Olfaction and predator detection inColeonyx brevis (Squamata: Eublepharidae), with comments on the functional significance of buccal pulsing in geckos

Oxidative stress and behavioral responses of moorish geckos (Tarentola mauritanica) submitted to the presence of an introduced potential predator (Hemorrhois hippocrepis)

Stressful situations induce an increase in the production of reactive oxygen species (ROS) which can lead to molecular damage and alteration of cell function. The introduction of new potential predators induces physiological stress in native fauna. However, behavioral responses have been reported in preys, demonstrating an induction of the defenses against alien species. Behavioral and antioxidant enzyme responses in the moorish gecko, Tarentola mauritanica, against the invasive predator horseshoe whip snake (Hemorrhois hippocrepis) were assessed. Behavior was recorded and a tissue sample from the tail was collected after placing the gecko in a terrarium with previous absence or presence of the snake in 'Control' and 'H. hippocrepis' groups, respectively. Fifteen behavioral variables were examined, including tongue flick (TF) and locomotion patterns. Antioxidant enzyme activities -catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR)-, and the levels of reduced (GSH) and oxidized glutathione (GSSG), glutathione/glutathione disulfide ratio (GSH/GSSG) and malondialdehyde (MDA) concentrations were measured in the tissue sampled. Geckos exposed to the snake's odor showed a higher number of TF, longer amounts of time remaining motionless or moving in slow motion and they spent less time on the ground in comparison to the 'Control' group. The presence of the snake produced a significant increase in the activities of CAT, SOD and GR and a decrease in the GSH/GSSG ratio in T. mauritanica individuals exposed to the snake's scent. Thus, both behavioral responses and oxidative stress biomarkers clearly showed that T. mauritanica is able to recognize H. hippocrepis as a potential predator, despite being a recently introduced snake at the Balearic Islands.

Behavioral patterns in the early-stage antipredator response change after tail autotomy in adult wall lizards

Autotomy is a drastic antipredator defense consisting of the voluntary shedding of a body part to escape from the predators. The loss of a body part may impair locomotion, feeding or mating, so animals may face a higher predation risk shortly after autotomy. Thus, until regeneration is completed, prey may adjust their behavior to reduce predation risk, and this could involve secondary costs. We assessed the effect of tail loss on the antipredator behavior of wall lizards (Podarcis muralis), comparing the behavior of tailed and tailless individuals exposed to a predatory snake (Coronella austriaca) scent, under controlled experimental conditions. Tailless lizards spent significantly more time performing behaviors with antipredatory significance (e.g., moving slowly), whereas tailed individuals performed exploratory walking for significantly more time. Moreover, tailless lizards spent more time basking, which probably increases the effectiveness of their cryptic design and decreases detection by predators. Lizards intensified the tongue flick rates when exposed to a pungent control or snake scents, as compared to their response to a neutral control. Besides, both tailed and tailless lizards intensified some aspects of their antipredator behavior (walking slowly and avoiding refuge use) when exposed to snake scent, which indicates discrimination of the smell of predatory snakes. Lizards decreased refuge use when exposed to predator scents, probably because the refuges are evaluated as unsafe due to a high concentration of snake scents. To conclude, our experiments showed that, after losing their tails, wall lizards modify their behavior in a way that likely minimizes predation risk.

Chemosensory cues of predators and competitors influence search for refuge in fruit by the coconut mite Aceria guerreronis

