Chemoreceptive responses of two sympatric water snakes to extracts of commonly ingested prey species

Newborn of two locally sympatric species of water snakes,Nerodia fasciata andN. erythrogaster, were exposed to skin extracts of frequently ingested prey. In southern Louisiana, fish account for 78% of the diet of adultNerodia fasciata and about 15% forNerodia erythrogaster. Anurans comprise most of the remainder of the diets of these water snakes. Responses of naive individuals were compared to the chemoreceptive response profiles of groups of snakes reared on limited diets of fish and/or frogs. All snakes were tested seven times over a nine-month period and ontogenetic changes were apparent. NewbornNerodia fasciata have a strong chemoreceptive response for fish extract that remains unchanged by early dietary restrictions for the first six months of life. After that time their responses are more variable and can be altered by recent feeding experience. In southern Louisiana, this species is the least specialized water snake, an observation supported by these laboratory results. While newbornN. erythrogaster did not respond preferentially to any of the prey extracts, a significant response rate for fish extract is established by two months of age that persists for several months regardless of dietary restrictions. A subsequent shift of the response to frog extract at eight months of age regardless of diet may reflect a maturational process. Field studies are in agreement with these results and support the notion of ontogenetic changes related to predator size and age. This is the first demonstration of an ontogenetic change in chemoreceptive response that is not related to dietary experience.     

Orientation of the fiddler crab,Uca cumulanta: responses to chemical and visual cues

Behavioral responses of the fiddler crab Uca cumulanta to flat geometric shapes mimicking natural objects were measured in a circular arena by using zonal recovery as a behavioral measurement. Crabs were tested either in presence or absence of odors from two common predator species, the blue crab Callinectes sapidus, and the pufferfish Sphoeroides testudineus. The study tested the hypothesis that U. cumulanta have different behavioral responses to visual cues in the presence of chemical cues associated with predators. Escape direction tests demonstrated that U. cumulanta is able to show zonal recovery behavior based upon astronomical references. When tested in water lacking predator odor, crabs failed to exhibit a consistent orientation if a single silhouette target was interposed in the landward direction. However, when animals were tested in different predator odor concentrations, an orientation response was obtained at 10 and 20 g/liter/hr blue crab odor and 10 g/liter/hr pufferfish odor, demonstrating U. cumulanta ability to detect the potential presence of its natural predators by this odor. Thus, the hypothesis was supported, and the results suggest that behavioral responses to chemical and visual cues are involved in predator avoidance.     

Responses by amphisbaenianBlanus cinereus to chemicals from prey or potentially harmful ant species

We tested the ability of amphisbaenians (Blanus cinereus) to discriminate between odors of ant species selected as prey (Pheidole pallidula) and odors of potentially harmful ant species (Messor barbarus) that are avoided. Tongue-flick rate to swabs impregnated with ant odors, cologne, or deionized water differed among treatments, showing that amphisbaenians were able to discriminate ant species odors. Amphisbaenians showed an aggressive response and bit applicators bearing the odor of harmful ants, while the odor of prey ants did not elicit bites to swabs. The possible evolutionary advantage of identifying and avoiding harmful ants is discussed in relation to the fossoriality of amphisbaenians.     

Analysis of chemicals from earthworms and fish that elicit prey attack by ingestively naive garter snakes (Thamnophis)

Materials previously shown to elicit increased tongue-flicking and prey attack in garter snakes (Thamnophis sirtalis) were isolated from both earthworms (Lumbricus terrestris) and fish (Pimephales promelas). Both high- and low-molecular-weight components from earthworms and fish stimulated attacks and increased tongue-flicking in previously unfed neonate garter snakes relative to distilled water controls. Earthworm collagen was also effective, but even concentrated fractions were less effective than raw extract. Conflicting reports on the effectiveness of collagen suggest that the salient chemical(s) is a smaller molecule tightly bound to collagen and resisting standard purification methods.     

