MCLISTER, JD; DEARING, MD; University of Utah; University of Utah: Differences in juniper consumption among woodrat species is related to different rates of phase I biotransformation

Herbivores may evolve the ability to consume a toxic plant either by developing specialized biotransformation pathways to deal with the secondary compounds specific to that plant (i.e., qualitative) or by increasing their overall ability to biotransform (i.e., quantitative). Woodrat species (Neotoma spp.) differ in how much juniper they include in their diets. To examine the link between differences in juniper consumption and differences in biotransformation physiology among species, we made a comparison between the ability of individuals of different species (N. albigula, N. stephensi, N. lepida) to feed on juniper and their general ability to biotransform compounds. As an in vivo assay of biotransformation ability, individuals were injected with hexobarbitol (dosage = 100 mg/kg). The duration of sleep time induced by hexobarbitol is known to be generally correlated with the overall rate of cytochrome P450 activity, a major component of phase I biotransformation. Juniper tolerance was assayed by offering them a homogenized 25% juniper diet and recording how much they consumed over a 24 hour period. For all individuals from all species, there was a strong correlation between juniper tolerance and hexobarbitol sleep time (r = -0.58; P = 0.007). ANCOVA found that the differences in juniper tolerance among species could be attributed to differences in the rate of phase I biotransformation. Among woodrats, therefore, any adaptive changes in phase I biotransformation to juniper consumption appear to be quantitative rather than qualitative.