Variation in phytochemical composition and diversity between and within plant species is an important dimension of biodiversity and mediates plant-herbivore-parasitoid interactions. Previous work comparing multiple species in the tropical genus Piper, found that phytochemical diversity is a predictor of herbivore diet breadth, diversity and parasitism. To expand on this work, we will address two main questions: 1) How does variation in phytochemical diversity between Piper species affect caterpillar immune response and thus parasitism? 2) How does abiotic factors, such as light, contribute to variation in phytochemical diversity of a single species of Piper and what are the potential implications to herbivores? To address these questions we took a holistic approach to investigate multiple aspects of phytochemical diversity by analyzing methanolic plant extracts using 1H-NMR and LC-MS. We combined immune data with chemical data to address the first question. For the second question we experimentally placed plants in varying light conditions and quantified the variation in phytochemical diversity and herbivory.
Results/Conclusions
How does variation in phytochemical diversity between Piper species affect caterpillar immune response and thus parasitism? We found that the immune function of specialist caterpillars was negatively associated with the phytochemical diversity of the Piper host plants, and rates of parasitism decreased with higher immune function.
How does abiotic factors, such as light, contribute to variation in phytochemical diversity of a single species of Piper and what are the potential implications to herbivores? We found that phytochemical diversity was inversely related to direct light transmittance. In partitioning phytochemical diversity, we found variation in compound composition and structural complexity. These differences in phytochemistry among individual plants caused by light heterogeneity significantly decreased herbivory. Feeding assays demonstrated a negative photoactive effect on generalist, but not specialist caterpillars.
Conclusion
Variation in phytochemical diversity between species and within species can structure plant-herbivore-parasitoid communities across the landscape and contribute to the maintenance of multi-trophic diversity.