Behavior Of Lizards Research Articles

Estradiol facilitates mounting behavior in male green anole lizards

Steroid hormones activate sexual behaviors across vertebrate species. In green anole lizards, testosterone is particularly important for the display of courtship and copulation by adult males. However, unlike a variety of other species, the role of its metabolite, estradiol, has been unclear. To evaluate its function and potential interaction with testosterone in the facilitation of reproductive behaviors, adult males were gonadectomized and given two treatments. The first consisted of either estradiol or its vehicle, and the second testosterone or a blank control. Parallel manipulations were done in the breeding and non-breeding seasons. Courtship and copulatory behaviors were more readily facilitated during the breeding than non-breeding season. As predicted based on previous experiments, testosterone increased the display of sexual behaviors. In addition, estradiol increased mount attempts. While this hormone did not influence the effects of subsequent testosterone exposure, the present data are consistent with the idea that it facilitates a component of reproduction in the green anole, as in species from other taxa.

Food supplementation and testosterone interact to influence reproductive behavior and immune function in Sceloporus graciosus

The energetic resources in an organism's environment are essential for executing a wide range of life-history functions, including immunity and reproduction. Most energetic budgets, however, are limited, which can lead to trade-offs among competing functions. Increasing reproductive effort tends to decrease immunity in many cases, and increasing total energy via supplemental feedings can eliminate this effect. Testosterone (T), an important regulator of reproduction, and food availability are thus both potential factors regulating life-history processes, yet they are often tested in isolation of each other. In this study, we considered the effect of both food availability and elevated T on immune function and reproductive behavior in sagebrush lizards, Sceloporus graciosus, to assess how T and energy availability affect these trade-offs. We experimentally manipulated diet (via supplemental feedings) and T (via dermal patches) in males from a natural population. We determined innate immune response by calculating the bacterial killing capability of collected plasma exposed to Escherichia coli ex vivo. We measured reproductive behavior by counting the number of courtship displays produced in a 20-min sampling period. We observed an interactive effect of food availability and T-patch on immune function, with food supplementation increasing immunity in T-patch lizards. Additionally, T increased courtship displays in control food lizards. Lizards with supplemental food had higher circulating T than controls. Collectively, this study shows that the energetic state of the animal plays a critical role in modulating the interactions among T, behavior and immunity in sagebrush lizards and likely other species.

Lipophilic Compounds from the Femoral Gland Secretions of Male Hungarian Green Lizards, Lacerta viridis

In spite of the importance of chemical signals (pheromones) in the reproductive behaviour of lizards, only a few studies have examined the role of specific chemical compounds as sexual signals. The secreted chemicals vary widely between species but whether this variation reflects phylogenetic or environmental differences remains unclear. Based on mass spectra, obtained by GC-MS, we found 40 lipophilic compounds in femoral gland secretions of male green lizards (Lacerta viridis), including several steroids, alpha-tocopherol, and esters of n-C16 to n-C20 carboxylic acids, and minor components such as alcohols between C12 and C20, squalene, three lactones and one ketone. We compared these chemicals with those previously found in other closely related green lizard species, and discussed how phylogenetical differences and/or environmental conditions could be responsible for the differential presence of chemicals in different lizard species.

Effect of refuge distance on escape behavior of side-blotched lizards (Uta stansburiana)

Side-blotched lizards ( Uta stansburiana Baird and Girard, 1852) use sagebrush desert habitat above cliffs and typically flee over and down the nearest cliff when disturbed. We tested antipredator escape tactics of lizards to a common local snake, the western yellowbelly racer ( Coluber mormon Baird and Girard, 1852). Our goal was to determine if lizards use cliffs as a refuge from snakes, which cannot climb the sheer rock face, and whether distance to refuge affects escape behavior. We located undisturbed lizards above a cliff and approached them from a random direction with a realistic rubber snake model. When the snake model approached, lizards fled nonrandomly toward the nearest cliff refuge, indicating considerable spatial awareness. Lizards fled more directly toward the cliff the farther from the cliff they were found. However, when beyond ~15 m from the cliff the escape behavior of lizards changed to one of flight in circles (nondirectional) without hiding. Performance capacity (endurance) of the lizards is much greater than 15 m, indicating that lizards have the physiological capacity to reach the cliff. We suggest that the costs of potential intraspecific interactions (i.e., escape into unfamiliar or a competitor’s territory) are greater than the immediate risks of predation by snakes.

