Evidence that pleiotropic alleles underlie adaptive divergence between natural populations

Abstract

The alleles used for adaptation can pleiotropically affect traits under stabilizing selection, and compensatory alleles can be favoured by selection to counteract such deleterious pleiotropy. Such compensatory alleles can segregate in interpopulation hybrids, causing segregation variance for traits where parents have the same phenotype. If adaptation typically involves pleiotropy and compensation, then the segregation variance for traits under stabilizing selection is expected to increase with the magnitude of adaptive phenotypic divergence between parents. This prediction has not been tested empirically, and I gathered data from experimental hybridization studies to evaluate it. I found that pairs of parents which are more phenotypically divergent beget hybrids with more segregation variance in traits where the parents do not differ. This result suggests that adaptive divergence between pairs of natural populations proceeds via pleiotropy and compensation, and that potentially deleterious transgressive segregation variance accumulates systematically as populations diverge.