Sex-based differences and similarities in locomotor performance, thermal preferences, and escape behaviour in the lizard Platysaurus intermedius wilhelmi

Differences between sexes in physiological performance have received little attention in animals. We tested for sex differences in maximum sprint speed and maximal exertion over a range of temperatures in a population of Platysaurus intermedius wilhelmi lizards. We also examined sex-based differences in selected temperature range, mean field body temperatures (T(b)), and thermal activity limits. Finally, we conducted field studies to quantify male and female responses to a potential predator, which may be affected by their respective performance capabilities. Males were faster than females at all temperatures, and body size had no significant effect on sprint speeds. Males and females also selected similar T(b)'s when placed in a thermal gradient, but in the field, male lizards' T(b)'s were different from those of the females. However, predicted sprint speeds for males and females at their field T(b)'s are similar. No significant differences were found between males and females with regard to maximal exertion. When approached in the field, adult male lizards took refuge significantly earlier than did adult females and also fled over shorter distances, suggesting that females rely on crypsis as an escape strategy.     

Field use of maximal sprint speed by collared lizards (Crotaphytus collaris): compensation and sexual selection

To understand how selection acts on performance capacity, the ecological role of the performance trait being measured must be determined. Knowing if and when an animal uses maximal performance capacity may give insight into what specific selective pressures may be acting on performance, because individuals are expected to use close to maximal capacity only in contexts important to survival or reproductive success. Furthermore, if an ecological context is important, poor performers are expected to compensate behaviorally. To understand the relative roles of natural and sexual selection on maximal sprint speed capacity we measured maximal sprint speed of collared lizards (Crotaphytus collaris) in the laboratory and field-realized sprint speed for the same individuals in three different contexts (foraging, escaping a predator, and responding to a rival intruder). Females used closer to maximal speed while escaping predators than in the other contexts. Adult males, on the other hand, used closer to maximal speed while responding to an unfamiliar male intruder tethered within their territory. Sprint speeds during foraging attempts were far below maximal capacity for all lizards. Yearlings appeared to compensate for having lower absolute maximal capacity by using a greater percentage of their maximal capacity while foraging and escaping predators than did adults of either sex. We also found evidence for compensation within age and sex classes, where slower individuals used a greater percentage of their maximal capacity than faster individuals. However, this was true only while foraging and escaping predators and not while responding to a rival. Collared lizards appeared to choose microhabitats near refugia such that maximal speed was not necessary to escape predators. Although natural selection for predator avoidance cannot be ruled out as a selective force acting on locomotor performance in collared lizards, intrasexual selection for territory maintenance may be more important for territorial males.     

Do female collared lizards change field use of maximal sprint speed capacity when gravid?

Locomotor ability is well-documented to decrease in gravid female lizards. However, no studies have examined what proportion of maximal sprint speed capacity gravid females use in nature or how a reduction in maximal capacity translates to changes in sprint speeds used in nature. Gravid females may compensate for reduced locomotor ability by increasing the proportion of their maximal capacity used in nature, or by changing their antipredator behaviour. I measured maximal sprint speed in the laboratory for female collared lizards (Crotaphytus collaris) while gravid and nongravid and then compared those to speeds used in the field while foraging and escaping predators, and also while gravid and nongravid. Females had significantly lower maximal sprint speed capacity while gravid, and they ran slower while foraging and escaping predators. However, gravid females did not increase the proportion of maximal capacity used in those contexts compared to when not gravid. Gravid females compensated for reduced locomotor capacity by staying closer to refugia but not by remaining more cryptic. These results suggest that the costs of reduced locomotor capacity may not be associated with direct costs while foraging or escaping predators, but instead with potential indirect effects associated with the change in antipredator behaviour.     

