Balancing selection on a floral polymorphism.

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.