Poison: It's what's for dinner( SALT LAKE CITY As the U.S. Southwe...)

SALT LAKE CITY As the U.S. Southwest grew warmer from 18,700 to 10,000 years ago, juniper trees vanished from what is now the Mojave Desert, robbing packrats of their favorite food. Now, University of Utah biologists have narrowed the hunt for detoxification genes that let the rodents eat toxic creosote bushes that replaced juniper.

"It was either eat it or move out," says biology Professor Denise Dearing, senior author of the study, published online Tuesday, April 7 in the journal Molecular Ecology.

During the study, eight packrats also known as woodrats were captured from each of two western regions: the Mojave Desert and the cooler Great Basin. Rats from both areas were fed rabbit chow mixed either with creosote or juniper. The scientists then scanned the rodents' genetic blueprints to look for active genes known as "biotransformation genes" because they produce liver enzymes to detoxify the poisons in creosote and the less-toxic juniper.

"We found 24 genes in woodrats from the Mojave Desert that could be key in allowing them to consume leaves from creosote bushes," she says. "The leaves are coated with a toxic resin that can comprise up to 24 percent of the dry weight of the plant."

Dearing says she conducted the study because "we don't really understand how wild animals process their diets, and how herbivores can feed on really toxic diets. If we can understand it, we may be able to understand how they will deal with climate change."

For example, "the toxins in creosote could respond to increases in [atmospheric] carbon dioxide," which causes global warming, she adds. "The plants may make more toxins under elevated CO2 conditions because these toxins are built from carbon atoms."

Dearing says once the actual creosote-detoxification genes are pinpointed among the 24 candidates identified by the new study, those genes someday might be used to modify cattle, sheep or other grazing animals
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