Rats adapt to changing climate

By Lana Groves, Asst. News Editor

Wood rats lost their favorite juniper snack more than 10,000 years ago when climate change dried the Mojave Desert, forcing them to adapt their diets. Now the projected speed of global warming could make adaptation more difficult for animals.

U biology professor Denise Dearing has been studying how wood rats adapted to the creosote bush, a toxic plant to many herbivores, thousands of years ago when the bush replaced juniper in the Mojave Desert. The plant can survive with limited water in the desert region of the Mojave that is home to many wood rats.

“Most mammals can’t tolerate milk after they’re weaned,” Dearing said. “They lose the ability to process lactose. Human populations that are pastoral have evolved the ability to keep their lactase gene switched on, but it’s not true for all humans. The same kind of thing happened to these wood rats.”

Wood rats evolved in their ability to tolerate the poison in creosote plants, but the species had about 7,000 years to adjust when their environment slowly began heating up 17,000 years ago. Even now, the plant only makes up 75 percent of a wood rat’s diet. If forced to take in any more of the plant, the rats will either show signs of toxicity or starve themselves.

In the drier parts of the Mojave Desert where the bush outlives other plants during parts of the year, wood rats starve themselves until other plant food grows, Dearing said.

However, global warming will make plants more toxic because of increased carbon in the air, which means wood rats might need to find an alternate food source.

“I don’t know what will happen in the Mojave,” Dearing said. “Creosote is an amazing desert shrub8212;it can tolerate really hot desert conditions. But if it becomes more toxic, the plant could be detrimental to wood rats. They could lose too much weight in the winter.”

Dearing and other researchers have spent the past few years trying to find enzymes in the rats’ livers that play a part in ingesting the plant’s toxin without negative side effects.

Researchers narrowed a list of 224 potentially helpful genes down to 25 in a study published online April 7 in the Journal of Molecular Biology.

Now Dearing’s research team will study the 25 genes to find which ones help wood rats ingest the poisonous plant.

By separately placing different wood rat genes in a combination with yeast and the plant’s toxin, researchers can compare how well the yeast grows in a combination without the poison. The yeast grows faster depending on which gene is injected because the gene counteracts the toxin.

Even after the second study, more research will need to be done, said Jael Malenke, a biology postdoctoral researcher in Dearing’s lab.

“Even though we see these animals can adapt, they may not be able to adapt fast enough, especially as the plant becomes more toxic,” Malenke said.

Dearing said researchers should be monitoring how many wood rats and other animals are thriving despite changing climate conditions.

U biology professor Jim Ehleringer is leading the Utah part of a National Science Foundation study to monitor rodent and bird abundance and diseases carried by insects and invasive plants, which could help study the effects of climate change on animals, Dearing said.

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Sean Sullivan

Biology professor Denise Dearing has shown that wood rats have the ability to adapt to their food sources, ingesting food that was once toxic to them without negative side effects. Yet, adaptations such as these may be more difficult for animals as global warming speeds up climate change.