Woodrats' Genes Arm Them Against Toxic Plants

Woodrats are armed and ready to consume any insidious food, for they possess a handful of genes that protect them against the toxic creosote plant, a main part of its diet, according to a new study.

It's long been a mystery exactly how the woodrat developed the ability to handle the chemicals in the creosote plant, which are toxic to other rodents. Previous research has suggested that they are protected by factors such as gut bacteria, but the new study reveals that several genes are involved. In two species of woodrat, when these genes are switched on the critters develop resistance to the plant's poisons, showing that the genes they are born with play a central role in whether they feel the effects of its toxic chemicals.

Ever since creosote bushes started sprouting in the deserts of the western United States, these rats have had to develop a way to survive. The plant developed a toxic resin containing the chemical nordihydroguaiaretic acid (NDGA) to protect itself from being eaten. This substance wreaks havoc on the livers and kidneys of most rodents, but woodrats detoxify the substance so they can eat the bush as a normal part of their diet. Due to this genetic survival technique, woodrats now have exclusive access to this food source.

Scientists from the University of Utah and Weber State University investigated the gene expression in two types of woodrats: Neotoma bryanti and Neotoma lepida. The researchers focused on what enzymes the species produced in reaction to the plant resin.

There were three groups of rodents involved in the study - "experienced" N.bryanti and N.lepida that had been exposed to creosote in the wild, and "naïve" N.bryanti, a population of woodrats for whom creosote was a new addition to their diet.

They found that when woodrats had been exposed to the creosote bush in the wild, a small number of similar genes were switched on by both species to detoxify the plant, despite having evolved the mechanisms at completely different times.

"We were surprised by how few genes were induced by woodrats of both species when they were consuming a toxin-laced diet. We expected a huge list of genes - instead we found very few," researcher Jael Malenke from the University of Utah said in a statement.

When the creosote was a new addition to the diet of individual N.bryanti woodrats, however, they exhibited signs of stress.

The study's findings were published in the journal BMC Ecology.