Pungency Control Research Articles

Odour-mediated Interactions Between an Apex Reptilian Predator and its Mammalian Prey

An important but understudied modality for eavesdropping between predators and prey is olfaction, especially between non-mammalian vertebrate predators and their prey. Here we test three olfactory eavesdropping predictions involving an apex reptilian predator, the sand goanna Varanus gouldii, and several species of its small mammalian prey in arid central Australia: 1) small mammals will recognize and avoid the odour of V. gouldii; 2) V. gouldii will be attracted to the odour of small mammals, especially of species that maximize its energetic returns; and 3) small mammals will be less mobile and will show higher burrow fidelity where V. gouldii is absent compared with where it is present. As expected, we found that small mammals recognized and avoided faecal odour of this goanna, feeding less intensively at food patches where the odour of V. gouldii was present than at patches with no odour or a pungency control odour. Varanus gouldii also was attracted to the odour of small mammals in artificial burrows and dug more frequently at burrows containing the odour of species that were energetically profitable than at those of species likely to yield diminishing returns. Our third prediction received mixed support. Rates of movement of three species of small mammals were no different where V. gouldii was present or absent, but burrow fidelity in two of these species increased as expected where V. gouldii had been removed. We conclude that olfaction plays a key role in the dynamic interaction between V. gouldii and its mammalian prey, with the interactants using olfaction to balance their respective costs of foraging and reducing predation risk. We speculate that the risk of predation from this apex reptilian predator drives the highly unusual burrow-shifting behaviour that characterizes many of Australia's small desert mammals.

The Asian grass lizard (Takydromus sexlineatus) does not respond to the scent of a native mammalian predator

AbstractLacertid lizards use chemical cues emitted by saurophagous snakes to evade predation. Whether these lizards can detect and respond to the chemical cues of predatory mammals has not been studied. As many mammals carry distinct body odours and/or use chemical cues for intraspecific communication, lizards can be expected to use these chemicals as early warning cues. To test this idea, we observed the behaviour of Asian grass lizards (Takydromus sexlineatus) that had been transferred to an unfamiliar test arena containing one of four scent treatments. No particular scent was applied to the arena in the control situation. Diluted aftershave served as a pungency control. In the snake treatment, scent of the Oriental whip snake (Ahaetulla prasina) was applied. We included this treatment to learn how Asian grass lizards react to predator chemical cues. Finally, in the mongoose treatment, the lizards were confronted with scent cues of several small Indian mongooses (Herpestes auropunctatus). Snake scent elicited foot shakes, startles and tail vibrations. These are behaviours that in lacertid lizards are associated with stressful situations such as predatory encounters. Surprisingly, lizards confronted with mongoose scent exhibited none of these stress‐indicating behaviours. In fact, their behaviour did not differ from that of lizards subjected to an odourless control treatment. These results raise concern. Mongooses are rapidly invading ecosystems worldwide. If lizards that have co‐evolved with mongooses are unable to detect these predators’ presence through chemical cues, it seems highly unlikely that evolutionary naïve lizards will develop this ability rapidly.

Variation of prey responses to cues from a mesopredator and an apex predator

AbstractDetection and avoidance of predator cues can be costly, so it is important for prey to balance the benefits of gaining food against the costs of avoiding predators. Balancing these factors becomes more complicated when prey are threatened by more than one type of predator. Hence, the ability to recognize species‐specific predator odours and prioritize behaviours according to the level of risk is essential for survival. We investigated how rock rats, Zyzomys spp. modify their foraging behaviour and giving‐up density (GUD) in the presence of an apex predator, the dingo Canis dingo, a mesopredator, the northern quoll Dasyurus hallucatus, a herbivore, the rock wallaby Petrogale brachyotis as a pungency control and water as a procedural control. Both dingoes and quolls consume rock rats, but because quolls can enter small crevices inhabited by rock rats, they pose a greater threat to rock rats than dingoes. Rock rats demonstrated a stronger avoidance to quoll odour than dingo odour, and no avoidance of the pungency control (rock wallaby) and the procedural control (water). GUD values declined significantly over the duration of the study, but did not differ between odour treatments. Our results support the hypothesis that prey vary behaviour according to perceived predator threat, and show stronger responses to potentially more dangerous predators.