The ontogeny of escape behavior,locomotor performance,and the hind limb in Sceloporus woodi

Flight initiation distance describes the distance at which an animal flees during the approach of a predator. This distance presumably reflects the tradeoff between the benefits of fleeing versus the benefits of remaining stationary. Throughout ontogeny, the costs and benefits of flight may change substantially due to growth-related changes in sprint speed; thus ontogenetic variation in flight initiation distance may be substantial. If escape velocity is essential for surviving predator encounters, then juveniles should either tolerate short flight initiation distances and rely on crypsis, or should have high flight initiation distances to remain far away from their predators. We examined this hypothesis in a small, short-lived lizard (Sceloporus woodi). Flight initiation distance and escape velocity were recorded on an ontogenetic series of lizards in the field. Maximal running velocity was also quantified in a laboratory raceway to establish if escape velocities in the field compared with maximal velocities as measured in the lab. Finally a subset of individuals was used to quantify how muscle and limb size scale with body size throughout ontogeny. Flight initiation distance increased with body size; larger animals had higher flight initiation distances. Small lizards had short flight initiation distances and remained immobile longer, thus relying on crypsis for concealment. Escape velocity in the field did not vary with body size, yet maximum velocity in the lab did increase with size. Hind limb morphology scaled isometrically with body size. Isometric scaling of the hind limb elements and its musculature, coupled with similarities in sprint and escape velocity across ontogeny, demonstrate that smaller S. woodi must rely on crypsis to avoid predator encounters, whereas adults alter their behavior via larger flight initiation distance and lower (presumably less expensive) escape velocities.     

Sex, Reproductive Status, and Cost of Tail Autotomy via Decreased Running Speed in Lizards

Autotomy, voluntary shedding of body parts to permit escape, is a theoretically interesting defense because escape benefit is offset by numerous costs, including impaired future escape ability. Reduced sprint speed is a major escape cost in some lizards. We predicted that tail loss causes decreased speed in males and previtellogenic females, but not vitellogenic females already slowed by mass gain. In the striped plateau lizard, Sceloporus virgatus , adults of both sexes are subject to autotomy, and females undergo large increases in body condition (mass/length) during vitellogenesis. Time required for running 1 m was similar in intact autotomized males and previtellogenic females, but increased by nearly half after autotomy. Vitellogenic females were slower than other lizards when intact, but their speed was unaffected by autotomy. Following autotomy, speeds of all groups were similar. Thus, speed costs of autotomy vary with sex and reproductive condition: decreased running speed is not a cost of autotomy in vitellogenic females or presumably gravid females. Costs of autotomy are more complex than previously known. Speed and other costs might interact in unforseen ways, making it difficult to predict whether strategies to compensate for diminished escape ability differ with reproductive condition in females.     

Functional and ecological relevance of intraspecific variation in body size and shape in the lizard Podarcis melisellensis (Lacertidae)

Within populations, individual animals may vary considerably in morphology and ecology. The degree to which variation in morphology is related to ecological variation within a population remains largely unexplored. We investigated whether variation in body size and shape among sexes and age classes of the lizard Podarcis melisellensis translates in differential whole-animal performance (sprint speed, bite force), escape and prey attack behaviour in the field, microhabitat use and diet. Male and female adult lizards differed significantly in body size and head and limb proportions. These morphological differences were reflected in differences in bite strength, but not in sprint speed. Accordingly, field measurements of escape behaviour and prey attack speed did not differ between the sexes, but males ate larger, harder and faster prey than females. In addition to differences in body size, juveniles diverged from adults in relative limb and head dimensions. These shape differences may explain the relatively high sprint and bite capacities of juvenile lizards. Ontogenetic variation in morphology and performance is strongly reflected in the behaviour and ecology in the field, with juveniles differing from adults in aspects of their microhabitat use, escape behaviour and diet.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 251–264.     

Divergent morphologies, performance, and escape behaviour in two tropical rock-using lizards (Reptilia: Scincidae)

The present study quantified microhabitat use, morphology, performance (sprinting, climbing, clinging, and jumping), and escape behaviour of two closely related tropical rock-using lizards. Specifically, the study tested whether: (1) a flatter body and longer limbs enhance performance in rocky habitats; (2) escape behaviour supports predictions based on habitat openness; and (3) there is a trade-off between sprinting and climbing performance. Despite the occupation of generally similar rocky habitats, the habitat of Carlia scirtetis was more open and composed of larger boulders with more regular surfaces, whereas the habitat of Carlia mundivensis was composed of more undergrowth and leaf litter, consisting of smaller boulders with irregular surfaces. The longer legs, flatter body, and greater sprinting and climbing ability of C. scirtetis, supports ecomorphological predictions. By contrast to predictions based on habitat openness, C. scirtetis allowed a potential threat to approach closer and ran further to a refuge than C. mundivensis , suggesting that escape behaviour as determined by performance may be species-specific or decoupled in these two species. The increased sprint speed of C. scirtetis highlighted a performance trade-off, with climbing speed lagging behind that of sprint speed. These results suggest that subtle differences in the structural microhabitat and the degree of habitat openness may ultimately result in substantial differences in morphology, performance, and threat behaviour in closely-related lizard species.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 85–98.     