Effects of predator chemical cues and behavioral biorhythms on foraging activity of terrestrial salamanders

Red-backed salamanders, Plethodon cinereus, show a variety of alarm responses to chemical cues from eastern garter snakes, Thamnophis sirtalis. We measured the foraging activity of red-backed salamanders exposed to water soiled by a garter snake (fed P. cinereus) or to unsoiled water. Salamanders exposed to snake-soiled water showed less foraging activity than salamanders exposed to unsoiled water; therefore, predators could have nonlethal effects on salamander populations. Our results also show additional factors influenced salamander foraging activity. Salamander foraging activity and responsiveness to chemical cues do not appear to have been affected by sex or food deprivation. Salamander foraging activity does appear to have been influenced by activity biorhythms. Foraging activity of animals in both treatments showed a bimodal periodicity that is consistent with natural activity patterns controlled by internal biorhythms. Exposure to snake-soiled water significantly reduced foraging activity during periods of peak foraging activity, but had a subtler effect0 on foraging activity during natural lulls in activity. We suggest that both activity biorhythms and exposure to chemical cues are important factors affecting salamander foraging behavior.     

Response to prey chemical cues by hatchling pine snakes (Pituophis melanoleucus): Effects of incubation temperature and experience

The ability of hatchling pine snakes (Pituophis melanoleucus) to select and follow or avoid chemical odors of prey (mice,Mus musculus) on a shavings and paper substrate was investigated in Y-maze experiments, as a function of incubation temperature and experience. Incubation temperature affected behavior in the maze, and the maze choices of naive snakes, but not of snakes that had already eaten a mouse. The data indicate that snakes that have eaten, preferentially enter the arm bearing chemical stimuli from mice, whereas those that have not eaten show no preference.     

Avoidance response of juvenile Pacific treefrogs to chemical cues of introduced predatory bullfrogs

Bullfrogs (Rana catesbeiana), native to eastern North America, were introduced into Oregon in the 1930's. Bullfrogs are highly efficient predators that are known to eat a variety of prey including other amphibians. In laboratory experiments, we investigated whether juvenile Pacific treefrogs (Hyla regilla) recognize adult bullfrogs as a predatory threat. The ability of prey animals to acquire recognition of an introduced predator has important implications for survival of the prey. We found that treefrogs from a population that co-occurred with bullfrogs showed a strong avoidance of chemical cues of bullfrogs. In contrast, treefrogs from a population that did not co-occur with bullfrogs, did not respond to the bullfrog cues. Additional experiments showed that both populations of treefrogs use chemical cues to mediate predation risk. Treefrogs from both populations avoided chemical alarm cues from injured conspecifics.     

Comparison of earthworm- and fish-derived chemicals eliciting prey attack by garter snakes (Thamnophis)

Materials eliciting increased tongue flicking and prey attack in garter snakes were isolated from both earthworm and fish prey. New extraction methods based on chloroform-methanol mixtures are valuable adjuncts to the more typical aqueous preparations. Both high- and low-molecular weight components from earthworms and fish were active. The similarity between the active chemicals in these two classes of prey was established using several methods of analysis. These included chromatography, carbohydrate and amino acid analyses, and nuclear magnetic resonance.     

The role of chemosensory cues in discrimination of prey odors by the amphisbaenianBlanus cinereus

Responses of amphisbaenians (Blanus cinereus) to deionized water, a control for pungency (cologne), and integumental prey odors (coleopteran larvae and adult ants) on cotton swabs were studied in experiments with a randomized blocks design to discover whether amphisbaenians use chemical cues to detect and identify prey. No individual bit the applicators. Amphisbaenians tongue-flicked at lower rates than epigean saurians, which are active foragers. Tongue-flick rate differed among treatments, but responses to prey odors were not significantly different from those to cologne. The number of directed tongue-flicks emitted during the 60-sec trials was, however, lower in response to deionized water than in response to cologne or prey odors. Response details, the low rate of tongue-flick, and absence of biting are discussed in relation to the foraging behavior and fossoriality of amphisbaenians. Evidence from this study indicates that the vomeronasal sense is used by amphisbaenians to identify odors, but our experiments failed to demonstrate that amphisbaenians discriminate between prey and nonprey odors.     

