Effect of experience with pine (Pituophis melanoleucus) and king (Lampropeltis getulus) snake odors on Y-maze behavior of pine snake hatchlings

The abilities of hatchling pine snakes (Pituophis melanoleucus) and king snakes (Lampropeltis getulus) to discriminate the chemical trails of pine and king snakes was investigated inY-maze experiments. Pine snakes were housed for 17 days either with shavings impregnated with pine snake odor, king snake odor, or no odor to test for the effect of experience on choice. Both pine and king snake hatchlings entered the arm with the pine snake odor and did not enter the arm with the king snake odor. The data support the hypothesis that hatchlings of both species can distinguish conspecific odors from other odors and that our manipulation of previous experience was without effect for pine snake hatchlings.     

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.     

Pheromone Trailing Behavior of the Brown Tree Snake, Boiga irregularis

The ability of snakes to follow pheromone trails has significant consequences for survival and reproduction. Of particular importance is the ability of snakes to locate conspecifics during the breeding season via the detection of pheromone trails. In this study, the ability of male brown tree snakes (Boiga irregularis), a tropical, rear-fanged colubrid, to follow pheromone trails produced by reproductively active conspecifics was tested in the laboratory by using a Y maze. Males displayed a trailing response to both female and male pheromone trails over blank controls. As males of this species display ritualized combat behavior, these responses likely represent both direct and indirect mechanisms, respectively, for the location of potential mates in the wild. Males did not, however, discriminate between male and female trails when given a choice on the Y maze.     

Responses by king snakes (Lampropeltis getulus) to chemicals from colubrid and crotaline snakes

Four litters of king snakes (Lampropeltis getulus), a snake-eating species, were tested for responses to chemicals from colubrid and crotaline snakes. King snakes presented with swabs rubbed against the dorsal skin of living snakes and with swabs treated with methylene chloride extracts of shed snake skins tongue-flicked more to swabs from a northern copperhead (Agkistrodon contortrix), a crotaline, than to swabs from some colubrid snakes or to blank swabs. Six out of 10 king snakes in one litter attacked and attempted to ingest swabs treated with snake skin chemicals, implicating these chemicals as feeding stimuli for these ophiophagous snakes. Ingestively naive king snakes presented with plain air and snake odors in an olfactometer tongue-flicked more to snake odors. This study and others suggest that crotaline and colubrid snakes can be distinguished by chemical cues.     

Chemical cues used by prairie rattlesnakes (Crotalus viridis) to follow trails of rodent prey

Each of 10 prairie rattlesnakes (Crotalus viridis) was exposed to three types of trails after striking rodent prey (Mus musculus). One trail was made with mouse urine, another was made with tap water, and the third consisted of materials from mouse integument. The snakes exhibited trailing behavior only when integumentary trails were available. It was concluded that prairie rattlesnakes do not utilize urinary cues; instead they attend to materials associated with rodent skin and fur.     

Chemical trail marking and following by caterpillars ofMalacosoma neustria

Chemical trail marking and following by gregarious caterpillars,Malacosoma neustria L. (Lepidoptera: Lasiocampidae), was studied in the laboratory. As in other species ofMalacosoma, larvae deposit a trail pheromone from a sternal secretory site when searching the host for food. Larvae in the vanguard of foraging columns establish chemical trails as they explore new territory. Marking behavior diminishes as successive unfed foragers utilize the trail. These exploratory trails are subsequently overmarked by fed larvae returning to the tent. Other foragers follow the trails of fed larvae in preference to trails of unfed larvae. Thus, like the eastern tent caterpillar,M. americanum, successful foragers ofM. neustria recruit colony-mates to feeding sites. The chemical activity of both recruitment and exploratory trails degrades slowly, suggesting that the trail pheromone ofM. neustria is a nonvolatile substance. Caterpillars ofM. neustria readily follow the nonvolatile trail pheromone which has been identified fromM. americanum, 5-cholestane-3,24-dione.     