Beyond black and white: divergent behaviour and performance in three rapidly evolving lizard species at White Sands

Determining which traits enable organisms to colonize and persist in new environments is key to understanding adaptation and ecological speciation. New environments can present novel selective pressures on colonists' morphology, behaviour, and performance, collectively referred to as ecomorphology. To investigate ecomorphological change during adaptation and incipient ecological speciation, we measured differences in morphology (body shape and size), behaviour (startle response), and performance (sprint speed) in three New Mexican lizard species: Holbrookia maculata, Sceloporus undulatus, and Aspidoscelis inornata. Each species is represented by dark morphs, cryptic on the brown adobe soils of the Chihuahuan Desert, and white morphs, cryptic on the gypsum substrate of White Sands. For each species, we then determined the effects of morphology and startle response on sprint speed on matched and mismatched substrate. For two of the three species, white morphs had larger body size and longer limbs. However, we found no statistical evidence that these morphological differences affected sprint speed. Colour morphs also exhibited different escape responses on the two substrates: in all species, dark morphs were less likely to immediately sprint from a simulated predator on white sand. As a result, escape response had a significant effect on sprint speed for two of the three species. Not surprisingly, all lizards sprinted faster on dark soil, which was probably due to the lizards' more immediate escape response and the higher compaction of dark soil. The relationship between escape response and sprint performance across the dark soil and white sand habitats suggests that behavioural differences may be an important component of adaptation and speciation in new environments. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 169–182.     

An intraspecific analysis of trade-offs in sprinting performance in a West Indian lizard species (Anolis lineatopus)

We examined whether a trade-off exists in sprinting ability among individuals within the Caribbean lizard Anolis lineatopus. Specifically, we made the following predictions: Longer-legged (relative to body size) individual lizards should sprint faster than shorter-legged lizards on a broad (5.1 cm diameter) rod. However, longer-legged lizards should also decline in sprinting performance to a greater extent than shorter-legged lizards when sprinting on rods of different diameters. To test these predictions, we examined morphology and sprinting performance in adult male, adult female and juvenile A. lineatopus. As predicted, longer-legged lizards are faster sprinters than shorter-legged lizards on the broad substrate, but they also decline more in speed between the broad and narrow (0.7 cm diameter) dowel. However, despite statistically significant morphological differences among intraspecific classes, differences in morphology did not result in differences in sprinting performance among intraspecific classes, with the exception that larger lizards run faster than smaller lizards on each dowel size.     

Thermal sensitivity of sprint-running in the lizard Sceloporus undulatus: support for a conservative view of thermal physiology

Summary The thermal sensitivity of sprint-running ability was investigated in two populations of Sceloporus undulatus that occupy thermally distinct habitats. Integration of field and laboratory data indicates that lizards inhabiting a cool, high-elevation habitat are frequently active at body temperatures that retard sprint-running velocity, which could affect adversely their ability to evade predators and to capture prey. These negative effects might be expected to select for local adaptation of thermal physiology. No differences in thermal physiology (optimal temperature for sprinting, critical thermal limits) were found, however, between lizards from the two habitats.Preferred body temperature of Sceloporus undulatus is lower than the body temperature that maximizes sprint velocity but is still well within an optimal performance range where lizards can run at better than 95% of maximum velocity. Analysis of data from other studies shows a similar concordance of preferred body temperature and temperatures that maximize sprint velocity for some, but not all lizard species studied.Low diversity of predators and high levels of food may compensate in part for the reduced sprinting ability of highelevation lizards active at low body temperatures. The lack of population differentiation supports the view that lizard thermal physiology is evolutionarily conservative.     

