The multidimensional consequences of the juvenile environment: towards an integrative view of the adult phenotype

Early juvenile environments influence trait expression in complex and often nonintuitive ways. Although the breadth of these effects is well recognized, researchers generally focus on the effect of single ecological triggers (such as resource availability, latitude or predator presence) on traits within a single dimension (e.g. morphological, behavioural or physiological phenotypes). This approach has yielded a wealth of knowledge about environmental conditions that trigger different plastic allocation strategies and reaction norms of a number of traits. However, it tells us little about the way in which early life conditions influence resource allocation, yielding differentially integrated adult phenotypes. Here, I argue that we must begin to understand how complex environments shape the conditional development and expression of suites of traits to produce complex, adaptive phenotypes. I begin by examining the importance of the juvenile environment when attempting to understand phenotypic expression at later life history stages. I describe how different types of plasticity affect relationships between traits, and I provide four case studies that illustrate the influence of plasticity on trait integration, which strongly suggests that evolution of norms of reaction must be considered if we are to understand the evolution of integrated phenotypes. I next highlight the importance of understanding the physiological and genetic underpinnings of this plasticity because such poorly understood aspects of the phenotype regulate developmental pathways that determine phenotypic expression. I conclude with suggestions as to how future research can begin to accommodate multidimensional approaches, and in doing so, further our understanding of an integrated phenotype concept.

► I describe the concept of an integrated phenotype and how this can improve our understanding of phenotypic evolution.
► I discuss the importance of examining traits across all dimensions to understand how they interact to create a phenotype.
► I use case studies to demonstrate how plasticity alters interactions between traits and how we view integrated phenotypes.
► I encourage researchers to examine the physiological and genetic underpinnings of plasticity to better understand trade-offs.
► I explain how an integrated phenotype concept will improve our understanding of trait covariation, fitness and evolution.