Sunday, March 06, 2016

Climate change may hurt animals' ability to live on toxic plants

Public Release: 12-Jan-2016
Poison warmed over
Climate change may hurt animals' ability to live on toxic plants
University of Utah

University of Utah lab experiments found that when temperatures get warmer, woodrats suffer a reduced ability to live on their normal diet of toxic creosote - suggesting that global warming may hurt plant-eating animals.


While not all animal diets are as toxic as those of woodrats and other rodents that eat plants like creosote bushes or juniper, most mammals eat some toxins in their diet. In an ongoing evolutionary battle, plants evolve chemical defenses against being eaten and animals evolve liver enzymes or other ways to overcome or avoid plant toxins.

Dearing notes that "over 40 percent of all existing mammals eat only plants" and many more eat some plants. "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," she adds. Birds also might be affected, she says.

Kurnath says animals with diets that contain toxic plants include rabbits, pikas, marmots, possums, deer, moose, elk, bighorn and domestic sheep, horses and even cows. "Any free-range domestic animal will face plants with toxins," she says.

Previous research suggested that plant chemicals ingested by mammals would become more toxic at warmer temperatures. The new study showed how temperature affects the ability of desert woodrats, Neotoma lepida - also known as pack rats - to tolerate the toxic resin from creosote bushes, which account for as much as three-fourths of their normal diet. Creosote resin contains hundreds of toxic compounds, and woodrats live on amounts that kill or cause kidney cysts in other laboratory rodents.


Agriculture research indicated that at higher temperatures, cows that got fescue toxicosis from eating fungi-laden grass were more likely to get sicker, lose weight, stop producing milk and have unhealthier calves than infected cows living in cooler temperature.

As for desert woodrats, Kurnath conducted an earlier study showing that at warmer temperatures, they had reduced liver function to process toxins. The pack rats were anesthetized, and the warmer rats slept longer than the cooler woodrats, indicating the latter processed the anesthetic more quickly.

Two other studies showed that white-throated woodrats ate more toxic juniper at cooler temperatures than at warmer temperatures, and that woodrats with a normal juniper diet could maintain body temperature more easily than woodrats eating rabbit chow - an indication that when the liver is working harder to break down toxins at cooler temperatures, it needs less of a boost to keep the body warm.


Previous studies found that mammals ranging from goats to koalas, possums and woodrats reduce eating to avoid too much plant toxin. The first experiment identified maximum creosote doses for desert woodrats living at warm and cool temperatures.


The researchers say liver processing of toxins may be reduced at warmer temperatures because woodrats must put more energy into regulating body temperature.

"The mechanism that makes it more difficult for woodrats to consume toxic diets at warmer temperatures likely is not restricted solely to woodrats, and applies to plant-eating mammals in general," Dearing says. "As the climate warms, herbivores may face even more restricted menu choices."

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