Prey chemical discrimination in ambush foragers: absence in representatives of two additional iguanian lizard families and probable olfactory mediation in a gekkonine gecko

Summary. Lingually mediated prey chemical discrimination in lizards has evolved in active foragers, been lost in taxa that have reverted to ambush foraging, and has not evolved in taxa that have retained the ancestral ambushing. Previous studies have shown that all families of insectivorous ambushers lack prey chemical discrimination, including most families of iguanian lizards and two gekkonid species. I conducted experimental studies of prey chemical discrimination in representatives of two additional iguanian families and a third gekkonid lizard. An oplurid species, Oplurus cuvieri and a corytophanid, Corytophanes cristatus, did not discriminate among prey chemicals and control substances. Prey chemical discrimination is now known to be absent in insectivorous ambush foragers in all but one of the families in Iguania, one of the two major lizard radiations. Hoplocercidae remains unstudied. Like other ambushing gekkonid lizards, Pachydactylus turneri did not exhibit elevated tongue-flick rates in response to prey chemicals. However, after tongue-flicking or being touched on the labial scales by cotton swabs, these lizards bit swabs bearing prey chemicals more frequently than control stimuli. They also exhibited buccal pulsing more frequently in response to prey chemicals than deionized water, suggesting olfactory sampling. The unusually highly developed olfactory organs of gekkonid lizards and their nocturnal habits suggest that olfaction may be more important to foraging than in other lizards. Further studies are needed to determine relative roles of olfaction and vomerolfaction in selective response to prey chemicals and to ascertain whether and to what extent the tongue may be used to locate and identify prey. Received 30 March 1999; accepted 26 July 1999     

Effects of movement and eating on chemosensory tongue-flicking and on labial-licking in the leopard gecko (Eublepharis macularius)

Summary Two forms of lingual protrusion, tongueflicking and labial-licking, were differentially affected by combinations of movement and eating conditions in a eublepharid gecko (Eublepharis macularius). Tongue-flicking, in which the tongue contacts substrates beyond the lizard's body, occurred at increased rates during locomotion and during locomotion was significantly more frequent after eating than in a baseline condition. Labial-licking, in which a protruded portion of the tongue touches the labial, mental or rostral scales that surround the mouth, increased after eating. Unlike tongue-flick rates, by far the highest labial-lick rates were observed in stationary lizards after eating. The elevated tongue-flicking rates during movement after eating may be a manifestation of a postingestive chemosensory search for prey. In addition to grooming, several possible chemosensory functions of labial-licking are discussed, including gustatory sampling, sampling prey chemicals on the labials for transfer to the vomeronasal system, and redistribution of chemicals on the tongue to enhance transfer. It is suggested that labial-licking might help motionless lizards maintain vigilance for visual prey stimuli associated with the specific chemical prey cues. Another possible explanation for the increased labial-lick rate while motionless after eating is that prey chemicals induce tongue-flicking, but that the distance protruded is lessened and the tongue does not contact environmental substrates. Tongue-flicking while stationary is unlikely to lead to detection of additional prey and might incur detection by the lizard's predators or prey.     

The peculiar case of an insectivorous iguanid lizard that detects chemical cues from prey

Summary. Ecological and phylogenetic factors determine which sensory modalities organisms use in their day-to-day activities. Among lizards, empirical studies indicate a tight association between foraging strategies and the ability to detect chemical cues from prey. Consequently, ambush insectivores do not detect food chemicals and these differences have a phylogenetic basis, as ambush lizards mainly belong to the Iguania clade. These data contrast, however, with the widespread uses of chemoreception in the Iguania genus Liolaemus, which are mostly insectivorous ambush predators. Moreover, observations from different Liolaemus species suggest a capability to find prey through chemoreception. In order to clarify the abilities of Liolaemus to detect chemical cues from prey, the chemoreceptive behavior of the insectivorous ambush predator, L. lemniscatus, was studied. Lizards were given the choice between areas with and without chemical cues from a food item (mealworms). Results show that test animals stayed for longer, moved more, and did more chemical exploration (tongue flicks) in the area where chemical cues from mealworms were present. Furthermore, in this area, more individuals displayed behaviors that suggest maintenance and defense of the prey patch. Thus, L. lemniscatus is the first insectivorous Iguania reported to be able to detect chemical cues from prey. Although I propose a mechanism for acquiring chemical detection of prey cues in Liolaemus, I also remark that it is necessary to reanalyze both the abilities to detect and use chemical foraging cues in Iguania at large, and the methodologies traditionally used to study these issues.     

