To run or hide? Age-dependent escape behaviour in the common flat lizard (Platysaurus intermedius wilhelmi)

Flat lizards Platysaurus intermedius wilhelmi occur on small discrete rock outcrops in Mpumalanga Province, South Africa. These rock outcrops are structurally simple and this, combined with the lizard's behaviour (ambush foraging in the open), make them ideal for field studies of anti-predatory behaviour. Lizards were approached in the field and how escape behaviour was influenced by habitat and age-sex class was recorded. Juveniles ( c. 4 months of age) responded quite differently to an approaching human 'predator' compared with adult males and females (which responded similarly). Compared to adults, juveniles allowed a closer approach by the investigator; took longer to find a refuge and therefore fled further; were more likely to remain visible in the open and maintain visual contact with the investigator; and more likely to flee into vegetation when given the opportunity to take refuge in a crevice. We suggest that because a greater suite of predators (including arthropods living in rock crevices) feed on small juvenile lizards, this may affect their choice of refuge and result in the avoidance of crevices when chased. Finally, because juveniles were frequently found on small rock outcrops, the influence of rock outcrop area on anti-predatory behaviour was tested. Escape behaviour (time to refuge) was independent of rock outcrop area.     

Ontogenetic and sexual differences of thermal biology and locomotor performance in a lacertid lizard,Eremias multiocellata

A viviparous lizard, Eremias multiocellata, was used to investigate the possible sexual and ontogenetic effects on selected body temperature, thermal tolerance range and the thermal dependence of locomotor performance. We show that adults are sexually dimorphic and males have larger bodies and heads than females. Adults selected higher body temperatures (34.5 vs. 32.4 °C) and could tolerate a broader range of body temperatures (8.1–46.8 vs. 9.1–43.1 °C) than juveniles. The sprint speed and maximum sprint distance increased with temperature from 21 °C to 33 °C, but decreased at 36 °C and 39 °C in both juveniles and adults. Adults ran faster and longer than juveniles at each tested temperature. Adult locomotor performance was not correlated with snout–vent length (SVL) or sex, and sprint speed was positively correlated with hindlimb length. Juvenile locomotor performance was positively correlated with both SVL and hindlimb length. The ontogenetic variation in selected body temperature, thermal tolerance and locomotor performance in E. multiocellata suggests that the effects of morphology on temperature selection and locomotor performance vary at different ontogenetic stages.     

The lizard ear: Cordylus, Platysaurus and Gerrhosaurus

In further consideration of the lizard ear, the fine structure of the cochlea has been investigated and related to auditory sensitivity in members of the family Cordylidae. The ear of this group of lizards is unusual in that a tectorial membrane is present only in a modified and seemingly vestigial form, and this membrane makes no connections with the auditory hair cells. These cells are provided instead with a series of sallets, small bodies extending in a single row through the dorsal and middle regions of the cochlea, where they rest upon the tips of the ciliary tufts and evidently bring about a stimulation of the hair cells because of their inertia. At the ventral end of the cochlea this line of sallets ends, and here is a single, relatively enormous structure, the culmen papillae, that serves a similar purpose for a large group of hair cells. Consideration is given to the manner of stimulation of the auditory sense cells in these species in relation to others with the usual arrangements involving connections between the ciliary tufts and a tectorial membrane. Included also is a study of a species of Gerrhosaurus, which some have included in the cordylid family and others have placed in a family of its own. The cochlear structure in this species is similar to that of the cordylids in many respects but differs in the ventral region, where instead of the culmen there is a heavy tectorial plate, similarly covering a large number of hair cells but connected to a tectorial membrane. The functioning of these ears is assessed in terms of the cochlear potentials, and is found to vary with species from better than average to excellent in comparison with other lizards investigated. The structural differentiation also is of fairly high degree, and hence it appears that ears without tectorial connections, or with such connections only in a limited region of the cochlea, can perform in a highly serviceable manner.     

