Response of a Single Trait to Selection

Abstract

Abstract The evolution of the trait mean in response to directional selection is an important ingredient of adaptive radiation and in the improvement of domestic stocks. Selection response is a function of genetic variance and the magnitude of directional selection. Experimenters have imposed deliberate selection for many generations to improve domesticated plants and animals and to gauge response in experimental lines. Steady change in the mean has often been observed for 10−120 generations, although sometimes the response is asymptotic. These observations reinforce the view that abundant genetic variation is usually available for most kinds of traits, even in small natural populations exposed to intense selection. The genetic underpinnings of selection response have been assessed in studies of quantitative trait loci (QTL and GWAS). A common finding is that traits are affected by dozens to hundreds of genes with locations sprinkled about the genome. Studies of geographic variation in quantitative traits suggest the trait mean has tracked spatial variation in the adaptive peak. Analysis of trait divergence on the scale of millions of generations indicates that long-continued directional selection of minute magnitude could account for the observed divergence. These diverse lines of evidence point to selection as the driver of adaptive radiations.