The cost of predator avoidance behaviors in an invasive freshwater snail

Predator avoidance behaviors are assumed to occur at a cost to the potential prey. The invasive New Zealand Mud Snail (Potamopyrgus antipodarum) exhibits several behaviors that appear to reduce the probability of predation when the snail chemically detects potential predators in both its native and invaded range. We conducted 2 experiments to determine if these predator-induced behavioral changes come at a cost of growth to the snail. In the 1st experiment, we exposed juveniles of 4 different populations (3 invasive and 1 New Zealand native) to plain water and to water with odor from a potential fish predator (Blacknose Dace, Rhinichthys atratulus). In the 2nd experiment, we exposed juvenile snails of 1 invasive population to plain water, water with crayfish odor, water with crayfish odor where the crayfish had been fed snails, and crushed snail odor. In both experiments we measured the change in length of the snails after ~7 wk. We found that different populations grew at different rates, and that fish odor resulted in snails growing at a slower rate than snails exposed to plain water. We found weak evidence that snails from different populations were affected differently by fish odor. In the 2nd experiment, we found that only odor from crayfish feeding on snails resulted in a reduced growth rate. These results demonstrate that the behavioral response to a chemical cue produced by a predator in this system comes at the cost of growth, which is likely caused by reduced foraging. The fact that invasive populations retain the ability to detect and behaviorally respond to predators, despite the growth cost, suggests that behavioral flexibility may play a role in the invasion success of this species.