Prey detection in juveniles of an agamid lizard, Calotes versicolor (Daudin, 1802) (Reptilia: Squamata)

The relative importance of visual and chemical cues of prey in their detection by the juveniles of Calotes versicolor was studied using laboratory-born, 2-month-old individuals starved for 48 hrs. Grasshoppers served as the prey in all experiments. In trials with deionized water and cologne water (pungency control), the lizards showed no tongue flicking. Presentation of prey-body chemical cues on cotton swabs also did not evoke tongue flicking in test lizards indicating a lack of response to different odors through the vomeronasal olfactory system. The same test lizards lunged at the transparent glass beaker housing an active prey, with their mouth open as if to catch it. They showed no tongue flicking. In contrast, when an immobile prey was presented similarly the test lizards ignored it. Apparently, chemical cues are of little value in prey detection in C. versicolor. The study shows that C. versicolor juveniles use visual cues and prey movements in detection and capture of prey.

Generalization of predator recognition: Velvet geckos display anti-predator behaviours in response to chemicals from non-dangerous elapid snakes

Abstract Many prey species detect chemical cues from predators and modify their behaviours in ways that reduce their risk of predation. Theory predicts that prey should modify their anti-predator responses according to the degree of threat posed by the predator. That is, prey should show the strongest responses to chemicals of highly dangerous prey, but should ignore or respond weakly to chemicals from non-dangerous predators. However, if anti-predator behaviours are not costly, and predators are rarely encountered, prey may exhibit generalised antipredator behaviours to dangerous and non-dangerous predators. In Australia, most elapid snakes eat lizards, and are therefore potentially dangerous to lizard prey. Recently, we found that the nocturnal velvet gecko Oedura lesueurii responds to chemicals from dangerous and non-dangerous elapid snakes, suggesting that it displays generalised anti-predator behaviours to chemicals from elapid snakes. To explore the generality of this result, we videotaped the behaviour of velvet geckos in the presence of chemical cues from two small elapid snakes that rarely consume geckos: the nocturnal golden-crowned snake Cacophis squamulosus and the diurnal marsh snake Hemiaspis signata. We also videotaped geckos in trials involving unscented cards (controls) and cologne-scented cards (pungency controls). In trials involving Cacophis and Hemiaspis chemicals, 50% and 63% of geckos spent long time periods (> 3 min) freezing whilst pressed flat against the substrate, respectively. Over half the geckos tested exhibited anti-predator behaviours (tail waving, tail vibration, running) in response to Cacophis (67%) or Hemiaspis (63%) chemicals. These behaviours were not observed in control or pungency control trials. Our results support the idea that the velvet gecko displays generalised anti-predator responses to chemical cues from elapid snakes. Generalised responses to predator chemicals may be common in prey species that co-occur with multiple, ecologically similar, dangerous predators.

Native Australian frogs avoid the scent of invasive cane toads

AbstractInvasive species can affect the ecosystems they colonize by modifying the behaviour of native taxa; for example, avoidance of chemical cues from the invader may modify habitat use (shelter site selection) by native species. In laboratory trials, we show that metamorphs of most (but not all) native frog species on a tropical Australian floodplain avoid the scent of invasive cane toads (Bufo marinus Linnaeus 1758). Cane toads also avoid conspecific scent. This response might reduce vulnerability of metamorph frogs and toads to larger predatory toads. However, similar avoidance of one type of pungency control (garlic), and the presence of this avoidance behaviour in frogs at the toad invasion front (and hence, with no prior exposure to toads), suggest that this may not be an evolved toad‐specific response. Instead, our data support the simpler hypothesis that the metamorph anurans tend to avoid shelter sites that contain strong and unfamiliar scents. Temporal and spatial differences in activity of frogs versus toads, plus the abundance of suitable retreat sites during the wet season (the primary time of frog activity), suggest that avoiding toad scent will have only a minor impact on the behaviour of native frogs. However, this behavioural impact may be important when environmental conditions bring toads and frogs into closer contact.

