Genotype- by- environment interactions and sexual selection in the leaf-footed cactus bugs, Narnia femorata (Hemiptera: Coreidae)

Sexual selection has resulted in the evolution of some of nature’s most stunning traits, including the dances and colors of dragonflies and damselflies, beetle horns, and the bizarre eye-stalks of stalk-eyed flies. Previous studies of mate choice and male-male competition for access to mates often reveal directional selection, yet substantial additive genetic variance often exists for these traits. The puzzle of how genetic variation in sexually selected traits is maintained in the face of strong directional selection is called the lek paradox. One solution to this paradox is that the male genotypes that are most successful at one place and time are not those that are most successful under other environmental conditions, a result of Genotype-by-Environment interactions (GxEs). Only recently have GxEs been investigated with regards to sexually-selected traits, and rarely have studies incorporated realistic environmental differences into experimental designs. We investigated GxEs for male mating success and male-male competitive ability in Narnia femorata, the leaf-footed cactus bug. This species naturally feeds on Opuntia cactus fruit, but at times cactus fruits are not available and it must survive on cactus pads alone. We used a half-sib, split-brood quantitative genetics design where nymphs were reared with or without cactus fruit. Our study examined sexual selection under the naturally-occuring, discrete variation in the environments in which these bugs live. We investigated how, and if, GxEs provide a mechanism to maintain genetic variation in sexually selected traits.