Maximal Locomotor Performance Research Articles

Weak sex-specific evolution of locomotor activity of Sepsis punctum (Diptera: Sepsidae) thermal experimental evolution lines

Elevated temperatures are expected to rise beyond what the physiology of many organisms can tolerate. Behavioural responses facilitating microhabitat shifts may mitigate some of this increased thermal selection on physiology, but behaviours are themselves mediated by physiology, and any behavioural response may trade-off against other fitness-related activities. We investigated whether experimental evolution in different thermal regimes (Cold: 15 °C; Hot: 31 °C; Intergenerational fluctuation 15/31 °C; Control: 23 °C) resulted in genetic differentiation of standard locomotor activity in the dung fly Sepsis punctum. We assessed individual locomotor performance, an integral part of most behavioral repertoires, across eight warm temperatures from 24 °C to 45 °C using an automated device. We found no evidence for generalist-specialist trade-offs (i.e. changes in the breadth of the performance curve) for this trait. Instead, at the warmest assay temperatures hot-selected flies showed somewhat higher maximal performance than all other, especially cold-selected flies, overall more so in males than females. Yet, the flies' temperature optimum was not higher than that of the cold-selected flies, as expected under the ‘hotter-is-better’ hypothesis. Maximal locomotor performance merely weakly increased with body size. These results suggest that thermal performance curves are unlikely to evolve as an entity according to theory, and that locomotor activity is a trait of limited use in revealing thermal adaptation.

Autotomy-induced effects on the locomotor performance of the ghost crab Ocypode quadrata.

The voluntary amputation of an appendage, or autotomy, is an effective defensive mechanism that allows an animal to escape aggressive interactions. However, animals may suffer long-term costs that can reduce their overall fitness. Atlantic ghost crabs (Ocypode quadrata) are one of the fastest terrestrial invertebrates, and regularly lose one or more limbs in response to an antagonist encounter. When running laterally at fast speeds, they adopt a quadrupedal gait using their first and second pairs of legs while raising their fourth, and sometimes the third, pair of legs off the ground. This suggests that some limbs may be more important for achieving maximal locomotor performance than others. The goal of this study was to determine whether the loss of certain limbs would affect running performance more than others, and what compensatory strategies were used. Crabs were assigned to four different paired limb removal treatments or the control group and run on an enclosed trackway in their natural habitat. Ghost crabs were found to adjust stride kinematics in response to limb loss. Loss of the second or third limb pairs caused a reduction in running speed by about 25%, suggesting that the remaining intact limbs were unable to compensate for the loss of either limb, either due to a lack of propulsive forces produced by these limbs or issues stemming from re-coupling limb arrangements. Loss of any of the other limbs had no detectable effect on running speed. We conclude that compensatory ability varies depending on the limb that is lost.

Casual movement speed but not maximal locomotor capacity predicts mate searching success.

Maximal locomotor performance is often used as a proxy for fitness. Maximal speed may be important under high-threat conditions, such as during predator escape. However, animals do not always move at a speed that reflects their maximal physiological capacities when undisturbed. The physiological factors that determine the movement speed chosen by animals, such as minimization of energy use, may be independent from maximal performance. As a result, the casual speed at which individuals move when undisturbed in a given context may better represent an individual's motivation to move. The casual speed may therefore be a better predictor of fitness in natural contexts than maximal performance capacity. We tested the hypothesis that casual movement speed rather than maximal speed predicts fitness in the golden orb-web spider, Nephila plumipes. We measured fitness in two separate contexts, mate-searching success and the positional rank near a female. We show that casual but not maximal locomotor speed predicted both aspects of fitness. Casual speed was linearly related to maximal speed, indicating that casual speed is determined by physiological optimization. Size and metabolic scope were not related to either maximal or chosen speeds, indicating that the supply of ATP does not limit locomotor performance in this species. Overall, our results demonstrate that locomotor performance is related to fitness, but suggest that different types of performance and not necessarily maximal physiological capacities are most relevant for particular ecologically relevant tasks.