Chemosensory cues associated with snake predators affect locomotor activity and tongue flick rate in the whiptail lizard, Aspidoscelis dixoni Scudday 1973 (Squamata Teiidae)

The unisexual teiid lizard Aspidoscelis dixoni Scudday 1973 is shown experimentally to be capable of detecting and responding to chemosensory stimuli from three species of naturally-occurring sympatric predatory snakes (Masticophis flagellum, M. taeniatus, Arizona elegans) and to discriminate these stimuli from those associated with a non-predatory snake (Leptotyphlops humilis segregus), as well as controls (water and cologne). Each lizard was exposed separately to the following: chemical stimuli from each of the predatory snakes, non-predatory, snake, water control, or pungency control (cologne). Lizards were placed in a test chamber whose floor was divided into 4 square grids of equal size, and for each trial, the number of times that a grid was crossed (locomotor activity), the number of tongue flicks observed (tongue flick rate, TFR), and time from beginning of trial to first tongue flick (latency), were recorded. Lizards crossed grid lines at significantly higher rates when exposed to chemosensory cues associated with all predatory snake species as compared to activity in the presence of nonpredator snake cues, water or cologne. There were no differences in number of grid crossings elicited by any of the three predatory snakes. TFR differed significantly among all treatments, but no significant difference was found among lizards exposed to water, cologne, or cues associated with L. h. segregus. TFRs were significantly higher, and latencies significantly lower, when lizards were exposed to chemosensory cues associated with predatory snake. Results suggest that because all lizards had no prior experience with any of the snakes, their ability to detect and respond to chemosensory cues of predators must be innate.

Chemosensory recognition by males of the Desert Pocket Mouse, Chaetodipus pencillatus to odors of various species of snakes

Studies were conducted to assess responses of the Desert Pocket Mouse Chaetodipus pencillatus, to chemosensory cues (treatment odors) associated with three naturally-occurring sympatric snake predators (Crotalus atrox, Pituophis melanoleucas, Elaphe guttata), and a snake that does not feed on mammals (Hypsiglena torquata), as well as an odorless control (water) and pungency control (cologne). Pocket mice were tested in a chamber where they were exposed to various treatments and their locomotor activity and defecation rate were recorded. Locomotor activity and defecation rates were significantly greater for mice exposed to odors associated with snake predators as compared to H. torquata or controls. There was no significant difference in responses of pocket mice to water or cologne treatments. Results suggest that because all test subjects had no prior experience with any of the snake species, their ability to detect and respond to odors associated with these predators must be innate.

Cologne as a pungency control in tests of chemical discrimination: effects of concentration, brand, and simultaneous and sequential presentation

Cologne has been used extensively as a pungency control in experiments on chemosensory behavior to assess responses to an odorous, readily detectable stimulus that is irrelevant to the adaptive response being studied. However, undiluted cologne may be aversive, its effects might differ among brands, it might suppress responses to simultaneously presented chemical stimuli, and might affect subsequent responsiveness to other stimuli. We present experimental data showing that undiluted cologne can be aversive, but that aversion can be eliminated by dilution. We also show that the utility of cologne as a pungency control varies among brands, that cologne does not suppress responses to food chemicals in some species, but does in others, and that prior exposure to cologne does not affect later response to food chemicals. In 60 s swab trials with the Balearic lizard (Podarcis lilfordi), the main chemosensory responses were unaffected by cologne concentration. However, one-fourth of lizards exhibited slight to moderate aversion to undiluted cologne and 3:1 water:cologne, but not to a readily detected lower concentration (9:1). Two cologne brands did not affect responses, but a third brand induced increased tongue-flick rates. Colognes that stimulate increased tongue-flicking might mask real experimental effects. Cologne presented simultaneously with cricket chemicals did not affect tongue-flicking and biting responses in two species, but caused increased tongue-flicking in a third species and weaker response to cricket chemicals in a fourth. Prior testing with cologne did not affect responsiveness to cricket chemicals in a subsequent trial. Although cologne is a useful pungency control, pilot tests are needed to verify its utility for unstudied cologne types and animal species.

