Effects of sensory mode in prey discrimination and predatory behaviour of rock lizards

An essential part of foraging ecology is to understand the processes of detection, recognition and discrimination of prey, as well as the sensorial modalities involved. Often, predators do not rely on a single sensory system but on multiple interacting senses. Specifically, lizards mainly use vision and vomerolfaction for prey pursuit. Here, we used an experimental approach to study how the Carpetan rock lizard, Iberolacerta cyreni, responds to different types of stimuli (chemical, visual, or both combined) from two prey species. The number of individuals approaching the prey and the number of attacks differed between treatments, however, we did not find differences in latency time, number of individuals attacking the prey or number of tongue flicks. Our results suggested that visual cues combined with chemical stimuli enhanced detection of both prey species and that prey discrimination occurred posteriorly and independently of using any or both types of stimuli.

Do lizards (Podarcis siculus) react to whip snake (Hierophis viridiflavus) scents? A comparative test on odour stimuli recognition

We tested the ability in the ruin lizard (Podarcis siculus) to discriminate between odour of a predator (the whip snake Hierophis viridiflavus) and those from harmless sources. We analysed two lizard populations: one (PP) predated by snakes and another (PNP) where no snakes occur. We tested the rate of tongue flick directed to cotton-tips impregnated with odours, and the rate of tongue flick, the time spent in immobility, escaping and exploring the terrarium containing a diffuse odour. We used the smell of the snake as dangerous stimulus, water as blank control, and cologne as complex control. Both populations did not discriminate snake cue from complex odour in both the experiments. PP individuals were more active and prone to analysing and exploring the stimuli and the environment than PNP lizards. In PP, the higher interest towards cologne and snake scents could be triggered just by their complexity that requires more tongue flicks to be ‘analysed’, with no apparent adaptive anti-predatory value. Overall, we observed a total responsiveness and activity pattern higher in the PP respect to PNP.

Thermal reception in the Mexican Lance-head rattlesnake, Crotalus polystictus

The sensory systems of Boidae and Crotalinae snakes detect subtle differences of thermal infrared energy. The complexity of this ability involves neurophysiological mechanisms with interspecific differences in the anatomy of thermoreceptor organs and functionally in thermal detection ranges and thermal thresholds, with ecological correlations that influence the thermo-reception. However, little is known about the information these snakes obtain and use from infrared radiation. We analyzed the behavioral response of adult Mexican Lance-head Rattlesnakes (Crotalus polystictus) to static thermal stimuli, evaluating the influence of distance from the snake of the thermal stimuli, and its lizard-like or mouse-like shape. The results reveal that C. polystictus is able to detect static thermal stimuli located from 20 to 200 cm away. Head movements and tongue-flicks were the most frequently performed behaviors, which suggests they are behaviors that can facilitate the detection of subtle differences in temperature of static stimuli. In addition, we suggest that stimulus shape and temperature are important in the timing of head orientation and frequency of tongue-flicks. We discuss the possible methodological and sensory implications of this behavioral response in C. polystictus.

Thermal reception in the Mexican Lance-head rattlesnake, Crotalus polystictus

The sensory systems of Boidae and Crotalinae snakes detect subtle differences of thermal infrared energy. The complexity of this ability involves neurophysiological mechanisms with interspecific differences in the anatomy of thermoreceptor organs and functionally in thermal detection ranges and thermal thresholds, with ecological correlations that influence the thermo-reception. However, little is known about the information these snakes obtain and use from infrared radiation. We analyzed the behavioral response of adult Mexican Lance-head Rattlesnakes (Crotalus polystictus) to static thermal stimuli, evaluating the influence of distance from the snake of the thermal stimuli, and its lizard-like or mouse-like shape. The results reveal that C. polystictus is able to detect static thermal stimuli located from 20 to 200 cm away. Head movements and tongue-flicks were the most frequently performed behaviors, which suggests they are behaviors that can facilitate the detection of subtle differences in temperature of static stimuli. In addition, we suggest that stimulus shape and temperature are important in the timing of head orientation and frequency of tongue-flicks. We discuss the possible methodological and sensory implications of this behavioral response in C. polystictus.

Chemical discrimination of pesticide-treated grapes by lizards (Gallotia galloti palmae, Fam. Lacertidae)

Lizards from the Canary Islands may act as pests of several cultivated plants. As a case in point, vineyard farmers often complain about the lizards’ impact on grapes. Though no specific pesticide is used for lizards, several pesticides are used in vineyards to control for insects, fungi, etc. We therefore tested whether lizards (Gallotia galloti palmae) could detect and discriminate pesticide-treated from untreated grapes. To answer this question, we performed experiments with adults of both sexes obtained from three localities in La Palma Island. Two of them were a vineyard and a banana plantation that had been treated with pesticides and the other one was in a natural (untreated) site. In the laboratory, lizards were offered simultaneously one untreated (water sprayed) and one treated (with Folithion 50 LE, diluted to 0.1%) grape placed on small plates. The behaviour of the lizards towards the fruits was filmed and subsequently quantified by means of their tongue-flick, licks or bite rates to each of the grapes. Results showed that only lizards from the natural (untreated) site clearly differentiated the two types of grapes, performing significantly more tongue-flicks, licks and bites to the untreated than to the pesticide-treated grapes. Lizards captured at the other two sites (cultivated fields with pesticide treatment), did not show a significantly different response to the two types of grapes. These results suggest that lizards living in or near cultivated fields may be habituated to pesticide-treated food and, therefore, do not clearly discriminate treated from untreated food items. However, another possibility is that natural selection (or maybe resistance) could be responsible by these individuals in the populations showing this kind of pesticide insensitiveness.

