Snake reproduction reproductive pheromones

The vomeronasal system is necessary in mediating a variety of reproductive behaviors-behaviors which are clearly sexually dimorphic. A male garter snake, for example, requires an intact vomeronasal system to court a female (Kubie et al., 1978). Female mice undergo several effects in response to pheromones of male conspecifics, including induction of estrus, estrus synchrony (in group-housed females), and pregnancy... 

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). 

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... 

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. 

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