If one looks closely, most plants bear some signs of having been chewed, mined, or otherwise eaten by insects. Another form of attacker, fungus and bacteria, is also common, and may be familiar through its effects on vegetables intended for human consumption; these pathogens create black spots, wilted leaves, or other signs of rot. Because each type of attacker is so common in nature, plants have evolved means of preventing or minimizing the damage they inflict. But just as the jack-of-all-trades is master of none, plants have difficulty defending themselves against all types of attacker simultaneously. That is, plants infected with bacteria are often more susceptible to insects, and vice versa. These phenomena are called trade-offs?negative interactions between behaviors or responses that otherwise benefit organisms?and their evolutionary origins and ecological consequences remain unclear. This project explores whether native plants are affected by a trade-off in defense against insects and bacteria, and how the defense status of individual plants affects how entire populations of the same plants respond to being attacked. Prior results show a positive association between bacterial abundance and attack by a leaf-mining fly across a wild population of a native plant, bittercress. This project will link the ecological impact of bacteria on bittercress and its herbivores to changes in plant chemistry and defenses that may underlie the observed effects, as well as genes and gene products in bacteria that may direct particular plant defenses.
Evidence for this defense trade-off has been found for many species of crops and likewise has been observed in laboratory conditions, but examples for native plants and their wild bacterial and insect attackers are missing. By using wild species in natural conditions, this project will provide a test of the hypothesis that leaf-dwelling bacteria act as a ubiquitous but cryptic third player in the relations between insects and plants. Results will help inform management of pests and pathogens in agricultural systems worldwide, with clear relevance to food security. Also, the researchers will mentor undergraduate students in collection and interpretation of data, and will work in public schools to share their results with teachers and high school students.