Foraging mode of serpentiform, grass-living cordylid lizards: a case study of Cordylus anguina

Foraging mode of the Cape grass lizard, Cordylus anguina, was determined by using three criteria: 1) the number of movements per minute (MPM) and the percentage of time spent moving (PTM) during periods of activity; 2) prey chemical discrimination ability; 3) stomach contents. To determine MPM and PTM, observations were made from an observation tower using a semi-natural outdoor enclosure, and through a one-way glass panel using a semi-natural indoor enclosure. Each lizard (n = 10) was observed for a 10 minute period during peak activity and the times it was moving and the times it was stationary were recorded. Data obtained in the indoor- and outdoor enclosures did not differ significantly and were pooled. MPM (0.37 ± 0.21 S.D.) and PTM (1.92 % ± 0.93 S.D.) values recorded for C. anguina fall within the range given as characteristic for sit-and-wait foragers. Nine C. anguina were habituated in glass terraria to accept mealworms offered to them. When all lizards accepted food without hesitation, they were tested for their ability to discriminate among three different odours presented to them in a randomized block design: prey odours consisting of mealworm surface odours, distilled water as an odourless control stimulus, and cologne as a pungency control. The number of tongue-flicks directed at the cotton applicator containing the stimulus odour during 60 seconds was recorded. No statistically significant differences were found among the responses to the three treatment odours. An analysis of the stomach contents of 21 C. anguina revealed a diet of mostly diurnally active arthropods.

Responses to Animal and Plant Chemicals by Several Iguanian Insectivores and the Tuatara, Sphenodon punctatus

We conducted experimental tests of the responses to food chemicals presented on cotton swabs or ceramic tiles by tuataras and insectivorous species from several families of iguanian lizards. Tu- ataras, which are primarily carnivorous, never tongue flicked but frequently bit cotton balls bearing prey surface chemicals, suggesting that they may be able to detect airborne prey chemicals via olfaction. None of the lizards tested, the agamids Chamaeleo pardalis and Acanthosaura crucigera, the polychrotids Anolis smallwoodi and Chamaeleolis chamaeleonides, the phrynosomatids Sceloporus variabilis and Uta stansburi- ana, and the crotaphytid Crotaphytus collaris, exhibited any differential responses among prey chemicals, chemicals from palatable plants, and pungency control or odorless control stimuli. The findings buttress previous work that has shown a lack of prey chemical discrimination in ambush foragers, including all sampled iguanian insectivores. Given that all tested omnivores and herbivores respond strongly to plant chemicals, they are also consistent with the hypothesis that discriminatory lingual and biting responses to plant chemicals occur only in species having diets with a large plant component. Correlated evolution between herbivory and plant chemical discrimination remains to be established. For unknown reasons, Sceloporus variabilis tongue flicked less frequently in tile tests with romaine lettuce stimuli than with cricket and banana stimuli.

Lingually mediated discrimination of prey, but not plant chemicals, by the Central American anguid lizard, Mesaspis moreletii

AbstractThe ability of the anguid lizard Mesaspis moreletii to identify food using only chemical cues was tested experimentally by presenting a series of chemical stimuli to lizards on the cotton tips of wooden applicators. The lizards responded much more strongly to cricket surface chemicals than to surface chemicals from romaine lettuce, diluted cologne (pungency control), and deionized water (odorless control). In a second experiment, there were no significant differences among conditions in tongue-flicks, tongue-flick attack scores, or number of individuals that bit swabs bearing stimuli from banana, white grape, dandelion, or deionized water. The absence of differential responses was not due to habituation because individuals tested again with cricket stimuli immediately after experiment two all bit the swabs. In the laboratory the lizards readily consumed insects, but refused to eat plants selected for their palatability to herbivorous lizards. Our data suggest that M. moreletii is carnivorous.

Lingual and Biting Responses to Food Chemicals by Some Eublepharid and Gekkonid Geckos

Lingual and Biting Responses to Food Chemicals by Some Eublepharid and Gekkonid Geckos

Elevated tongue-flicking and biting by the insectivorous lygosomine skink Mabuya macularia to prey, but not plant, chemicals

