in five of the streams were restored by simulating the deposition of a small number of adult Atlantic salmon Salmo salar carcasses at the end of the spawning period, while five reference streams were left as controls. Telomere lengths and expression of the telomerase reverse transcriptase (TERT) gene that may act to lengthen telomeres were then measured in the young fish when 15 months old. While TERT expression was unrelated to any of the measured variables, telomere lengths were shorter in salmon living at higher densities and in areas with a lower availability of the preferred substrate (cobbles and boulders). However, the adverse effects of these habitat features were much reduced in the streams receiving nutrients. These results suggest that adverse environmental pressures are weakened when nutrients are restored, presumably because the resulting increase in food supply reduces levels of both competition and stress.

Thermal acclimation leads to variable muscle responses in two temperate labrid fishes

Temperature can be a key abiotic factor in fish distribution, as it affects most physiological processes. Specifically, temperature can affect locomotor capabilities, especially as species are exposed to temperatures nearing their thermal limits. In this study, we aimed to understand the effects of temperature on muscle in two labrids that occupy the Northwest Atlantic Ocean. When exposed to cold temperatures in autumn, cunner (Tautogolabrus adspersus) and tautog (Tautoga onitis) go into a state of winter dormancy. Transitions into dormancy vary slightly, where tautog will make short migrations to overwintering habitats while cunner overwinter in year-round habitats. To understand how muscle function changes with temperature, we held fish for 4 weeks at either 5 or 20°C and then ran muscle kinetic and workloop experiments at 5, 10 and 20°C. Following experiments, we used immunohistochemistry staining to identify acclimation effects on myosin isoform expression. Muscle taken from warm-acclimated cunner performed the best, whereas there were relatively few differences among the other three groups. Cunner acclimated at both temperatures downregulated the myosin heavy chain, suggesting a transition in fiber type from slow-oxidative to fast-glycolytic. This change did not amount to a detectable difference in muscle power production and kinetics. However, overall poor performance at cold temperatures could force these fishes into torpor to overwinter. Tautog, alternatively, retained myosin heavy chains, which likely increases locomotor capabilities when making short migrations to overwintering habitats.

Thermal modulation of anthropogenic estrogen exposure on a freshwater fish at two life stages

Human-mediated environmental change can induce changes in the expression of complex behaviors within individuals and alter the outcomes of interactions between individuals. Although the independent effects of numerous stressors on aquatic biota are well documented (e.g., exposure to environmental contaminants), fewer studies have examined how natural variation in the ambient environment modulates these effects. In this study, we exposed reproductively mature and larval fathead minnows (Pimephales promelas) to three environmentally relevant concentrations (14, 22, and 65ng/L) of a common environmental estrogen, estrone (E1), at four water temperatures (15, 18, 21, and 24°C) reflecting natural spring and summer variation. We then conducted a series of behavioral experiments to assess the independent and interactive effects of temperature and estrogen exposure on intra- and interspecific interactions in three contexts with important fitness consequences; reproduction, foraging, and predator evasion. Our data demonstrated significant independent effects of temperature and/or estrogen exposure on the physiology, survival, and behavior of larval and adult fish. We also found evidence suggesting that thermal regime can modulate the effects of exposure on larval survival and predator-prey interactions, even within a relatively narrow range of seasonally fluctuating temperatures. These findings improve our understanding of the outcomes of interactions between anthropogenic stressors and natural abiotic environmental factors, and suggest that such interactions can have ecological and evolutionary implications for freshwater populations and communities.

Precision of archerfish C-starts is fully temperature compensated

Hunting archerfish precisely adapt their predictive C-starts to the initial movement of dislodged prey so that turn angle and initial speed are matched to the place and time of the later point of catch. The high accuracy and the known target point of the starts allow a sensitive straightforward assay of how temperature affects the underlying circuits. Furthermore, archerfish face rapid temperature fluctuations in their mangrove biotopes that could compromise performance. Here, we show that after a brief acclimation period the function of the C-starts was fully maintained over a range of operating temperatures: (i) full responsiveness was maintained at all temperatures, (ii) at all temperatures the fish selected accurate turns and were able to do so over the full angular range, (iii) at all temperatures speed attained immediately after the end of the C-start was matched - with equal accuracy - to 'virtual speed', i.e. the ratio of remaining distance to the future landing point and remaining time. While precision was fully temperature compensated, C-start latency was not and increased by about 4 ms per 1°C cooling. Also, kinematic aspects of the C-start were only partly temperature compensated. Above 26°C, the duration of the two major phases of the C-start were temperature compensated. At lower temperatures, however, durations increased similar to latency. Given the accessibility of the underlying networks, the archerfish predictive start should be an excellent model to assay the degree of plasticity and functional stability of C-start motor patterns.

