Prey Preference As A Function Of Feeding Experience And Prey Type In Neonate Gartersnakes (Colubridae: Thamnophis)

Abstract

Several species of potential prey have been introduced into the geographic range of the Two-striped Gartersnake, Thamnophis hammondii. Some of these prey species possess defenses that present novel challenges to the snake predator. Despite novel predator defense mechanisms (including secretions from skin glands), adult T. hammondii ingest several of these prey species without adverse effects. Although ~dult T hammondii are dietary generalists, almost nothing is known about prey preferences in newborn individuals that lack feeding experience. My study determined whether or not T. hammondii innately exhibits a preference among native and introduced prey types. Furthermore, I compared the degree of prey preference expressed by T. hammondii to that seen in another species of Thamnophis.

I presented neonate snakes of both species with chemical cues from three prey types, two of which have been introduced within the range of the snake, and one of which is native. I used distilled water and cologne as visual and olfactory controls, respectively. The total number of tongue-flicks and latency to attack was recorded. Following five daily consecutive presentations, all subjects were fed exclusively White Cloud Minnows (Tanichthys sp.} for two weeks and then presented again with the chemical cues (assessing responses following a feeding bias). Compared to the introduced prey types, both snake species preferred the native Pacific Treefrog in both naive and experienced presentations. Both T. hammondii and T. sirtalis only attacked cotton swabs with Pacific Treefrog odor, and bite frequency was similar for both species; however, females of T. sirtalis attacked more frequently than males. Only T. hammondii neonates showed a preference for cues·from non-native African Clawed Frogs. A strongerresponse to cues from clawed frogs was also elicited by T. hammondii during naive following experienced presentations. My study indicates that T. hammondii is a generalist throughout its life history, and that the species appears to exhibit a preference for toxic prey types not seen in other Thamnophis species. I further discuss the development of an innate predatory response in T. hammondii, and llow this species might be a useful resource in eradication efforts of invasive prey species.

Date of Award	2010
Original language	American English
Awarding Institution	Eastern Illinois University
Supervisor	Stephen Mullin (Supervisor)