Meeting Abstract
Adaptive phenotypic plasticity can evolve when populations experience variable environments. For organisms that feed on a variety of foods, plasticity in the shape and size of mouthparts may allow greater intake and efficiency in eating. In this study we examined mouthpart plasticity in the leaf-footed cactus bug, Narnia femorata. This insect uses its long mouthparts to reach seeds within the cactus fruit. Some species of cacti have seeds buried deep within large fruits, while other cacti have shallow seeds. We first tested the effect of the insect’s current host plant species versus a novel species with deep seeds on mouthpart length. We found that insects fed the novel cactus species grew longer mouthparts, as predicted. To address possible mechanisms of mouthpart plasticity, we also tested the effect of unripe cactus fruit (without seeds) on mouthpart length. Interestingly, insects that developed on unripe fruit also developed longer mouthparts. This pattern suggests that mouthparts respond to the absence of seeds with an increase in length. We next examined possible consequences of mouthpart plasticity for body size and sexual dimorphism. We found that the insects that grew longer mouthparts and were presumably able to reach seeds in the novel host fruits achieved larger sizes. The result was an increased size disparity between the sexes, as the relatively smaller males with shorter mouthparts were unable to reach the seeds. Additionally, this further reduced male expression of sexually selected traits. When fruit was unripe and seeds were not present, insects with longer mouthparts did not enjoy additional benefits. The evidence suggests that beak length has adaptive plasticity in this species, yet this plasticity has limits and where these limits lie can have consequences for sexual selection.