Thermal and Temporal Stability of Swimming Performance in the European Sea Bass

Studies of locomotor performance have contributed to the elucidation of how suborganismal traits ultimately relate to fitness. In terrestrial populations, exploring the physiological and environmental contributions to whole-animal performance measures has improved our understanding of phenotypic selection. Conversely, very little is known about the links between phenotypic selection and swimming abilities in fish. Most research on swimming performance in fish has focused on morphological, physiological, and biochemical traits contributing to performance or has used swimming performance as a measure of environmental suitability. Few studies have explored how swimming performance is integrated with life-history traits or contributes to Darwinian fitness. In addition, while there are many studies on how the environment influences the swimming performance of fish, few have been done at the individual level. The objective of this study was to broaden our understanding of the relevance of fish swimming performance studies by testing the hypothesis that swimming performance (endurance and sprint) is ontogenetically and temporally stable across fluctuating environmental conditions. We found that individual sprint performances recorded at 12 degrees C were significantly repeatable after a 4-wk acclimation to 22 degrees C, although relative sprint performance of fish that survived 6 mo of natural conditions in a mesocosm was not significantly repeatable. Endurance swimming performance, as measured by critical swimming speed (U(crit)) before and after the 6-mo exposure to simulated natural conditions, was significantly repeatable within survivors. Relative sprint and critical swimming performances were not significantly related to each other. We concluded that within a time frame of up to 6 mo, the swimming performances of individual bass are ontogenetically nearly stable (sprint) to stable (endurance) despite large fluctuations in environmental conditions. Moreover, because they rely on different physiological performance traits, critical swimming and sprinting follow different patterns of change. This observation suggests the absence of a trade-off between these two swimming modes and introduces the possibly of independent selection trajectories.

Thermal sensitivity of metabolic rates and swimming performance in two latitudinally separated populations of cod, Gadus morhua L

Atlantic cod populations live in a wide thermal range and can differ genetically and physiologically. Thermal sensitivity of metabolic capacity and swimming performance may vary along a latitudinal gradient, to facilitate performance in distinct thermal environments. To evaluate this hypothesis, we compared the thermal sensitivity of performance in two cod stocks from the Northwest Atlantic that differ in their thermal experience: Gulf of St Lawrence (GSL) and Bay of Fundy (BF). We first compared the metabolic, physiological and swimming performance after short-term thermal change to that at the acclimation temperature (7 degrees C) for one stock (GSL), before comparing the performance of the two stocks after short-term thermal change. For cod from GSL, standard metabolism (SMR) increased with temperature, while active metabolism (AMR, measured in the critical swimming tests), EMR (metabolic rate after an exhaustive chase protocol), aerobic scope (AS) and critical swimming speeds (U (crit) and U (b-c)) were lower at 3 degrees C than 7 or 11 degrees C. In contrast, anaerobic swimming (sprint and burst-coasts in U (crit) test) was lower at 11 than 7 or 3 degrees C. Factorial AS (AMR SMR(-1)) decreased as temperature rose. Time to exhaustion (chase protocol) was not influenced by temperature. The two stocks differed little in the thermal sensitivities of metabolism or swimming. GSL cod had a higher SMR than BF cod despite similar AMR and AS. This led factorial AS to be significantly higher for the southern stock. Despite these metabolic differences, cod from the two stocks did not differ in their U (crit) speeds. BF cod were better sprinters at both temperatures. Cod from GSL had a lower aerobic cost of swimming at intermediate speeds than those from BF, particularly at low temperature. Only the activity of cytochrome C oxidase (CCO) in white muscle differed between stocks. No enzymatic correlates were found for swimming capacities, but oxygen consumption was best correlated with CCO activity in the ventricle for both stocks. Overall, the stocks differed in their cost of maintenance, cost of transport and sprint capacity, while maintaining comparable thermal sensitivities.

The predictive start of hunting archer fish: a flexible and precise motor pattern performed with the kinematics of an escape C-start

