University of Utah study focuses on animals with toxic diets

No animal with any notion of self-preservation will touch the leaves of a creosote bush, let alone make it a part of its diet.

After all, creosote leaves are loaded with as many toxins and polysyllabic carcinogens as cigarette smoke, and the bush produces a tarlike substance that has kept railroad ties from weathering.

But remarkably, this nasty, invasive bush that's been around since the ice age isn't killing the varmints that eat it all winter long in the southwestern United States.

It's helping them survive.

That rodents on the range could adapt to daily doses of poison isn't that remarkable. How their livers effectively detoxify a poison was the interesting question for University of Utah professor Denise Dearing and her colleagues.

Although all kinds of herbivores and ruminants do it, "we don't really understand how wild animals process their diets and how they can feed on really toxic diets," Dearing said. "If we can understand it, we may be able to understand how they will deal with climate change." By pinpointing the detoxification genes, others might be found that could turn cattle and sheep into creosote tolerators one day.

Dearing and her colleagues captured eight packrats — or woodrats, as they're known in these parts — from the Mojave Desert and the Great Basin. They were served rabbit kibble with bits of either creosote or juniper mixed into each portion.

The scientists analyzed the rodents' DNA to look for active genes known as "bio-transformation genes" that produce liver enzymes to detoxify the poisons in creosote and the less-toxic juniper.

The results can be found in the current issue of the journal Molecular Ecology.

Turns out 24 genes in woodrats from the Mojave are involved in the process that allows them to consume creosote leaves.

Creosote bushes arrived some 10,000 years or so ago with the warming climate after the big melt and pushed out juniper trees native to what is now effectively a desert.

Creosote products have held in check many known human and animal infections and have been particularly useful to sheep ranchers who annually "doc" the herd, but cattle ranchers won't tolerate its scent because of that close tie to sheep, the long-disparaged yet more widely ranged ranch animal.