Survival trade-offs associated with inducible defences in snails: the roles of multiple predators and developmental plasticity

P>For decades, organisms with inducible defences have been used extensively as model systems for addressing the ecology and evolution of phenotypic plasticity. However, our current understanding of inducible defences comes largely from studies that have examined the survival benefits of an inducible defence in a predator environment vs. the growth or reproductive costs in a no-predator environment. Moreover, this work has focused on a single point in prey development. Unfortunately, this approach neglects the role that functionally different predator species (with divergent selection pressures) may play in maintaining inducible defences in prey populations and overlooks the dynamic nature of prey responses and prey vulnerability over development. In this study, we used freshwater snails and a subset of their predators to address the survival costs and benefits of predator-induced plasticity in response to functionally different predators at multiple points in development. We found that snails altered unique suites of traits over development in response to three different caged predator environments. Moreover, short-term predation trials demonstrated that the phenotype induced by one predator had higher survival with that predator than any alternative phenotype but lower survival with a different predator species (i.e. survival trade-offs). However, the trade-off was only strongly detected midway in development before a size refuge was attained from predation and after morphological defences had formed in the snails. Our study suggests that functionally different predators favour inducible defences in freshwater snails, and that incorporating development into tests of the adaptive plasticity hypothesis can provide valuable information about the dynamics of trait induction and variation in fitness trade-offs over time.