A chemical trail factor from the silk of the eastern tent caterpillarMalacosoma americanum (Lepidoptera: Lasiocampidae)

The leaf-feeding larvae of the eastern tent caterpillarMalacosoma americanum (Fabricius) follow silk trails laid down on branches leading from their communal tent to distant foraging sites. The response of colonies reared in the laboratory under seminatural conditions to silk trails washed in methylene chloride and to chemical trails prepared from a solvent extract of their tent or trail silk, showed that one or more soluble components of their trail is essential to the elicitation of the following response. The demonstrated ability of the caterpillars to distinguish between old and newly reinforced silk trails most likely occurs in response to a temporal change in the detectable chemical properties of their trail.     

A complex,cross-taxon,chemical releaser of antipredator behavior in amphibians

Prey species show diverse antipredator responses to chemical cues signaling predation threat. Among terrestrial vertebrates, the red-backed salamander, Plethodon cinereus, is an important species in the study of these chemical defenses. During the day and early evening, this species avoids rinses from garter snakes, Thamnophis sirtalis, independent of snake diet, but late at night, avoids only those rinses from garter snakes that have recently eaten P. cinereus. We tested whether the selective, late-night response requires the ingestion or injury of salamanders. In three experiments, we tested P. cinereus for their responses to separate or combined rinses from salamanders (undisturbed, distressed, and injured P. cinereus) and snakes (unfed, earthworm fed, and salamander-fed T. sirtalis). When paired against a water control, only rinses from salamander-fed snakes were avoided. When salamander treatments (undisturbed or distressed) were combined with the snake treatments (unfed or earthworm-fed) and tested against a water control, the combinations elicited avoidance. When selected treatments were paired against the standard rinse from salamander-fed snakes, only the combined rinses from salamanders and snakes nullified the avoidance response to the standard rinse. These data reveal a prey defense mechanism involving chemical elements from both the predator and prey that does not require injury or ingestion of the prey in the formation of the cue.     

Specificity of laboratory trail following by the argentine ant,Iridomyrmex humilis (Mayr), to (Z)-9-hexadecenal,analogs, and gaster extract

In laboratory trail-following bioassays of Argentine ant workers,Iridomyrmex humilis (Mayr), the geometric isomer, (E)-9-hexadecenal, of the trail pheromone component (Z)-9-hexadecenal elicited insignificant trail following as did the potentially more stable formate analogs, (Z)-7-tetradecenyl formate, (E)-7-tetradecenyl formate, and tetradecyl formate. Further, in direct choice tests, workers showed no preference for gaster extract trails (0.002 ant equiv/cm) over trails of (Z)-9-hexadecenal (0.2 ng/cm). Moreover, a 10-fold increase in synthetic trail concentration to 2.0 ng/cm caused (Z)-9-hexadecenal trails to be significantly preferred over gaster extract trails by trail-following ants.     

Hexyl Decanoate, the First Trail Pheromone Compound Identified in a Stingless Bee, Trigona recursa

Foragers of many species of stingless bees guide their nestmates to food sources by means of scent trails deposited on solid substrates between the food and the nest. The corresponding trail pheromones are generally believed to be produced in the mandibular glands, although definitive experimental proof has never been provided. We tested the trail following behavior of recruits of Trigona recursa in field experiments with artificial scent trails branching off from natural scent trails of this stingless bee. First-time recruits (newcomers) did not follow these trails when they were laid with pure solvent or mandibular gland extract. However, they did follow trails made with labial gland extract. Chemical analyses of labial gland secretions revealed that hexyl decanoate was the dominant component (72.4 ± 1.9% of all volatiles). Newcomers were significantly attracted to artificial trails made with synthetic hexyl decanoate, demonstrating its key function in eliciting scent-following behavior. According to our experiments with T. recursa, the trail pheromone is produced in the labial glands and not in the mandibular glands. Hexyl decanoate is the first component of a trail pheromone identified and proved to be behaviorally active in stingless bees.     

