Maternal Effects in Insect Life Histories

Abstract

Natural selection can occur when phenotypic variation in a trait related to fitness is heritable (26, 39). The trait can be simple (e.g. appendage length) or complex (e.g. shape, reaction norms), but as long as individuals vary in their expression, and such variance is genetically based, natural selection can act. If over several generations natural selection is consistent and unconstrained by other factors such as antagonistic pleiotropy (145) or physiological thresholds (170), then a population will evolve. Although selection acts upon phenotypic variation, the resulting changes in genotypic frequencies affect evolution. Thus, the developmental mechanisms linking phenotype to genotype are of fundamental concern to an understand­ ing of evolutionary change. Because development is an elaborative process and adult phenotype is a summation of activities accrued over the life span of the individual, developmental events occurring early in the life cycle can significantly influence the phenotype at later stages. In some cases, such developmental variation will be dampened as a result of homeostatic mech­ anisms [e.g. targeted growth of body size in mice (136), brain size allometry (135), or developmental programming (183)], while in others developmental