Food and environmental cues trigger an inducible offence

Polyphenisms, in particular inducible defences, have been the focus of much research on the ecological and evolutionary importance of functional morphologies. Less attention has been paid to inducible offences, traits that enhance competitive ability or feeding ability of consumers, particularly those that are capable of changing during the lifetime of an individual. For most taxa with phenotypically plastic feeding morphologies, changes are usually use-induced, due to direct mechanical feedback to the feeding apparatus created by consumption of a particular food. I tested whether the direct consumption of food or chemical cues associated with feeding habitat were sufficient to trigger a new morphology in two species of snails in the genus Lacuna. I found that although diet had an influence on the shape of teeth induced, environmental cues were also important induction cues. L. variegata produced blunt teeth when fed epiphytes on eelgrass, independent of their feeding environment. They also produced blunt teeth when fed kelp, but were exposed to an eelgrass environment. If, however, they were fed kelp in a kelp bed environment, L. variegata produced pointed teeth. For L. vincta the pattern was not as extreme, but there was a significant effect of both diet and environment type oh the shapes of teeth produced. There was variability among individuals of both species in the propensity to change morphology under different circumstances. This variability could be due to differences in experience, recent feeding or environmental history, or genetic differences among individuals. This inducible offence is not just a simple use-induced morphological change. Induction patterns are similar to those of inducible defences assumed to be adaptive.