Tests of inbreeding effects on host-shift potential in the phytophagous beetle Ophraella communa

Although inbreeding, on average, decreases additive genetic variance, some inbred populations may show an increase in phenotypic variance for some cha racters. In those populations with increased phenotypic variance, character changes by peak shifts may occur because of the effects of the higher vari ance on the adaptive landscape. A population's increased phenotypic varianc e may place it in the domain of attraction of a new adaptive peak or increa se the likelihood of a selection-driven peak shift as the landscape of mean fitness flattens. The focus of this study was to test for increased varian ce, in inbred populations, in a behavioral character involved in adaptive d iversification and probably speciation. We examined the effect of inbreedin g on feeding responses of the leaf beetle Ophraella communa in a series of inbred lineages across a range of levels of inbreeding (f = 0.25, 0.375, 0. 5). We measured the feeding response of inbred lineages of O. communa on it s normal host, Ambrosia artemisiifolia, and on two novel plants, Chrysopsis villosa and Iva frutescens, that are the hosts of other Ophraella species. The results show that feeding responses on the different plants are not co rrelated, indicating that the feeding responses to the different plants are to some degree genetically independent. Despite apparent genetic variation in lineage feeding responses, we could not statistically demonstrate incre ases in phenotypic variance within the lineages. Thus, the experimental res ults do not support the idea that host shifts in this beetle evolved by pea k shifts in bottlenecked populations.