Body borne loads impact walk-to-run and running biomechanics

The purpose of this study was to perform a biomechanics-based assessment of body borne load during the walk-to-run transition and steady-state running because historical research has limited load carriage assessment to prolonged walking. Fifteen male military personnel had trunk and lower limb biomechanics examined during these locomotor tasks with three different load configurations (light, ∼6kg, medium, ∼20kg, and heavy, ∼40kg). Subject-based means of the dependent variables were submitted to repeated measures ANOVA to test the effects of load configuration. During the walk-to-run transition, the hip decreased (P=0.001) and knee increased (P=0.004) their contribution to joint power with the addition of load. Additionally, greater peak trunk (P=0.001), hip (P=0.001), and knee flexion (P<0.001) moments and trunk flexion (P<0.001) angle, and reduced hip (P=0.001) and knee flexion (P=0.001) posture were evident during the loaded walk-to-run transition. Body borne load had no significant effect (P>0.05) on distribution of lower limb joint power during steady-state running, but increased peak trunk (P<0.001), hip (P=0.001), and knee (P=0.001) flexion moments, and trunk flexion (P<0.001) posture were evident. During the walk-to-run transition the load carrier may move joint power production distally down the kinetic chain and adopt biomechanical profiles to maintain performance of the task. The load carrier, however, may not adopt lower limb kinematic adaptations necessary to shift joint power distribution during steady-state running, despite exhibiting potentially detrimental larger lower limb joint loads. As such, further study appears needed to determine how load carriage impairs maximal locomotor performance.

Critical Tail Autotomy for Reduction of Maximal Swimming Performance in a Plethodontid Salamander (Desmognathus quadramaculatus)

Although tail autotomy often has an immediate survival benefit, tail loss may subsequently hinder locomotion and the ability to escape from predators. Maximal locomotor performance can be reduced after tail autotomy in the plethodontid salamander Desmognathus quadramaculatus. The loss of a large proportion of the tail length (>60%) is costly for this semiaquatic species in terms of a reduction in maximal swimming performance (i.e., burst speed is about 50% less after such autotomy). However, the minimal amount of tail loss that causes a significant reduction in swimming performance (i.e., the “critical tail autotomy” for locomotion) is unknown. I examined the effect of partial tail loss (either 15% or 30% of tail length) on burst swimming performance. After the loss of about 15% of tail length in one experimental group (N = 15), burst speeds for individuals were not significantly different from preautotomy burst speeds. After the loss of about 30% of tail length in a second experimental group (N = 15), burst speeds for individuals were significantly less than preautotomy burst speeds. These results indicate that the critical tail autotomy for reduction of maximal swimming performance is between 15% and 30% of tail length. About 50% of individuals in the field (N = 69) experienced tail autotomy and most (80%) of these individuals lost more than 30% of their tails. This study shows that tail autotomy often results in a reduction in maximal swimming performance and thus a locomotor cost for individuals of this species.

Effect of body size on tail regeneration and recovery of swimming performance after caudal autotomy in a plethodontid salamander

I examined the effect of body size on the locomotor cost of caudal autotomy in the plethodontid salamander Desmognathus quadramaculatus. In this primarily aquatic species, larger individuals autotomize the tail less readily than smaller individuals, and this may be related to a greater locomotor cost of tail loss for larger individuals. To determine whether the rate of regeneration for tail length and the recovery of maximal locomotor performance after caudal autotomy vary with body size, I measured the rate of tail re-growth and the swimming burst speed for 14 individuals (snout-vent length = 42-106 mm) as they regenerated their tails. Burst speeds of individuals were significantly reduced after caudal autotomy. With the loss of about 62% of tail length, mean burst speed declined about 50%. Thus, caudal autotomy was costly in terms of a reduction in maximal locomotor performance in an aquatic environment. After the regeneration of 50% of the tail length that was lost, post-autotomy swimming speeds were not significantly different from pre-autotomy swimming speeds. The time required for this amount of tail length regeneration (about 63-143 d) increased significantly with body size. The rate of re-growth for the lost tail length declined significantly after the regeneration of 50% of tail length. These results demonstrate that the locomotor cost of tail loss is greater for larger individuals of D. quadramaculatus, and this may be related to a lower propensity for caudal autotomy and a greater propensity for alternative antipredator mechanisms (e.g., biting) for such individuals.

