Do floral pigmentation genes also influence resistance to enemies? The W locus in Ipomoea purpurea
Biochemical pathways that produce floral pigments often also produce secondary compounds that are believed to protect plants from natural enemies. Mutations that affect floral pigment patterns are thus also expected to influence the production of compounds conferring resistance to natural enemies, suggesting that the evolution of floral pigment patterns may be guided not just by interactions with pollinators, but also by indirect selection exerted by enemies on resistance. In particular, mutations that block production of floral pigments may be expected either to block production of defensive compounds or, alternatively, to lead to increased production of defenses, depending on the position of the blockage in the pathway. This expectation was examined in the morning glory Ipomoea purpurea by assessing whether white-flowered genotypes are more or less susceptible to attack by natural enemies than pigmented genotypes. No such difference in susceptibility was detected, although resistance to capsule-feeding insects exhibited a pigment genotype x background genotype interaction. While this negative result indicates that natural enemies probably do not influence the evolution of floral pigment pattern in I. purpurea, this remains a possibility in other systems.
Fineblum, WL; Rausher, MD
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