Attraction of predatorily naive postlarval lobsters to extracts of metabolites of common prey:Mytilus edulis,Mya arenaria,Cancer irroratus,andAsterias vulgaris

Postlarval lobsters (4th–7th stage) exclusively fed frozen brine shrimp (Artemia saline) were assayed for food-search response to extracts and metabolites from four common prey: soft clams (Mya arenaria), blue mussels (Mytilus edulis), rock crabs (Cancer irroratus), and sea stars (Asterias vulgaris). Concentrations of soluble primary amines, protein, and ammonia in prey tissues and metabolites were determined. No significant responses were observed for any prey metabolites diluted to 1 and 10%, while onlyA. vulgaris evoked a significant response at full strength, suggesting that predatorily naive lobsters have yet to develop more pronounced chemosensory responses shown by field-collected lobsters. Removal of protein with retention of small-molecular-weight polar molecules did not appear to affect response to prey extracts. EC₅₀s, as micromoles per liter amines, computed from prey extract dose-response curves indicate differences per unit amine between prey extracts, withA. vulgaris extract more potent as an attractant than either bivalve extract.C. irroratus extract was equally attractive as the other three extracts. Ammonia levels excreted into seawater over 3 hr were similar for all prey species, while soluble primary amines and proteins were undetectable. Ammonia and protein per gram whole prey varied significantly between extracts of prey species, while primary amines were similar. Lobsters may be attracted preferentially to carrion species with higher concentrations of amines and/or higher potency of attractants per unit amine.     

Responses of Cambarid Crayfish to Predator Odor

The responses of individuals of four sympatric species of cambarid crayfish to the introduction of the odor of a common predator, the snapping turtle Chelydra serpentina, were recorded in the laboratory. Adult Orconectes virilis spent significantly more time in a lowered posture and reduced the frequency of nonlocomotory movements following introduction of snapping turtle odor but showed no change in behavior upon introduction of the odor of painted turtle (Chrysemys picta). Recently released young O. virilis did not respond to snapping turtle odor initially but did so after turtle odor and conspecific alarm odor had been paired. Individuals of O. propinquus did not respond to snapping turtle odor. Initial tests with O. rusticus did not yield any response to snapping turtle odor but after experience with paired turtle and alarm odor, individuals showed a decrease in nonlocomotory movements when just snapping turtle odor was introduced. Individuals of Cambarus robustus spent less time in the lowered posture, less time in their burrow, and more frequently executed nonlocomotory movements, in response to snapping turtle odor. The differences in responses to the odor of a common predator are correlated with ecological differences among the crayfish species.     

Responses to major categories of food chemicals by the lizard Podarcis lilfordi

Many lizards are capable of identifying food using only chemical cues from food surfaces, but almost nothing is known about the types of compounds that are effective stimuli. We experimentally studied lingual and biting responses by a lacertid lizard, Podarcis lilfordi, to single representatives of three major categories of food chemicals, sucrose as a carbohydrate, pure pork fat as a mixture of lipids, and bovine gamma globulin as a protein. In 60-sec trials in which stimuli were presented on cotton swabs, the lizards detected all three stimuli, exhibiting more tongue-flicks, licks, or bites, or a greater tongue-flick attack score (TFAS; overall measure of response strength to prey stimuli) than to deionized water. The initial response to all stimuli was tongue-flicking, but the lizards discriminated among the types of chemical stimuli. After preliminary tongue-flicks, the lizards responded to sucrose solutions by licking at high rates, to pure pork fat by biting, and to protein by a combination of additional tongue-flicks and biting. Biting is a feeding response to prey or solid plant material. Licking is a feeding response to sugars in nectar or ripe fruit. Its frequency increased with sucrose concentration. Our data suggest that lizards can identify several types of chemicals associated with food and direct feeding attempts to sources of such chemicals in the absence of visual cues.     

Use of odor baits in traps to test reactions to intra- and interspecific chemical cues in house mice living in outdoor enclosures

House mice (Mus musculus) living in outdoor enclosures were tested for urinary chemical cue preferences using odor-baited traps. In the first experiment, with only volatile cues available, odors from conspecific males and females of various age classes and reproductive conditions were tested; no preferences were exhibited. In the second experiment mice had both nonvolatile and volatile cues available from the same sources as in experiment I. All age and sex class and female reproductive condition groups exhibited odor cue preferences except juvenile females. There were no specific odor cue preferences exhibited by any of the responder types with regard to odors from juvenile females. In the third and fifth experiments, mice were presented with nonvolatile plus volatile or only volatile urine odor cues, respectively, from four genera,Mus, Peromyscus, Microtus, andHomo. Mice of all age classes and both sexes preferredMus musculus odor, were neutral towardMicrotus ochrogaster odor, and avoided odors fromPeromyscus leucopus andHomo sapiens; these patterns were the same regardless of whether only volatile or both volatile and nonvolatile cues were presented. The fourth and sixth experiments involved testing volatile cues only and volatile cues plus nonvolatile cues from human sweat or feces from dogs, cats, or shrews. Mice avoided the human sweat and feces from cats and shrews, but were neutral toward the odor of dog feces. There were effects on whether mice were trapped in the interior of the enclosure or on the perimeter for some odors tested in these six experiments. The findings provide insights regarding possible functions of odor cues in the behavioral ecology of house mice. Odor-baiting traps can be an effective tool with respect to testing some, but not all questions pertaining to olfactory cues and house mouse social biology.     