Tantalising tongues: male carpet pythons use chemoreception to differentiate among females

For animals sparsely distributed across a landscape, finding and identifying a receptive female during a short breeding period can be a challenge for males. Many snakes appear to rely on the production of sex-specific pheromones to synchronise the timing of reproductive behaviour. The rare Australian south-west carpet python (Morelia spilota imbricata) displays non-aggressive mating aggregations of up to six males around a receptive female, suggesting that males are responding to some chemical signal that enables multiple males simultaneously to identify and locate the female. We investigated chemoreceptive response (tongue-flicking) of 10 male pythons under laboratory conditions to 12 (randomly ordered) treatments each presented for three minutes. Cutaneous chemicals (dissolved in hexane solvent) were collected on cotton buds from the skin of six female pythons and male responses to these were compared with six control treatments. Male pythons produced a greater number of tongue flicks during the first minute of each trial, with fewer in minutes 2 and 3. Male chemoreceptive response in the third minute varied significantly between treatments and was only maintained for trials presenting cutaneous chemicals collected from the three relatively largest female pythons. This experiment suggests that male carpet pythons can use chemoreception to obtain information about their social environment, identifying pheromone cues from large, potentially fecund females. This ability would be adaptive for male mate-selection behaviour and is likely to also reduce costs of searching behaviour.

Observaciones sobre algunos aspectos del comportamiento depredador en condiciones naturales y en cautividad de la serpiente diurna mastigodryas pleei (dumeril, bibron y dumeril 1854)

Se evaluaron algunos aspectos del comportamiento depredador de la serpiente diurna Mastigodryas pleei frente a dos tipo de presa: mamíferos (ratón de laboratorio) y lagartos (Cnemidophorus lemniscatus), cuantificando la duración de cada paso en la secuencia de depredación y midiendo variables como el número de movimientos de la lengua (tongue flicks), latencia de ataque, distancia de ataque y posición de la mordida sobre el cuerpo de la presa. Se encontró que la máxima distancia de ataque para este colúbrido diurno varia dependiendo de la naturaleza de la presa. La máxima distancia de ataque registrada (12 cm) desplegada durante el ataque a un lagarto y la minima (3 cm) desplegada a un ratón. La distancia de ataque puede estar relacionada con el reconocimiento de un peligro potencial atribuido a las características de una presa, exhibiendo tácticas diferenciales de aproximación y captura para atacar presas inofensivas o presas potencialmente peligrosas. Este hecho se evidencia durante la secuencia de depredación en el lugar específico en donde se propicia la mordida y la distancia relativa del ataque. Los tiempos de cada paso en la secuencia y el número de movimientos de lengua no mostraron diferencias significativas entre tratamientos.

Chemosensory species recognition may reduce the frequency of hybridization between native and introduced lizards

The introduction of alien species to islands by human activity can cause catastrophic consequences for small populations of island endemics. Hybridization between the endangered and endemic insular lizard Podarcis atrata (Boscá, 1916) from the Columbretes Islands (Mediterranean, Spain) and the common mainland lizard Podarcis hispanica (Steindachner, 1870) could potentially occur because mainland haplotypes have already been detected in the islands, the two species are closely genetically related, and the frequency of visitors to these islands is increasing. However, reproductive decisions of lizards are often mediated by species recognition mechanisms based on chemical cues. On the basis of this observation, even if some mainland P. hispanica lizards were introduced to the islands, interspecific recognition might make rare an eventual hybridization with the insular P. atrata. We examined interspecific chemical recognition between the insular P. atrata and the mainland P. hispanica. Our results showed that lizards of both sexes responded more strongly (i.e., directed a significantly higher number of tongue flicks) to scents of conspecific individuals than to scents of heterospecifics. Chemical recognition of conspecifics by endemic island P. atrata lizards may reduce the occurrence of hybridization with introduced mainland P. hispanica lizards and protect the insular gene pool.

Elevated tongue-flicking rate to cricket surface chemicals by the arthropodivorous rough green snake Opheodrys aestivus

The rough green snake Opheodrys aestivus is a dietary specialist on insects and other arthropods. In a laboratory experiment, I tested chemosensory responses to chemical cues from several taxa palatable to other snakes and two control stimuli presented on cotton swabs. The snakes tongue-flicked at significantly higher rates in response to cues from crickets than from any of the other stimuli, and none of the other potential prey types elicited more tongue-flicks than cologne, the control for response to an odorous substance irrelevant to feeding. These findings are consistent with existing data for a few other species of snakes that are prey specialists, suggesting that correlated evolution may occur between diet specialization and chemosensory responsiveness to cues from the specialized prey. Tests of additional species of prey specialists are needed to establish whether this hypothesis is correct.