Organisms are adapted to recognize environmental cues that can provide information about predation risk or competition. Non-vagrant eriophyoid mites mainly avoid predation by using habitats that are difficult for predators to access (galls or confined spaces in plants) such as the meristematic region of the coconut fruit, which is inhabited by the phytophagous mites Aceria guerreronis and Steneotarsonemus concavuscutum. The objective of this study was to investigate the response of A. guerreronis to cues from the predators Neoseiulus baraki and Amblyseius largoensis in coconut fruits, cues from conspecifics (A. guerreronis injured) and cues from the phytophage S. concavuscutum. The test was carried out through the release of about 300 A. guerreronis on coconut fruits previously treated with cues from predators, conspecific or heterospecific phytophagous. We also observed the walking behaviour of A. guerreronis exposed to the same chemical cues using a video tracking system. The infestation of fruits by A. guerreronis was greater in the presence of predator cues and reduced in the presence of S. concavuscutum cues, but cues from injured conspecifics did not interfere in the infestation process. In addition, the cues also altered the walking parameters of A. guerreronis: it walked more in response to cues from predators and the heterospecific phytophage. Aceria guerreronis spent more time in activity in the treatments with clues than in the control treatment. These results suggest that A. guerreronis recognizes cues from predators and competitors and modifies its behaviour to increase its fitness.

Antipredatory behaviour of a mountain lizard towards the chemical cues of its predatory snakes

The ability to early detect a potential predator is essential for survival. The potential of Iberolacerta cyreni lizards to discriminate between chemical cues of their two predatory snakes Coronella austriaca (a non-venomous active-hunter saurophagous specialist) and Vipera latastei (a venomous sit-and-wait generalist) was evaluated herein. A third snake species, Natrix maura, which does not prey on lizards, was used as a pungent control. Thus, the behaviour of I. cyreni was studied regarding four treatments: (1) C. austriaca scent, (2) V. latastei scent, (3) N. maura scent and (4) odourless control. Lizards showed antipredator behaviour (such as slow-motion and tail waving) to C. austriaca and V. latastei chemicals. The antipredatory response was similar for both predators. This ability to react with an intensive behavioural pattern to the chemical cues of their predatory snakes may prevent lizards from being detected, and, if detected, dissuade the predator from beginning a pursuit.

Antipredatory reaction of the leopard gecko Eublepharis macularius to snake predators

Ability to recognize a risk of predation and react with adaptive antipredatory behavior can enhance fitness, but has some costs as well. Animals can either specifically react on the most dangerous predators (threat-sensitive avoidance) or they have safe but costly general wariness avoiding all potential predators. The level of threat may depend on the predator's foraging ecology and distribution with the prey with sympatric and specialist species being the most dangerous. We used 2 choice trials to investigate antipredatory behavior of captive born and wild-caught leopard geckos confronted with different snake predators from 2 families (Colubridae, Boidae) varying in foraging ecology and sympatric/allopatric distribution with the geckos. Predator-naïve subadult individuals have general wariness, explore both chemically and visually, and perform antipredatory postures toward a majority of snake predators regardless of their sympatry/allopatry or food specialization. The most exaggerated antipredatory postures in both subadult and adult geckos were toward 2 sympatric snake species, the spotted whip snake Hemorrhois ravergieri, an active forager, and the red sand boa Eryx johnii, a subterranean snake with a sit-and-wait strategy. In contrast, also subterranean but allopatric the Kenyan sand boa Eryx colubrinus did not elicit any antipredatory reaction. We conclude that the leopard gecko possesses an innate general antipredatory reaction to different species of snake predators, while a specific reaction to 2 particular sympatric species can be observed. Moreover, adult wild caught geckos show lower reactivity compared with the captive born ones, presumably due to an experience of a real predation event that can hardly be simulated under laboratory conditions.

Breathing life into dinosaurs: tackling challenges of soft-tissue restoration and nasal airflow in extinct species

The nasal region plays a key role in sensory, thermal, and respiratory physiology, but exploring its evolution is hampered by a lack of preservation of soft-tissue structures in extinct vertebrates. As a test case, we investigated members of the "bony-headed" ornithischian dinosaur clade Pachycephalosauridae (particularly Stegoceras validum) because of their small body size (which mitigated allometric concerns) and their tendency to preserve nasal soft tissues within their hypermineralized skulls. Hypermineralization directly preserved portions of the olfactory turbinates along with an internal nasal ridge that we regard as potentially an osteological correlate for respiratory conchae. Fossil specimens were CT-scanned, and nasal cavities were segmented and restored. Soft-tissue reconstruction of the nasal capsule was functionally tested in a virtual environment using computational fluid dynamics by running air through multiple models differing in nasal soft-tissue conformation: a bony-bounded model (i.e., skull without soft tissue) and then models with soft tissues added, such as a paranasal septum, a scrolled concha, a branched concha, and a model combining the paranasal septum with a concha. Deviations in fluid flow in comparison to a phylogenetically constrained sample of extant diapsids were used as indicators of missing soft tissue. Models that restored aspects of airflow found in extant diapsids, such as appreciable airflow in the olfactory chamber, were judged as more likely. The model with a branched concha produced airflow patterns closest to those of extant diapsids. These results from both paleontological observation and airflow modeling indicate that S. validum and other pachycephalosaurids could have had both olfactory and respiratory conchae. Although respiratory conchae have been linked to endothermy, such conclusions require caution in that our re-evaluation of the reptilian nasal apparatus indicates that respiratory conchae may be more widespread than originally thought, and other functions, such as selective brain temperature regulation, could be important.

Is naïveté forever? Alien predator and aggressor recognition by two endemic island reptiles

The disproportionate impacts of invasive predators are often attributed to the naïveté (i.e., inefficient or non-existing anti-predator behavior) of island native species having evolved without such predators. Naïveté has long been regarded as a fixed characteristic, but a few recent studies indicate a capacity for behavioral adaptation in native species in contact with alien predators. Here, we tested whether two reptiles endemic to New Caledonia, a skink, Caledoniscincus austrocaledonicus, and a gecko, Bavayia septuiclavis, recognized and responded to the odor of six introduced species (two rodents, the feral cat, and three species of ants). We used an experimental design in which reptiles had a choice of retreat sites with or without the odor of predators or aggressors. Skinks avoided two or three of the predators, whereas geckos avoided at most one. These results suggest that diurnal skinks are more responsive than nocturnal geckos to the odor of introduced predators. Neither skinks nor geckos avoided the three species of ants. Thus, the odors of alien predators are shown to influence retreat site selection by two native island reptiles. Moreover, the study suggests that this loss of naïveté varies among native species, probably as a consequence of the intensity of the threat and of time since introduction. These findings argue for re-thinking the behavioral flexibility of ectothermic reptiles in terms of their responses to biological invasion.

Inertial feeding in the teiid lizard Tupinambis merianae: the effect of prey size on the movements of hyolingual apparatus and the cranio-cervical system

In most terrestrial tetrapods, the transport of prey through the oral cavity is accomplished by movements of the hyolingual apparatus. Morphological specializations of the tongue in some lizard taxa are thought to be associated with the evolution of vomerolfaction as the main prey detection mode. Moreover, specializations of the tongue are hypothesized to compromise the efficiency of the tongue during transport; thus, driving the evolution of inertial transport. Here we use a large teiid lizard, Tupinambis merianae, as a model system to test the mechanical link between prey size and the use of inertial feeding. We hypothesize that an increase in prey size will lead to the increased recruitment of the cranio-cervical system for prey transport and a reduced involvement of the tongue and the hyolingual apparatus. Discriminant analyses of the kinematics of the cranio-cervical, jaw and hyolingual systems show that the transport of large prey is indeed associated with a greater utilization of the cranio-cervical system (i.e. neck and head positioning). The tongue retains a kinematic pattern characteristic of lingual transport in other lizards but only when processing small prey. Our data provide evidence for an integration of the hyolingual and cranio-cervical systems; thus, providing partial support for an evolutionary scenario whereby the specialization of the tongue for chemoreception has resulted in the evolution of inertial transport strategies.

