The giant panda is undoubtedly one of the most recognizable and adored species in the world due to its distinctive black and white coloring. However, there are a handful of giant pandas that aren't black and white in color. These majestic creatures with brown and white fur live in a mountain range in China. Scientists have found the possible explanation.
White-brown panda bear PHOTO Twitter
The work, which involved studying the genetics of several pandas in the wild and in captivity, suggested that the bears with brown and white fur are the result of natural variation rather than a sign of inbreeding in a declining population, CNN notes.
The first brown panda known to science was a female named Dandan. A local resident found the sick bear in the Qinling Mountains of Shaanxi Province in March 1985. The specimen was kept in captivity until its death in 2000.
Since Dandan's discovery decades ago, 11 other sightings have been reported, documented through official news sources or personal accounts shared with the authors of this latest study, which appeared in the journal PNAS on March 4.
“Athis trait can be inherited. However, to date, the genetic basis underlying brown and white fur color remains unclear.”the authors wrote.
Gaining a better understanding of the distinctive coloration could help efforts to breed the species in captivity, said lead author Dr. Fuwen Wei, a professor of ecology and wildlife conservation biology at the Institute of Zoology of the Chinese Academy of Sciences in Beijing.
Currently, the giant panda is considered a vulnerable species, according to the International Union for Conservation of Nature, being on the Red List of Threatened Species.
An example of a family tree of a brown-white panda
To understand what's behind the trait, 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.
Compared under a microscope to hair samples from three black and white pandas, Qizai's brown fur had fewer and smaller melanosomes, tiny structures found in cells that are responsible for skin and hair pigment in mammals. What's more, melanosomes were more likely to be irregularly shaped, the study team found.
The researchers then collected genetic information about Qizai and created his family tree. They discovered the identity of his 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 a wider panda populations.)
Scientists studied genetic information from Qizai's family members and compared it with genetic information from 12 black-and-white pandas in the Qinling Mountains and 17 black-and-white pandas from other regions of China, using information taken from blood samples and excrement.
Although none of Qizai's immediate family members had brown fur, the researchers were able to show that his parents and son all had one copy of the recessive trait on a gene known as Bace2, while Qizai had two children.
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 possess a copy of the genetic variant and pass it on for the trait to appear in offspring, as is the case with Qizai.
Genetic analysis solves an enigma
Thanks to the analysis of a tissue sample stored for more than two decades in ethanol, scientists were also able to sequence the genome of Dandan, the first known brown panda. Dandan had the same recessive trait, the researchers found.
The scientists then carried out a wider analysis of 192 black and white giant pandas to check the gene responsible as Bace2. The mutation that causes the brown color was only present in two pandas in the Qinling Mountains of Shaanxi, not Sichuan province, where most of China's giant pandas live.
To confirm the findings, 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 change reduced the number and size of melanosomes in the mice.
“The fur color of the knockout mice is light brown”said Wei, who is also president of Jiangxi Agricultural University in Nanchang, China's Jiangxi Province.
“It demonstrates that this deletion has the potential to alter the coat color of a mouse, as the pigmentation pathway is relatively conserved (shared) between mammals. Therefore, it is very likely that this mutation influences the color of a brown panda's fur.”
Natural variation vs. inbreeding
It is not clear what exactly 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 does not appear to be a result of inbreeding, as once suspected, he said.
“It 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”Wei added.
Tiejun Wang, an associate professor in the department of natural resources at the University of Twente in the Netherlands, said it was good news that this unique coloration 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 the species, this is a positive development,” said Wang, who said he worked as a forester for 10 years.
Wang said he applauded the team “for their extraordinary efforts in trying to shed light on this scientific question”.
