Interspecific hybridization and herbivore abundance in Borrichia

Interspecific plant hybridization can have important evolutionary consequences, not only for the plants, but also for the organisms that they interact with. In this dissertation hybridization between Borrichia frutescens and B. arborescens and its influences on Borrichia 's herbivores and their parasitoids were investigated in the Florida Keys. Nuclear and chloroplast genetic loci and log - likelihood assignment tests were used to identify hybrid and parent genotypes, study population genetic patterns, and investigate the utility of leaf and flower morphology for hybrid identification. Hybrid and parent plants were censused for herbivorous insects to determine what patterns of herbivore abundance exist on the hybrids relative to the parental plants. Both reciprocal transplants and a common garden experiment were employed to help determine the influence of environmental variation on the relationship between hybridization and insect abundance. Finally, the effects of plant hybridization on tri-trophic interactions were investigated by determining the levels of parasitism of the herbivores, Asphondylia borrichiae and Pissonotus quadripustulatus on the hybrids and parentals. Possible mechanisms of plant mediated protection from parasitism were also investigated.; Genetic analyses confirmed the identity of the hybrid and parent plants that were used for the morphological and ecological studies. Together, leaf and flower morphology can be used identify hybrid and parental types with moderate accuracy (with 4% error rate). Population genetic analyses suggest that B. frutescens and B. arborescens are exhibiting positive assortative mating in the Florida Keys. Field censuses indicated that herbivore abundances vary on hybrid hosts relative to parent plant species and that different herbivores may exhibit different patterns of abundance on hybrid and parental hosts. Genotype-by-environment interactions were indicated by the results of the reciprocal transplant and common garden experiments and there was some evidence that clonal variation in herbivore resistance within the parent species may influence patterns of hybrid resistance relative to the parent plants. Finally, hybridization between host plants did have effects at higher trophic levels. Parasitism of A. borrichiae and P. quadripustulatus varied between the different host plant species, but the data also suggest that a trade-off may exist between enemy escape and other fitness components of the herbivores.