Detox Genes Helped Pack Rats Adapt Diet

Pack rats living in the U.S.'s Mojave Desert are able to survive during hardscrabble times by adapting to a diet of toxic plants. A research team led by biologist M. Denise Dearing of the University of Utah has pinpointed a set of the rodent's genes that code for the production of liver enzymes that make this diet-switching possible (Mol. Ecol., DOI: 10.1111/j.1365- 294X.2009.04171.x). Pack rats normally eat "mildly toxic" juniper bushes supplemented with seasonal plants. But when creosote bushes gradually replaced juniper in the Mojave Desert some 10,000 years ago, pack rats there began feeding on the leaves of creosote bushes, which contain resinous compounds that are highly toxic to mammals. Dearing's team used a microarray screening technique to sift through the genomes of pack rats from different regions and identified 24 genes in Mojave animals that signal the liver to make detox enzymes when the animals eat creosote leaves. The enzymes modify the toxic compounds so that they are more water soluble and thus excreted quickly. The identified "biotransformation" genes give scientists a better understanding of diet-switching and could be used to modify grazing animals such as cattle and sheep so they can forage on more types of plants, Dearing says.