A new study by University of Utah scientists found that increased temperatures can hinder the ability of woodrats, Neotoma lepida, to survive on their standard diet of toxic creosote, leading the scientists to hypothesize that global warming might be having a negative effect on herbivores.

"This study adds to our understanding of how climate change may affect mammals, in that their ability to consume dietary toxins is impaired by warmer temperatures," Denise Dearing, senior author of the research, said in a press release.

"We found that desert woodrats have a harder time eating their natural diet at slightly warmer temperatures," said Patrice Kurnath, first author of the study. "In terms of climate changes, this study suggests that plant-eating animals all over the world may have problems dealing with their preferred food sources."

Woodrats eat a toxic diet, one that is much more toxic than other plant-eating rodents, but nevertheless most mammals have diets that contain at least some toxins. Due to the habits of plant-eating mammals, plants evolve chemical defenses to prevent them from eating them and in turn, animals evolve liver enzymes and other biological mechanisms to minimize the effects of these toxins.

"Most plants produce toxins, so the majority of plant-eating mammals eat toxic compounds, and this may become more difficult to deal with as the climate warms," Dearing said.

Although previous studies suggested that plant chemicals ingested by mammals would likely increase in toxicity at higher temperatures, the current study shows concrete evidence of this effect in woodrats by showing an increased toxicity of creosote bushes, which compromise approximately 75 percent of their standard diet.

The study utilized two experiments, each of which fed the woodrats a standard diet of rabbit chow treated with toxic creosote resin. The first experiment pinpointed the maximum creosote doses that the woodrats could handle living at warm and cool temperatures, whereas the second experiment examined woodrats at room and cool temperatures.

The results showed that woodrats living in cool temperatures could tolerate a toxic diet, as opposed to those at room and warm temperatures. This is contrary the team's expectation that their creosote tolerance would progressively decrease in all temperature conditions.

"That was a huge surprise," Kurnath said. "We expected warmer temperatures to gradually be worse, but there might be a tipping-point temperature."

"There seems to be a threshold at which it becomes significantly harder for mammals to eat toxins," Dearing added. "We've identified this threshold [77 degrees F in the second experiment]. With climate change, they are going to spend more time above the temperature threshold, and it's going to be harder for them."

The findings were published in the Jan. 13 of the Proceedings of the Royal Society B: Biological Sciences.