Comparison of lower body strength, power, acceleration, speed, agility, and sprint momentum to describe and compare playing rank among professional rugby league players

Success in rugby league football seems heavily reliant on players possessing an adequate degree of various physical fitness qualities, such as strength, power, speed, agility, and endurance, as well as the individual skills and team tactical abilities. The purpose of this study was to describe and compare the lower body strength, power, acceleration, maximal speed, agility, and sprint momentum of elite first-division national rugby league (NRL) players (n = 20) to second-division state league (SRL) players (n = 20) players from the same club. Strength and maximal power were the best discriminators of which players were in the NRL or SRL squads. None of the sprinting tests, such as acceleration (10-m sprint), maximal speed (40-m sprint), or a unique 40-m agility test, could distinguish between the NRL or SRL squads. However, sprint momentum, which was a product of 10-m velocity and body mass, was better for discriminating between NRL and SRL players as heavier, faster players would possess better drive forward and conversely be better able to repel their opponents' drive forward. Strength and conditioning specialists should therefore pay particular attention to increasing lower body strength and power and total body mass through appropriate resistance training while maintaining or improving 10-m sprint speed to provide their players with the underlying performance characteristics of play at the elite level in rugby leagues.     

Loss of body mass under predation risk: cost of antipredatory behaviour or adaptive fit-for-escape?

Predation risk may compromise the ability of animals to acquire and maintain body reserves by hindering foraging efficiency and increasing physiological stress. Locomotor performance may depend on body mass, so losing mass under predation risk could be an adaptive response of prey to improve escape ability. We studied individual variation in antipredatory behaviour, feeding rate, body mass and escape performance in the lacertid lizard Psammodromus algirus. Individuals were experimentally exposed to different levels of food availability (limited or abundant) and predation risk, represented by reduced refuge availability and simulated predator attacks. Predation risk induced lizards to reduce conspicuousness behaviourally and to avoid feeding in the presence of predators. If food was abundant, alarmed lizards reduced feeding rate, losing mass. Lizards supplied with limited food fed at near-maximum rates independently of predation risk but lost more mass when alarmed; thus, mass losses experienced under predation risk were higher than those expected from feeding interruption alone. Although body mass of lizards varied between treatments, no component of escape performance measured during predator attacks (endurance, speed, escape strategy) was affected by treatments or by variations in body mass. Thus, the body mass changes were consistent with a trade-off between gaining resources and avoiding predators, mediated by hampered foraging efficiency and physiological stress. However, improved escape efficiency is not required to explain mass reduction upon predator encounters beyond that expected from feeding interruption or predation-related stress. Therefore, the idea that animals may regulate body reserves in relation to performance demands should be reconsidered.     

Locomotor compensation creates a mismatch between laboratory and field estimates of escape speed in lizards: a cautionary tale for performance-to-fitness studies

A key assumption in evolutionary studies of locomotor adaptation is that standard laboratory measures of performance accurately reflect what animals do under natural circumstances. One widely examined measure of performance is maximum sprint speed, which is believed to be important for eluding predators, capturing prey, and defending territories. Previous studies linking maximum sprint speed to fitness have focused on laboratory measurements, and we suggest that such analyses may be appropriate for some species and intraspecific classes, but not others. We provide evidence for a general inverse relationship between maximum laboratory sprint speed and the percentage of maximum capacity that animals use when escaping from a threat in the field (the model of locomotor compensation). Further, absolute values of field escape speed and maximum laboratory speed are not significantly related when comparing across a diverse group of Anolis and lacertid lizards. We show that this pattern of locomotor compensation holds both within (i.e., among intraspecific classes) and among lizard species (with some exceptions). We propose a simple method of plotting field escape speed (y-axis) versus maximum laboratory speed (x-axis) among species and/or intraspecific classes that allows researchers to determine whether their study organisms are good candidates for relating laboratory performance to fitness. We suggest that species that reside directly on, or near the "best fitness line" (field escape speed = maximum laboratory speed) are most likely to bear fruit for such studies.     