Network structure and parasite transmission in a group living lizard, the gidgee skink, Egernia stokesii

Gidgee skinks (Egernia stokesii) form large social aggregations in rocky outcrops across the Flinders Ranges in South Australia. Group members share refuges (rock crevices), which may promote parasite transmission. We measured connectivity of individuals in networks constructed from patterns of common crevice use and observed patterns of parasitism by three blood parasites (Hemolivia, Schellackia and Plasmodium) and an ectoparasitic tick (Amblyomma vikirri). Data came from a 1-year mark-recapture study of four populations. Transmission networks were constructed to represent possible transmission pathways among lizards. Two lizards that used the same refuge within an estimated transmission period were considered connected in the transmission network. An edge was placed between them, directed towards the individual that occupied the crevice last. Social networks, a sub-set of same-day only associations, were small and highly fragmented compared with transmission networks, suggesting that non-synchronous crevice use leads to more transmission opportunities than direct social association. In transmission networks, lizards infested by ticks were connected to more other tick-infested lizards than uninfected lizards. Lizards infected by ticks and carrying multiple blood parasite infections were in more connected positions in the network than lizards without ticks or with one or no blood parasites. Our findings suggest higher levels of network connectivity may increase the risk of becoming infected or that parasites influence lizard behaviour and consequently their position in the network.

COMPORTAMENTO DE TERMORREGULAÇÃO EM LAGARTOS BRASILEIROS

Reptiles present one of the most complex mechanisms found within vertebrates to regulate body temperature. In lizards, this regulation mechanism achieves a remarkable degree of refinement in which behavior plays a crucial role. The present review deals with a set of factors of thermoregulation in Brazilian lizards, illustrating it as the result of a physiological and behavioral process in lizards and discussing other factors such as the relationship between phylogeny and body temperature in activity, the environmental sources of heat, the costs of behaviors associated with thermoregulation, the complex relationships between body temperature, foraging intensity and diet, and the relationship between thermoregulation and some aspects of their life history such as degree of herbivory and reproductive condition. Based on various sources of information available on body temperature regulation by Brazilian lizards, we aimed at providing a comprehensive review on the subject of thermoregulatory behaviors in Brazilian lizards.

Invasive fire ants alter behavior and morphology of native lizards

Nonnative species introductions are becoming more common, but long-term consequences of the novel pressures imposed by invaders on native species remain poorly known. The red imported fire ant, Solenopsis invicta, is an invasive species with potential global impact. Comparison of lizards across the invasive range within the United States reveals novel antipredator strategies and altered morphologies that mitigate potentially lethal attack by these ants, within 70 years of their introduction. The likelihood that adult lizards will behaviorally respond to fire ant attack increases with time since invasion, but hatchlings exhibit high levels of antipredator behavior irrespective of their site of origin. Adults and hatchlings from sites invaded longer ago also have relatively longer hind limbs. This trait increases the effectiveness of behavioral strategies for removing ants and is likely an adaptive response to minimize envenomation during attack. The observed changes are not correlated with habitat, exposure to fire ants, or latitude, arguing against phenotypic plasticity and learning as causal mechanisms, and museum specimens show that morphological differences were not evident prior to fire ant invasion. These data contribute to our growing awareness that ecological invasions can prompt adaptive responses, altering the nature of interactions between invaders and the natives they contact.

Fence Lizard

A fence lizard (Sceloporus undulatus) basks in the afternoon sunshine. Life has been less peaceful for these fence lizards since fire ants (Solenopsis invicta) were introduced to the USA ~70 years ago. These invaders aggressively attack fence lizards. The consequences can be lethal, but these lizards have begun to fight back. Fence lizards from populations that have coexisted with fire ants for longer periods increase their chances of survival by performing vigorous body twitches that remove attacking ants, and by fleeing from the source of the assault. They also have longer hind limbs, which enhance the effectiveness of these strategies. A juvenile fence lizard, Sceloporus undulatus, basking next to an active invasive fire ant mound, Solenopsis invicta, that can be seen along the right hand edge of the garden railing. These photographs illustrate the article “Invasive fire ants alter behavior and morphology of native lizards,” by Tracy Langkilde, tentatively scheduled to appear in Ecology 90(1), January 2009.

