Although it is generally believed that pollinators are the primary selective agents driving flower-color evolution, it has recently been suggested that pleiotropic effects of mutations affecting flower color may serve as important constraints on floral evolution. We examined this hypothesis using white-flowered variants of the common morning glory, Ipomoea purpurea. Previous experiments indicate that the white-flowered a allele has a transmission advantage because of increased selfing and no detectable pollen discounting. We confirm this transmission advantage using a large field experiment in which both selfing rate and outcross success were measured for all three genotypes at the A locus. We also demonstrate that this transmission advantage is opposed by apparent pleiotropic effects in aa individuals manifested as reduced survival from germination to flowering. The magnitude of this effect, in combination with the known magnitude of inbreeding depression, more than compensates for the transmission advantage. Our results thus support the notion that deleterious pleiotropy may influence the evolutionary trajectory of flower-color mutants.
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Vol. 62 • No. 5