Most mammals are herbivores. Some face serious challenges: their bodies must handle up to hundreds of toxic chemicals from the plants they consume each day. "Plant toxins determine which plants a herbivore can eat," says Kohl.
Liver enzymes help animals detoxify such poisons. Researchers previously isolated toxin-degrading microbes from herbivores, but Kohl and Dearing say that, until now, scientists have lacked strong evidence for what has been conventional wisdom: Gut microbes also help some herbivores eat toxic plants.
The study involved desert woodrats (Neotoma lepida) grayish rodents native to western North American deserts. Woodrats somehow acquired novel toxin-degrading gut microbes to adapt to climate and vegetation changes that began 17,000 years ago.
"In a natural climatic event at the end of the last glacial period, the Southwest dried out and our major deserts were formed," Dearing says. Creosote, which was native to Mexico, moved north into the Mojave Desert and replaced juniper there, but did not go farther north into Great Basin deserts. Desert woodrats in the Mojave started eating creosote bushes, while desert woodrats in the Great Basin kept eating toxic juniper, to which they had adapted earlier.
At first, the ancient juniper eaters in the Mojave likely were poorly equipped to eat invading creosote, but scientists believe microbes sped up their dietary adjustment. Though slow, evolutionary genetic changes in herbivores play an important role in adapting to new diets. "Transfer of toxin-degrading microbes from one organism to the other is much more rapid," Dearing says.
How do woodrats get their tiny, but valuable bacterial helpers today?
"Mammals acquire microbes during birth, through contact with their mother's vaginal and fecal microbes," Kohl says. "Other possible places to get microbes include leaf surfa
|Contact: Lee J. Siegel|
University of Utah