Tri-objective Co-evolutionary Algorithms and Application of Mechanism Design Based on Bionics of Lizard Behavior

Bionic research on three kinds of male side-spot lizard’s behavior and survival of multiply mechanism, one kind of co-evolutionary algorithm for tri-objective optimization is presented. Taking three design objectives as three kinds of lizard and mapping design variables as lizard population’s chromosome, three kinds of lizard’s self-genetic factor are formed from the chromosomes, by adopting computing factor’s index and fuzzy clustering method. Based on three kinds of lizard’s behavior, the mapping relationship between self-adaptive function and three objective functions has been established, in order to evaluate these three lizard individual ability of adapting to nature. By taking self-adaptive function as objective for co-evolutionary, the relative optimal genes of those three kinds of lizard has been obtained. Then a new chromosome has been made with the optimal genes. Based on the converge condition, the optimal chromosome is obtained with multi-generation evolution. Taking tri-objective optimization of luffing mechanism of compensative shave block for example, computed results show that this algorithm is effective.

Mainland versus island differences in behaviour of Podarcis lizards confronted with dangerous prey: the scorpion Buthus occitanus

Rapid divergence in behaviour of populations invading novel habitats is often considered adaptive as it may allow a species to exploit novel resources. Here we explore the behavioural response of two closely related species of Podarcis lizards living in different habitats, the Spanish mainland and a dry volcanic island, towards a potentially dangerous prey. Our results show that whereas insular lizards attacked scorpions and consequently considered them to be potential prey, mainland lizards tended to flee or ignored them. Sexual differences in the response to scorpions were pronounced in the insular habitat. Males tended to attack scorpions while females tended to ignore them. Inter‐specific and inter‐sexual differences in the responses of lizards may be mediated by body size differences between populations and sexes. The rapid changes in behaviour allowing insular lizards to recognize scorpions as potential prey may have allowed these animals to capitalize on an abundant food resource in a depauperate environment.

Basking in the Australian water dragon Physignathus lesueurii; why do alpha males not respond to operative temperatures in the same way as adults and sub-adults?

AbstractObservations have been made on the behaviour of the Australian water dragon Physignathus lesueurii in southeast Australia. Physical models that explore the thermal environment at a similar spatial level as real lizards were related to ontogenetic changes in lizard behaviour. Current theory predicts that a heliotherm will bask in open locations to optimise heating rates in order to attain target body temperatures as quickly as possible. Movement to shaded or partially shaded areas then maintains thermal stability. Regression equations of basking intensity in relation to operative temperatures were employed to test this theory. The behaviour of adults, which were not alpha males, and sub adults was in agreement with the prediction, but the behaviour of alpha males was not: the regression coefficient did not differ significantly from 0. In general, sub adult lizards were more active and fed more often than larger lizards although this relationship changed with different times of the day. The results suggest differing costs for thermoregulation for different size classes, particularly in alpha males where territory defence has a key role.

Correlates of reproductive success in male lizards of the alpine species Iberolacerta cyreni

We followed a field population of the alpine lizard Iberolacerta cyreni over 2 consecutive breeding seasons and assigned paternity to the offpring using 8 microsatellite markers. Paternity data, combined with observations of the behavior, morphology, and spacing patterns of lizards, allowed us to document the extent of polygamy, the phenotypic correlates of the number of offspring sired, and the correlation between male reproductive success (RS) and probability of recapture the second year of our study. Multiple paternity was observed in nearly 50% of clutches, and the mating system was highly polygynandrous. In the first year of our study, male RS increased with body size, activity, tail length, and color saturation of the dorsum. In the second year, male RS increased with activity and body condition. Overall, increased male activity, a trait that is expected to decrease survivorship, was the explanatory variable that had the greatest effect on RS. However, the residents of our first study year that were recaptured in the second year had longer tails, were more active, and sired more offspring than their conspecifics that were not recaptured. Thus, contrary to expectations, no negative correlation between present reproduction and future survival was found, which suggests that male investment in reproduction is condition dependent and positively correlated with the ability to pay the underlying costs of increased activity. Key words: activity, lizard, microsatellites, polygamy, reproductive costs, reproductive success, survivorship. [Behav Ecol]

Experimental support for the cost–benefit model of lizard thermoregulation: the effects of predation risk and food supply

