The effects of calcium in mediating the inducible morphological defenses of a freshwater snail,Physa acuta

Predation risk is known to induce numerous, often adaptive, plastic changes in the morphology, life history, and behavior of prey. However, little is known about how abiotic factors such as environmental nutrient availability affect these responses. In this experiment, a freshwater pulmonate snail (Physa acuta) was used to determine how predator-induced shell morphology was affected by the availability of an abiotic nutrient important for shell growth (calcium). Each snail was reared individually in a factorial experiment consisting of two predator treatments (chemical cues from crayfish present or absent) and three calcium concentrations (20, 45, or 70 mg/L). Calcium induced larger, heavier, and thicker shells, while predator cues induced heavier and thicker shells. Importantly, the magnitude of the predator effect on shell thickness (i.e., the inducible defense) increased with additional calcium availability. Our results demonstrate the importance of nutrient availability in mediating and limiting the amount of adaptive predator-induced plasticity.