The mechanism of chemical delivery to the vomeronasal organs in squamate reptiles: a comparative morphological approach

Vomeronasal chemoreception, an important chemical sense in squamate reptiles (lizards and snakes), is mediated by paired vomeronasal organs (VNOs), which are only accessible via ducts opening through the palate anteriorly. We comparatively examined the morphology of the oral cavity in lizards with unforked tongues to elucidate the mechanism of stage I delivery (transport of chemical-laden fluid from the tongue tips to the VNO fenestrae) and to test the generality of the Gillingham and Clark (1981. Can J Zool 59:1651-1657) hypothesis (based on derived snakes), which suggests that the sublingual plicae act as the direct conveyors of chemicals to the VNOs. At rest, the foretongue lies within a chamber formed by the sublingual plicae ventrally and the palate dorsally, with little or no space around the anterior foretongue when the mouth is closed. There is a remarkable conformity between the shape of this chamber and the shape of the foretongue. We propose a hydraulic mechanism for stage I chemical transport in squamates: during mouth closure, the compliant tongue is compressed within this cavity and the floor of the mouth is elevated, expressing fluid from the sublingual glands within the plicae. Chemical-laden fluid covering the tongue tips is forced dorsally and posteriorly toward the VNO fenestrae. In effect, the tongue acts as a piston, pressurizing the fluid surrounding the foretongue so that chemical transport to the VNO ducts is effected almost instantaneously. Our findings falsify the Gillingham and Clark (1981. Can J Zool 59:1651-1657) hypothesis for lizards lacking forked, retractile tongues.

Functional morphology and evolution of aspiration breathing in tetrapods

In the evolution of aspiration breathing, the responsibility for lung ventilation gradually shifted from the hyobranchial to the axial musculoskeletal system, with axial muscles taking over exhalation first, at the base of Tetrapoda, and then inhalation as well at the base of Amniota. This shift from hyobranchial to axial breathing freed the tongue and head to adapt to more diverse feeding styles, but generated a mechanical conflict between costal ventilation and high-speed locomotion. Some "lizards" (non-serpentine squamates) have been shown to circumvent this speed-dependent axial constraint with accessory gular pumping during locomotion, and here we present a new survey of gular pumping behavior in the tuatara and 40 lizard species. We observed gular pumping behavior in 32 of the 40 lizards and in the tuatara, indicating that the ability to inflate the lungs by gular pumping is a shared-derived character for Lepidosauria. Gular pump breathing in lepidosaurs may be homologous with buccal pumping in amphibians, but non-ventilatory buccal oscillation and gular flutter have persisted throughout amniote evolution and gular pumping may have evolved independently by modification of buccal oscillation. In addition to gular pumping in some lizards, three other innovations have evolved repeatedly in the major amniote clades to circumvent the speed-dependent axial constraint: accessory inspiratory muscles (mammals, crocodylians and turtles), changing locomotor posture (mammals and birds) and respiratory-locomotor phase coupling to reduce the mechanical conflict between aspiration breathing and locomotion (mammals and birds).

Chemically Mediated Species Recognition in Closely Related Podarcis Wall Lizards

In many animals, chemical signals play an important role in species recognition and may contribute to reproductive isolation and speciation. The Iberian lizards of the genus Podarcis, with up to nine currently recognized lineages that are often sympatric, are highly chemosensory and provide an excellent model for the study of chemically mediated species recognition in closely related taxa. In this study, we tested the ability of male and female lizards of two sister species with widely overlapping distribution ranges (Podarcis bocagei and P. hispanica type 1) to discriminate between conspecific and heterospecific mates by using only substrate-borne chemical cues. We scored the number of tongue flicks directed at the paper substrate by each individual in a terrarium previously occupied by a conspecific or a heterospecific lizard of the opposite sex. Results show that males of P. bocagei and P. hispanica type 1 are capable of discriminating chemically between conspecifics and heterospecifics of the opposite sex, but females are not. These results suggest that differences in female, but not male, chemical cues may underlie species recognition and contribute to reproductive isolation in these species. The apparent inability of females to discriminate conspecific from heterospecific males, which is not because of reduced baseline exploration rates, is discussed in the context of sexual selection theory and species discrimination.