Huey and Slatkin's (Q Rev Biol 51:363-384, 1976) cost-benefit model of lizard thermoregulation predicts variation in thermoregulatory strategies (from active thermoregulation to thermoconformity) with respect to the costs and benefits of the thermoregulatory behaviour and the thermal quality of the environment. Although this framework has been widely employed in correlative field studies, experimental tests aiming to evaluate the model are scarce. We conducted laboratory experiments to see whether the common lizard Zootoca vivipara, an active and effective thermoregulator in the field, can alter its thermoregulatory behaviour in response to differences in perceived predation risk and food supply in a constant thermal environment. Predation risk and food supply were represented by chemical cues of a sympatric snake predator and the lizards' food in the laboratory, respectively. We also compared males and postpartum females, which have different preferred or "target" body temperatures. Both sexes thermoregulated actively in all treatments. We detected sex-specific differences in the way lizards adjusted their accuracy of thermoregulation to the treatments: males were less accurate in the predation treatment, while no such effects were detected in females. Neither sex reacted to the food treatment. With regard to the two main types of thermoregulatory behaviour (activity and microhabitat selection), the treatments had no significant effects. However, postpartum females were more active than males in all treatments. Our results further stress that increasing physiological performance by active thermoregulation has high priority in lizard behaviour, but also shows that lizards can indeed shift their accuracy of thermoregulation in response to costs with possible immediate negative fitness effects (i.e. predation-caused mortality).

Not All Signals are Equal: Male Brown Anole Lizards (Anolis sagrei) Selectively Decrease Pushup Frequency Following a Simulated Predatory Attack

AbstractThe use of conspicuous communication signals often increases a signaler's risk of predation. Many species communicate with a repertoire of signals that may differ in their conspicuousness to predators. Few studies have examined the ability of prey to selectively decrease the use of individual signals in their displays under heightened predation risk. Here, I examined the behavior of male brown anole lizards (Anolis sagrei) in response to a simulated predatory attack from a model kestrel. This species communicates with three major visual signal types, the head‐bob, pushup, and dewlap extension, which vary in their motion and spectral characteristics. I predicted that lizards would decrease frequencies of the dewlap extension and pushup following the attack, but not the head‐bob. Males modulated their use of individual signals by decreasing pushup rates, but not head‐bob rates. Decreases in dewlap frequency were marginally significant. One explanation for these results is that lizards decrease frequencies of signal types based partly on their conspicuousness. The energetic cost of each signal type may be an equally important factor that determines the signaler's response to predators, particularly if a predatory attack is perceived as imminent.

Male-biased predation of western green lizards by Eurasian kestrels

Selective predation can be an important force driving the evolution of organisms. In particular, sex-biased predation is expected to have implications for sexual selection, sex allocation and population dynamics. In this study, we analysed sex differences in the predation of the western green lizard (Lacerta bilineata) by the Eurasian kestrel (Falco tinnunculus) during the reproductive season. In addition, we investigated whether the rate of predation differed during the 8-year study period and among the three habitats studied. We collected lizard remains from nest boxes of kestrels. Freshly killed lizards were sexed by visual inspection, whilst the sex of head remains was assigned by analysing the cephalic scale morphology using geometric morphometrics. Our results show that the risk of being predated by a kestrel in our population was overall about 3.55 times higher for males than for females. To our knowledge this is the first study showing a male-biased predation in a lizard species. The selective predation of males was consistent between years over the 8-year study period (1999-2006) and also consistent between the three types of kestrel hunting habitat. Overall predation rates on lizards differed between habitats, depending on the year. We propose that the observed sex-biased predation is mainly due to sex differences in lizard behaviour.

Evolution of jumping capacity in Tropidurinae lizards: does habitat complexity influence obstacle-crossing ability?

Jumping performance is relevant for lizards in many ecological contexts and might be favoured during the colonization of structurally complex habitats. Although ground-dwelling lizards use jumps to overcome small obstacles in their natural environments, jumping capacity has been mostly studied in arboreal species. Here, we analysed the evolution of jumping behaviour and performance in lizards from eight ground-dwelling species of Tropidurinae attempting to cross obstacles of different heights in a jumping track, both when undisturbed and under continuous stimulation. To establish ecological correlates with habitat complexity, individuals from two contrasting Brazilian habitats, the arid Caatingas (sand species) and the savannah-like Cerrados (rock species), were compared. Rock species jumped more often and crossed higher obstacles than sand ones in both tests, and performed more vertical than horizontal jumps. Although sand species performed less jumps, they were more successful at crossing the obstacles presented in comparison with rock species. Phylogenetic analyses confirmed these findings and demonstrated a large divergence in jumping capacity between sister-species from different habitats. Therefore, the differences in propensity and endurance for jumping activity appear to be independent of phylogenetic relationships in Tropidurinae and likely reflect an adaptation to the contrasting environments inhabited. The ecological implications of these findings are discussed. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 393–402.

