Learning, memory and predator avoidance by freshwater snails: effects of experience on predator recognition and defensive strategy

Learning may allow animals to fine-tune predator avoidance responses to specific environments, but the degree to which predator avoidance behaviour depends on experience is not known for most taxa. We assessed whether perception of predation risk and choice of defensive strategies by the snail Physa acuta is influenced by experience by performing three experiments in which we manipulated exposure to predators and then assayed behavioural responses to predator cues. We first assessed the scope for learned avoidance behaviour by comparing the antipredator response of wild snails (exposed to predators) and captive-reared snails (not exposed to predators). Wild-caught snails showed a stronger response than did captive-reared snails to predators feeding on insect prey, predators feeding on snails and crushed-snail cues. A second experiment in which snails were reared with and without exposure to crayfish predators showed that snails from both rearing treatments responded to fish and crayfish, but the choice of defensive strategy depended on experience. Snails reared without exposure to predators responded to fish cues by moving under cover, whereas snails reared with crayfish responded to fish by moving to the water's surface. The final experiment also manipulated exposure to predators and showed that although snails from a fish-free pond responded to both fish and crayfish, their responses did not depend on experience. Overall, the effects of experience were significant but small relative to the overall effects of predator cues on snail habitat use, showing that the antipredator responses of P. acuta are largely innate.