A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth.

The large theropod dinosaur Tyrannosaurus rex underwent remarkable changes during its growth from <10 kg hatchlings to >6000 kg adults in <20 years. These changes raise fascinating questions about the morphological transformations involved, peak growth rates, and scaling of limb muscle sizes as well as the body's centre of mass that could have influenced ontogenetic changes of locomotion in T. rex. Here we address these questions using three-dimensionally scanned computer models of four large, well-preserved fossil specimens as well as a putative juvenile individual. Furthermore we quantify the variations of estimated body mass, centre of mass and segment dimensions, to characterize inaccuracies in our reconstructions. These inaccuracies include not only subjectivity but also incomplete preservation and inconsistent articulations of museum skeletons. Although those problems cause ambiguity, we conclude that adult T. rex had body masses around 6000–8000 kg, with the largest known specimen (“Sue”) perhaps ∼9500 kg. Our results show that during T. rex ontogeny, the torso became longer and heavier whereas the limbs became proportionately shorter and lighter. Our estimates of peak growth rates are about twice as rapid as previous ones but generally support previous methods, despite biases caused by the usage of scale models and equations that underestimate body masses. We tentatively infer that the hindlimb extensor muscles masses, including the large tail muscle M. caudofemoralis longus, may have decreased in their relative size as the centre of mass shifted craniodorsally during T. rex ontogeny. Such ontogenetic changes would have worsened any relative or absolute decline of maximal locomotor performance. Regardless, T. rex probably had hip and thigh muscles relatively larger than any extant animal's. Overall, the limb “antigravity” muscles may have been as large as or even larger than those of ratite birds, which themselves have the most muscular limbs of any living animal.

Is locomotor performance optimised at preferred body temperature? A study of Liolaemus pictus argentinus from northern Patagonia, Argentina

We studied the relationship between locomotor performance and temperature in Liolaemus pictus argentinus, from the Andean–Patagonian forest, Argentina. We determined the running speed in long and sprint runs at four different body temperatures, the panting threshold, and minimum critical temperature. The results are discussed in relation to body temperature in the field and thermal preference in the laboratory ( T pref). L. p. argentinus achieved higher speed in sprint runs than in long runs at all temperatures. In order to know if pregnancy constrains performance in this viviparous species, the differences between pregnant females and the other adults were analysed. Pregnant females were at a disadvantage when running long distances, but in sprint runs they were able to run as efficiently as the rest of the individuals, suggesting that they mainly use sprint runs and this may explain their conspicuous more-withdrawn behaviour. In long runs, the performance optimal temperature for L. p. argentinus ( T o=30.7 °C) was below the 25th percentile for all body temperatures selected in the laboratory (set-point range of T pref=34.6–37.9 °C), but similar to the mean field body temperature (32.1 °C). However, in sprint runs the T o (36.3 °C) was within the set-point range of T pref. The mean panting threshold (42.8 °C) and the mean minimum critical temperature (6.9 °C) were similar to those of other liolaemids. The results are evidence that L. p. argentinus is well-adapted to the temperatures available in their environment and that the species has a T pref that allows the achievement of maximal locomotor performance in the most frequently used and probably the most important run type, the sprint run.