Chemosensory recognition of the marbled whiptail lizard, Aspidoscelis marmorata (Squamata: Teiidae) to odors of sympatric lizards (Crotophytus collaris, Coleonyx brevis, Eumeces obsoletus and Uta stansburiana) that represent different predation risks

The ability of the whiptail lizard Aspidoscelis marmorata (Teiidae) to detect and discriminate chemical stimuli associated with the integument of a sympatric saurophagous lizard (Crotaphytus collaris) was tested. Females of A. marmorata were presented with cotton swabs containing chemical cues from C. collaris and three species of nonsaurophagous lizards, as well as water and cologne (pungency control), and total number of tongue-flick (TF) recorded. Other responses were assessed including directed TF rate, time from initial presentation of the stimulus to first TF (latency), time spent fleeing from the stimulus, and number of flight bouts. The number of TFs, directed TF rate, and number of attempts at fleeing exhibited by were significantly greater when females were presented with swabs containing cues from C. collaris as compared to nonsaurophagous lizards and both control treatments. A. marmorata required significantly less time to elicit their first TF when presented with cues from C. collaris as compared to all other treatments. Most previous studies have focused on the responses of lizards to cues associated with snake predators. This study provides the first available data on responses of a teiid to cues associated with a saurophagous lizard.     

Role of surface chemical signals in egg cannibalism and intraguild predation in ladybirds (Coleoptera: Coccinellidae)

Summary. The eggs of some ladybirds are known to be toxic to intraguild ladybird predators. However, this defence is of little value if the eggs are killed before their toxicity becomes apparent. The results presented in this paper indicate that chemicals on the surface of the eggs of two species of ladybirds signal the relative risk of cannibalism and intraguild predation. In Adalia bipunctata and Coccinella septempunctata, 87% of the chemicals are alkanes. Each species of ladybird is less reluctant to eat their own eggs than those of the other species. This asymmetry is to be expected because there is a greater risk to ladybirds from intraguild predation than cannibalism. Similar alkanes to those on the surface of the eggs of A. bipunctata are present in tracks left by larvae and on the elytra of the adults of this species. Those in the larval tracks deter females from ovipositing in patches of prey already being attacked by their larvae and those on the elytra are used in mate recognition. That different context dependent messages could be signalled by similar chemicals is an example of semiochemical parsimony. Received 25 February 2000; accepted 22 May 2000     

Prey odor discrimination by ingestively naive coachwhip snakes(Masticophis flagellum)

Summary Ingestively naive hatchling coachwhip snakes(Masticophis flagellum) detected integumentary chemicals from several potential prey species and discriminated them from chemical stimuli from other animals and from distilled water, strongly suggesting a genetic basis for these abilities. The strongest responses were to lizard and snake stimuli, which form a major part of the diet. Variable responses to chemical cues from other taxa are discussed. Responses by coachwhip snakes to prey chemicals appear to be highly specific, as suggested by the stronger reaction to vomodors of sympatric than of allopatric lizard species. The highly developed use of chemical cues by the diurnal, visually oriented coachwhip snake emphasizes the general importance of chemical senses to predation by nonvenomous snakes, regardless of the involvement of vision.     

