Why are all black bears so important?
Cinnamon-haired black bears are a unique subspecies of the American black bear known for its distinctive reddish-brown fur. These bears are found in several areas of North America, including the western United States.
Researchers from HudsonAlpha, the University of Memphis and the University of Pennsylvania have discovered the true cause of the cinnamon-colored coat in certain black bears.
Bears are more common than the brown-colored grizzly bear in Yellowstone National Park, and in the coastal areas of the Pacific Northwest, the term “brown bear” usually refers to a grizzly bear.
The different colors of American black bears (Ursus americanus) can be subtle, such as B. brown (aka cinnamon), blonde, or bluish-grey. Some bears have coats that are a combination of multiple colors.
Researchers from HudsonAlpha, the University of Memphis, and the University of Pennsylvania have discovered what causes the cinnamon color, which clears up this color confusion.
Emily Puckett, Ph.D., an assistant professor of biology at the University of Memphis, has devoted her career to studying bear development and evolution. With the help of partners in state, regional and federal wildlife agencies, she collected hundreds of DNA and hair samples from North American bears. Greg Barsh, MD, Ph.D., is a HudsonAlpha faculty researcher and animal pigmentation expert.
Melanin is produced by skin cells called melanocytes, and pheomelanin is red or yellow in mammals. It is known that genetic variation in melanin biosynthesis has led to differences in hair, eye and skin color.
The TYRP1 gene produces an enzyme in melanocytes that helps create eumelanin, so it makes sense that the cinnamon and grizzly bears have less eumelanin due to their TYRP1R153C and TYRP1R114C mutations.
“We were surprised to discover that the TYRP1R153C variation responsible for cinnamon U. americanus is the same one previously described as the cause of oculocutaneous albinism (OCA3) in humans,” says Barsh. Characterized by reddish skin and hair and frequent vision changes, OCA3 is most common in people of African or Puerto Rican descent. However, bears with TYRP1 mutations have normal skin and can see well.
The TYRP1R153C variant was found most frequently in the southwestern United States, but later also in southeastern Alaska and the Yukon Territory. It is thought to be responsible for nearly all color variation in U. americanus.
Researchers looked at the TYRP1R153C mutation to determine whether it originated in grizzly bears or evolved into black bears, but demographics suggested it didn’t. Instead, the TYRP1R153C mutation arose spontaneously 9,360 years ago in black bears living in the western United States.
Puckett: “The TYRP1R153C mutation that evolved in black bears over 9,000 years ago likely gave the cinnamon bears an advantage.” We also ruled out another hypothesis related to thermoregulation.
The researchers propose a new explanation for why the variation in coat color arose in the first place: crypsis. Typically, Krypsis is found in prey and ambush predators that are color-matched to their surroundings. Here, they argue, crypsis is a broader adaptive mechanism for large-bodied animals.
“These results show how genetic variations in melanin biosynthesis may underlie iconic phenotypes and help in our understanding of color variation and recent evolution in large carnivores,” says Barsh.
Emily E Puckett, Isis S Davis, Dawn C Harper, Kazumasa Wakamatsu, Jerrold L Belant, Colin Carpenter, Anthony P Crupi, David L Fowler, Mark Haroldson, Shosuke Ito, Carl Lackey and Gregory S Barsh , December 16, 2022, Current Biology. DOI: 10.1016/j.cub.2022.11.042