The effect of hypoxia on locomotor performance and behaviour during escape in Liza aurata

Escape performance was investigated in the golden grey mullet Liza aurata exposed to various levels of oxygen: >85 ( i.e. normoxia), 50, 20 and 10 % air saturation. Since the golden grey mullet performed aquatic surface respiration when air saturation approached 15–10 %, escape performance was tested at 10 % air saturation with and without access to the surface (10 % S and 10 % C, respectively). Various locomotor and behavioural variables were measured, such as cumulative distance, maximum swimming speed, acceleration, responsiveness (per cent of responding fish), response latency and directionality. Golden grey mullet showed a decrease in responsiveness when the oxygen level was reduced to 10 % air saturation, whether the surface access was obstructed or not. Hypoxia did not have any effect on the response latency. Cumulative distance and maximum swimming speed over a fixed time were significantly different between normoxic conditions and 10 % C, while no differences were found in maximum acceleration. While the fish's 'C‐bend' was mainly directed away from the stimulus in normoxia, the proportion of away and towards 'C‐bend' was random when the oxygen was ≤20 % air saturation. This suggested an impairment of the left‐right discrimination at the initiation of the fast start. Hypoxia affected golden grey mullet escape performance mainly through an impairment of responsiveness and directionality, while locomotor performance was affected only in severe hypoxia when the surface was obstructed. The study showed that, in addition to forcing the fish to the surface as shown by previous studies, hypoxia may also reduce fish elusiveness facing a predator by directly impairing its escape performance.     

Sex-based differences in vigor and site preferences of Juniperus communis subsp. nana

Dioecious alpine juniper has been influenced by human impacts, management and climate changes; hence, its present populations are remnant fragments of its former distribution in central Europe. Complex environmental shifts have had fatal consequences for growth, reproduction and health of juniper and hence for its population structure. We asked the questions: 1) what was the population size structure, the sex ratio and the health status of individuals? 2) How were the population parameters linked with the environmental conditions and surrounding vegetation? The study area was close and above the upper forest limit in central Europe, the Hrubý Jeseník Mts. The parameters of each juniper individual and its environmental conditions were obtained, Ellenberg's indicator values and habitat categories were also determined. Proportions of sex categories, shrub size and environmental conditions were investigated to assess relationships between the population categories and environmental factors. We revealed linkage among the shrub size, health vigor, vegetation cover, a habitat and environmental factors. While there was equal ratio of females and males (1:1), small individuals of undetermined sex predominated that reducing the effective population size. Juniper health vigor was associated with surrounding vegetation cover. Individuals of undetermined sex were smaller than those of remaining sex categories and prefer specific habitats at higher elevation, underlining the effect of abiotic conditions on sex performance and ratio. The observed pattern, which was attributed to shift in land-use practices in the middle of 20th century and climate changes, could be improved by management. We recommended experimental local grazing and mowing accompanying by profound and continuing assessment of interaction among environmental factors and juniper performance.     

Hindlimb asymmetry reduces escape performance in the lizard Psammodromus algirus

Locomotor performance of lizards and its relationship to the ecology and morphology of the forms concerned has been well studied recently. Asymmetry of limbs might make the body unstable and make performance less effective. However, their effects on terrestrial locomotion remain almost unexplored. In this article, the escape performance of the lizard Psammodromus algirus running at high speed was related to hindlimb morphology and fluctuating asymmetry levels. Femur length was significantly shorter than crus length. However, absolute fluctuating asymmetry in femur length was significantly larger than in crus length. Asymmetry was not related to body or limb size, thus larger individuals or those with longer limbs did not have significantly greater fluctuating asymmetry. Neither body size nor the length of the limbs (femur or crus) were significantly related to any of the variables describing escape performance. However, escape performance was affected by femur-length fluctuating asymmetry, which resulted in significantly reduced overall escape speeds. In contrast, asymmetry in crus length did not affect escape performance. We discuss the possible basis of these alterations of locomotion, the relevance of reduced performance for the ecology of this species, and how individuals may compensate for the costs of asymmetry.     