Conspecific scent trailing by garter snakes (Thamnophis sirtalis) during autumn Further evidence for use of pheromones in den location

Adult garter snakes (Thamnophis sirtalis), collected in October near a traditional, communal hibernaculum in central Wisconsin, were acclimated to autumnal conditions and subjected to laboratory tests to determine whether they could follow scent trails of a conspecific. Graded responses were obtained, but 75% of the sample showed at least some inclination to follow scent trails. The results suggest that pheromone cues may be used by male and female garter snakes to locate traditional dens during autumnal migrations. Evidence from this and other studies suggests that pheromones are probably used in conjunction with other homing mechanisms and that the role of pheromones in den location may be more important in younger snakes and in populations inhabiting northern latitudes.     

Naive ophiophagus lizards recognize and avoid venomous snakes using chemical cues

Monitor lizards prey on snakes. Conversely, venomous snakes prey on juvenile monitor lizards. Immediately after hatching, monitor lizards are naive to all prey items, thus correct assessment of snake prey is paramount for survival. Experiments were conducted to determine how hatchling monitor lizards (Varanus albigularis) with no previous exposure to snakes reacted to sympatric venomous and nonvenomous snakes. Hatchling lizards attacked harmless snakes, but avoided venomous species. Lizards readily accepted meat from skinned snakes, regardless of species. When invertebrate prey covered with skin segments from venomous snakes were restrained from moving, they were usually investigated by tongue-flicking and rejected. Unrestrained skin-covered prey, however, were generally attacked and eaten without prior evaluation by tongue-flicking. Attack was inhibited in trials in which unrestrained prey were tongue-flicked, suggesting that chemical cues contained in snake skins mediate avoidance of venomous snakes. Selection for the ability to perceive snake integumental chemicals may be especially strong in species that both consume and are consumed by snakes.     

Communal Foraging Behavior and Recruitment Communication in Gloveria sp.

The caterpillars of Gloveria sp. mark trails with a pheromone they deposit by dragging the ventral surface of the tip of the abdomen along branch pathways as they move between their communal nest and distance feeding sites. The threshold sensitivity of the caterpillar for an extract prepared from the secretory site was approximately 0.5 × 10^–3 caterpillar equivalents/cm of trail. Bioassays show that Gloveria follows neither authentic trails of Malacosoma americanum nor artificial trails prepared from 5-cholestane-3-one, a chemical previously reported to elicit trail following from other social caterpillars. Although our observations show that fed caterpillars mark heavily as they return to their nest, we found no evidence that individual caterpillars are able to recruit hungry nestmates to new food finds. In this species, recruitment to food occurs only after many caterpillars have reinforced a trail to a newly discovered food source. In contrast, hungry caterpillars of the confamilial species M. americanum, tested under identical conditions, responded strongly to the postprandial trails of individual caterpillars and rapidly abandoned depleted sites in favor of new food finds. We postulate that the difference in the efficiency with which these two species recruit nestmates to food evolved in response to differences in the spatial distribution of their food supplies.     

Alarm response by a plethodontid salamander (Desmognathus ochrophaeus): Conspecific and heterospecific “Schreckstoff”

The detection of chemical alarm cues plays an important role for predator avoidance in many taxonomic groups, but little is known about the presence of such chemical cues in adult or caudate amphibians. We investigated the response (i.e., aversion or nonaversion) to chemical cues from damaged salamander skin and mealworms (Tenebrio molitor) in the plethodontid salamander,Desmognathus ochrophaeus. Avoidance responses were demonstrated to skin extracts of both conspecific and heterospecific salamanders. However, salamanders (D. ochrophaeus) did not avoid heated conspecific skin, fresh conspecific viscera, fresh mealworm, or freshPlethodon richmondi skin extracts. These results indicate that chemical alarm cues are: (1) present in the skin ofDesmognathus salamanders, (2) not present in mealworm or the viscera ofDesmognathus salamanders, and (3) denatured or deactivated by heating. These results also suggest that an avoidance response to chemical cues from damaged conspecifics has adaptive value in predator avoidance in terrestrial as well as aquatic vertebrates.     