Once their shots have successfully dislodged aerial prey, hunting archer fish monitor the initial values of their prey's ballistic motion and elicit an adapted rapid turning maneuver. This allows these fish to head straight towards the later point of catch with a speed matched to the distance to be covered. To make the catch despite severe competition the fish must quickly and yet precisely match their turn and take-off speed to the initial values of prey motion. However, the initial variables vary over broad ranges and can be determined only after prey is dislodged. Therefore, the underlying neuronal circuitry must be able to drive a maneuver that combines a high degree of precision and flexibility at top speed. To narrow down which neuronal substrate underlies the performance we characterized the kinematics of archer fish predictive starts using digital high-speed video. Strikingly, the predictive starts show all hallmarks of Mauthner-driven teleost C-type fast-starts, which have previously not been noted in feeding strikes and were not expected to provide the high angular accuracy required. The high demands on flexibility and precision of the predictive starts do not compromise their performance. On the contrary, archer fish predictive starts are among the fastest C-starts known so far among teleost fish, with peak linear speed beyond 20 body lengths s-1, angular speed over 4500 deg. s-1, maximum linear acceleration of up to 12 times gravitational acceleration and peak angular acceleration of more than 450 000 deg. s-2. Moreover, they were not slower than archer fish escape C-starts, elicited in the same individuals. Rather, both escapes and predictive starts follow an identical temporal pattern and all kinematic variables of the two patterns overlap. This kinematic equivalence strongly suggests that archer fish recruit their C-start escape network of identified reticulospinal neurons, or elements of it, to drive their predictive starts. How the network drives such a rather complex behavior without compromising speed is a wide open question.

Both Incubation Temperature and Posthatching Temperature Affect Swimming Performance and Morphology of Wood Frog Tadpoles (Rana sylvatica)

In many oviparous vertebrates, hatchling phenotypes are influenced by egg incubation temperature. Many of those phenotypic traits can also acclimate to long-term thermal conditions of juveniles and adults, yet the interactive effects of prehatching and posthatching temperatures on phenotypes have not been studied. To address such interaction, we incubated eggs of wood frogs (Rana sylvatica) at two temperatures and subsequently reared larvae at three temperatures in a fully factorial design. We measured body size, size-independent morphology, and burst swimming speed at one developmental stage. Body size was independent of egg temperature but decreased significantly with increasing larval temperature. Size-independent morphology depended in complex ways on both temperature treatments directly and on their interaction. Burst speed was not influenced directly by egg temperature but was influenced by larval temperature and by the interactions among egg temperature, larval temperature, and test temperature. Our results indicate pervasive effects of egg temperature even late in the larval period and show that prehatching and posthatching temperatures can interact to affect various phenotypic traits. Tadpoles may be able to alter the long-term effects of incubation temperature by choosing particular larval developmental temperatures. Thus, the importance of incubation temperature in oviparous vertebrates should be evaluated by considering the effects of posthatching temperatures.

Thermal acclimation effects differ between voluntary, maximum, and critical swimming velocities in two cyprinid fishes

Temperature acclimation may be a critical component of the locomotor physiology and ecology of ectothermic animals, particularly those living in eurythermal environments. Several studies of fish report striking acclimation of biochemical and kinetic properties in isolated muscle. However, the relatively few studies of whole-animal performance report variable acclimation responses. We test the hypothesis that different types of whole-animal locomotion will respond differently to temperature acclimation, probably due to divergent physiological bases of locomotion. We studied two cyprinid fishes, tinfoil barbs (Puntius schwanenfeldii) and river barbels (Barbus barbus). Study fish were acclimated to either cold or warm temperatures for at least 6 wk and then assayed at four test temperatures for three types of swimming performance. We measured voluntary swimming velocity to estimate routine locomotor behavior, maximum fast start velocity to estimate anaerobic capacity, and critical swimming velocity to estimate primarily aerobic capacity. All three performance measures showed some acute thermal dependence, generally a positive correlation between swimming speed and test temperature. However, each performance measure responded quite differently to acclimation. Critical speeds acclimated strongly, maximum speeds not at all, and voluntary speeds uniquely in each species. Thus we conclude that long-term temperature exposure can have very different consequences for different types of locomotion, consistent with our hypothesis. The data also address previous hypotheses that predict that polyploid and eurythermal fish will have greater acclimation abilities than other fish, due to increased genetic flexibility and ecological selection, respectively. Our results conflict with these predictions. River barbels are eurythermal polyploids and tinfoil barbs stenothermal diploids, yet voluntary swimming acclimated strongly in tinfoil barbs and minimally in river barbels, and acclimation was otherwise comparable.

Physiological basis of temperature-dependent biogeography: trade-offs in muscle design and performance in polar ectotherms

Polar, especially Antarctic, oceans host ectothermic fish and invertebrates characterized by low-to-moderate levels of motor activity; maximum performance is reduced compared with that in warmer habitats. The present review attempts to identify the trade-offs involved in adaptation to cold in the light of progress in the physiology of thermal tolerance. Recent evidence suggests that oxygen limitations and a decrease in aerobic scope are the first indications of tolerance limits at both low and high temperature extremes. The cold-induced reduction in aerobic capacity is compensated for at the cellular level by elevated mitochondrial densities, accompanied by molecular and membrane adjustments for the maintenance of muscle function. Particularly in the muscle of pelagic Antarctic fish, among notothenioids, the mitochondrial volume densities are among the highest known for vertebrates and are associated with cold compensation of aerobic metabolic pathways, a reduction in anaerobic scope, rapid recovery from exhaustive exercise and enhanced lipid stores as well as a preference for lipid catabolism characterized by high energy efficiency at high levels of ambient oxygen supply. Significant anaerobic capacity is still found at the very low end of the activity spectrum, e.g. among benthic eelpout (Zoarcideae).