Ontogenetic shifts in thermal tolerance, selected body temperature and thermal dependence of food assimilation and locomotor performance in a lacertid lizard, Eremias brenchleyi

We used Eremias brenchleyi as a model animal to examine differences in thermal tolerance, selected body temperature, and the thermal dependence of food assimilation and locomotor performance between juvenile and adult lizards. Adults selected higher body temperatures (33.5 vs. 31.7 degrees C) and were able to tolerate a wider range of body temperatures (3.4-43.6 vs. 5.1-40.8 degrees C) than juveniles. Within the body temperature range of 26-38 degrees C, adults overall ate more than juveniles, and food passage rate was faster in adults than juveniles. Apparent digestive coefficient (ADC) and assimilation efficiency (AE) varied among temperature treatments but no clear temperature associated patterns could be discerned for these two variables. At each test temperature ADC and AE were both higher in adults than in juveniles. Sprint speed increased with increase in body temperature at lower body temperatures, but decreased at higher body temperatures. At each test temperature adults ran faster than did juveniles, and the range of body temperatures where lizards maintained 90% of maximum speed differed between adults (27-34 degrees C) and juveniles (29-37 degrees C). Optimal temperatures and thermal sensitivities differed between food assimilation and sprint speed. Our results not only show strong patterns of ontogenetic variation in thermal tolerance, selected body temperature and thermal dependence of food assimilation and locomotor performance in E. brenchleyi, but also add support for the multiple optima hypothesis for the thermal dependence of behavioral and physiological variables in reptiles.     

Sex differences in lizard escape decisions vary with latitude,but not sexual dimorphism

Sexual selection is a powerful evolutionary mechanism that has shaped the physiology, behaviour and morphology of the sexes to the extent that it can reduce viability while promoting traits that enhance reproductive success. Predation is one of the underlying mechanisms accounting for viability costs of sexual displays. Therefore, we should expect that individuals of the two sexes adjust their anti-predator behaviour in response to changes in predation risk. We conducted a meta-analysis of 28 studies (42 species) of sex differences in risk-taking behaviour in lizards and tested whether these differences could be explained by sexual dichromatism, by sexual size dimorphism or by latitude. Latitude was the best predictor of the interspecific heterogeneity in sex-specific behaviour. Males did not change their escape behaviour with latitude, whereas females had increasingly reduced wariness at higher latitudes. We hypothesize that this sex difference in risk-taking behaviour is linked to sex-specific environmental constraints that more strongly affect the reproductive effort of females than males. This novel latitudinal effect on sex-specific anti-predator behaviour has important implications for responses to climate change and for the relative roles of natural and sexual selection in different species.     

青海沙蜥的热耐受性、选择体温及摄食和运动表现的热依赖性

研究了青海沙蜥(Phrynocephalus vlangalii)成体的选择体温、热耐受性及食物同化和运动表现的热依赖性。结果显示:选择体温、临界低温和临界高温无显著的两性差异,其平均值分别为33.3、0.9℃和46.9℃。在27-35℃实验温度范围内,体温显著影响日摄食量,表观消化系数(ADC)和同化效率(AE)无显著影响。停顿次数随着体温的升高而降低,至39℃时停顿次数最少,但与37℃和41℃处理下的停顿次数无显著差异。疾跑速在17-39℃范围内随体温升高而加快,在39℃体温下最快。体温大于39℃后速度减慢。在17-27℃体温范围内,随体温的升高持续运动距离无显著差异。持续运动距离在29-41℃体温下大于较低体温(17-27℃)下的测定值。     

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.     

