HALEY, S.H.; LAMB, J.G.; DEARING, M.D.; University of Utah, Salt Lake City: Detoxification of plant secondary compounds in creosote (Larrea tridentata) by a woodrat herbivore Neotoma lepida

Dietary specialization in mammalian herbivores is extremely rare. Existing mammalian specialists are believed to express a unique pattern of induced detoxification enzymes that permit elimination of the large concentrations of secondary compounds present in a diet of a single species of plant. We tested this hypothesis with two populations of Neotoma lepida that consume different species of plants. Neotoma lepida in the Mojave Desert specializes on creosote (Larrea tridentata) whose leaves and stems are coated with toxic phenolic resin. In contrast, N. lepida from the Great Basin have never been exposed to creosote but rather feeds heavily on juniper (Juniperus osteosperma), which is high in terpenes, but lacks the phenolic resins in creosote. We took a pharmacological approach by assaying for enzyme activity of five major groups of detoxification enzymes (cytochrome P450s, NAD(P)H: quinone oxidoreductase, glutathione conjugation, sulfation and glucuronidation) in both populations fed a diet of 5% creosote resin. The Mojave population of N. lepida had greater induced levels of cytochrome P450s and glutathione conjugation liver enzymes. Furthermore, the Mojave population expressed higher levels of distinct cytochrome P450 isozymes (CYP2B, CYP1A) compared to the Great Basin population. Our results suggest that elevated levels of P450s and glutathione conjugation enzymes may facilitate specialization on creosote in the Mojave population.