Effects of early stress on behavioral syndromes: An integrated adaptive perspective

This paper presents a behavioral ecologist's view on adaptive responses to early stress. I first summarize two approaches to this topic drawn from other papers in this Special Issue: the ‘inoculation model’ and the ‘adaptive calibration model’. I then describe three relevant modeling approaches from behavioral and evolutionary ecology: models of adaptive plasticity, models of adaptive prey behavior under uncertainty about risk, and models of state-dependent adaptive behavioral syndromes. These models generate some novel predictions on factors that explain variation in how organisms might respond adaptively to early stress. In particular, the state-dependent models of adaptive behavioral syndromes emphasize the importance of feedback loops between behavior and state variables in explaining the long-term persistence of effects of early experiences. State variables can include aspects of physiology, morphology or life history, differences among individuals in information state or skill, or even in social state (e.g., social rank). The feedbacks between behavior and individual state suggest a framework for an integrative approach to understanding responses to stress. The behavioral syndrome approach also emphasizes the importance of understanding stress carryovers – e.g., situations where effects of one kind of stressor (e.g., early social stress) carry over to influence other stress responses (e.g., response to danger) later in life. Finally, I discuss how responses to early stress might relate to variation in the ability of animals to cope well with novel conditions associated with human-induced rapid environmental change, a ubiquitous problem that animals face in the modern world.

► I present a behavioral ecologist's view on adaptive responses to early stress.
► I first summarize two existing views based on other papers in this Special Issue.
► I then describe new insights from three adaptive, cost–benefit models.
► Models of adaptive plasticity clarify when early stress should affect later phenotypes.
► Adaptive behavior under uncertainty does not always match earlier predictions.
► Predictions from adaptive state-dependent models with feedbacks were most insightful.
► A behavioral syndrome approach emphasized the importance of stress carryovers.
► Finally, I discussed the importance of responses to novel human-induced stressors.