Artificial neural network modeling of caste odor discrimination based on cuticular hydrocarbons in termites

Summary. Individuals in an insect colony need to identify one another according to caste. Nothing is known about the sensory process allowing nestmates to discriminate minute variations in the cuticular hydrocarbon mixture. The purpose of this study was to attempt to model caste odors discrimination in four species of Reticulitermes termites for the first time by a non-linear mathematical approach using an "artificial neural network" (ANN). Several rounds of testing were carried out using 1 – the whole hydrocarbon mixtures 2 – mixtures containing the hydrocarbons selected by principal component analysis (PCA) as the most implicated in caste discrimination. Discrimination between worker and soldier castes was tested in all four species. For two species we tested discrimination of four castes (workers, soldiers, nymphs, neotenics). To test cuticular pattern similarity in two sibling species (R. santonensis and R. flavipes), we performed two experiments using one species for training and the other for query. Using whole hydrocarbons mixtures, worker/soldier discrimination was always successful in all species. Network performance decreased with the number of hydrocarbons used as inputs. Four-caste discrimination was less successful. In the experiment with the sibling species, the ANN was able to distinguish soldiers but not workers. The results of this study suggest that non-linear mathematical analysis is a good tool for classification of castes based on cuticular hydrocarbon mixture. In addition this study confirms that hydrocarbon mixtures observed are real chemical entities and constitute a true chemical signature or odor. Whole mixtures are not always necessary for discrimination. Received 23 July 1998; accepted 9 October 1998.     

Mechanism of predator–prey detection and behavioral responses in some anuran tadpoles

Predator–prey relationship was studied in three sympatric species of anuran tadpoles. The study design consisted of allowing predaceous Hoplobatrachus tigerinus tadpoles to devour prey tadpoles (Sphaerotheca breviceps and Bufo melanostictus) placed in a plastic tub (five tadpoles of each species, stage ~27) in 30 min. In trials without refugia, more tadpoles of Bufo fell prey compared to Sphaerotheca. In contrast, provision of refugia using hydrilla plant reversed predation risk of the two species. The swimming speed (V _max = 64.55 ± 1.45 cm/s) of Hoplobatrachus tadpoles was much higher compared to the prey species (Bufo: 3.6 ± 0.4 cm/s; Sphaerotheca: 27.6 ± 1.6 cm/s). Poor swimming ability may account for the observed vulnerability of the Bufo tadpoles to predation especially in clear waters; refugia overcame predation to some extent. On the other hand, Sphaerotheca tadpoles that swim faster than the toad tadpoles were less vulnerable in open areas; refugia actually hindered swimming and increased predation. Experiments with association choice tests show that predaceous tadpoles detect prey based on both visual and chemical cues. On the other hand, the prey tadpoles detected predator based exclusively on chemical rather than visual cues. The antipredator defense strategy of the toad tadpoles is manifested in the form of reduced movements, remaining still for longer times and, increased burst speed. The present findings also suggest that in both prey species predator detection has a genetic basis since naive tadpoles with no prior exposure to predators exhibit fright response on first encounter with them.     

Chemical trail communication in the amblyoponine species Mystrium rogeri Forel (Hymenoptera, Formicidae, Ponerinae)

Summary. Workers of the amblyoponine species Mystrium rogeri employ trail communication during recruitment to food sources and new nest sites. The trail pheromone originates from a hitherto unknown sternal gland located in the 7th abdominal sternite. The recruiting ant deposits the gland secretions by a special gaster-dragging behavior. The recruitment behavior can be complemented by a rapid vertical body shaking performed by some recruiting ants inside the nest. M. rogeri workers possess a large pygidial gland, the secretion of which elicits a repellent response in other ant species. Received 25 May 1998; accepted 15 June 1998.     

Prey chemical discrimination and strike-induced chemosensory searching in the lizardLiolaemus zapallarensis

Summary Experimental tests were conducted to determine whether the ambush foraging iguanian lizard,Liolaemus zapallarensis, was capable of discriminating prey chemicals from control substances and whether this lizard exhibits strike-induced chemosensory searching (SICS) or its components after biting prey. The two components of SICS are a poststrike elevation in tongue-flicking rate (PETF) and apparent searching movements for relocation of prey that has been bitten, but released or escaped.Liolaemus zapallarensis failed to discriminate prey chemicals from control substances, but exhibited significant PETF lasting one minute. SICS was absent inL. zapallarensis because no post-strike movements were observed. The absence of both prey chemical discrimination and SICS exhibited byL. zapallarensis is common to all the insectivorous iguanians and ambush foraging lizards studied to date. However,L. zapallarensis is the first insectivorous iguanian species shown to exhibit PETF. The results suggest thatL. zapallarensis does not use the tongue for detection, identification, or relocation of prey while foraging. The possibility does remain thatL. zapallarensis may be capable of chemically identifying prey once the prey stimuli reach the oral cavity.     

