With its striking color, the giant panda is an instantly recognizable species.
However, a handful of giant pandas exist that are not black and white. These majestic creatures with brown and white fur inhabit a single mountain range in China. And now, scientists may have unraveled the mystery of the ultra-rare pandas' unusual fur, according to new research.
The work, which studied the genetics of multiple pandas in the wild and in captivity, has suggested that pandas with brown and white coats are the result of natural variation, and not a sign of inbreeding in a declining population.
The first brown panda known to science was a female named Dandan. A local forest ranger found the sick bear in March 1985 in Foping County in the Qinling Mountains of Shaanxi Province. The panda was kept in captivity until her death in 2000.
Since Dandan's discovery decades ago, 11 reported sightings have been documented through official news sources or personal accounts shared with the authors of this latest study published March 4 in the journal PNAS.
"The recurring cases of brown pandas imply that this trait may be hereditary. However, to date, the genetic basis underlying the brown-white coat color remains unclear," the authors wrote.
Gaining a better understanding of the distinctive coloration could aid efforts to breed brown-and-white pandas in captivity, said senior author Dr. Fuwen Wei, professor of wildlife ecology and conservation biology at the Institute of Zoology of the Chinese Academy of Sciences. Beijing. According to the International Union for Conservation of Nature's Red List of Threatened Species, the status of the giant panda as a species is vulnerable.
A panda family tree
To understand what lies behind this trait, the researchers studied Qizai, a male brown panda who was rescued as a cub from the Foping National Nature Reserve in Hanzhong in 2009. He is currently the only brown panda in captivity.
Compared under a microscope to hair samples from three black and white pandas, Qizai's brownish fur had fewer and smaller melanosomes, small structures found in cells responsible for skin and hair pigment in mammals. In addition, the melanosomes likely had an irregular shape, the research team found.
The researchers then collected genetic information about Qizai and compiled his family tree. Fresh feces, or bear scat, collected at the nature reserve revealed the identity of its wild mother, a black-and-white female panda wearing a tracking collar and 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 a broader population of pandas.)
The scientists studied the genetic information of Qizai's relatives 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 in China using information from scat and blood samples. .
Although none of Qizai's immediate relatives had brown fur, the researchers were able to show that his parents and son each had one copy of the recessive trait of a gene known as Bace2, while Qizai had two copies.
An individual's genes can carry recessive traits, such as blue eyes or red hair in humans, without this appearing 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 is the case with Qizai.
Genetic analysis solves a mystery
Thanks to an analysis of a tissue sample preserved in ethanol for more than twenty years, the scientists were also able to sequence the genome of Dandan, the first known brown panda. Dandan had the same recessive trait, the researchers discovered.
The scientists then conducted a broader analysis of 192 black and white giant pandas to verify the gene responsible as Bace2. The mutation that caused the brown fur was only present in two pandas from the Qinling Mountains in Shaanxi, and not in Sichuan province, where the majority of China's giant pandas live.
To confirm the findings, the scientists used the CRISPR-Cas9 gene editing tool to remove the genetic sequence that they determined caused the mutation in the Bace2 gene in 78 laboratory mice. The change reduced the number and size of melanosomes in the mice.
"The coat color of knockout mice is light brown," said Wei, who is also president of Jiangxi Agricultural University in Nanchang, China's Jiangxi province.
"It proves that this deletion has the potential to change a mouse's coat color, because the pigmentation pathway is relatively conserved (shared) among mammals. It is therefore very likely that this mutation affects the coat color of a brown panda."
Natural variation versus inbreeding
It is not clear what caused the genetic mutation. Wei said it must be related to the specific environment of the Qinling Mountains, which has a different climate from Sichuan. The genetic mutation did not appear to be the result of inbreeding as once suspected, he said.
"It is more likely to be a result of natural variation than inbreeding. Our kinship analysis indicates that Qizai's parents are not closely related," Wei added.
Tiejun Wang, associate professor in the department of natural resources at the University of Twente in the Netherlands, said it was good news that the unique coloration did not appear to be the result of inbreeding. Wang, who has studied brown pandas, was not involved in the research.
"For those concerned about this species, this is a positive development," said Wang, who said he worked as a mountain ranger for 10 years.
Wang said he commended the team "for their tremendous efforts to shed light on this scientific question."
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