Trail-Following Pheromones in Basal Termites, with Special Reference to Mastotermes darwiniensis

In the framework of an evolutionary study, trail pheromones have been studied in the most basal extant termite, Mastotermes darwiniensis (Mastotermitidae), and two other basal termites, the Termopsidae Porotermes adamsoni (Porotermitinae) and Stolotermes victoriensis (Stolotermitinae). Although workers of M. darwiniensis do not walk in single file while exploring a new environment under experimental conditions and are unable to follow artificial trails in ‘open field’ experiments, they do secrete a trail-following pheromone from their sternal glands. This unique behavior might reflect a primitive function of communication of the sternal gland. The major component of the pheromone appears to be the same in the three basal species: the norsesquiterpene alcohol (E)-2,6,10-trimethyl-5,9-undecadien-1-ol. This represents a new chemical category of trail-following pheromones for termites. The quantity of pheromone was estimated as 20 pg/individual in M. darwiniensis, 700 pg/individual in P. adamsoni, and 4 pg/individual in S. victoriensis. The activity threshold was 1 ng/cm in M. darwiniensis and 10 pg/cm in P. adamsoni. In M. darwiniensis, the trail pheromone was secreted by sternal gland 4 and to a lesser degree by sternal gland 3, sternal gland 5 being almost inactive. This study highlighted phylogenetic relationships between the Mastotermitidae and two subfamilies of the Termopsidae, the Porotermitinae and the Stolotermitinae. Furthermore, it indicated a heterogeneity within the Termopsidae, with Porotermitinae and Stolotermitinae on one hand, and Termopsinae on the other. Finally, Mastotermitidae and Termopsidae, with C14 trail pheromones, are clearly separated from the Kalotermitidae, Rhinotermitidae, and Termitidae that secrete C12 or C20 trail pheromones.     

Responses by corn snakes (Elaphe guttata) to chemicals from heterospecific snakes

Young corn snakes,Elaphe guttata, were tested for responses to chemicals from heterospecific snakes. Corn snakes exhibited more tongue-flicks to swabs freshly rubbed against the skin of an ophiophagous kingsnake,Lampropeltis getulus, than to blank swabs. Responses toL. getulus and a nonophiophagous western plains garter snake,Thamnophis radix haydeni, did not differ significantly. Corn snakes exhibited more tongue-flicks to swabs treated with chloroform extracts of the shed skins ofL. getulus; an ophiophagous eastern coachwhip,Masticophis flagellum; and a nonophiophagous gray ratsnake,Elaphe obsoleta, than to blank swabs, but they did not discriminate between ophiophagous and nonophiophagous species in every case. Corn snakes, when offered shelters containing bedding from the home cages of a nonophiophagous water snake,Nerodia erythrogaster, an occasionally ophiophagous water moccasin,Agkistrodon pisdvorus; orL. getulus and untreated bedding, failed to reside under snake-scented shelters at a rate significantly different from that expected by chance. The responses of corn snakes are compared with those reported for other snakes presented with heterospecific snake chemicals.     

Purification and preliminary characterization of a frog-derived proteinaceous chemoattractant eliciting prey attack by checkered garter snakes (Thamnophis marcianus)

A potent proteinaceous chemoattractant, eliciting prey attack by checkered garter snakes (Thamnophis marcianus) was isolated from aqueous washes of the common frogRana temporaria and purified by preparative continuous-elution electrophoresis. The biological activity of the frog crude extract or of the purified chemoattractive protein, measured by a snake bioassay, was unaffected by freezing, lyophilization, or dialysis but was lost after proteolytic digestion. The purified chemoattractant is glycosylated, has an apparent molecular mass of 24 kDa, estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE), and a pI of 4.8. It gave one spot in two-dimensional electrophoresis. The bioassay showed that this protein is highly attractive to snakes. The lowest concentration yielding positive responses in the snake bioassay was approximately 25 µg/ml. These results suggest that a water-soluble Mr 24 kDa glycoprotein molecule produced by the common frog may be a vomeronasal stimulus used by checkered garter snakes for prey recognition.     