Buccal oscillation and lung ventilation in a semi-aquatic turtle, Platysternon megacephalum

Movements of the hyobranchial apparatus in reptiles and amphibians contribute to many behaviors including feeding, lung ventilation, buccopharyngeal respiration, thermoregulation, olfaction, defense and display. In a semi-aquatic turtle, Platysternon megacephalum, x-ray video and airflow measurements from blowhole pneumotachography show no evidence that above water hyobranchial movements contribute to lung inflation, as in the buccal or gular pump of amphibians and some lizards. Instead, hyobranchial movements produce symmetrical oscillations of air into and out of the buccal cavity. The mean tidal volume of these buccal oscillations is 7.8 times smaller than the mean tidal volume of lung ventilation (combined mean for four individuals). Airflow associated with buccal oscillation occurs in the sequence of inhalation followed by exhalation, distinguishing it from lung ventilation which occurs as exhalation followed by inhalation. No fixed temporal relationship between buccal oscillation and lung ventilation was observed. Periods of ventilation often occur without buccal oscillation and buccal oscillation sometimes occurs without lung ventilation. When the two behaviors occur together, the onset of lung ventilation often interrupts buccal oscillation. The initiation of lung ventilation was found to occur in all phases of the buccal oscillation cycle, suggesting that the neural control mechanisms of the two behaviors are not coupled. The pattern of occurrence of both buccal oscillation and lung ventilation was found to vary over time with no obvious effect of activity levels.

History and the global ecology of squamate reptiles

The structure of communities may be largely a result of evolutionary changes that occurred many millions of years ago. We explore the historical ecology of squamates (lizards and snakes), identify historically derived differences among clades, and examine how this history has affected present-day squamate assemblages globally. A dietary shift occurred in the evolutionary history of squamates. Iguanian diets contain large proportions of ants, other hymenopterans, and beetles, whereas these are minor prey in scleroglossan lizards. A preponderance of termites, grasshoppers, spiders, and insect larvae in their diets suggests that scleroglossan lizards harvest higher energy prey or avoid prey containing noxious chemicals. The success of this dietary shift is suggested by dominance of scleroglossans in lizard assemblages throughout the world. One scleroglossan clade, Autarchoglossa, combined an advanced vomeronasal chemosensory system with jaw prehension and increased activity levels. We suggest these traits provided them a competitive advantage during the day in terrestrial habitats. Iguanians and gekkotans shifted to elevated microhabitats historically, and gekkotans shifted activity to nighttime. These historically derived niche differences are apparent in extant lizard assemblages and account for some observed structure. These patterns occur in a variety of habitats at both regional and local levels throughout the world.

Stimulus control of predatory behavior by the Iberian wall lizard (Podarcis hispanica, Sauria, Lacertidae): Effects of familiarity with prey

The authors examine the relative roles of vision and chemoreception and the influence of previous experience with prey on the predatory behavior of Iberian wall lizards (Podarcis hispanica). Experiment 1 compared the responses to visual, chemical, and a combination of visual and chemical cues of a familiar prey by 2 groups of lizards that had been kept in captivity for either 3 months or 21 days. Experiment 2 assessed the responses of lizards kept in the laboratory for more than 3 months to a novel prey species. The results reveal that feeding on a prey species affects the lizards' responses to chemical stimuli from that prey. The response to chemical cues of a novel prey requires a 1st-feeding experience with that prey. Lizards that have been fed the same prey species for several months cease responding to the chemical stimuli of that particular prey.

