Meeting Abstract
Juniper foliage is a major component in the diet of some woodrats, even though it contains high levels of potentially toxic terpenes. In order to biotransform the terpenes in their diets, juniper specialists must utilize efficient metabolic pathways. Nitrogen is often a limiting factor for herbivores because plants have low levels of nitrogen and because nitrogen is lost in urine and feces. Thus it is important for herbivores to rely on biotransformation mechanisms that spare nitrogen. We analyzed liver samples from multiple populations of woodrats (genus Neotoma) that were either juniper specialists (N. stephensi and N. lepida from the Great Basin Desert) or not (N. albigula, a dietary generalist, and N. lepida from the Mojave Desert, a creosote specialist). This comparison allowed us to determine how strongly juniper specialists rely on the biotransformation enzyme glutathione S-transferase (GST). GST is an expensive phase II biotransformation enzyme because the conjugate contains three amino acids. We used the liver cytosolic fractions to measure variations in GST activity levels through absorption spectroscopy. While on juniper diets, both juniper specialists down-regulated their GST activity, while both non-juniper feeding species up-regulated their GST activity. The down-regulation of GST by juniper specialists likely conserves nitrogen, which is scarce in the juniper foliage. Utilizing nitrogen sparing biotransformation pathways may represent an integral step in woodrats’ adaptation to diets low in nitrogen and high in terpenes.