Larval chemical defence and evolution of host shifts in Chrysomela leaf beetles

Summary. Larvae of Chrysomela leaf beetles release for defence volatile compounds belonging to various chemical families. This study focuses on the defensive strategy based on the esterification of isobutyric acid and 2-methylbutyric acid with a wide variety of alcohols taken up from the host plant. To date, only two species are known to produce these repellents C. interrupta, which is associated with Betulaceae and C. lapponica which occurs either on Betulaceae or Salicaceae.? In order to know if other species have developed this chemical defence and how the food plant influences the secretion of these toxins, we targeted by mass spectrometry the presence of iso- and 2-methylbutyric acids and esters of them in the defensive secretions of Chrysomela larvae exclusively associated with Betulaceae or Salicaceae. ?Screening analyses reveal that the synthesis of these compounds is a common character restricted to all the members belonging to the C. interrupta group sensu Brown (1956) regardless of the host-plant family. These results suggest that the biochemical mechanism leading to the synthesis of these compounds could be considered as a synapomorphy meaning that the group is probably monophyletic. ?Defensive secretions of the members of the interrupta group are quantitatively assayed for iso- and 2-methylbutyric acids and their (Z)-3-hexenyl esters. Results reveal a chemical plasticity developed by Chrysomela species associated with Salicaceae. The amounts of iso- and 2-methylbutyric acids derivatives and of salicylaldehyde in their larval secretions depend on the food plant and on its content in phenolglucosides. Received 5 October 1998; accepted 25 November 1998.     

Chemically mediated avoidance of a predatory odonate (Anaxjunius) by American toad (Bufoamericanus) and wood frog (Ranasylvatica) tadpoles

Predators can have significant nonlethal effects on prey by modifying prey behaviour through chemically mediated interactions. We examined behavioural responses of wood frog (Ranasylvatica) and American toad (Bufoamericanus) tadpoles to both direct and indirect chemical signals associated with a predatory odonate (Anaxjunius). In laboratory trials, tadpoles of both species responded strongly to water conditioned with Anax nymphs by decreasing foraging rates, becoming immobile, and moving away from the stimulus. The responses to water conditioned with starved Anax versus Anax that fed on conspecific tadpoles did not differ significantly; these results suggest that tadpoles rely primarily on direct signals to detect odonates. Rana did not respond to water conditioned with conspecific tissue extracts, while Bufo responded with behaviours that were indistinguishable from those of tadpoles exposed to Anax chemicals. In a field experiment, the responses of R. sylvatica tadpoles to Anax chemicals were similar to those of tadpoles observed in the laboratory. Collectively, our data indicate that tadpoles of both species use chemical cues to assess predation risk from other community members. Tadpoles can selectively distinguish members who pose a threat, and only evacuate food patches or reduce foraging rates when in danger. These behaviours appear to be adaptive and are consistent with the predictions of optimality theory. Received: 1 August 1997 / Accepted after revision: 22 November 1997     

Predatory behavior and chemical communication in two Metapone species (Hymenoptera:Formicidae)

Summary. Colonies of two species of Metapone (M. madagascarica, M. new species.) were collected in Madagascar and established in laboratory nests. It could be demonstrated that both species are specialist predators of termites (Cryptotermes kirbyi). During hunting the ants sting the termites and thereby paralyze and preserve the prey alive. In this way prey can be stored in the ant nest for extended periods. During foraging and colony emigrations the ants lay chemical trails with poison gland secretions. Among the seven compounds identified in the venom only methyl pyrrole-2-carboxylate elicits trail following behavior in both Metapone species. Received 11 February 2002, accepted 23 February 2002.     

