Inducible defenses are widespread in nature. These plastic traits can involve behavior, morphology, or life history. Closely related species (and even different individuals of the same species) often express very different defense strategies. It has been proposed that some strategies may be interchangeable, i.e., distinct defense strategies provide equal fitness. In the zooplankton genus Daphnia, for example, it has been observed that individuals will modify either life history or behavior in response to a predator, but rarely both. Additionally, an emerging body of research has shown that there are important costs of phenotypic plasticity, for example, production and maintenance costs. Using physiologically-structured models developed for zooplankton in which behavior and resource allocation are specified as flexible functions, I employed genetic algorithms to identify optimal defense strategies in different stochastic environments. Environments were characterized by resource density and size-specific predation risk. Results/Conclusions
Within this modeling framework, I investigated how different costs of phenotypic plasticity constrain the evolution of inducible defenses in different environments. I also explored the conditions under which multiple optimal strategies exist. Finally, I identified environmental conditions that promote the evolution of phenotypic plasticity in multiple traits.