Evolutionary Ecology of Arabidopsis thaliana: Interactions with Biotic and Abiotic Environmental Factors

Previous studies have demonstrated that plants may be affected by their interactions with both biotic and abiotic environmental factors. An important biotic factor that usually affects the performance of plants is insect herbivory. In addition, abiotic factors such as light, or more specifically ultraviolet B (UVB) radiation, can also affect growth and physiological processes in plants. Arabidopsis thaliana is an annual herbaceous plant species with documented defense strategies including resistance and tolerance. Studies have also shown that these plant responses to insect herbivory may be modified by other abiotic factors such as UVB radiation. In a series of common garden experiments, the role of insect herbivory per se and in combination with UVB radiation was evaluated. Using a population of recombinant inbred lines of A. thaliana, the first experiment (described in Chapter 1) investigated the role of plant trichomes and size on patterns of plant use by an insect community. In this experiment, it was also evaluated whether insect herbivory imposes selection on trichome production and plant size. In a second experiment (described in Chapters 2 and 3), the effect of UVB radiation on plant resistance and tolerance to insect herbivory as well as on their potential fitness costs was assessed. This experiment also evaluated the role of UVB on patterns of plant utilization by insect herbivores and whether this important abiotic factor may influence plant phenotypic responses. Results from these experiments revealed that plant trichomes influenced levels of herbivore damage and plant size had an effect on colonization of plants by insect herbivores. In addition, results from selection analyses revealed that insect herbivores exerted directional selection on trichome density in A. thaliana. The second study showed that UVB radiation influenced the expression of resistance and tolerance as well as their associated fitness costs. Similarly, patterns of plant utilization by insect herbivores and phenotypic responses of plants to insect herbivory were modified by UVB radiation. Overall, these results highlight the importance of evaluating complex environments, including both abiotic and biotic factors, as it relates to the evolution and maintenance of traits related to plant defense against insect herbivor