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With its striking colouration, the giant panda is an instantly recognizable species.
There are a handful of giant pandas that aren’t black and white, though. These majestic creatures with brown and white fur live in a single mountain range in China. And now, scientists may have solved the mystery of pandas’ unusual coats, according to new research.
The work, which involved studying the genetics of multiple pandas in the wild and in captivity, suggested that pandas with brown-and-white coats are the result of natural variation, rather than a sign of inbreeding in a declining population.
The first brown panda known to science was a female named Dandan. The sick bear was found by a local ranger in Foping County in the Qinling Mountains of Shaanxi province in March 1985. The panda was kept in captivity until it died in 2000.
Since Dandan’s discovery decades ago, there have been 11 reported sightings documented through official news sources or personal accounts shared by the authors of this latest study that appeared in the journal PNAS on March 4.
“The recurrent cases of brown pandas suggest that this trait may be inherited. To date, however, the genetic basis underlying the brown-and-white coat color is unclear,” the authors wrote.
A better understanding of the distinctive coloration could help inform 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 Zoology of the Chinese Academy of Sciences in captivity. Beijing. The giant panda’s status is as a vulnerable species, according to the International Union for Conservation of Nature’s Red List of Threatened Species.
Panda family tree
To understand what is behind the trait, the researchers studied Qizai, a male brown panda rescued as a cub in 2009 from the Foping National Nature Reserve in Hanzhong. He is the only brown panda in captivity at the moment.
When compared under a microscope to hair samples from three black-and-white pandas, Qizai’s brown fur had fewer melanomas and fewer, small structures found in cells responsible for skin and hair pigmentation in mammals. What’s more, the melanosomes were more likely to be irregularly shaped, the study team found.
The researchers then collected genetic information about Qizai and assembled his family tree. Fresh scat, or bear droppings, collected at the nature reserve revealed the identity of its wild mother, a black-and-white female panda wearing a tracked collar known as Niuniu.
The researchers also identified Qizai’s son, a black and white panda born in captivity in 2020. (The study team later identified Qizai’s father, Xiyue, a wild but tracked black-and-white panda, by studying genetics the wider population. pandas.)
The scientists studied the genetic information from the Qizai family members and compared it with the genetic information from 12 black-and-white pandas from the Qinling Mountains and 17 black-and-white pandas from other regions in China. using information taken from scat and blood samples. .
Although none of Qizai’s immediate family members had brown hair, the researchers were able to show that both his parents and his son had one copy of the recessive trait on a gene called Bace2, and Qizai had two copies.
An individual’s genes can carry recessive traits, such as blue eyes or red hair in humans, without appearing as a physical characteristic. Each parent must have a copy of the genetic variant and pass it on for the trait to appear in the offspring, as in Qizai’s case.
Genetic analysis solves an enigma
Thanks to the analysis of a tissue sample that had been stored in ethanol for more than twenty years, the scientists were also able to sequence the genome of Dandan, the first known brown panda. Dandan, the researchers found, had the same recessive trait.
The scientists then carried out a wider analysis of 192 black-and-white giant pandas to verify the responsible gene as Bace2. The mutation that caused the brown coats was only present in two pandas that came from the Qinling Mountains in Shaanxi, not Sichuan province, where most of China’s giant pandas live.
To confirm the results, the scientists used the gene editing tool CRISPR-Cas9 to delete the genetic sequence they identified as the cause of the mutation in the Bace2 gene in 78 laboratory mice. The mutation reduced the number and size of melanosomes in the mice.
“The coat color of the defeated mice is light brown,” said Wei, who is also president of Jiangxi Agricultural University in Nanchang in China’s Jiangxi province.
“It proves that this deletion has the potential to change coat color in mice, because the pigment pathway is relatively conserved (shared) among mammals. Therefore, it is very unlikely that this mutation affects the color of the brown panda’s coat.”
Natural variation vs. inbreeding
It is not clear what caused the genetic mutation. Wei said it must be linked to the specific environment of the Qinling Mountains, which has a different climate than Sichuan. The genetic mutation does not appear to have been the result of inbreeding, as was once suspected, he said.
“It is more likely to be the result of natural variation rather than inbreeding. Our kinship analysis shows 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 coloring did not appear to be the result of inbreeding. Wang, who studied brown pandas, was not involved in the study.
“For those who are concerned about this species, this is a positive development,” said Wang, who said he had worked as a park ranger in the mountains for 10 years.
Wang said he praised the team “for their great efforts in trying to shed light on this scientific question.”
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