Turning Over an Old Leaf- do Mammalian Herbivores Retain the Ability to Biotransform Toxic Ancestral Diets?

Herbivores are frequently exposed to potentially toxic doses of plant secondary metabolites (PSMs). Furthermore, the plant species available and their associated PSMs may change over extended time periods. To understand the ability of herbivores to biotransform novel PSMs, we investigated populations of one species of mammalian herbivore that had undergone a radical diet shift, i.e., the desert woodrat's (Neotoma lepida) switch juniper (Juniperus spp) to creosote bush (Larrea tridentata). To determine whether woodrats currently feeding on creosote also retain the ability to consume and biotransform the PSMs in their ancestral diet of juniper, we compared various metrics of hepatic biotransformation in a population that ingests creosote bush (Mojave woodrats) to one that specializes on the ancestral diet of juniper (Great Basin woodrats). We investigated PSM biotransformation capabilities by quantifying the hepatic metabolism of α-pinene, a common terpene in juniper. We also measured total cytochrome P450 content, cytochrome P450 2B (CYP2B) and glutathione S-transferase (GST) concentrations, and the activity of GST in the livers of both populations consuming control (rabbit chow) and juniper diets. There were no differences in hepatic metabolism of α-pinene, total P450 content, or CYP2B concentration between woodrat populations when feeding on juniper. The only difference found was that the Mojave woodrats had higher GST activity compared to the Great Basin woodrats when feeding on juniper. Our results suggest that despite the change to a novel toxic diet, the Mojave woodrats maintain the capacity to metabolize their ancestral diet of juniper.