Extending the integrated phenotype: covariance and correlation in plasticity of behavioural traits

In the field of behavioural ecology there has been a longstanding interest in the evolution of phenotypic plasticity, as plasticity in behavioural traits such as foraging, mating, and reproduction governs the capacity of organisms to cope with environmental variability. In this paper we highlight the need for an integrated perspective to phenotypic plasticity of traits, taking into account covariation among plastic responses of traits. We discuss new perspectives on the importance of integrated plasticity of traits for adaptive behavioural strategies. We review empirical evidence for correlated plasticity across behavioural traits in insects, for example, through genetic correlation, a shared pool of resources or dependency on a common developmental path. Taking on an integrated plasticity perspective, we suggest an alternative explanation for the apparent lack of costs of plasticity, and offer a better understanding of the relative benefits of plasticity or canalization of traits.