Effect of Caudal Autotomy on Aquatic and Terrestrial Locomotor Performance in Two Desmognathine Salamander Species

Plethodontid salamanders within the genus Desmognathus range from species that are primarily aquatic to species that are fully terrestrial. Thus, these species are a good model system to use for a comparison of the effect of tail loss on maximal swimming and running performance, and propensity for caudal autotomy in closely related species that primarily inhabit either aquatic or terrestrial environments. I examined the effect of caudal autotomy on maximal swimming and running speeds in D. quadramaculatus (a larger, more aquatic species) and in D. ocoee (a smaller, primarily terrestrial species). Prior to tail loss, aquatic burst speeds were greater than terrestrial burst speeds for individuals of D. quadramaculatus, but the converse was true for individuals of D. ocoee. During aquatic locomotion in each species, burst speed was significantly reduced after autotomy. With the loss of about 65% of tail length, swimming burst speed declined about 50% for D. quadramaculatus and 40% for D. ocoee. Terrestrial burst speed was not reduced in either species after autotomy. These results show that tail loss is costly for primarily aquatic desmognathine salamanders in terms of a reduction in maximal locomotor performance. The time required for caudal autotomy increased significantly with body size in each species, and larger individuals of D. quadramaculatus would bite prior to autotomy. Thus, larger individuals of D. quadramaculatus may utilize caudal autotomy less readily and rely more on alternative antipredator mechanisms such as biting, and this may be related to a higher locomotor cost of autotomy for such individuals.

Fight versus flight: the interaction of temperature and body size determines antipredator behaviour in tegu lizards

Ectotherm antipredator behaviour might be strongly affected both by body temperature and size: when environmental temperatures do not favour maximal locomotor performance, large individuals may confront predators, whereas small animals may flee, simply because they have no other option. However, integration of body size and temperature effects is rarely approached in the study of antipredator behaviour in vertebrate ectotherms. In the present study we investigated whether temperature affects antipredator responses of tegu lizards, Tupinambis merianae, with distinct body sizes, testing the hypothesis that small tegus (juveniles) run away from predators regardless of the environmental temperature, because defensive aggression may not be an effective predator deterrent, whereas adults, which are larger, use aggressive defence at low temperatures, when running performance might be suboptimal. We recorded responses of juvenile (= small) and adult (= large) tegu lizards to a simulated predatory attack at five environmental temperatures in the laboratory. Most differences between the two size classes were observed at low temperatures: large tegus were more aggressive overall than were small tegus at all temperatures tested, but at lower temperatures, the small lizards often used escape responses whereas the large ones either adopted a defensive posture or remained inactive. These results provide strong evidence that body size and temperature affect the antipredator responses of vertebrate ectotherms. We discuss the complex and intricate network of evolutionary and ecological parameters that are likely to be involved in the evolution of such interactions.

Evolutionary trade-offs in locomotor capacities in lacertid lizards: are splendid sprinters clumsy climbers?

We tested the hypothesis that an evolutionary trade-off exists between the capacity to run on level terrain and the ability to climb inclined structures in lacertid lizards. Biomechanical and physiological models of lizard locomotor performance suggest that the morphological design requirements of a ground-dwelling vs. scansorial life style are difficult to reconcile. This conflict is thought to preclude simultaneous evolution of maximal locomotor performance on level and inclined terrain. This notion has been corroborated by comparative studies on lizard species from other groups (Anolis, Chamaeleo, Sceloporus), but is not supported by our data on 13 species from the family Lacertidae. We found no indication of a negative association between maximal sprint speed of lizards over a level racetrack (indicative of ground-dwelling locomotor performance), on an inclined stony surface (indicative of climbing performance over rock faces) and inclined mesh surface (indicative of clambering performance among vegetation). Moreover, morphological characteristics associated with fast sprinting capacities (e.g. long hind limbs) apparently enhance, rather than hinder climbing and clambering performance. We conclude that in our sample of lacertid lizards, the evolution of fast sprinting capacity on level terrain has not inflicted major restrictions on climbing and clambering performance.

