Species specificity of methyl ketone profiles in the skin lipids of female garter snakes, genus Thamnophis

• We compare methyl ketone profiles among garter snake species (genus Thamnophis).
• Methyl ketone profiles in female Thamnophis skin lipids are species specific.
• Sympatric Thamnophis species exhibit greater variation in methyl ketone profiles.
• Methyl ketones may play a role in reproductive isolation for Thamnophis species.

One of the relatively few vertebrate pheromones to be chemically identified, the female sex pheromone of the red-sided garter snake (Thamnophis sirtalis parietalis) is a series of saturated and monounsaturated methyl ketones contained within female skin lipids. During the breeding season, this pheromone is responsible for eliciting male courtship behaviors and males are able to utilize pheromonal variation to discriminate among females. While the pheromone system of the red-sided garter snake has been the subject of many studies, relatively little is known about the pheromone systems of other garter snakes. Through chemical analyses, we demonstrate that female skin lipids of the red-spotted garter snake (Thamnophis sirtalis concinnus), northwestern garter snake (Thamnophis ordinoides), and plains garter snake (Thamnophis radix) contain similar methyl ketones. The methyl ketone profiles of these snakes differ qualitatively from one another and from the methyl ketone profiles of red-sided garter snakes with differences particularly pronounced between sympatric species. Our results provide evidence that the use of methyl ketones in sexual signaling may be ubiquitous for Thamnophis species and suggest that these compounds could play a role in reproductive isolation between species in this genus.