A comparison of habitat use, morphology, clinging performance and escape behaviour among two divergent green anole lizard (Anolis carolinensis) populations

We measured available and actual habitat use, morphology, escape behaviour and clinging ability in a large sample ( N  = 242) of green anoles, Anolis carolinensis , in a habitat consisting primarily of segregated dense clumps of broad leaves, Aspidistra elatior (Tulane University campus, LA) to compare against similar data collected previously from a more typical habitat c. 30 km away, consisting of continuous strands of bushes and trees (Good Hope Field, St. Charles Parish, LA). At Tulane the anoles perched primarily on the broad, smooth leaves of broad leaves, whereas in Good Hope Field (GHF) they predominantly perched on branches and tree trunks. The two populations differed significantly in morphology. In Tulane, the anoles tended to have shorter distal hindlimb elements, longer forelimb elements, and were more 'slender' than those at GHF. A comparison of escape behaviour showed population and sex differences. In both populations, females had significantly longer approach distances (i.e. were more 'wary') than males. These distances were, in addition, significantly longer at GHF than at Tulane for both sexes; this may be due to the potentially higher diversity and abundance of predators at GHF, although habituation to humans may also play a role. Anoles at Tulane had significantly larger toepads and higher clinging abilities than those at GHF. The enhanced clinging abilities of anoles at Tulane may have arisen due to their propensity to use smooth leaves as their primary substrate. Overall, our data reveal substantial ecological, behavioural, morphological, and functional differences among populations, some of which may be adaptive.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 223–234.     

Proximate causes of intraspecific variation in locomotor performance in the lizard Gallotia galloti.

To understand the evolution of biological traits, information on the degree and origins of intraspecific variation is essential. Because adaptation can take place only if the trait shows heritable variation, it is important to know whether (at least) part of the trait variation is genetically based. We describe intra- and interindividual variation in three performance measures (sprint speed, climbing, and clambering speed) in juvenile Gallotia galloti lizards from three populations and examine how genetic, environmental (incubation temperature), and ontogenetic (age, size) effects interact to cause performance variation. Moreover, we test whether the three performance traits are intercorrelated phenotypically and genetically. Sprint speed is highest in juveniles incubated at the lowest temperature (26 degrees C) irrespective of population. Climbing speed differs among populations, and the differences persist at least until the lizards are 30 wk old. This suggests that the three populations experience different selective pressures. Moreover, mass, snout-vent length, and hindlimb length seem to affect climbing performance differently in the three populations. The variation in sprinting and climbing ability appears to be genetically based. Moreover, the two performance traits are intercorrelated and thus will not evolve independently from each other. Clambering speed (i.e., capacity to climb up an inclined mesh) varies among individuals, but the origin of this variation remains obscure.     

Environmental maternal effects on locomotor performance in the common lizard (Lacerta vivipara)

Environmental (i.e. non-genetic) maternal effects have the potential to associate the environmental conditions faced by mothers during gestation or before egg laying with the phenotype of their offspring. For this reason, maternal effects may play a major role in determining offspring phenotype independently of the genotype of the individuals, and can thus be considered a mechanistic basis of phenotypic plasticity. Despite the ecological and evolutionary implications of environmental maternal effects, few studies have experimentally investigated this phenomenon in reptiles. Here we report the results of an experimental laboratory study on the effects of maternal feeding rate and density on offspring locomotor performance in the common lizard (Lacerta vivipara). Lacerta vivipara is a viviparous lizard, and viviparity enhances the probability of a maternal influence on offspring phenotype. We focused on a particular phenotypic trait, maximal sprint running speed, because this trait is thought to be selectively important in squamates. Sprint speed was a repeatable trait, and it varied significantly among families. Maternal feeding rate significantly affected sprint speed, whereas density had no effect on this trait. The effect of maternal feeding rate differed according to the sex of the offspring and their body size, resulting in significant two-way and three-way interactions among these factors. In other words, the maternal feeding rate changed the shape of the allometric relationship between speed and size, but differently for males and females. The complexity of such effects makes it extremely difficult to offer an adaptive interpretation, but emphasizes the role played by the environment in shaping phenotypes among generations.     

Seasonality provokes a shift of thermal preferences in a temperate lizard,but altitude does not

1. We compared the mean, limits and breadth of the preferred thermal range (PTR) of two Iberian populations of the lizard Psammodromus algirus separated by 700 m altitude in May and July.     