Field presentation of male secretions alters social display in Sceloporus virgatus but not S. undulatus lizards

Lizards have communicative displays involving primarily vision and chemicals, and recent work suggests trade-offs between these two modalities. In reptiles, little work assesses effects of conspecific chemicals on subsequent signaling behavior. Here, we studied responses to conspecific secretions in two Sceloporus species differing in visual signaling: male Sceloporus undulatus have blue abdominal patches used in aggressive territorial encounters, while Sceloporus virgatus males have evolutionarily lost the patches and have low rates of aggressive display. We measured behavior of free-ranging males following presentation of swabs with conspecific male chemicals from femoral glands and the cloaca, or of clean swabs. For male S. undulatus (blue), neither likelihoods nor rates of behavioral responses differed between swab treatments. In contrast, male S. virgatus (white) presented with secretions had significantly higher likelihood of performing head bob, push-up, and shudder displays, than males in control swab trials. Rates of behavior also differed for S. virgatus, with higher rates of push-up display and tongue flick in trials with conspecific chemicals, but rates of other displays, number of moves, and mean total distance moved did not differ between treatments. Male S. undulatus moved significantly greater distances than S. virgatus, independent of treatment. In sum, male S. virgatus responded to conspecific male chemicals by increasing their low rates of display behavior, whereas male S. undulatus did not alter their already high rates of display or movement following chemical exposure. Chemical signals may play a different role in social signaling in the species with the loss of the abdominal color signal.     

Seaweed secondary metabolites as antifoulants: effects of Dictyota spp. diterpenes on survivorship, settlement, and development of marine invertebrate larvae

Summary. A recent investigation showed that the brown seaweed Dictyota menstrualis was unfouled relative to co-occurring seaweeds, and that larvae of fouling invertebrates avoided settling on D. menstrualis due to chemicals on its surface. The secondary metabolites dictyol E and pachydictyol A are among the compounds found on this alga's surface. In the present study, we tested the effects of specific diterpenes from Dictyota on the survivorship, growth, and development of invertebrate larvae and developing juveniles that could foul seaweeds. Exposure to dictyol E, dictyol B acetate, pachydictyol A, and dictyodial from Dictyota menstrualis and D. ciliolata caused significant larval mortality, abnormal development, and reduce growth rates for three species of co-occurring invertebrates when their larvae were forced into contact with these metabolites. Larvae were damaged at metabolite concentrations as low as 5% of maximum possible surface concentrations of these compounds for the populations of Dictyota we studied. The negative effects of these secondary metabolites on potential foulers, in conjunction with data demonstrating larval avoidance of dictyol-covered surfaces, suggest that these compounds could function as chemical defenses against fouling, and could select for larvae that avoid hosts producing these metabolites. Received 25 May 1998; accepted 22 June 1998.     

Induction of host specificity in larvae of Manduca sexta: chemical dependence controlling host recognition and developmental rate

Summary. The tobacco hornworm, Manduca sexta L. (Lepidoptera: Sphingidae) is a specialist on Solanaceae. This host specificity is induced as the larva feeds on solanaceous foliage, so that solanaceous-reared larvae will refuse to feed on other plants. Experiments were designed to determine the role of dietary constituents on the induction of host specificity and the effects of these on development of M. sexta. Choice assays using leaf discs of cowpea, Vigna sinensis (Fabaceae), were used to monitor the isolation of relevant chemical cues from foliage of potato. An aqueous extract of potato foliage strongly stimulated feeding. This extract was partitioned with n-butanol under alkaline conditions to obtain a highly active butanol extract. Reversed phase flash chromatography with a water-methanol gradient gave an active fraction that was used as a supplement for wheat germ-based artificial diet. Larvae reared on this s-diet became dependent on potato allelochemicals for initiation and continuation of feeding activity. These larvae also developed faster than larvae reared on the control p-diet, but no effect on adult mass was detected. Further flash chromatography of the active fraction under alkaline conditions provided a highly active sub-fraction, and semi-preparative HPLC using gradients of water and acetonitrile resulted in the isolation of a single compound. Bioassays indicated that this compound alone can account for host recognition by solanaceous-reared larvae. The results suggest that the mechanism of induced host specificity in M. sexta involves development of dependence on this compound. Received 21 December 1999; accepted 14 March 2000     

