Almost all known organisms, from humans to soybeans, are attacked by parasites that cause disease. Parasites vary in their transmission rate, which influences how quickly they can spread; and in their virulence, a measure of how strongly they worsen the health of their hosts. Recent research now shows that other organisms in the environment can influence the transmission and virulence of parasites. For example, antibiotics in milkweed plants that are eaten by monarch butterflies can protect the butterflies from parasites, and female monarchs that are already infected with parasites show a preference for laying their eggs on plants containing high concentrations of the antibiotics. But what makes one milkweed plant contain more or less antibiotic than another? Fungi in the soil interact with the roots of plants to influence the concentration of antibiotics in plant leaves, and so may be determining rates of parasitism above ground. Using monarchs as a model, this project explores interactions between soil fungi, plants, herbivores, and their parasites. The researchers hypothesize that the abundance and identity of the fungi in the soil help determine the infection rates of the butterflies above ground, and that plants that are colonized by soil fungi become more attractive to egg-laying butterflies that are already infected with parasites.
This work has broad impacts beyond the study of butterflies. The parasites studied in the project are related to those that cause malaria in humans, so the research may help understand the transmission and virulence of human parasites. Many crop pests have parasites that might be made more effective by managing soil fungi. Students trained on this project will come from diverse backgrounds and join established mentoring programs at the University of Michigan and Emory University. Schoolteachers will develop teaching plans in association with the project, and monarch butterflies remain popular for teaching scientific principles to the general public.