Pheromone trailing, snakes

Ford, N.B. (1981) Seasonality of pheromone trailing behavior in two species of garter snake, Thamnophis (Colubridae). Southwest. Nat. 26, 385-388. 

Gehlback, F.R., Watkins, J.F. and Kroll, J.C. (1971) Pheromone trail-following studies of typhlopid, leptotyphlopid, and colubrid snakes. Behaviour 40, 282-294. 

The blind snake Leptotyphlops dulcis is a specialized burrower that feeds on termites and ant brood. It follows the ant pheromone trails to find its prey (Section 12.1). when attacked by ants, this snake tilts its scales individually so that the skin appears silvery. While it writhes, it covers itself with feces and a clear viscous fluid, discharged from the anus. It may also assume a stationary coiled position. when it resumes searching and feeding, it is no longer attacked by ants. The effect lasts from 3 to 30 minutes (Gehlbach etal., 1968). Here a predatory species protects itself from the defensive actions of its prey. 

Blind snakes find their prey by using the prey s pheromones. The wormlike Texas blind snake, Leptotyphlops dulcis, of the southwestern United States leads a subterranean life and feeds on termites and ant brood. It finds ants by following their pheromone trails (Gehlbach etal, 1968). Other blind snakes such as the American blindsnake, Typhlops pusillus (Gehlbach et al, 1971), and the Australian blindsnake, Ramphotyphlops nigrescens (Webb and Shine, 1992), also follow odor trails of ants, their prey. Texas blind snakes are attracted to the simple alkaloid skatole (methyl indole Fig. 12.4), an amine with an unpleasant odor from the ant Neivamyrmex sp. (Watkins etal, 1969). 

Species specificity of sex pheromone trails of sympatric and allopatric garter snakes Thamnophis). Copeia 1,10-13. 

Greene, M. J., Stark, S. L., and Mason, R. T., 2001, Pheromone trailing behavior of the brown tree snake, Boiga irregularis, J. Chem. Ecol. 27 2193-2201. 

Ford, N. B. 1986. The role of pheromone trails in the sociobiology of snakes. In Chemical Signals in Vertebrates (Ed. by D. Duvall, D. Muller-Schwarze R. M. Silverstein), pp. 261- 278. New York Plenum. 

Ford, N. B., 1978, Evidence for species specificity of pheromone trails in two sympatric garter snakes, Thamnophis, Herpetol. Rev., 9 10. 

I review the role of trailing in these social activities, discuss how snakes orient to pheromone trails and describe some aspects of the evolution of trail pheromones. 

Snakes, as a group, are visually cryptic and auditorially impoverished. Therefore, it is probable that chemical cues are quite important in mate location. The utilization of pheromone trails in the reproductive activity of snakes has been examined to some extent in temperate zone colubrids. In these snakes, sexual behavior occurs primarily in the spring. Males leave the hibernacula first and remain in the vicinity to court the females when they emerge. At this time, female snakes leave trails for the males to follow. The pheromone involved is likely the same lipoprotein (vitellogenin) which the females produce in the liver and secrete through the skin to stimulate male courtship activity (Garstka and Crews, 1981, this volume), although the only evidence for this is that the sexual pheromone trails are also produced by skin secretions and, like a lipoprotein, are non-volatile and persistent (Ford and Low, 1984). 

Male snakes are able to extract several pieces of information from the pheromone trail. There is evidence that they can tell both the species and the sexual receptivity of the female laying the trail. 

Species-specific pheromone trails would be a useful prezygotic reproductive isolating mechanism as they would decrease the chance of hybrid matings. Such specificity would also save the male the energy of trailing a nonreceptive heterospecific female and reduce the male s exposure to predators. It seems likely that all species of snakes using trails in a... 

Aggregations of female snakes that are nearing parturition have been recorded for several species (Duvall et al., 1985 Gregory, 1975 Henderson et al., 1980 Shine, 1979), Females may be aggregating at this time because of a scarcity of suitable refugia or to swamp predators with a mass crop of young. Whether pheromone trails are involved in the formation of these aggregations has not been examined. 

Fig. 6. Hypothesized mechanism for male snakes to determine direction of a female snake. (A) Female laying a trail. Note she pushes against the anterolateral surface of the pegs. (B) Behavior of a male snake when he encounters a female trail. Stippling on the first peg represents the probable deposition of the pheromone there, whereas the dashed lines represent the pheromone trail on the substrate. From Ford and Low (1984).

Table 5. Ability of male plains garter snakes, Thamnophis radix to determine direction of a female pheromone trail under three different physical conditions. For experiments I and II a one-tailed binomial test of the hypothesis that the males would follow the trail in the direction of the female was conducted. For experiment III the hypothesis tested was that the males would go the direction the pegs "indicated . From Ford and Low (1984). 

It appears from these studies that pheromone trail specificity played an early role in the evolution of species reproductive isolation in Thamnophis. Behavioral assays of trail specificity of a variety of snakes would be valuable as they may be important clues to ancestral relationships of snakes and the ecological pressures during their evolution. 

Although the database from experimental studies of pheromone trailing behavior in snakes is small, it is apparent from this review that such work is quite valuable in evaluating the role of olfaction in snake sociobiology. Trailing activity can be used as an easily quantified visual bioassay of chemosensory input relating to the various social responses of snakes. In addition, aspects of this activity may be useful in other disciplines of herpetology (i.e., evolution and taxonomy). 

Ford, N. B., 1979, Aspects of Pheromone Trailing in Garter Snakes (Thamnophis), Ph.D. Dissertation, Miami Univ. Ohio. 

Ford, N. B., and O Bleness, M., in press. Species and sexual specificity of the pheromone trails of the checkered garter snake, Thamnophis marcianus, J. Herp. 

Ford, N. B., and Schofield, C. W., 1984, Species specificity of sex pheromone trails in the plains garter snake, Thamnophis radix, Herpetologica 40 51. 

LeMaster, M.P. and Mason, R.T. (2001) Evidence for a female sex pheromone mediating male trailing behavior in the red-sided garter snake, Thamnophis sirtalis parietalis. Chemoecology 11, 149-152. 

Male garter snakes do not pursue already mated females. These females carry a gelatinous mating plug in their cloaca for about 2 days. Copulatory fluids around her cloaca contain a copulatory pheromone that inhihits males advances. Males detect this copulatory pheromone on a female s trail hy tongue flicking from a distance (O Donnell etat. 2004). 

Red-sided garter snakes from different regions of Manitoba, Canada show signs of isolation by chemical cues. In choice tests, males from a hiber-naculum (overwintering den) in central Manitoba preferred females from their own population to females from western Manitoba. Males from western Manitoba showed no preference. When confronted with experimental trails, males made the same choices. This demonstrated that a chemical factor is involved. Furthermore, the sexual attractiveness pheromone of females, a series of ty-9-cis-unsaturated methyl ketones, varies between the populations. Specifically, the... 

Ford, N. B. and Low, J. R. (1984). Sex pheromone source location by garter snakes a mechanism for detection of direction in nonvolatile trails. Journal of Chemical Ecology 10, 1193-1199. 

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