Responses of ecologically dissimilar populations of the water snakeNatrix s. sipedon to chemical cues from prey

Three populations of the water snake,Natrix s. sipedon, were tested for their responses to surface water extracts prepared from various prey species. It was clearly shown that these snakes can distinguish between different prey genera on the basis of chemical cues alone. Adult snakes caught at a fish hatchery where goldfish (Carassius auratus) were abundant responded most to goldfish extract, as did laboratory-born snakes reared on goldfish for one year. However, snakes caught in a relatively undisturbed mountain stream environment and naive young born to a mountain female responded more to the extracts of various sympatric-mountain fish and amphibians. The evidence indicates that newborn snakes have genetic predispositions for sympatric species of the classes of prey normally eaten. These preferences can be enhanced or inhibited during ontogeny.     

Multivariate discrimination of host use by dwarf mistletoeArceuthobium vaginatum subsp.cryptopodum: Inter- and intraspecific comparisons

The parasitic dwarf mistletoeArceuthobium vaginatum attacksPinus ponderosa as its primary host andP. contorta as an occasional host. Within ponderosa pine stands there is also differential parasitism among individual trees. We compared biochemical features of phloem and xylem oleoresin between infected individuals of the two pine species (N=15 for each species) and also between infected (N=30) and nearby uninfected (N=30) ponderosa pine conspecifics. There were significant differences in chemical features, both at the interspecific (P. ponderosa vs.P. contorta) and intraspecific (P. ponderosa) levels. Discriminant function analysis based on chemical features of phloem correctly classified all trees used in the analysis as eitherP. ponderosa orP. contorta, and 95% of all ponderosa pine trees as either parasitized or nonparasitized. Monoterpene composition of oleoresin was distinct between species, and differences between parasitized and nonparasitizedP. ponderosa were also significant. Many of the observed chemical differences are probably constitutive, although levels of nonstructural carbohydrates and -pinene may change in response to dwarf mistletoe infection. Biochemical differences at the intraspecific level were distinct from interspecific differences. Patterns of differential attack can have genetic consequences upon both the parasite and its hosts, and, in the process, may contribute to the evolution of host races of the parasite and to the evolution of host resistance within ponderosa pine.     

Predatory response of brown tree snakes to chemical stimuli from human skin

The brown tree snake (Boiga irregularis) is an exotic pest species on Pacific islands, most notably on Guam where it has caused considerable ecological and economic damage. On Guam, the snake commonly associates with people and can be found near or in human habitations. Bites are common, approximately 1 of 1200 emergency room visits to Guam hospitals were reported to be the result of B. irregularis bites; 80% of these victims were attacked while sleeping. Most of the attacks occurred on fingers and hands and the attacks appeared to be predatory, rather than defensive, in nature. In order to characterize the mechanism releasing this unusual behavior, we measured the predatory response of B. irregularis to chemical stimuli from humans and controls using a lab population that originated from Guam and a wild population from the species' native range in Queensland, Australia. To quantify behavior we measured the proportion of snakes displaying predatory behavior to each of the stimuli, the latency to attack, and the number of tongue-flicks displayed. We quantified predatory behavior using the tongue-flick attack score for repeated measures [TFAS(R)], a common method for quantifying predatory behavior in squamate reptiles. Captive brown tree snakes responded to human skin stimuli with feeding behavior, including predatory attacks, at the same frequency as they did to prey stimuli derived from mice, while never responding to controls with such behavior. Captive snakes also responded to human skin stimuli and prey stimuli with significantly higher TFAS(R) scores than to controls, although there were no differences between the human and mouse stimuli. Wild-caught animals in Australia also responded with predatory attacks to human skin stimuli, while not showing predatory behavior to a blank control and with higher TFAS(R) scores to human skin stimuli than to the control. As B. irregularis is a generalized predator that relies heavily on chemical signals to recognize prey, we hypothesize that the snakes recognize compounds on human skin that may be shared with other prey.