Herbivory on Toxic Plants and Gut Microbial Diversity in Tropical Katydids
- Elizabeth Braker, Associate Professor of Biology, Occidental College
- Shana Goffredi , Dr. , Occidental College
Members of the Orthopteran family Tettigoniidae are among the best leaf mimics in the Costa Rican rainforest. While camouflage helps protect against predators, there is still the danger of consuming plants loaded with toxic compounds such as members of the Piperaceae family. I hypothesized that microbes may help herbivores digest toxic plants, and I predicted that the amount of Piper that katydids ate and the level of microbial diversity in the katydid digestive tract would have a negative correlation. To examine herbivory on toxic Piper plants, 36 katydids from 13 morphospecies were subjected to feeding trials with three different choices, P. xanthostachyum, P. cenocladum and P. auritum – each containing high levels of terpenes, Piper amides and polyphenols, respectively. For all katydids that ate, the leaf area eaten was significantly different among Piper species (Kruskal-Wallis analysis of variance, P ≤ 0.007), suggesting that the katydids tested had a preference among toxic plants. I studied two katydid species in more depth because they demonstrated the extremes for amount of herbivory on Piper species. Individuals belonging to morphospecies ‘A’ ate the most Piper, while those from morphospecies ‘I’ ate the least. The individuals from species ‘A’ had a more diverse microbial community in their digestive tracts compared to those from species ‘I’. Because species ‘I’ ate very little and contained a low diversity microbial gut community, going against the prediction, it can be suggested that species ‘I’ may be specialists on a different, currently unknown, genus or family of plant. This study will lead to future research exploring the high herbivory rates of species ‘A’ and low microbial diversity found in the gut of species ‘I’, and suggests that Piper specialists may make use of several different types of gut microfauna that help them digest this family of toxic plants.