Introduction to the symposium-uniting evolutionary and physiological approaches to understanding phenotypic plasticity.

Diverse subfields of biology have addressed phenotypic plasticity, but have emphasized different aspects of the definition, thereby shaping the questions that are asked and the methodological approaches that are employed. A key difference between studies of plasticity in the fields of evolutionary biology and physiology is the degree of focus upon the contribution of genetic variance to plastic traits. Although evolutionary biology is generally focused on the heritability and adaptive value of plastic traits and therefore the potential for plasticity to impact changes in traits across generations, physiological studies have historically focused on the timing and reversibility of plastic change across seasons or ages and the mechanisms underlying traits' plasticity. In this review and the symposium from which it emerged, we aimed to highlight ways that integrative biologists can better communicate about their research and design better studies to address phenotypic plasticity. Evolutionary theory clarifies the need to assess fitness using reliable measures, such as survival and reproductive success, and to consider the heritability and genetic variance underlying plasticity. Reciprocally, physiological research demonstrates that understanding the mechanisms that permit, or limit, plasticity, whether through pleiotropic effects, developmental, or functional linkages between traits, or epigenetic modifications, will shed light on limitations to phenotypic plasticity. Uniting the fields of evolution and physiology to address all aspects of phenotypic plasticity will be increasingly important as the rate of anthropogenic environmental change increases and biologists must predict the responses of wild populations to novel environments, as well as determine the most effective conservation interventions.