The Evolutionary Ecology of Arabidopsis Thaliana: Genotypic Diversity, Herbivory, and Elevated Carbon Dioxide

110 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2004.In this study, I evaluated the impact of elevated CO2 and insect herbivory on the genotypic response of Arabidopsis thaliana . I performed greenhouse and field experiments to examine plant ecological traits related to life history, fitness, and resistance and their variation under different abiotic and biotic conditions. Results from a greenhouse experiment provided evidence that herbivory by the diamondback moth, Plutella xylostella, can modify the fitness response of A. thaliana to enriched CO2 conditions. Even though elevated CO 2 significantly enhanced plant fitness in the absence of herbivores, diamondback moth herbivory either decreased or suppressed the fitness response of A. thaliana to elevated CO2 (fitness decreased by 22--50% across genotypes). I further tested the hypothesis that elevated CO2 and herbivory can disrupt and restructure functional associations among plant fitness-related traits. This investigation demonstrated that elevated CO2 alone, and CO2 combined with herbivory modified levels and patterns of trait associations in A. thaliana and that this response was genotype-specific. In addition, I also assessed how enriched CO2 environments affected chemical and structural defense responses of A. thaliana genotypes (i.e., glucosinolate contents and trichomes) to diamondback moth herbivory. Herbivory induced a significant 28% to 62% increase in glucosinolate concentrations, although only under elevated CO2. These inducible chemical responses were both genotype-specific and dependent on the individual glucosinolate considered. Finally, I demonstrated that differences in Arabidopsis thaliana life history (i.e., early and late flowering phenology) influenced the fitness response of different genotypes to natural levels of insect herbivory in a field experiment. Early flowering genotypes were more successful in escaping insect herbivory and thus, had greater vegetative biomass and fitness than late flowering ones. These results suggest that insect herbivory is a likely candidate to impose selection for early flowering in those environments where the abundance of insect herbivores peaks later in the reproductive season. Overall, results from my experiments suggest a strong role of genotypic diversity and life history in A. thaliana influencing the response of this plant species, in terms of phenology, growth, resistance and fitness, to the numerous challenges imposed by the physical and biological environment.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD