DISSERTATION RESEARCH: Plant toxicity at the top of a tropical mountain

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The "chemical arms race" between plants and their specialist herbivores is characterized by high diversities of both plant defenses and insect herbivores with adaptations to those defenses, and is considered to be a driving force of biodiversity. The newly discovered plant toxins in the tropical pepper plant, Piper kelleyi, are consumed and metabolized by caterpillars that specialize on this plant. These chemicals are toxic to all other insects, especially in higher light environments. The research will quantitatively measure how the abundance and diversity of plant toxins respond to different light intensities and will document how specialized caterpillars evolve in response to differences in plant chemistry. The research strategy links the most recent advances in genetics and organic chemistry with important ecological questions about plant-insect interactions. The project will enhance graduate education and will promote science education through interactive projects with local K-12 students, teachers, and an international group of collaborators. In addition to providing insight into the origins of biodiversity, documenting the effects of variation in plant chemistry on interacting trophic levels provides data that could be useful for pharmacology and agriculture.The dissertation research will provide a significant contribution to studies of how plant secondary metabolites contribute to the origin and maintenance of biodiversity in the tropics. The work examines specific hypotheses relevant to coevolutionary theory using the recently discovered plant secondary metabolites of the tropical understory shrub, Piper kelleyi (Piperaceae). These compounds, which dimerize and are more toxic at higher light levels, are consumed and metabolized by specialist geometrid caterpillars in the genus Eois but they are very toxic to generalists. The hypotheses tested using this model system include: 1) if distinct phytochemical profiles are found in different host plant populations, these can function as isolating mechanisms for herbivores, and 2) these isolating mechanisms lead to speciation of specialist herbivores. Light intensities will be manipulated to quantify their effects on intraspecific phytochemical variation, and population genomics techniques will provide tests for local adaptation of detoxification of these compounds by specialist caterpillars. The project will also provide opportunities for the graduate student, who will promote science education through interactive projects with local K-12 students, teachers, and an international team of chemists and biologists.