In contrast to the cold-adapted eurytherms of the Arctic, polar (especially Antarctic) stenotherms minimize standard metabolic rate and, as a precondition, the aerobic capacity per milligram of mitochondrial protein,thereby minimizing oxygen demand. Cost reductions are supported by the downregulation of the cost and flexibility of acid—base regulation. At maintained factorial scopes, the reduction in standard metabolic rate will cause net aerobic scope to be lower than in temperate species. Loss of contractile myofilaments and, thereby, force results from space constraints due to excessive mitochondrial proliferation. On a continuum between low and moderately high levels of muscular activity, polar fish have developed characteristics of aerobic metabolism equivalent to those of high-performance swimmers in warmer waters. However, they only reach low performance levels despite taking aerobic design to an extreme.

Inability of adult Limnodynastes peronii (Amphibia: Anura) to thermally acclimate locomotor performance

Despite several studies on adult amphibians, only larvae of the striped marsh frog (Limnodynastes peronii) have been reported to possess the ability to compensate for the effects of cool temperature on locomotor performance by thermal acclimation. In this study, we investigated whether this thermal acclimatory ability is shared by adult L. peronii. We exposed adult L. peronii to either 18 or 30 degrees C for 8 weeks and tested their swimming and jumping performance at six temperatures between 8 and 35 degrees C. Acute changes in temperature affected both maximum swimming and jumping performance, however there was no difference between the two treatment groups in locomotor performance between 8 and 30 degrees C. Maximum swimming velocity of both groups increased from 0.62+/-0.02 at 8 degrees C to 1.02+/-0.03 m s(-1) at 30 degrees C, while maximum jump distance increased from approximately 20 to >60 cm over the same temperature range. Although adult L. peronii acclimated to 18 degrees C failed to produce a locomotor response at 35 degrees C, this most likely reflected a change in thermal tolerance limits with acclimation rather than modifications in the locomotor system. As all adult amphibians studied to date are incapable of thermally acclimating locomotor performance, including adults of L. peronii, this acclimatory capacity appears to be absent from the adult stage of development.

The effects of acute and developmental temperature on burst swimming speed and myofibrillar ATPase activity in tadpoles of the Pacific tree frog, Hyla regilla

The effects of acute and developmental temperature on maximum burst swimming speed, body size, and myofibrillar ATPase activity were assessed in tadpoles of the Pacific tree frog, Hyla regilla. Tadpoles from field-collected egg masses were reared in the laboratory at 15 degrees (cool) and 25 degrees C (warm). Body size, maximum burst swimming speed from 5 degrees to 35 degrees C, and tail myofibrillar ATPase activity at 15 degrees and 25 degrees C were measured at a single developmental stage. Burst speed of both groups of tadpoles was strongly affected by test temperature (P<0. 001). Performance maxima spanned test temperatures of 15 degrees -25 degrees C for the cool group and 15 degrees -30 degrees C for the warm group. Burst speed also depended on developmental temperature (P<0.001), even after accounting for variation in body size. At most test temperatures, the cool-reared tadpoles swam faster than the warm-reared tadpoles. Myofibrillar ATPase activity was affected by test temperature (P<0.001). Like swimming speed, enzyme activity was greater in the cool-reared tadpoles than in the warm-reared tadpoles, a difference that was significant when assayed at 15 degrees C (P<0. 01). These results suggest a mechanism for developmental temperature effects on locomotor performance observed in other taxa.

Seasonal changes in sheltering: effect of light and temperature on diel activity in juvenile salmon

Previous work has shown that juvenile Atlantic salmon, Salmo salar L, are predominantly nocturnal during winter (spending the day sheltering in streambed refuges) but become active 24 h a day in the summer. Observations of salmon in a semi-natural stream revealed how light, temperature and time of year determined these activity patterns; we also tested whether the life-history strategy of the fish affected diel activity, comparing fish that would migrate to sea the following spring with those that would be resident in fresh water for at least an additional year. Fish tended to hide at high light levels whenever the water was cold but were increasingly likely to emerge as the winter progressed. There were significant differences between the two groups of fish: the putative migrants sheltered more than the resident group in winter, but this trend was reversed in the spring. Reducing the risk of predation in winter may be one of the reasons for this seasonal change in behaviour.Copyright 1997 The Association for the Study of Animal BehaviourCopyright 1997The Association for the Study of Animal Behaviour.