The cost of carryover effects in a changing environment: context-dependent benefits of a behavioural phenotype in a coral reef fish

Abstract

The fear of predation can have marked effects on an individual's phenotype, and the resulting phenotype is selected to increase an individual's chance of survival during a predator encounter. However, for species with inducible defences, such defensive phenotypes must be costly enough to prevent them from becoming constitutive. While morphological and life-history adaptations have been shown to incur costs, much less research has been done on the costs of behavioural adaptations, which are often thought of as plastic, with limited associated costs. In this study, we document the costs of a high-risk behavioural phenotype. Under high-risk conditions, damselfish are known to exhibit a high-risk phenotype, which among other traits, confer a significant survival advantage during encounters with predators. We exposed juvenile damselfish to a high-risk or low-risk environment for 4 days. We then set up competitive encounters between size-matched pairs of high-risk and low-risk conspecifics. To test for context dependency, we also ran trials when the pair was exposed to a novel predator odour during the competitive encounter. Our results indicate that low-risk fish were the superior competitors in a low-risk environment, but not in a high-risk environment. This result may be explained by an increase in motivation by high-risk individuals to seek shelter from a potential predation threat. Our results highlight (1) the existence of significant costs, even for rapidly induced behavioural phenotypes, and (2) the importance of investigating the adaptive value of phenotypes within the context in which they develop.