Balancing selection on a floral polymorphism

Abstract.— The common morning glory, Ipomoea purpurea , exhibits a flower color polymorphism at the W locus throughout the southeastern North America. The W locus controls whether flowers will be darkly pigmented ( WW ), lightly pigmented ( Ww ), or white with pigmented rays ( ww ). In this report, we describe results of a perturbation, or convergence, experiment using five plots designed to determine whether balancing selection operates on the W locus. The pattern of gene frequency changes obtained are indicative of balancing selection operating at the W locus, providing direct evidence that both the alleles are actively maintained by selection.