| Description |
Herbivorous animals often ingest plants that protect themselves with chemicals, and these toxins typically differ in composition from plant to plant. For instance, juniper (Juniperus osteosperma) is dominated by terpenes, such as α-pinene, whereas creosote bush (Larrea tridentata) contains a cocktail of many compounds including terpenes and phenols. Neotoma lepida (the desert woodrat) is a widely-dispersed herbivorous mammal that is able to survive on either juniper or creosote bush. Although woodrats that live in White Rocks, Utah feed extensively on juniper, which is the ancestral diet of woodrats, those from Lytle Ranch, Utah and the Armargosa Valley of California have evolved to eat substantial quantities of creosote bush. Whether populations of the same species differ in their abilities to consume native toxic diets, i.e., those present in their natural diet, versus novel toxins consumed by conspecifics, is a central question in nutritional ecology. To quantify the maximum tolerance of woodrats to these toxin-rich foods (creosote and juniper) I conducted feeding trials on three populations of N. lepida, two that feed on creosote (Amargosa Valley, CA and Lytle Ranch, UT) and one that feeds on juniper (White Rocks, UT). I expected persistence to be higher on their native diet to due adaptation to the specific toxins in their native diet in comparison to populations that do not have experience with that same diet. I found that maximum tolerance to creosote resin and persistence in creosote resin feeding trials was higher for the native creosote feeders when compared to the novel creosote feeding population consuming creosote resin. However, there was no difference in juniper tolerance for all three populations including the juniper specialist. Populations with creosote experience had higher tolerances to that diet, with Lytle Ranch and Amargosa Valley animals being able to consume more creosote relative to the juniper specialist (White Rocks) that has never encountered creosote. These differences in tolerance between the populations feeding on novel and native toxic diets support the idea that the native creosote feeding populations have retained their ability to feed on juniper. |