Food-chemical discrimination and correlated evolution between plant diet and plant-chemical discrimination in lacertiform lizards

Lizards use chemical cues to locate and identify prey and plant food, assess the nutritional quality of food, and detect plant toxins. Among insectivorous lizards, all actively foraging species studied respond strongly to prey chemicals sampled lingually, but ambush foragers do not. Much recent research has been devoted to assessing differential responses to food and nonfood chemicals (i.e., food-chemical discrimination) by omnivorous and herbivorous species and determining whether correlated evolution has occurred between plant diet and plant-chemical discrimination. We conducted experimental studies of food-chemical discrimination by two species of teiid lizards, the omnivorous Cnemidophorus murinus and the actively foraging insectivorous Ameiva ameiva. The omnivore distinguished both prey and plant chemicals from control substances. The insectivore exhibited prey-chemical, but not plant-chemical, discrimination, as indicated by tongue-flicking and biting. A comparative analysis using concentrated-changes tests showed that correlated evolution has occurred between plant consumption and plant-chemical discrimination in a major lizard taxon, Lacertiformes. These results extend and strengthen previous findings of similar correlated evolution to a new group and add to a growing database indicating that omnivorous lizards use chemical cues to assess both prey and plant foods.

Food chemical cues elicit general and population-specific effects on lingual and biting behaviors in the lacertid lizard Podarcis lilfordi

Actively foraging lizards are capable of identifying prey using only chemical cues sampled by tongue-flicking, and the relatively few omnivorous and herbivorous lizards tested similarly can identify both animal and plant foods from chemical cues. Whether lizards that eat plants respond to cues specific to preferred plant types and whether there is geographic variability in responses to cues from various plants correlated with the importance of those plants in local diets is unknown. In three populations of an omnivorous lacertid, the Balearic lizard Podarcis lilfordi, we studied chemosensory sampling and feeding responses to chemical cues from plant and animal foods presented on cotton swabs. Each lizard population is endemic to one islet off the coast of Menorca, Balearic Islands, Spain. Lizards in all three populations discriminated chemical cues from plant and animal foods from control substances. Our results extend findings of prey chemical discrimination and plant chemical discrimination in omnivores, increasing confidence that correlated evolution has occurred between plant diet and chemosensory response to palatable plants. There were no consistent differences among populations in tongue-flicking and biting responses to stimuli from flowers of syntopic and allopatric plant species. The lizards may respond to cues indicative of palatability in a wide range of plant species rather than exhibiting strong responses only to locally available plant species. Nevertheless, tongue-flicking and biting frequencies varied among plant species, perhaps indicating food preferences. In addition, there were differences among populations in tongue-flick rates, latency to bite, and licking behavior. Licking was observed in only one lizard population as a response to floral chemicals from only one of the plants species tested, raising the possibility of a population-specific linkage between identification of a particular plant species and performance of an appropriate feeding response.

Omnivorous lacertid lizards (Gallotia) from El Hierro, Canary Islands, can identify prey and plant food using only chemical cues

We studied lingual and biting responses to food chemicals by two species of omnivorous lacertid lizards, the Canary Island endemics Gallotia simonyi (the giant lizard of El Hierro) and Gallotia caesaris (Boettger's lizard), to ascertain their ability to discriminate between prey and plant food chemicals on the one hand and control stimuli on the other. We recorded frequencies of tongue-flicking and latency to bite in 60-s trials in which chemical stimuli on cotton-tipped applicators were presented to the lizards. Both species exhibited prey-chemical discrimination, as indicated by elevated tongue-flick rates and higher proportions of individuals biting in response to surface chemicals from crickets. Both species exhibited plant-chemical discrimination, as indicated by significantly greater tongue-flick rates and biting frequency in response to chemicals from tomato fruit than to the control stimuli. Juvenile G. simonyi responded much more strongly to chemical stimuli from tomato fruit than from leaves of Psoralea bituminosa, which is not a preferred food for juveniles. The findings are consistent with the hypothesis that chemosensory discrimination evolves in omnivorous lizards to permit evaluation of food quality, resulting in correspondence between plant diet and plant-chemical discrimination, both being absent in insectivores. The results are also consistent with the hypothesis that prey-chemical discrimination is retained and plant-chemical discrimination evolves in the omnivorous lizards derived from actively foraging insectivores.