Fight versus flight: Body temperature influences defensive responses of lizards

In laboratory studies we determined that the defensive responses used by two agamid lizards, Agama savignyi and A. pallida, change as a function of body temperature. At high body temperatures, these lizards flee rapidly from predators. At lower body temperatures, which reduce sprint speed, the lizards rarely run but instead hold their ground and attack aggressively. This temperature-dependent switch in defensive behaviour may have evolved because cold lizards that live in open habitats would have little chance of outrunning predators. Defensive behaviours of animals may in general be sensitive to physiological variables that influence locomotor performance.     

Locomotor capacity and foraging behaviour of kalahari lacertid lizards

Closely related lacertid lizards (Eremias, Nucras) in the Kalahari desert differ in patterns of foraging behaviour. Some species are relatively sedentary (‘sit-and-wait’) whereas others are more active (‘widely-foraging’) predators. We determined whether whole-animal locomotor capacities (cruising endurance on a treadmill, initial speed and maximum burst speed in a racetrack, and sprint endurance in a torus-shaped track) correlated with interspecific differences in foraging behaviour. Two of three widely-foraging species had greater cruising endurance, graater sprint endurance, but lower burst speed than did a sit-and-wait species. However, the two species that sprinted quickly also had limited endurance, and vice versa. Pre-feeding negatively influenced endurance but not sprint capacity. Theoretical models of foraging behaviour should recognize that ectotherms have limited endurance, that there can be a trade-off between speed and endurance, and that pre-feeding can reduce some aspects of locomotor capacity.     

Ontogenetic and individual variation in size, shape and speed in the Australian agamid lizard Amphibolurus nuchalis

The present study investigates relationships among size, shape and speed in the Australian agamid lizard Amphibolurus nuchalis . Maximal running speed, body mass, snout-vent length, tail length, fore- and hind limb spans and thigh muscle mass were measured in 68 field-fresh individuals spanning the entire ontogenetic size range (1.3 48 g). Relative lengths of both foreand hind limbs decrease with increasing body mass (= negative allometry), whereas relative tail length and thigh muscle mass increase with body mass (= positive allometry). Repeatable and significant differences in maximal running speed exist among individuals. Maximal running speed scales as (body mass)^0.161, and 59% of the variation in maximal speed was related to body mass. Based on the results of the present and previous studies, data on scaling of body proportions alone appear inadequate to infer scaling relationships of functional characters such as top speed.
Surprisingly, individual variation in maximal speed is not related to individual variation in shape (relative limb, tail and body lengths). These components of overall shape are not independent; individuals tended to have either relatively long or relatively short limbs, tails and bodies for their body mass. Even the significant difference in multivariate shape between adult males and females has no measurable consequences for maximal speed. Speeds of field-fresh animals did not vary on a seasonal basis, and eight weeks of captivity had no effect on maximal running speeds. Gravid females and long-term (obese) captive lizards were both approximately 12% slower than field-fresh lizards.     

Differences in morphology, performance and behaviour between recently diverged populations of Podarcis sicula mirror differences in predation pressure

We investigated the possible role of variation in predation pressure in the phenotypic divergence of two island populations of the Italian wall lizard, Podarcis sicula . In 1971, ten adult specimens from the island of Pod Kopište (Adriatic Sea, Croatia) were transported to the island of Pod Mrčaru, 3.5 km east, where they founded a new population. Although the two islands resemble each other in general physiognomy (size, elevation, microclimate) and in the absence of terrestrial predators, lizards from the newly established population are now on average larger and have shorter hind limbs. They also exhibit lower maximal sprint speed as measured on a racetrack, and fatigue faster when chased in a torus track. In the field, lizards from the original population of Pod Kopište respond to a simulated predatory attack by fleeing at larger approach distances and by running further from the predator than lizards from Pod Mrčaru. These changes in morphology, behaviour and performance may result from the relaxed predation intensity on the latter island. Our analysis of the structural features of the microhabitats suggests that the vegetation on Pod Mrčaru offers more protection to lizards. Also, plasticine models of lizards, laid out on the islands, less often exhibited signs of being attacked by birds on Pod Mrčaru than on Pod Kopište. Our findings provide an example of how changes in (possibly a single) environmental factor may simultaneously produce responses in behaviour, morphology and whole-animal physiology, and this on a surprisingly small spatial and temporal scale.     

