Chemical Prey Preference Polymorphism in Newborn Garter Snakes Thamnophis Sir Talis

Abstract

AbstractNewborn, previously unfed garter snakes (Thamnophis sirtalis) respond with prey attack and tongue flicking to water based extracts prepared from the surface substances of normally eaten prey and presented on cotton swabs. The present experiments demonstrate reliable individual differences in preferred stimuli among members of the same litter. (I) Of 12 snakes tested on six different days with redworm extract, minnow extract, and distilled water, six responded reliably more to worm and one reliably more to minnow. Redworm was overall more effective than minnow. Using two ranking procedures, individual responsivity to redworm was not correlated with responsivity to minnow. Although distilled water was relatively ineffective, correlations of individual snake scores to extracts and water were high and often significant, in contrast to the low correlations between extracts. (2) Of an entire litter of 13 snakes tested on seven days with extracts from two species of earthworms and two species of fish, 11 responded significantly more to worm extracts and one significantly more to fish extracts. The two worm extracts gave almost identical overall scores and the same occurred for the two fish extracts, with the worm being more effective. While individual responsivities to the two worm or two fish extracts were highly correlated, responsivities across worms and fish were not. A few snakes discriminated between individual worm or fish extracts. (3) In 15 sibling newborn snakes tested on three concentrations (100%, 10%, 1%) of earthworm and fish extracts, most responded more to worm regardless of concentration, a 1% worm extract being more effective than 100% fish. The method of limits was used in both ascending and descending sequences. (4) In all three litters, the snakes could be divided into a few discrete groups based on the relative preference for fish or worm extracts. However, there was wide individual variation in attack frequency, attack latency, and tongue flicking in absence of prey attack. (5) The results are discussed in terms of a genetically based perceptual polymorphism. The phenomenon's possible role in the natural history and evolution of snakes, especially the interaction with feeding experience, is elaborated.