Volatile shell-investigation cues of land hermit crabs: Effect of shell fit,detection of cues from other hermit crab species,and cue isolation

Land hermit crab responses to volatile shell-investigation cues from land hermit crabs and from marine hermit crabs are analogous to the responses of marine hermit crabs to shell-investigation cues from marine crabs and from snails. Land hermit crabs attracted to shell cues are in worse-fitting shells and are more likely to investigate conspecifics' shells than are crabs attracted to feeding cues. Moving land hermit crabs from worse shells to better shells decreases the number of crabs investigating shells, while moving crabs from better shells to worse shells increases the number of crabs investigating shells. Gravid females have better-fitting shells than nongravid females or males. Crabs from two different populations in Panama have different shell fits and show different levels of responses to shell-investigation cues. Land hermit crabs respond to volatile shell-investigation cues from both land and marine hermit crabs, but marine hermit crabs do not respond to cues from land hermit crabs. A cue detection system for volatile cues most likely evolved in land hermit crabs during their transition from a marine to a terrestrial existence. Thus, the cues found in land hermit crabs and marine hermit crabs may be chemically similar. Volatile compounds collected from hermit crabs onto Tenax columns can be eluted with ethanol and act as shell-investigation cues in field assays.     

Predatory behavior inTupinambis teguixin (Sauria: Teiidae). I. Tongue-flicking responses to chemical food stimuli

Black tegu lizards (Tupinambis teguixin) have the ability to detect food odors and discriminate between them and nonfood odors. This was tested by offering chemical stimuli on cotton-tipped applicators to the animals. Stimuli were from two plant and two animal species known to be principal items in these lizards' diets, demineralized water as an odorless control, and eaude-cologne as an odorous control lacking feeding or social importance. Tongueflick attack score, latency to attack, preattack tongue-flicks, and number of attacks were analyzed. The results clearly demonstrated that this species responds to chemical food stimuli, but does not respond to odorless nonfood stimuli. Responses differed among food types. There were no sex differences. These results are in agreement with the prediction that lizards having forked tongues and an active foraging mode rely on chemical cues for feeding.     

Responses of Mud Snails and Periwinkles to Environmental Odors and Disaccharide Mimics of Fish Odor

Estuarine snails, periwinkles (Littoraria irorata), and mud snails (Ilyanassa obsoleta) were tested for behavioral responses to aqueous extracts of tissue macerates, odors of living intact organisms, and to disaccharides derived from heparin. Extracts included salt-marsh cordgrass (Spartina alterniflora), pink shrimp (Penaeus duorarum), crushed periwinkles, and crushed mud snails. Odors included live periwinkles, mud snails, stone crab (Menippe mercenaria), striped hermit crab (Clibanarius vittatus), tulip snail (Fasciolaria hunteria), and mummichog (Fundulus heteroclitus). Responses were determined upon contact by snails of a ring of solution in the bottom of an otherwise dry bowl and by presenting snails in seawater with 25 l of solution on a cotton swab. In each test, the response of 30 individuals was determined. Behaviors were recorded as fed, alarm, and no response. The strongest alarm response (>80% of all snails tested) in both snails was elicited by crushed mud snails. The strongest feeding response was to shrimp and periwinkle extract for mud snails (>70%), and salt-marsh cordgrass extract attracted periwinkles. High percentages of mud snails and periwinkles fled in response to the odors of intact snail predators, stone crabs, tulip snails, and mummichogs. Mud snails and periwinkles did not flee in response to nonpredator odors, including each other's odor, as well as that of hermit crabs, shrimp, and marsh cordgrass. Heparin disaccharides were tested because other studies reported that biological activity of predatory fish odor is due to similar disaccharides originating from fish mucus. Mud snail responses to disaccharides indicate that they respond to the same kinds of molecules as crustacean larvae and that the modified amine on the disaccharide is essential for activity. The Q-tip assay is appropriate for bioassay-directed purification of alarm signals originating in fish body odor.     

