Collaborative Research: Understanding the Evolution of Diet Breadth through Ecoimmunology

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Human commerce and other anthropogenic activities have caused widespread changes in the geographic ranges of species, affecting how species interact within their communities. Since plant-feeding insects represent a large part of Earth's terrestrial biomass, understanding the factors that influence them to change their diets is central to predicting if and how newly organized ecosystems will function. Ecoimmunology is an emerging discipline that highlights the role of the immune system in species interactions and the evolution of life history traits. Although research in plant-insect interactions has long recognized that the range of plant species eaten by insects is shaped not only by characteristics of the plants, but also by enemies such as predators and parasites, the role played by immunological defense in determining dietary breadth is a new area of study. This research explores the hypothesis that resistance to pathogens attained via enhanced immunity can affect the likelihood of incorporating new plant species into insect herbivore diets. To test this hypothesis, researchers will combine approaches from ecoimmunology, chemical ecology and microbiology, using a model system of four butterfly species, all of which have incorporated the introduced plant, Plantago lanceolata (Plantaginaceae), into their diets. Researchers will assess whether the use of the introduced plant is associated with altered disease risk by quantifying parasitism rates and environmental levels of two common pathogens in different populations of each butterfly species that vary in their use of P. lanceolata. In the laboratory, genetic stock from these populations will be used to compare the immunological response to microbial pathogens and simulated parasitism among caterpillars feeding on P. lanceolata and ancestral host plant species. Researchers will experimentally investigate the interplay between diet, the sequestration of plant chemicals, and the bacteria residing in the insect gut by measuring the immune response when these factors have been manipulated. Finally, they will test whether larval infection history affects which plants are chosen by ovipositing females, or whether shifts to P. lanceolata reflect selection on innate host preference.