Differential detoxification strategies in closely related herbivore species across a sharp ecotone
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Authors
Whitehead, Lilly
Issue Date
2023
Type
Thesis
Language
Keywords
chemical ecology , cytochrome P450 , detoxification , diet adaptations , small mammals , woodrats
Alternative Title
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 ward off 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. Neotoma 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 answer the following questions: 1) How to CYPs detoxify 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 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. We found that N. bryanti and N. lepida do use CYPs for detoxification, on both known and unknown plant secondary metabolites. Additionally, we found that while both woodrat species were able to modify plant toxins in the unfamiliar diet, it was not to the same ability for both species on plant compounds, indicating species and prior diet exposure are both important factors in detoxification chemistry. This lowered detoxification ability for the unfamiliar diets limits their potential to expand their range across this sharp ecotone as well as lowering the likelihood of hybridization with the other Neotoma species nearby, as they would be less likely to spend time on the opposite side of this ecotone, thereby reinforcing the species boundary.