Avoidance response of a terrestrial salamander (Ambystoma macrodactylum) to chemical alarm cues

Organisms from a wide variety of taxonomic groups possess chemical alarm cues that are important in mediating predator avoidance. However, little is known about the presence of such alarm cues in most amphibians, and in particular terrestrial salamanders. In this study we tested whether adult long-toed salamanders (Ambystoma macrodactylum) showed an avoidance response to stimuli from injured conspecifics. Avoidance of stimuli from injured conspecifics could represent avoidance of a chemical alarm cue or, alternatively, avoidance of a territorial pheromone or conspecific predator odor. Consequently, we also tested whether salamanders avoided stimuli from noninjured conspecifics. Salamanders avoided stimuli from injured but not from noninjured conspecifics. Therefore, we concluded that the response to injured conspecifics represents avoidance of a chemical alarm cue and not avoidance of a territorial pheromone or predator cue. This is the first clear demonstration of chemical alarm signaling by a terrestrial amphibian and the first report of chemical alarm signaling in an ambystomatid salamander. By avoiding an area containing stimuli from injured conspecifics, long-toed salamanders may lower their risk of predation by avoiding areas where predators are foraging.     

Response to walnut olfactory and visual cues by the parasitic wasp Diachasmimorpha juglandis

Diachasmimorpha juglandis is a specialist parasitoid attacking fly larvae in the genus Rhagoletis that feed exclusively on walnut fruit husks. In a free-foraging assay comparing response to uninfested, infested, and mechanically damaged fruits, we first determined that D. juglandis use host feeding damage on the fruit as a cue for host presence. In another free-foraging assay that used artificial walnut models and wind tunnel experiments, D. juglandis distinguished infested from uninfested fruits by using either olfactory or visual cues separately. However, the response rate of wasps in the wind tunnel was raised considerably when visual cues were also available. We analyzed the volatile compounds emitted by cohorts of uninfested, mechanically damaged, and infested fruits 1, 3, 5, 8, and 10 days after oviposition by flies into the infested fruits. Total volatile emissions did not differ significantly among treatments, but quantitative changes in volatiles distinguished infested fruits from uninfested and damaged fruits. The fact that parasitoids did not distinguish between infested and damaged fruits in assays where damage was visible indicates that they rely on visual cues when those are available.     

Comparative study of hermit crab responses to shell-related chemical cues

The responses of Australian hermit crabs to two types of shell-related odor cues were compared. Introduction of gastropod snail odor elicited an increase in grasping of shells in all four species tested (Clibanarius infraspinatus, C. taeniatus, C. virescens, andDiogenes avarus). However, the magnitude of response in the case ofC. virescens was significantly lower than the responses of individuals of the other species. Individuals ofC. infraspinatus responded to introduction of conspecific hemolymph with an increase in both locomotion and the frequency of grasping of shells.C. infraspinatus also responded to the hemolymph of the other three species, and there were no differences in the magnitude of the responses depending upon the source of the hemolymph. When individuals ofC. infraspinatus were exposed to snail odor and conspecific hemolymph at the same time, the responses were indistinguishable from those shown to hemolymph alone.     

Timber Rattlesnakes (Crotalus horridus) Use Chemical Cues to Select Ambush Sites

Chemicals left by organisms moving through the environment are used by other organisms to mediate interspecific interactions. Most studies of chemical eavesdropping focus on prey responding to chemical cues from predators, despite the fact that chemical cues are frequently used by predators as a source of information about prey. Crotalus horridus uses a foraging strategy that is widespread among sedentary predators: the snake chooses a site where it is likely to encounter prey and remains immobile for many hours. I investigated this ambush hunting behavior in captive-raised timber rattlesnakes and provide evidence that sit-and-wait predators may discriminate among prey chemical cues, even when they have no prior experience with the prey. Snakes explored chemical cues with chemosensory behaviors, and more frequently adopted a stereotyped ambush foraging posture toward chemical cues from prey sympatric with their population of origin than either allopatric prey or sympatric nonprey species that are eaten by other viperids. These results support the notion that intra- and interspecific variation in diet may be mediated proximally by innate recognition of cues from particular prey items. This system also describes a bioassay that may be used in the isolation and identification of prey-derived kairomones. Studies such as this can be used to determine more realistic parameters for models of predator-prey interaction and foraging behavior that involve secretive, less active predators.