DISSERTATION RESEARCH: Consequences of environmentally-mediated resistance and immunity for disease dynamics in a changing world

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

All animals, from butterflies to humans, must defend themselves against diseases. Like us, many animals have immune systems that help them to fight diseases. However, many animals also use medicines. Animals often use plants as sources of medicine and must search their local ?green pharmacy? for the appropriate drugs. These natural medicines are used together with the immune system to help the animal fight infection. But what happens when the quality of plant-based medicines changes because the environment changes? Scientists do not fully understand how our rapidly changing world will affect animal immunity and, through it, disease in natural populations. Monarch butterflies are attacked by a parasite that is related to those that cause malaria and toxoplasmosis in humans. When monarchs get infected with their parasite, they find it difficult to fly and to reproduce. However, monarchs can use natural medicines in milkweed plants in combination with their own immune systems to help combat their parasites. This research will help scientists understand how the medicinal compounds that are available in milkweed change with the environment, and how changes in medicines available to the butterflies affect their ability to use them to fight the parasite. New diseases are emerging at an unprecedented rate and the impacts of environmental change on animal immune function may make this trend worse. Understanding the influence of environmental change on animal immunity will help scientists and managers to predict which animals are most at risk and where, as well as facilitate improved management decisions. This project will address how changing medicinal and nutritional quality affects parasites' ability to harm their hosts. It will do so by exploring the effects of elevated concentrations of atmospheric CO2 on the medicinal (secondary chemistry) and nutritional (carbon, nitrogen, phosphorus) quality of host diet. The researchers will examine how dietary effects on immunity underlie corresponding shifts in a host?s ability to limit parasite infection success, and mitigate the fitness costs of infection at a given pathogen load. This work will be conducted using a system with a high degree of diet dependency: the monarch butterfly, Danaus plexippus, and its protozoan parasite, Ophryocystis elektroscirrha (OE). Secondary and primary metabolites of the milkweed (Asclepias) plants that monarchs consume convey increased performance against OE. Critically, elevated CO2 alters the medicinal and nutritional quality of milkweed foliage. This research will be the first to elucidate the effects of whole plant chemistry on host immunity and performance.