The use of chemical cues in predator recognition by western toad tadpoles

Abstract

Western toad, Bufo boreas, tadpoles were collected from a lake in the Cascade Mountains of central Oregon, where they occur in sympatry with backswimmers, Notonectaspp., giant waterbugs, Lethocerus americanus, common garter snakes, Thamnophis sirtalis, roughskin newts, Taricha granulosaand rainbow trout, Oncorhynchus mykiss. Backswimmers, waterbugs and snakes prey on toad tadpoles. Newts and trout are potential tadpole predators, but they find toad tadpoles unpalatable. In laboratory tests, groups of tadpoles responded with anti-predator behaviour when exposed to live backswimmers, waterbugs and snakes, but not when exposed to either newts or trout. In subsequent tests, when only chemical cues from the stimulus animals were presented, the toad tadpoles again responded to backswimmers, waterbugs and snakes, but not to either newts or trout. When tests were conducted using only visual cues, tadpoles did not respond with anti-predator behaviour to any of the heterospecifics with the possible exception of garter snakes. These results show that western toad tadpoles can distinguish between predatory and non-predatory heterospecifics with which they co-occur, and that predator recognition by toad tadpoles is primarily based on chemical cues.