Phenotypic Integration and Environmental Change

Abstract

nformation on developmental processes is now being incorporated into theories of the evolution of phenotypic characteristics (Cheverud 1984, Lande 1982). Such theories typically focus on the developmental trajectory expressed in a single environment. But biologists have recently recognized the need to incorporate developmental flexibility in multiple environmental conditions into evolutionary theories (Schlichting 1986, Stearns and Koella 1986, Sultan 1987, Via and Lande 1985). Phenotypic plasticity, the morphological and physiological responses of an organism's phenotype to a change in environmental conditions, represents the interplay between ecological factors and the developmental program of the organism. Some plastic responses are obviously adaptive, but answers to questions concerning the way in which adaptive plasticity and norms of reaction evolve are elusive (Via 1988). What does a plastic response of a trait involve? Some plastic responses may simply be changes in scale, as for example when plants simply grow less when they lack nutrients. But how much growth is stunted under the same conditions can vary among genotypes. Such differences in phenotypic plasticity represent genetic differences in their developmental programs. Other types of plastic response may Heterogeneous environments favor the