Balancing selection on a floral polymorphism

The common morning glory, Ipomoea purpurea, exhibits a flower color polymor phism 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 result s of a perturbation, or convergence, experiment using five plots designed t o determine whether balancing selection operates on the W locus. The patter n of gene frequency changes obtained are indicative of balancing selection operating at the W locus, providing direct evidence that both the alleles a re actively maintained by selection.