Constraint and developmental dissociation of phenotypic integration in a genetically accommodated trait.

The genetic accommodation of novel adaptive traits may be accompanied by the evolution of correlated traits that constrain adaptive evolution. Very little is known about the removal of maladaptive correlated traits. In the present study, body size was found to have evolved as a correlated trait during the artificial selection for a polyphenism and a monophenism, and the developmental basis underlying this correlated trait was investigated. The body size and coloration were found to be developmentally integrated by titers of the insect developmental hormone, juvenile hormone (JH). Attempts to uncouple the two traits resulted in the evolution of one of the body size determinants-the critical weight-but not the delay period whose evolution is constrained by JH titers. Thus, maladaptive correlated traits can be removed when multiple developmental modules exist, and the evolution of one or more of these modules is not constrained.