Meeting Abstract
Herbivores face many dietary challenges including those presented by the toxins that are produced as defense mechanisms by many plants. To understand the evolution of toxin tolerance in herbivores, we are investigating two species of woodrats, Neotoma lepida and Neotoma bryanti, and their hybrids. Both species experienced a shift in their diet about 18,000 years ago, as creosote bush (Larrea tridentata) expanded its geographic range and replaced the ancestral diet of juniper (Juniperus spp.). Creosote bush contains numerous toxic compounds that differ from the compounds found in juniper and require different detoxification mechanisms. We conducted feeding trials with woodrats from 2 species and their hybrids from 13 geographic locations to determine the maximum tolerable dose (MTD) of creosote resin. Some populations are creosote feeders, whereas others feed on the ancestral diet of cactus and juniper. We found that MTDs vary between species, where the MTD of N. lepida is approximately 1.5 times higher than that of N. bryanti. Hybrids showed intermediate tolerances. This pattern was reflected across all the populations, including sites where both species and their hybrids are found. We found that the presence of creosote explains some of the variation in MTD. Furthermore, MTD is negatively correlated with distance from the origin of creosote invasion suggesting that evolutionary history (duration of exposure) with creosote has allowed for greater adaptation to this diet.