Geographic variation in antisnake tactics: the evolution of scent-mediated behavior in a lizard

We used modern comparative methods to examine the evolution of scent-mediated antisnake behavior in the rock-dwelling velvet gecko (Oedura lesueurii). The selective agent is a snake species (broad-headed snake, Hoplocephalius bungaroides) that feeds primarily on velvet geckos by remaining sedentary in rock crevices for days or weeks, waiting to ambush lizards. The past and present distribution of this predator is well documented because of its threatened conservation status. We used this information to sample lizards from three populations distributed with snakes (sympatric) and three populations that appear never to have been distributed with snakes (allopatric) in each of two widespread but geographically distinct genetic groups of velvet gecko (as determined using allozyme electrophoresis). Wild-caught immature geckos from sympatric populations showed higher tongue-flick rates and stronger shifts in locomotion (increased duration of crawling and remaining stationary while pressed against the rock) toward snake-scented rocks than did lizards from allopatric populations. However, predation environment did not significantly affect a lizard's tendency to display other typical antisnake tactics such as tail waving or fleeing. These results were highly repeatable across the two sampled genetic groups of velvet gecko, despite demonstrable genetic divergence between groups. Experiments with hatchling lizards that had no experience with predators indicate that qualitative components of antisnake behaviors are probably inherited. The method of phylogenetically independent contrasts strongly suggests that the presence or absence of snakes has driven the evolution of behavior in velvet geckos. Collectively, these results provide support for an often suggested but speculative expectation that prey can adapt to predation pressure on a local scale.

Chemosensory discrimination of plant and animal foods by the omnivorous iguanian lizard Pogona vitticeps

Most iguanian lizards are insectivores that do not use chemical cues sampled by tongue-flicking to identify prey before attacking, but the sole iguanian herbivore previously studied did so. To investigate the effects of a partially herbivorous diet on responses to food chemicals, I conducted an experiment to determine whether the omnivorous bearded dragon (Pogona vitticeps) has a similar ability. Chemical stimuli from crickets and carrots, both preferred foods, and alfalfa sprouts, and deionized water (a nonpreferred food and odorless control, respectively) were presented on cotton-tipped applicators. The lizards responded more strongly to both preferred foods than to the controls, performing more tongue flicks and biting the cotton in a greater number of trials. It is hypothesized that lingually mediated food-chemical discrimination is useful to herbivorous and omnivorous lizards for identifying plant and animal foods and for evaluating the quality of plant foods. The insectivorous ambush foragers ancestral to P. vitticeps could not locate prey by tongue-flicking repeatedly at an ambush post and do not exhibit prey-chemical discrimination. Adding plants to the diet altered the selective milieu because plants approached using visual cues can be evaluated using chemical cues, allowing the evolution of the ability to discriminate between plant-food chemicals. The ability to identify animal prey by tongue-flicking may have evolved through correlated evolution with chemosensory identification of plants or specifically for locating or identifying immobile prey.

Can an orbital gland function in the vomeronasal sense? A study of the pygopodid Harderian gland

The Harderian gland occurs in the orbit of most tetrapod vertebrates. A growing body of evidence suggests that this gland is associated with the chemoreceptive function of the vomeronasal organ. In the present study, the morphology of the Harderian gland in two species of pygopodids was examined, and the results were contrasted with those from both geckos and snakes. The results show that the pygopodid Harderian gland shares histochemical and ultrastructural features with that of the geckos. However, in several gross morphological features, the pygopodid Harderian gland more closely resemble that of snakes than that of geckos. In both pygopodids and snakes, the nasolacrimal duct forms a direct link between the Harderian gland and the vomeronasal organ, which indicates that this specialized connection between the Harderian gland and vomeronasal organ is a convergent evolutionary attribute of these two groups.