Behavior as a Tool for Welfare Improvement and Conservation Management in the Endangered Lizard (Gallotia bravoana)

The study assessed the behavior of Gallotia bravoana (La Gomera, Canary Islands, one of the world's most threatened reptiles) to facilitate management decisions and improve welfare during initial stages of a species' recovery plan. The study analyzed—and remote-controlled video cameras filmed—the behavior of lizards housed in 3 outdoor enclosures, from May to September 2000. Daily activity showed a bimodal or unimodal pattern, all specimens basking more during June, with the largest male was the most active. Adults ate a higher percentage of vegetable items; subadults, a comparatively larger proportion of larvae and adult insects. The study analyzed individual compatibility; all interacted during 2 short periods. Aggression occurred mainly between males; because most directed high-intensity aggression toward a specific lizard, the study recommended isolating this lizard in a separate enclosure. The study recommended keeping 2 male-female pairs, who demonstrated social tolerance, as breeding pairs in separated terraria. Typical courtship behavior (head-bob sequences) occurred mainly during July, with highest frequency by the oldest male. Behavioral assessment provided data for improving the individuals' welfare in the enclosures and to select specific pairs for breeding.

Determinants of sexual differences in escape behavior in lizards of the genus Anolis: a comparative approach

Males and females are known to differ in a whole suite of characteristics, such as morphology, physiology, ecology, and behavior. Intersexual differences are generally believed to arise because of differences in selective pressures on either sex. In this study, we investigated whether intersexual differences in escape behavior exist in lizards of the genus Anolis, and whether these could be explained by intersexual differences in body size and/or microhabitat use. To do so, we compared the behavioral response to an approaching human predator in the field in males and females of 12 Anolis species. We found that ecomorphs and sexes differ greatly with respect to escape behavior. Twig anoles have the shortest approach distance (i.e., distance between the observer and the lizard when it starts fleeing) and final distance (i.e., distance between the observer and the lizard when it stops moving), compared with the other ecomorphs. The distance fled, on the contrary, is greatest in twig anoles. Also, females flee less soon and run over shorter distances than do males. Since twig anoles are considered the most cryptic anoles, and females may be less conspicuous than males, these results corroborate the idea that well camouflaged animals allow predators to come closer. The interspecific variation in sexual dimorphism in escape behavior, however, cannot be explained by the interspecific variation in sexual size dimorphism or sexual dimorphism in microhabitat use. Thus, escape behavior appears determined by different factors in males and females.

Lateralized righting behavior in the tortoise ( Testudo hermanni)

Lateralization of brain and behaviour at the population level has been documented in all vertebrate classes. Research was mostly carried out on mammalian and avian species, the least investigated class with this regards being the Reptilia, with studies concentrating on lateralized aggressive behaviour in lizards. No research has been carried out on lateralization in the Chelonian order. We investigated the presence of motor asymmetries in the tortoise Testudo hermanni, using the righting response (i.e. the animal is positioned upside-down and the left/right side to which it uprights is observed), a procedure already employed to assess behavioural lateralization in amphibians. The ability of righting has a particularly high adaptive value in tortoises, as in case of overturning, and consequent exposure to sunrays, changes in body temperature and difficulties in respiration could occur leading to serious conditions. Thirty-four tortoises underwent a series of righting tests in a standardized apparatus, 15 tortoises were also retested 10 months later. A bias at the individual as well as at the population level was found for preferentially turning on the right side. Consistency of responses at retest was also observed. The results are discussed with reference to the implications for the evolution of brain lateralization in vertebrates.

Permanent magnetic system design for the wall-climbing robot

This paper presents the design and analysis of the permanent magnetic system for a wall-climbing robot with permanent magnetic tracks. Based on the behaviour of gecko lizards, the architecture of t...