Plants display and impressive array of characters thought to defend them against attack by herbivores and pathogens. Many biologists have interpreted the principal function of these plant resistance characters to be the defense of the plant against its natural enemies. However, others have suggested that these resistance characters serve other functions and that the effects of these characters on herbivores are incidental. Despite this ambiguity, the interaction between herbivores and plant resistance characters has played a critical role in the development of theories on the coevolution of plants and herbivores. Two assumptions mark theories on the evolution of plant resistance characters such as secondary chemicals and trichomes (1) resistance has evolved primarily as a defense against natural enemies of plants and (2) resistance is costly in terms of fitness to the plant. Neither of these assumptions has been adequately tested. This research aims to test these assumptions using both laboratory strains and natural populations of the annual plant, Arabidopsis thaliana (Brassicaceae), in both the field and a growth chamber. In particular, this research will use quantitative genetical techniques to determine: (1) whether herbivorous insects and pathogens exert selection on genetic variation for resistance and (2) whether resistance characters are evolutionarily costly. The results of this research will shed light on the mechanisms of the evolution of resistance in plants to herbivores and pathogens.
