Measuring natural selection on phenotypic plasticity

To understand natural selection we need to integrate its measure across env ironments. We present a method for measuring phenotypic selection that comb ines the potential for both environmental variation and phenotypic plastici ty. The method uses path analysis and a measure of selection that is analog ous to selection on breeding values. For individuals growing in alternative environments, paths are created that represent potential changes in the en vironment. The probabilities for these changes are then multiplied by the p ath coefficients to calculate selection coefficients. Selection on plastici ty is measured as the difference in selection within each environment. We i llustrate these methods using data on selection in an experimental populati on of Arabidopsis thaliana. individuals from 36 families were grown in one of four environments, a factorial combination of shaded/open and early/late shading. For final height of the inflorescence, there was positive selecti on in both the open and shaded environments and negative selection on plast icity of height. For bolting time, there was also positive selection in bot h environments, but no selection on plasticity. We show how to use this inf ormation to examine how selection would change with changes in environmenta l frequencies and their transition probabilities. These methods can be expa nded to encompass continuous traits and continuous environments as well as other complexities of natural selection.