KINGSOLVER, J.G.*; GOMULKIEWICZ, R.; University of North Carolina, Chapel Hill; Washington State University: Environmental variation and selection on performance curves

Many aspects of physiological and organismal performance vary with some continuous environmental variable: e.g. photosynthetic rate as a function of light intensity; growth rate or sprint speed as a function of temperature. For such performance curves, the environment plays two distinct roles: it affects both the levels of performance expressed, and the relationship between performance and fitness. How does environmental variation determine variation in natural selection on performance curves? We describe an approach to this question that has three components: a selection analysis relating phenotypic (or genetic) variation in performance curves to variation in fitness in the field; an analysis quantifying patterns of environmental variation experienced during selection; and a model relating performance to fitness. We illustrate these steps using data on performance curves of short-term growth rate as a function of temperature (thermal performance curves) in Pieris caterpillars. We use this approach to explore two related issues: Can we predict quantitatively how changes in temperature variation affect selection on thermal performance curves for growth rate ? Does selection act primarily on growth rate at specific temperatures, or on more integrated aspects of growth?