Food chemical discriminations by an herbivorous lizard, Corucia zebrata

Adjustment of chemosensory response to diet should be apparent in evolutionary changes corresponding to dietary shifts. Because most lizards are generalist predators of small animals, relationships between chemosensory behavior and diet are difficult to detect. Nevertheless, the evolution of herbivory by a small number of lizards provides an opportunity to detect any corresponding change in response to plant chemicals. I studied tongue-flicking and biting by the large, herbivorous scincid lizard Corucia zebrata in response to chemical cues from crickets, romaine lettuce, and control stimuli presented on cotton swabs. The skinks exhibited significantly stronger response to plant and animal chemicals than to controls for several variables: greater number of individuals that bit swabs, shorter latency to bite, greater rate of tongue-flicks, and greater tongue-flick attack score. The clearest differences were observed for tongue-flick attack score, a composite variable that combines the effects of tongue-flicking and biting. An insectivorous member of the same subfamily, Scincella lateralis, shows strong tongue-flicking and biting response to chemical prey cues, but not to plant chemicals. This suggests that response to plant chemicals by C. zebrata may have evolved in tandem with the incorporation of plants into the diet and that response to cricket chemicals has been retained, perhaps due to similarities between plant and animal food. The findings support the hypothesis that dietary shifts induce corresponding changes in chemosensory response, but provide only a single independent contrast for a study of correlated evolution between plant diet and chemosensory response to plants. J. Exp. Zool. 286:372-378, 2000.

Feeding kinematics of phelsuma madagascariensis (Reptilia: gekkonidae): testing differences between iguania and scleroglossa

The kinematics of feeding in the gekkotan lizard Phelsuma madagascariensis (Scleroglossa) was investigated using high-speed cinematography (200–300 frames s(−)(1)) and X-ray films (64 frames s(−)(1)). Qualitative kinematic analysis of the head and jaw displacement of the prey to (capture) and within (reduction, transport, swallowing, licking) the buccal cavity are compared for two types of prey (crickets and mealworms) in 30 feeding sequences from four individuals. Maximal displacement of structures and timing of events are compared statistically to assess the differences among the phases and the prey using analysis of variance. P. madagascariensis uses its jaws only to capture the two types of prey item, and the capture jaw cycle is divided into fast-opening (FO), fast-closing (FC) and slow-closing (SC) stages only. As in iguanians and other scleroglossans, the reduction and transport cycles always involve a slow opening (SOI and SOII) stage before the FO stage, followed by FC and SC stages: this last stage was not easily identified in all feeding phase. Transport of the prey was followed by a large number of licking cycles. Our data show (i) that the capture profile in gekkotans is similar to that observed for other scleroglossans and different from that described for iguanians (e.g. the absence of an SO stage); (ii) that the kinematics of jaw and related hyo-lingual cycles of intraoral manipulation (reduction and transport) are similar in lizards with a very different hyo-lingual system (Iguania, Gekkota and Scincomorpha), suggesting a basic mechanism of feeding cycles in squamates, transformed in varanids and snakes; and (iii) that prey type affects the kinematics of capture and manipulation, although the high level of variation among lizards suggests a possible individual modulation of feeding mechanism. A principal components analysis was performed to compare capture and transport cycles in this study of P. madagascariensis (Gekkota) and a previous study of Oplurus cuvieri (Iguania). This analysis separated the capture cycle of each species, but the transport cycles were not completely separated. These results demonstrate the complexity of the modulation and evolution of feeding process in squamates.

Contribution of gular pumping to lung ventilation in monitor lizards

A controversial hypothesis has proposed that lizards are subject to a speed-dependent axial constraint that prevents effective lung ventilation during moderate- and high-speed locomotion. This hypothesis has been challenged by results demonstrating that monitor lizards (genus Varanus) experience no axial constraint. Evidence presented here shows that, during locomotion, varanids use a positive pressure gular pump to assist lung ventilation. Disabling the gular pump reveals that the axial constraint is present in varanids but it is masked by gular pumping under normal conditions. These findings support the prediction that the axial constraint may be found in other tetrapods that breathe by costal aspiration and locomote with a lateral undulatory gait.