Integrating chemical and long-term ecological data in phytochemical comparisons of the genus Piper

Background/Question/Methods

Plants produce a diverse mixture of defensive natural products. Quantifying these defensive compounds and understanding their role in anti-herbivore defenses has been the focus of numerous chemical ecology studies. The assiduous process of extracting and isolating these compounds for structure determination and ecological studies for a single species is a major undertaking; however, accomplishing this for hundreds of species would take a lifetime.  A main question driving our research is how to compare phytochemical diversity between species without the arduous task mentioned above.  The genus Piper has over 1500 species and produces secondary metabolites from over 20 classes.  Can phytochemical diversity explain Piper species diversity? To begin to answer large ecological questions like this we first need to determine how we measure phytochemical diversity and optimize how we handle the data. To start, we collected, made crude extracts and ran NMR on over 100 species of Piper.  From those, the major components were determined in about 60 samples and the raw NMR data were analyzed  to produce a chemogram. For 24 species we combined NMR data with herbivory and herbivore community data.

Results/Conclusions

In the cluster analysis, species containing some major components, such as prenylated benzoic acids, chalcones and amides, grouped well together.  Interestingly, amides produced through long chain fatty acid biosynthesis fell out separately from those produced through shikimate biosynthesis.   Through structural equation modeling we found a high level of fitness for an a priori model in which herbivore diversity drives chemical diversity and is positively related to herbivory.  In return chemical diversity is had a negative effect on herbivory.  Both of these new approaches to analyzing raw NMR data indicate the potential for answering big questions in ecology and a potential use in predicting patterns of herbivore diversity.