Periodic Reporting for period 2 - CARDEVOL (Evolutionary consequences of novel plant defences)
Berichtszeitraum: 2022-08-01 bis 2024-01-31
Plants are under constant attack by natural enemies such as pathogens and insect herbivores, many of which cause substantial yield losses in agricultural production. In naturally evolved systems, plants produce a diverse array of defensive traits, including entire arsenals of toxic chemical compounds to fight off these enemies. However, while such defenses are effective weapons when they first evolve, over time herbivores respond by evolving tolerance mechanisms to cope with these plant defenses, similar to how pest insects evolve tolerance to pesticides. The project CARDEVOL uses an unusual plant system to better understand the mechanisms by which novel defenses provide fitness advantages for the plant, and how in turn herbivores evolve tolerance to novel defenses. The wallflowers (genus Erysimum) have recently evolved a novel chemical defense which enabled them to escape most of their herbivores. CARDEVOL aims to understand how this novel defense affects plant survival and fitness under natural conditions, how remaining herbivores cope with the novel defense, and how herbivore tolerance of the novel defense could evolve given sufficient selection pressures. CARDEVOL thereby makes an important contribution to our fundamental understanding of the evolutionary relationship between plants and their co-evolved herbivores. Ultimately this may yield important insights for the agricultural management of pest insects with reduced pesticide input.
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.
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.
CARDEVOL makes use of an unusual plant that is rarely studied but promises to provide unique insights into the role of novel chemical defenses in a system that lacks co-evolved herbivores. In addition, CARDEVOL combines a two-sided approach not commonly employed in comparable studies, allowing for direct integration of plant results into herbivore projects and vice versa. By the end of the project, CARDEVOL is expected to uncover the genetic architecture that controls variation in chemical defense of the wallflowers, and to substantially deepen our understanding of how this variation affects plant fitness under natural conditions. At the same time, CARDEVOL is expected to identify the main genetic and physiological mechanisms by which herbivores can tolerate the novel wallflower defense, and to answer whether these mechanisms can serve as steppingstones for herbivore specialization under the right evolutionary conditions.