By: Samuel Lin
The sun shines overhead in the cloudless sky; the tangible heat thickens the air. A huge, brown, lumbering bear idles in a river, looking intensely through the clear water for fish. Suddenly the bear puts his head under the water and returns with a flopping fish. Though this brown bear looks like a grizzly bear, it is a mutated black bear.
American Black bears, known to be black, are slowly changing colors to shades of brown after a genetic mutation. The genetic mutation makes it confusing to distinguish between Black bears and Brown or Grizzly bears that live in similar regions. The mutation happened around 9,000 years ago, somewhere in the southwest.
Dr. Emily Puckett, a biologist at the University of Memphis, led a study that found the gene that caused the genetic mutation.
“The bears don’t pass through the Great Plains,” Dr. Puckett said. “If they wanted to go east, they would have to go up north to Canada, across the Canadian [Prairies], around the Great Lakes and then drop back down into the eastern populations. That would take a long time. We do see that it’s happening and is moving [eastward], but it’s a process that takes time.”
The mutation is more common in the west than in the east. In Eastern states, such as in Minnesota, only 5% of black bears are brown.
“In the eastern part of North America, where I grew up, we have American black bears, and they’re only black,” said Dr. Puckett. On the other hand, over 50% of black bears in the west, such as in Arizona and Nevada, are brown.
One reason for this is that the origin of the genetic mutation was in the Southwest.
“Our demographic modeling identified that the most likely place where the mutation arose was somewhere in the western region, very likely in the Southwest,” said Dr. Puckett. “From there, it expanded through gene flow throughout populations.”
Dr. Puckett discovered that a gene called TYRP1 is responsible for the genetic mutation. The mutation changes the amino acid, causing the bear’s skin to look brown or cinnamon-colored. This mutation is very similar to albinism in humans.
Dr. Puckett and her coworkers are studying why the mutation has survived. One hypothesis is that brown coats absorb less heat than black coats. This is beneficial in the southwest, where temperatures can reach up to 90 degrees.
Another hypothesis is that the brown coat helps the bear blend in with its surroundings. This allows it to avoid predators such as Mountain lions, wolves, bobcats, and even Grizzly bears, and sneak up on prey such as deer and moose.
Sources:
https://www.nytimes.com/2022/12/16/science/cinnamon-black-bear-mutation.html