The ability of an insectivorous scincid lizard, Mabuya macularia to discriminate among prey chemicals and control substances and its responses to chemical cues from several plant species eaten by herbivorous and omnivorous lizards were examined experimentally using the swab method. We presented cotton swabs bearing chemical cues to the lizards and recorded the numbers of tongue-flicks directed to swabs in 60 sec and whether or not they bit the swab. The lizards exhibited much stronger responses to prey chemicals (cricket) than to stimuli from romaine lettuce, diluted cologne (pungency control), and deionized water (odorless control). Responses to romaine lettuce stimuli did not differ from those to the two control stimuli. In further observations, there were no significant differences in response strength between deionized water and chemical stimuli from strawberry, red grape, and dandelion flower. These findings support the hypothesis that insectivorous lizards do not exhibit strong chemosensory investigation of plants that are palatable and do induce high rates of tongue-flicking and/or biting in herbivorous lizards. Although insufficient comparative data are available to test the hypothesis that plant chemical discrimination evolves in response to dietary shifts from insectivory to omnivory or herbivory, the present data and all published data are consistent with the hypothesis. The data for M. macularia suggest that plant chemical discriminations may have been absent in basal lygosomine skinks and derived in the herbivorous lygosomine Corucia zebrata.

Discriminative Response to Animal, But Not Plant, Chemicals by an Insectivorous, Actively Foraging Lizard, Scincella lateralis , and Differential Response to Surface and Internal Prey Cues

Responses by the insectivorous, actively foraging scincid lizard, Scincella lateralis, to chemical cues from a plant food favored by herbivorous lizards, its ability to discriminate prey chemicals from control substances, and its relative response to internal and surface prey chemicals were studied experimentally. We presented chemical cues to the lizards on cotton swabs and recorded their tongue-flicks and biting attacks on the swabs. The lizards exhibited significantly greater tongue-flick rates and biting frequencies to prey surface cues than to plant surface chemicals from romaine lettuce, diluted cologne (pungency control), and deionized water. Responses to the plant stimuli did not differ from those to the two control stimuli, in contrast with strong responses to the same plant cues by herbivores. This finding provides the first information suggesting that chemosensory response may be adapted to diet, with responsiveness to plant stimuli evolving de novo in herbivores. Biting and tongue-flicking responses were significantly greater to cricket chemicals than to all other stimuli, among which there were no differences. Thus, the lizards are capable of prey chemical discrimination, which may be ubiquitous among actively foraging lizards. The lizards exhibited more frequent biting and higher tongue-flick rates to internal than surface prey chemicals. Although different methods of stimulus preparation are appropriate for different purposes, we conclude that prey surface chemicals available to foraging lizards are most desirable for studies bearing on location and identification of prey.

Evaluation of Swab and Related Tests as a Bioassay for Assessing Responses by Squamate Reptiles to Chemical Stimuli

The ability of squamates to detect chemical cues from adaptively important sources including prey, predators, and conspecifics has been tested frequently by presenting stimuli on cotton-tipped swabs or ceramic tiles. In many such studies the primary response variable is tongue-flicking, which is widely interpreted to indicate sampling for vomerolfaction. I review the basic experimental method and consider limitations regarding its application and interpretation and ways to overcome them. Effects of experimenter proximity and the assumed invisibility of chemical stimuli are considered, as are use of cologne as a pungency control, senses used in making chemical discriminations, and interpretation of results when there are no significant response differences among stimulus classes. Although the assumption that tongue-flicking reveals vomerolfactory sampling and the necessity of an intact vomeronasal system for normal responses to pheromones have been demonstrated where tested, very few species have been examined. In some squamates for which these assumptions have not been examined experimentally, especially eublepharid geckos, attacks on swabs bearing prey chemicals and performance of antipredatory displays in response to predator chemicals occur with no prior tongue-flicking. Not only are assays based on tongue-flicking useless in such cases, but the discriminations are likely based on olfaction. Issues specific to the study of responses to prey chemicals, predator chemicals, and pheromones are discussed. For many purposes, swab tests provide rapid, conclusive assays of ability to respond differentially to biologically relevant stimuli. However, other methods may be superior for studying some responses, and swab tests are not always applicable.

