INTERPOPULATION DIFFERENCES IN TOLERANCE TO CREOSOTE BUSH RESIN IN DESERT WOODRATS (NEOTOMA LEPIDA)

Abstract

Plant secondary metabolites (PSMs) can affect survival, reproduction, and distribution of herbivores. Individuals with a high capacity to tolerate PSMs will experience fewer and smaller adverse effects than less tolerant individuals. Theoretically, the capacity to tolerate PSMs can be acquired during development, modulated during adulthood, or genetically fixed. We studied tolerance to phenolic resin from creosote bush (Larrea tridentata) in two populations of desert woodrats as a first step in understanding phenotypic habituation and genetic adaptation of this species to creosote resin. One population was from Mojave desert habitat where woodrats eat creosote bush, and the other from the Great Basin desert, where creosote bush is not present and woodrats consume mainly juniper (Juniperus osteosperma). For >1 mo in the laboratory, woodrats from both populations were fed rabbit chow with increasing amounts of phenolic resin extracted from creosote bush until they lost body mass or showed any sign of sickness. Woodrats from the Mojave population maintained body mass at higher concentrations of resin and remained in the experiment longer. There were no differences between populations in food intake across all resin levels; however, maximum resin intake was 25% higher for the Mojave population. Food intake decreased with increasing resin intake. Glucuronic acid excretion in urine, one indicator of detoxification capacity, did not differ between populations. Water consumption increased with increased levels of creosote resin in the diet in woodrats from both populations. The results are consistent with the idea of differential tolerance to creosote bush phenolic resin in desert woodrat populations. Woodrats appear to be a promising natural system to study the developmental or genetic factors underlying vertebrate adaptation to plant secondary metabolites.