Before creosote invaded the Southwest from South America, woodrats ate juniper throughout what is now the Great Basin of Utah and Nevada and the Mojave Desert of southwestern Utah, southern Nevada and inland southeastern California.
But things were changing as the last Ice Age waned. "As the glaciers were receding, creosote bush was invading," says Dearing. "The Southwestern deserts were being formed as the land was becoming hotter and drier, and creosote bush replaced juniper trees in those areas."
Woodrats also are known as packrats because they build yard-wide, 2-foot-tall "middens" using twigs, branches, pottery shards and other debris. The middens are typically above ground under juniper trees in the Great Basin and yucca in the Mojave.
Because ancient middens are preserved, scientists have analyzed their contents, which included juniper pollen, showing packrats throughout the Southwest ate juniper before the climate warmed. Creosote pollen shows the bushes had spread through the Mojave by 10,000 years ago.
"I see this as a tale of two poisons or a tale of two diets two populations of the same species that feed on very different staple foods: creosote and juniper," says Dearing. "It's like suddenly having your food coated with a different poison than you are used to. It's interesting to see the response of these animals to a natural climate change event where they were forced to change their diet and adapt to a new type of toxin."
Dearing says that as creosote invaded, some woodrats already had genes to let them eat creosote or there was a mutation in existing detoxification genes that allowed creosote consumption. Over time, Mojave woodrats with those genes were more likely to survive on creosote, while those in the Great Basin stuck to juniper.
Searching for Detoxification Genes
In the new study, Dearing and colleagues used microarrays desig
|Contact: Lee Siegel|
University of Utah