Not all pandas turned out to be black and white: scientists have found an explanation

The work, which included studying the genetics of many pandas in the wild and in captivity, suggested that pandas with brown and white fur are the result of natural variation rather than a sign of inbreeding in a dwindling population.

According to CNN, the first brown panda known to science was a female named Dandan. A local ranger discovered a sick bear in Foping County in the Qinling Mountains of Shaanxi Province in March 1985. The panda was kept in captivity until his death in 2000.

Since Dandan’s discovery decades ago, there have been 11 sightings documented by official news sources or personal accounts shared by the authors of this latest study, published in the journal PNAS on March 4.

“Repeated sightings of brown pandas suggest that this trait may be inherited. However, to date, the genetic basis underlying the brown-white coat color remains unclear,” the study authors write.

A better understanding of distinctive coloration could help efforts to breed brown-and-white pandas in captivity, according to senior study author Dr. Fuwen Wei, a professor of wildlife ecology and conservation biology at the Institute of Zoology of the Chinese Academy of Sciences in Beijing. The giant panda’s status as a species is vulnerable, according to the International Union for Conservation of Nature’s Red List of Threatened Species.

To understand what lies behind this trait, the researchers studied Qizai, a male brown panda rescued as a cub in 2009 from Foping National Nature Reserve in Hanzhong. He is currently the only brown panda in captivity.

When compared under a microscope with fur samples from three black and white pandas, Qizai’s brownish fur was found to have fewer melanosomes, tiny structures found in cells that are responsible for the pigmentation of skin and hair in mammals. Moreover, the research team found that the melanosomes were likely irregularly shaped.

The researchers then collected genetic information about Qizai and pieced together his family tree. Fresh scat collected from a nature reserve has led to the identification of his wild mother, a black-and-white female panda who wears a tracking collar and is known as Niuniu.

The researchers also identified Qizai’s son, a black and white panda born in captivity in 2020. (The research team later identified Qizai’s father, Xiyue, a wild but tracked black and white panda, by studying the genetics of the broader panda population.)

The scientists examined the genetic information of Qizai’s family members and compared it with the genetic information of 12 black-and-white pandas from the Qinling Mountains and 17 black-and-white pandas from other regions of China, using information obtained from stingrays and blood samples.

Although none of Qizai’s immediate relatives had brown fur, the researchers were able to show that his parents and son had one copy of a recessive trait in a gene known as Bace2, while Qizai had two copies.

An individual’s genes may carry recessive traits, such as blue eyes or red hair in humans, without manifesting as a physical characteristic. Each parent must possess a copy of the genetic variant and pass it on for the trait to appear in the offspring, as in the case of Qizai.

Through analysis of a tissue sample stored in ethanol for more than two decades, scientists were also able to sequence the genome of Dandan, the first known brown panda. The researchers found that Dandan had the same recessive trait.

The scientists then conducted a broader analysis of 192 black-and-white giant pandas to confirm the presence of the responsible gene, Bace2. The mutation causing brown fur was present in only two pandas native to the Qinling Mountains in Shaanxi, not Sichuan Province, where most of China’s giant pandas live.

To confirm their findings, the scientists used the gene-editing tool CRISPR-Cas9 to remove a genetic sequence they identified as causing a mutation in the Bace2 gene in 78 laboratory mice. The change reduced the number and size of melanosomes in mice.

“The fur color of knockout mice is light brown,” said Wei, who is also president of Jiangxi Agricultural University in Nanchang. “This shows that this deletion could potentially change the fur color of the mouse, since the pigmentation pathway is relatively conserved (common) in mammals.” Therefore, it is very likely that this mutation affects the coat color of the brown panda.”

It is unclear what caused the genetic mutation. Wei said that this must be due to the specific environment of the Qinling Mountains, whose climate is different from that of Sichuan Province. The genetic mutation did not appear to be the result of inbreeding, as previously thought, he said.

“This is most likely the result of natural variation rather than inbreeding. Our relationship analysis shows that Kizai’s parents are not closely related,” Wei added.

Tiejun Wang, an associate professor of natural resources at the University of Twente in the Netherlands, said the good news is that the unique coloration does not appear to be the result of inbreeding. Wang, who studied brown pandas, was not involved in the study.

“For those concerned about the species, this is a positive development,” said Wang, who said he worked as a field ranger in the mountains for 10 years.

Wang said he applauds the team “for their tremendous efforts in trying to shed light on this scientific question.”