CARDEVOL consists of two complementary parts, each focusing on one side of the plant-herbivore interaction. On the plant side, we have performed extensive screening of hundreds of individuals of the wormseed wallflower (Erysimum cheiranthoides, a member of the Brassicaceae) to characterize the natural variation in chemical defense of this species. We have identified substantial variation in the types of novel defense compounds produced, much of which we could causally link to a few gene regions that control this variation. The different prevalence of certain defense compounds in different populations strongly suggests that these compounds are involved in the adaptation of plants to the local environment. Next, we placed a set of wallflower plants with distinct defense traits in a field and observed natural herbivory over two years. We found that in an environment dominated by herbivores specialized on Brassicaceae plants, wallflowers were minimally damaged compared to related plants that lack the novel defense. However, among wallflower individuals, variation in the novel chemical defense only partially explained herbivore damage patterns, with other traits related to growth and plant structure being more important.
On the herbivore side, we have studied several herbivore species that remain associated with the wallflowers and have begun to identify what appears to be a multitude of strategies that allow them to at least survive, if not prosper, on these plants even in the absence of specialized tolerance mechanisms. We finally are in the process of evolving populations of the diamondback moth (Plutella xylostella) for increased resistance to cardenolides over multiple generations. This will allow us to test the evolutionary potential for rapid evolutionary change in nature, and to observe in real time how tolerance mechanisms to novel plant defenses may evolve.
