Life is tough for woodrats in deserts of the U.S. Southwest. There are few plants for food, and those plants produce poison to deter rodents（啮齿动物） , insects and other animals. A new University of Utah study shows how certain woodrats put themselves on a diet to avoid poisoning: They sample a smorgasbord（大杂烩） of toxic plants, eat smaller meals, increase time between meals and drink more water if it is available.

"For decades, we have been trying to understand how herbivores（食草动物） deal with toxic diets," says biology Professor Denise Dearing, senior author of the study, published online Tuesday, Aug. 9 in the British Ecological Society's journal Functional Ecology.

"This study compares woodrats that eat only a single plant – juniper – with another species that eats several kinds of plants, including a small amount of juniper," Dearing says. "We were trying to understand how they regulate the dose of toxic chemicals they eat by observing how often and how much they ate."

"We found that the woodrat that eats many types of plants was better at limiting toxin intake than the woodrat that eats only juniper," she adds.

The "specialists" – woodrats that eat only juniper – have evolved liver enzymes to metabolize large amounts of juniper toxins, so they did not change the amount of juniper they ate and did not drink more water. But "generalists" – woodrats that can metabolize small amounts of many different plant toxins – actually changed their eating and drinking behavior to avoid an excessive dose of any one plant poison.

Dearing conducted the research with first author and Utah biology Ph.D. student Ann-Marie Torregrossa – who now is a postdoctoral fellow at Florida State University – and Anthony Azzara of Bristol-Myers Squibb in Princeton, N.J. The research was funded by the National Science Foundation and the American Museum of Natural History.