Embryonic behaviour in the lizard, Lacerta vivipara

The behaviour of embryos of the lizard Lacerta vivipara has been studied in cultured eggs, removed from the mother. Spontaneous movements begin at a time when the embryo is still unresponsive to touch, and about two days before the appearance of reflex responses. The earliest movements consist of lateral flexion which gradually gives place to dorsiventral flexion. Embryonic movements are not necessarily related to contractions of the amnion. The activity of the embryo, as measured by the number of times movements were initiated and the amount of time spent in activity during a half hour period, rises to a plateau and then decreases sharply as the time of hatching approaches. Activity of the tail is prominent, particularly at times when other movements occur in rapid succession. Serpentine movements were not observed in embryos younger than stage 39; some prematurely born animals showed such activity in response to contact with the substratum. During embryonic life any part of the animal may move individually or in combination with any other part, such combined movements being unco-ordinated. In these respects the spontaneous motility of the lizard embryo closely resembles that of the chick. Statistical analysis of the embryonic movements provides evidence of rhythmic activity within the developing central nervous system.     

Thermal biology and locomotor performance of the Andean lizard Liolaemus fitzgeraldi (Liolaemidae) in Argentina

Ectotherms thermoregulate to maintain their body temperature within the optimal range needed for performing vital functions. The effect of climate change on lizards has been studied as regards the sensitivity of locomotor performance to environmental temperatures. We studied thermoregulatory efficiency and locomotor performance for Liolaemus fitzgeraldi in the Central Andes of Argentina. We determined body temperature, micro-environmental temperatures and operative temperatures in the field. In the laboratory, we measured preferred temperatures and calculated the index of thermoregulatory efficiency. We estimated the thermal sensitivity of locomotion by measuring sprint speed (initial velocity and long sprint) and endurance at five different body temperatures. Body temperature was not associated with either micro-environmental temperature, nor did it show differences with preferred temperatures. Thermoregulatory efficiency was moderate (0.61). Initial velocity and long sprint trials showed differences at different temperatures; however, endurance did not. Moreover, the optimal temperatures for the performance trials showed no significant differences among themselves. We conclude that Liolaemus fitzgeraldi has thermal sensitivity in locomotor performance with respect to body temperature and that it is an eurythermic lizard that experiences a large variation in body temperature and that has thermal flexibility in the cold.     

Mite load predicts the quality of sexual color and locomotor performance in a sexually dichromatic lizard

Since Darwin, the maintenance of bright sexual colors has recurrently been linked to mate preference. However, the mechanisms underpinning such preferences for bright colors would not be resolved for another century. Likely, the idea of selection for colors that could decrease the chances of survival (e.g., flashy colors that can inadvertently attract predators) was perceived as counterintuitive. It is now widely accepted that these extreme colors often communicate to mates the ability to survive despite a “handicap” and act as honest signals of individual quality when they are correlated with the quality of other traits that are directly linked to individual fitness. Sexual colors in males are frequently perceived as indicators of infection resistance, in particular. Still, there remains considerable discord among studies attempting to parse the relationships between the variables associating sexual color and infection resistance, such as habitat type and body size. This discord may arise from complex interactions between these variables. Here, we ask if sexual color in male Florida scrub lizards (Sceloporus woodi) is an honest signal of resistance to chigger mite infection. To this end, we use linear modeling to explore relationships between mite load, different components of sexual color, ecological performance, body size, and habitat type. Our data show that that the brightness of sexual color in scrub lizards is negatively associated with the interaction between mite load and body size, and scrub lizards suffer decreased endurance capacity with increases in mite load. Our data also indicate that mite load, performance, and sexual color in male scrub lizards can vary between habitat types. Collectively, these results suggest that sexual color in scrub lizards is an honest indicator of individual quality and further underscore the importance of considering multiple factors when testing hypotheses related to the maintenance of sexual color.