Response of Multiple Traits to Selection

Abstract In the short term, the response of multiple traits to directional selection is a function of the G-matrix and the vector of selection gradients, β. Directional selection on a particular trait is expected to change the mean of that trait, but selection may also induce responses in genetically correlated traits. This phenomenon is familiar to plant and animal breeders, who counteract the undesirable correlated responses to selection by selecting on a special linear combination of traits. In the common case in which natural selection alone acts on the multivariate phenotype, the initial response may be biased towards directions with abundant genetic variation. On longer time scales, evolution may be temporarily constrained for certain kinds of traits, especially those that represent trait combinations with low mutation rates and little standing genetic variation. For most traits, however, evolution in the long term is not constrained by genetic variation. Calculations of minimum selective mortality indicate that only a small amount of directional selection each generation is required to account for even appreciable trait change that is observed in the fossil record.