Environment-dependent trade-offs and phenotypic plasticity in metamorphic timing

Background: Fitness trade-offs of plastic traits between alternative environments are a prerequisite for the evolution of phenotypic plasticity; however, the costs associated with plastic traits have yet to be determined. Most empirical studies have assessed the costs of plastic traits by investigating just two environments (to elicit plasticity), and only one or two environments to evaluate the consequences of plasticity. In contrast, in nature, organisms are constantly subjected to multiple environments, and the expression and magnitude of the costs of plastic traits are occasionally context-dependent. Objective: Analyse the costs of plastic traits across multiple environments. Methods: We determined the benefits and costs of two plastic responses (predator- and preyinduced morphologies) of larvae of the salamander Hynobius retardatus to larval survival, time to metamorphosis, and body size at metamorphosis in three different environments [using tadpoles of an anuran frog as prey, larvae of a predatory dragonfly, or no change agent (conspecific larvae only)]. Results: The benefits of the alternative phenotypes were evident in the two inducing environments, but the costs were greater or more easily detected in crossover environments. The tradeoffs appeared in combinations in the crossover environments, and thus were context-dependent. Conclusions: The cross-environmental costs of plastic traits are necessary for the evolution of phenotypic plasticity. Our findings highlight the importance of measuring the costs and benefits of plastic traits across multiple environments.