Predation risk assessment by green frog (<Emphasis Type="Italic">Rana clamitans</Emphasis>) tadpoles through chemical cues produced by multiple prey

Many prey assess predation risk through predator chemical cues. Numerous studies have shown that (1) prey sometimes respond to chemical cues produced by heterospecifics and (2) that many species are capable of associative learning. This study extends this research by focusing on predation risk assessment and antipredator behavior in environments containing chemical cues produced by multiple prey species. The results show that green frog (Rana clamitans) tadpoles (1) assess risk from the chemical cue produced during predation by a heterospecific (gray tree frog, Hyla versicolor, tadpoles) and (2) can exhibit similarly strong behavioral responses to a mix of conspecific and heterospecific cues compared to conspecific cue alone, depending on their conditioning environment. I then discuss how the prey choice of the predators and the relative abundances of the prey species should influence the informational value of heterospecific cues.     

Cercopagis pengoi and Mysis spp. alter their feeding rate and prey selection under predation risk of herring (Clupea harengus membras)

The anti-predator behaviour of Baltic crustacean planktivores was studied in feeding experiments under predation pressure of herring. The experiments were conducted with pelagic mysids: Mysis mixta and Mysis relicta, and with Cercopagis pengoi, a non-indigenous cladoceran, which invaded the Baltic Sea in 1992. Zooplankton was offered as prey. Two kinds of experiments were performed in the absence and presence of chemical predator cues: (1) two-prey experiments with prey, which have poor or good escape responses and all three planktivores and (2) natural prey experiments with mysids in natural zooplankton assemblages. The results showed that all three species reacted to the chemical cue of herring by decreasing their feeding rate and altering prey selection. C. pengoi selected easily captured prey (rotifers) in two-prey experiments under predation risk while selection for any prey was evident in mysids in natural prey experiments only in the absence of predator cues. This indicates that planktivores have different anti-predator strategies, which are modified by their own prey capture abilities. C. pengoi was a very efficient predator on small prey with size-specific prey consumption rate 5 to 18 times the rate of mysids. Results show that the studied planktivores are capable of adjusting their feeding behaviour to decrease their conspicuousness in order to increase survival under predation risk. Further, results support the view that C. pengoi has adapted well to the Baltic ecosystem, sharing food niche with pelagic mysids and most probably having a strong influence on the whole pelagic food web.     

Oviposition stimulant for the zebra swallowtail butterfly, Eurytides marcellus, from the foliage of pawpaw, Asimina triloba

Summary. We have isolated a caffeoylcyclohexane-1-carboxylic acid derivative, 3-caffeoyl-muco-quinic acid (3-CmQA), as a contact oviposition stimulant for the zebra swallowtail butterfly, Eruytides marcellus (Papilionidae), from the foliage of its primary host plant, Asimina triloba (Annonaceae). This compound alone was as active in stimulating oviposition by females as were the parent ethanolic plant extract and the host plant itself. Other tested isomers of 3-CmQA, including 5-caffeoylquinic acid (5-CQA or trans-chlorogenic acid), were inactive. We found, however, that experienced female butterflies responded strongly to host volatiles, which enhanced landing rates and hence oviposition.? This is the first report of an oviposition stimulant for a swallowtail butterfly of the tribe Graphiini. We found 3-CmQA to be the major caffeoylcyclohexane-1-carboxylic acid isomer in plants of the genus Asimina. These plants lack appreciable amounts of 5-CQA, which has been shown previously to be one of the oviposition stimulants for certain Rutaceae- or Apiaceae-feeding swallowtails of the related tribe Papilionini.? Our findings, along with earlier results from the tribes Troidini and Papilionini, suggest that responses by swallowtails to hydroxycinnamic acid derivatives as oviposition cues date back at least to the ancestor of the subfamily Papilioninae. Received 24 March 1998; accepted 27 May 1998.