Chapter Seven - Community Genetic and Competition Effects in a Model Pea Aphid System

Abstract

Abstract The effect of within-species (intraspecific) genetic variation on associated ecological communities (community genetic effects) has been well documented. However, little is known about the relationship between community genetic effects and other ecological forces. Community genetic effects are likely to be especially important in clonal systems, such as aphids, where individuals experience pressures exerted by both interspecific and intraspecific competitors in the context of variation among host plants. In these systems, the genotypes and genetic variation of both host plants and competitors are likely to be important influences on performance of the other species in the system. Here, we examine the effects of different types of competition and community genetics using a model system of aphids and their faba bean host plants. We observe the effects on a focal aphid experiencing both interspecific and intraspecific competition. We found that among aphids, competition was strongest (i.e. had the greatest negative effect on the fitness of the focal aphid) when competitors were conspecifics and that this relationship persisted in more complex environments. However in all cases, plant genetic environment influenced the outcome of competition, although with seemingly less influence than the aphid competitors themselves. Aphid behaviour (i.e. change in feeding site preference) was strongly influenced by community genetic effects of the host and both interspecific and intraspecific competition, although the patterns of distribution did not seem to follow those of fitness. Our findings highlight the importance of understanding the complex interactions of ecology and evolution in agro-ecosystems.