PS 10-118 - Differential detoxification strategies in closely related herbivore species across a sharp ecotone

Abstract: Herbivores face a continual challenge of balancing their nutritional needs with the toxicity that they encounter in their diets. Plants produce toxic phytochemicals to defend against herbivores, while herbivores have evolved methods of detoxifying these chemicals. One such method is the use of cytochrome P450 enzymes (CYPs), many of which are found in the liver. While there has been much study of CYPs in model systems, there has been little research on CYPs in wild systems. The woodrat species Neotoma lepida and N. bryanti live across a sharp ecotone in which they encounter plants with vastly different chemistry. N. lepida, more of a specialist, prefers the cyanogenic glycoside-containing Prunus fasciculata, while N. bryanti, more of a generalist, has a more varied diet including a large proportion of the anthraquinone-containing Frangula californica. We investigated woodrat CYP activity to ask the following questions: 1) What is the role of CYPs in detoxifying specialized diets in N. lepida and N. bryanti? 2) How does CYP detoxification ability limit diet switching in N. lepida and N. bryanti? To answer these questions, we performed feeding trials and developed an in vitro assay to isolate liver CYPs and test their activity on plant extracts as well as individual compounds, using LCMS-TOF to compare post-assay chemistry. Here we found that N. lepida showed a limited ability to detoxify anthraquinones using CYPs compared to N. bryanti, indicating that CYP detoxification ability limits their ability to eat the anthraquinone-containing F. californica. However, neither woodrat species appears to use CYPs as a major method of detoxification of cyanogenic glycosides, which prompts further investigation into other detoxification pathways. In conclusion, this study suggests that CYP detoxification enzymes play an integral role in maintaining the species boundary between N. lepida and N. bryanti at their hybrid zone by limiting their capacity to switch diets. Additionally, the development of this assay can lead to future studies of CYPs in other wild systems.