Strategic Escape Direction: Orientation,Turning, and Escape Trajectories of Zebra‐Tailed Lizards (Callisaurus draconoides)

A prey's body orientation relative to a predator's approach path may affect risk of fleeing straight ahead. Consequently, prey often turn before fleeing. Relationships among orientation, turn, and escape angles and between these angles and predation risk have not been studied in terrestrial vertebrates and have rarely been studied in the field. Escape angles are expected to lead away from predators and be highly variable to avoid being predictable by predators. Using approach speed as a risk factor, we studied these issues in the zebra‐tailed lizard, Callisaurus draconoides. Lizards fled away from human simulated predators, but most did not flee straight away. Escape angles were variable, as expected under the unpredictability hypothesis, and had modes at nearly straight away (i.e., 0°) and nearly perpendicular to the predator's approach path (90°). The straight away mode suggests maximal distancing from the predator; the other mode suggests maintaining ability to monitor the predator or possibly an influence of habitat features such as obstacles and refuges that differ among directions. Turn angles were larger when orientation was more toward the predator, and escape angles were closer to straight away when turn angles were larger. Turning serves to reach a favorable fleeing direction. When orientation angle was more toward the predator, escape angle was unaffected, suggesting that turn angle compensates completely for increased risk of orientation toward the predator. When approached more rapidly, lizards fled more nearly straight away, as expected under greater predation risk. Turn angles were unrelated to approach speed.     

EVOLUTIONARY PATTERNS OF THE THERMAL SENSITIVITY OF SPRINT SPEED IN ANOLIS LIZARDS

I present evidence that the thermal sensitivity of sprint speed of Anolis lizards has evolved to match the activity body temperatures (T_b) experienced by local populations in nature. Anolis lizards from a range of altitudes in Costa Rica have limited thermoregulatory abilities and consequently have field T_b that differ substantially in median and interquartile distance (a measure of variability). Experimentally determined maximal sprint temperatures (T_b at which lizards run fastest) were positively correlated with median field T_b, and performance breadths (ranges of T_b over which lizards run well) were correlated with the variability (interquartile distance) of field T_b in the species I examined. Such correlations would be expected if the thermal sensitivity of sprint speed and field T_b had evolved together to improve the sprint performance of lizards in nature. Integration of laboratory and field studies indicates that several species of Anolis regularly experience impaired sprint speeds in the field, despite apparent evolutionary modification of their thermal physiologies. However, this impairment would have been more severe if the thermal sensitivities of sprint speed had not evolved. Data from other groups of lizards indicate that the thermal sensitivity of sprint speed has not evolved to match T_b of local populations (Hertz et al., 1983; Crowley, 1985). These lizards experience less variable T_b and less impairment of sprint speeds in the field than do the anoles. Thus, selection for modification of the thermal sensitivity of sprint speed might have been stronger for anoles than for other groups of lizards.     

Effects of Microhabitat‐Dependent Predation Risk on Vigilance during Intermittent Locomotion in Psammodromus algirus Lizards

Animals should be able to adjust their behavior by tracking changes in predation risk level continuously. Many animals show a pattern of intermittent locomotion with short pauses that may increase detection and vigilance of predators. These locomotor patterns may depend on the microhabitat structure, which affect predation risk levels. We examined in detail in the laboratory the characteristics of spontaneous locomotion, scanning behavior, and the escape performance of Psammodromus algirus lizards moving in two different microhabitats (leaf litter patches and open sand areas). Results showed that in leaf litter, lizards moved at slower speed and had shorter bursts of locomotion both in distance and duration, than in sand substrates. This locomotor pattern allowed lizards to increase scanning rate and total time spent in vigilance behavior. When lizards were forced to flee, they escaped to longer distances and during more time in open sand areas, but lizards were able to attain similar escape speed in the two substrates. Lizards may be able to compensate the cost of moving between different microhabitats with different predation risk by behaviorally changing their locomotor and vigilance patterns. However, complex interactions between the visibility of lizards to predators and the ability of lizards to detect predators, together with the need of attending simultaneously to other conflicting demands, may lead to apparently non‐intuitive solutions in locomotor patterns and the rate of vigilance behavior.