Plant genetics affects arthropod community richness and composition: Evidence from a synthetic eucalypt hybrid population

To examine how genetic variation in a plant population affects arthropod co mmunity richness and composition, we quantified the arthropod communities o n a synthetic population of Eucalyptus amygdalina, E. risdonii, and their F I and advanced-generation hybrids. Five major patterns emerged. First, the pure species and hybrid populations supported significantly different commu nities. Second, species richness was significantly greatest on hybrids (F-1 > F-2 > E. amygdalina > E. risdonii). These results are similar to those f rom a wild population of the same species and represent the first case in w hich both synthetic and wild population studies confirm a genetic component to community structure. Hybrids also acted as centers of biodiversity by a ccumulating both the common and specialist taxa of both parental species (1 00% in the wild and 80% in the synthetic population). Third, species richne ss was significantly greater on F(1)s than the single F-2 family, suggestin g that the increased insect abundance on hybrids may not be caused by the b reakup of coadapted gene complexes. Fourth, specialist arthropod taxa were most likely to show a dominance response to F-1 hybrids, whereas generalist taxa exhibited a susceptible response. Fifth, in an analysis of 31 leaf te rpenoids that are thought to play a role in plant defense, hybrids were gen erally intermediate to the parental chemotypes. Within the single F-2 famil y, we found significant associations between the communities of individual trees and five individual oil components, including oil yield, demonstratin g that there is a genetic effect on plant defensive chemistry that, in turn , may affect community structure. These studies argue that hybridization ha s important community-level consequences and that the genetic variation pre sent in hybrid zones can be used to explore the genetic-based mechanisms th at structure communities.