Their black and white fur makes them one of the most recognizable animals on the planet, but did you know some giant pandas are brown? It’s incredibly rare, and for a long time the reason why was unknown, but a recent study found a genetic mutation that explains the mystery of the brown panda.
It wasn’t until 1985 that the first brown bear became known to scientists. It was a female named Dandan, discovered by a local ranger in the Qinling Mountains, Shaanxi province. Sadly, Dandan wasn’t in the best of health when she was found, and she was held in captivity until her death in 2000.
Over the nearly four decades since Dandan’s discovery, there have only been 11 more documented sightings, seven of whom are still living. The authors behind the most recent study investigating the color difference, published in the journal PNAS on March 4, earlier this year, looked at these brown pandas and nearly 200 black and white ones.
Due to the brown and white pandas’ extreme rarity, there is considerable interest in breeding them. Researchers wanted to know if the difference in coloration could be inherited, according to the senior author Dr. Fuwen Wei, a professor of wildlife ecology and conservation biology at the Chinese Academy of Sciences’ Institute of Zoology in Beijing.
“The recurring instances of brown pandas imply that this trait may be inheritable. However, to date, the genetic basis underlying the brown-and-white coat color remains unclear,” the authors explained at the start of their study.
Qizai, a brown male panda, first rescued as a cub back in 2009 from Foping National Nature Reserve in Hanzhong, was at the center of the study. He is currently the only brown panda in captivity and they examined his hair under a microscope, comparing it to three black and white bears.
Genetic results suggested that pandas with brown and white coats are the result of natural variation, rather than a sign of inbreeding in a dwindling population. They found that Qizai’s brownish fur had fewer and smaller melanosomes. Melanosomes are tiny organelles found in cells of mammals, responsible for skin and hair pigment. As well as less and smaller melanosomes in the brown fur, they were also more likely to be irregularly shaped, according to the study.
From the study, the scientists were able to build a family tree for Qizai, adding to the black-and-white-furred son they knew he had fathered in 2020. Via fresh poop found at the Foping National Nature Reserve, they were able to identify his mother as a wild, black and white bear called Niuniu. Qizai’s father was also a wild, black and white panda. He was known as Xiyue.
Based on this, Wei wrote: “[Brown fur] is more likely to be a result of natural variation rather than inbreeding. Our kinship analysis indicates that Qizai’s parents are not closely related.”
They then analyzed 192 more black-and-white giant pandas, attempting to verify a gene mutation responsible for brown fur, called Bace2. The mutation, which they knew was found in brown pandas and could be traced back to Dandan, was only present in two of these 192 conventional-looking pandas. Both of them came from the Qinling Mountains in Shaanxi, close to where all the brown pandas have been found in the wild.
Finally, to confirm the findings, the scientists used “the CRISPR-Cas9 gene-editing tool to delete the genetic sequence they had identified as causing the mutation in the Bace2 gene in 78 lab mice,” according to CNN. It reduced the number and size of melanosomes in the mice.
“The coat color of knockout mice is light brown,” Wei continued. “It proves that this deletion has the potential to alter the coat color of a mouse, as the pigmentation pathway is relatively conserved (shared) among mammals. Therefore, it is very likely that this mutation influences the coat color of a brown panda.”
According to Nature, this is the first time that an absent genetic segment has been linked to a change in color.
While they don’t know the exact reason for the mutation, they know it must be linked to the environment in the Qinling Mountains.
As rare as brown giant pandas are, the status of the entire species is vulnerable, according to the International Union for Conservation of Nature Red List of Threatened Species.
“For those who are concerned about this species, this is a positive development,” said Tiejun Wang, an associate professor at the University of Twente in the Netherlands.
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