A Comparative Analysis of the Ecological Significance of Maximal Locomotor Performance in Caribbean Anolis Lizards

A Comparative Analysis of the Ecological Significance of Maximal Locomotor Performance in Caribbean Anolis Lizards

The effect of metamorphosis on the repeatability of maximal locomotor performance in the Pacific tree frog Hyla regilla.

Measuring the repeatability of inter-individual differences in locomotor performance is an important first step in elucidating both the functional causes and the ecological consequences of performance variation. Thus, repeatability of whole-animal performance traits provides a crucial link between functional and evolutionary biology. In the present study, repeatability of maximal burst locomotor performance was estimated for a single population of the Pacific tree frog Hyla regilla. Animals were reared individually from eggs through metamorphosis in the laboratory. Maximum burst swimming speed of tadpoles was measured before metamorphosis (Gosner stage 37) and again at the onset of the metamorphic climax (stage 42). Maximum jump distance was measured on the same individuals as juvenile frogs. Locomotor performance was repeatable over a 24h period for both premetamorphic tadpoles and juvenile frogs. Performance was not repeatable across metamorphosis or between any two of the three developmental stages investigated. A high-performance individual at one developmental stage does not necessarily retain that performance advantage at another stage. This lack of repeatability contrasts sharply with several previous studies on non-metamorphosing vertebrates, but concurs with a single previous study on a metamorphosing salamander. Metamorphosis appears to place strict temporal constraints on individual consistency in locomotor ability.

Limits to maximal performance.

Body size fundamentally affects maximal locomotor performance in mammals. Comparisons of performances of different-sized animals yield different results if made using relative, rather than absolute scales. Absolute speed may be a reasonable way to evaluate the locomotor performance of an animal that must escape predators in real time. However, comparisons of metabolic power in animals of different size can only be made meaningfully on a mass-specific basis. Numerous factors associated with the mechanics, energetics, and storage of elastic energy during locomotion change with body size, which results in allometric relationships that make the energetic cost of locomotion (alpha Mb-0.3) more expensive for small mammals than for large mammals. Small mammals have lower enzymatic capacities for anaerobic glycolysis (alpha Mb0.15) and higher specific aerobic capacities (alpha Mb-0.13) than large mammals. However, the energetic cost of transport increases more than aerobic power as mammals get smaller. The higher ratio of cost to available power in small mammals may explain why they run more slowly than large mammals, as a rule. Maximum aerobic capacity is allometrically related to body size. Limits to VO2max can be imposed by mitochondrial oxidative capacity, as in goats, or by the O2 transport system, as in humans and horses. No single step in the O2 transport system can limit the flux of O2 by itself; however, in an average non-athletic species of mammal, any of the steps in the system might appear to be the weakest link. In highly aerobic athletic species, and possibly elite athletic individuals of other species (e.g. humans), the malleable elements of the O2 transport system may develop to the point that their O2 transport capacities approach that of the least malleable element in the system, the lung. VO2max is very high in such individuals, and appears to be limited by simultaneous failure of all components of the O2 transport system.

Time Budgets, Thermoregulation, and Maximal Locomotor Performance: Are Reptiles Olympians or Boy Scouts?

SYNOPSIS. DO ectothermal vertebrates routinely make full use of their locomotor capacities in nature? We address this question by asking whether reptiles ever sprint at maximum burst speeds and whether they often move at speeds near maximum aerobically sustainable levels. Relevant data are largely anecdotal but suggest that lizards (and perhaps other vertebrate ectotherms) do not routinely perform at maximal capacities. They appear to do so only in situations that have a critical impact on fitness. Nevertheless, active lizards do thermoregulate carefully such that they usually maintain the potential for performing at maximal capacity. We consider alternative, but not exclusive, explanations for why reptiles might maintain apparently “excessive” capacities and conclude with suggestions for new field and laboratory studies that would more rigorously address these issues.