Prey Chemical Discrimination and Foraging Mode in Gekkonoid Lizards

Relationships among phylogeny, foraging mode, and prey chemical discrimination by tongue-flicking were investigated by experimentally testing for the presence of lingually mediated prey chemical discrimination in representatives of two families of gekkonoid lizards having different foraging modes. In the experiments, the tongue-flicking and biting responses of each lizard were recorded in response to cotton swabs bearing three classes of stimuli: prey surface chemicals, cologne as a pungency control, and deionized water as an odorless control. In a eublepharid species, Eublepharis macularius, the tongue-flick rate, the proportion of individuals attacking the swab, and a composite measure combining effects of tongue-flicking and attack (TFAS(R)) were significantly higher and the latency to attack significantly shorter in the prey stimulus condition than in the other conditions, which did not themselves differ. In contrast, no tongue-flicking or attacks were observed in any of the conditions for two gekkonid species, Thecadactylus rapicauda and Gekko gecko. Because eublepharids are active foragers whereas gekkonids are ambush foragers, prey chemical discrimination was associated with active foraging, as predicted. Prior to this report, all families of ambush-foraging lizards known to lack prey chemical discrimination belonged to a single clade, Iguania. Actively foraging carnivorous lizards identify prey by chemical cues and belong to Scleroglossa, which includes the families studied here. It is argued that adoption of active foraging may have induced selection for gain of prey chemical discrimination involving tongueflicking in eublepharids. Phylogeny and the presence or absence of prey chemical discrimination are closely related in lizard families because foraging mode is conservative in the major clades Iguania and Scleroglossa.

Chemical discrimination of prey by naive neonate Gould's monitorsVaranus gouldii

Previous studies have demonstrated that actively foraging autarchoglossan lizards rely in part on chemoreception to detect and locate prey. In one of two experiments, neonate Gould's monitorsVaranus gouldii were studied to determine whether they were able to discriminate between multiple prey odors and control odors by tongue-flicking. Responses of lizards to deionized water, a pungency control (cologne), mouse, gecko, and cricket odors on cotton-tipped applicators were studied in experiments using repeated-measures designs and using the tongue-flick attack score (TFAS) as the primary measure of response strength. The TFAS was greater in response to cricket odors than to other prey odors or to either of the control stimuli, and there was no statistically significant difference in response between control stimuli. Range of tongue-flicks elicited by cricket odor were greater than those for other prey odors and control stimuli. Only applicators bearing cricket odor were bitten. In the second experiment, lizards were tested to determine whether they respond differently to chemical stimuli taken from the exoskeleton vs. internal fluids of crickets. TFAS were slightly higher for chemical stimuli taken from internal fluids, but not significantly so. Lizards bit applicators in both conditions. Details of responses to experimental trials are discussed in relation to the feeding behavior of this species.

Interspecific odour discrimination by a lizard ( Eumeces laticeps)

When presented with odours on cotton swabs, adult borad-headed skinks ( Eumeces laticeps) of both sexes flicked their tongues at much higher rates to conspecific odour stimuli than to those of their most closely related congeners, E. fasciatus and E. inexpectatus, during 60-s exposures to cloacal odours from lizards of the opposite sex. A successive discrimination design was used in which each lizard responded to five different odour treatments in a random sequence. In addition to the three lizard odours, water was used as a measure of baseline tongue protrusion rates and a cologne was used as a pungency control. There were no significant differences among the four non-conspecific odour treatments in numbers of tongue flicks elicited, but the skinks emitted significantly greater numbers of tongue flicks to conspecific cloacal odours than to any of the other stimuli. It is hypothesized that E. laticeps produces a pheromone which may function for species identification. Although it is tempting to speculate that the pheromone may serve as a pre-mating mechanism for maintaining reproductive isolation from syntopic congeners, insufficient information is avialable to draw firm conclusions regarding such a function.

Interspecific Odour Discriminations Among Syntopic Congeners in Scincid Lizards (Genus Eumeces)

In a successive discrimination experiment several odours were presented to male Eumeces fasciatus on cotton-tipped applicators. The males displayed higher tongue-flick rates during a 60 second interval when responding to cloacal odours of conspecific females than to cloacal odours of females belonging to two very closely related species in the fasciatus group of Eumeces, water, or a pungency control. Similarly, male E. inexpectatus emitted higher tongue-flick rates to cloacal odors of conspecific females than to those of female E. fasciatus. Because male E. laticeps, which can follow female scent trails, also can discriminate conspecific from heterospecific female odors and because all three of these lizards tongue-flick repeatedly at the outsets of potential social encounters, chemical signals appear to be a basis for important social discriminations in the fasciatusgroup.