Risky Business: Predator Chemical Cues Mediate Morphological Changes in Freshwater Snails.

Many prey organisms respond to the nonconsumptive effects of predators by altering their physiology, morphology, and behavior. These inducible defenses can create refuges for prey by decreasing the likelihood of consumption by predators. Some prey, as in marine mollusks, have been shown to alter their morphology in response to the presence of size-limited predation. To extend this work, we exposed pointed campeloma snails (Campeloma decisum) to chemical cues from a natural predator, the rusty crayfish (Faxonius rusticus), to better understand how snail morphology changes under the threat of predation. The total force needed to crush shells, total shell length, aperture width, and total weight, along with changes to these 3 body measurements, were recorded for each individual and used to quantify morphological changes as a function of risk. Snails exposed to crayfish chemical cues had shells that required significantly more force to crush their shells than controls (P = 0.023). Total shell length was greater in crayfish-exposed snails than in control snails (P = 0.012), and snails in the crayfish treatment also showed significantly more change in shell length than control snails (P = 0.007). Similarly, aperture width was significantly greater in exposed snails (P = 0.011). However, exposed snails exhibited significantly less change in aperture width than controls (P = 0.03). Finally, we found that snails exposed to crayfish weighed significantly more than snails in the control (P = 0.008). Thus, the results of this study show that morphology of gastropods is altered in the presence of predators, and this may be an antipredator tactic directly related to predation risk.