Not everything in life is always black and white. Neither are giant pandas.
For years, scientists — and the public — in China have been fascinated by Qizai, the only brown-and-white panda in captivity. Found abandoned in the wild, he lives at Louguantai Wild Animal Breeding and Protection Center in Xi’An. Only seven brown-and-white pandas have ever been documented — all from Qinling, a mountain range in the Chinese province of Shaanxi.
Now, a team of researchers has found out why the 14-year-old male bear has such unusual fur, with the findings also likely to apply to wild brown pandas.
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The brown pandas are missing a short sequence of DNA in Bace2, a pigmentation-related gene, according to a study published today by the Proceedings of the National Academy of Sciences.
Bears in brown
Qinling pandas are “rather different” from those in Sichuan — the province that most giant pandas (Ailuropoda melanoleuca) inhabit — according to Hu Yibo, a co-author of the paper.
“Previous studies suggested that Qinling pandas may have been separated from Sichuan pandas around 300,000 years ago,” says Hu, a conservation geneticist at the Institute of Zoology at the Chinese Academy of Sciences (CAS) in Beijing.
Hu and his colleagues studied the genomic information of three ‘family trios’ — a pair of panda parents and their cub — associated with two brown pandas, along with the genomes of 29 other black-and-white pandas.
The trios were Qizai and his parents; Qizai, his mate and their cub; and Dandan — the first brown panda to be documented in China, nearly four decades ago — her mate and their cub. Among them, only Qizai and the now-deceased Dandan are brown and white.
Missing information
The researchers believe that the brown pandas are homozygous for a particular version of Bace2 — that is, they have identical copies of the gene. Genetic sequencing confirmed that both copies of Bace2 in the brown bears were missing the same stretch of 25 base-pairs, the basic unit of a molecule of DNA or RNA. “This essentially means that the coding sequence for the protein is disrupted, which leads to a malfunction of the protein,” Hu explains.
Further genetic sequencing of 192 other black-and-white pandas in captivity showed that none was homozygous for this version of Bace2. In a lab experiment, mice genetically modified to have the mutation had light-coloured coats.
The team also found that when compared with the hairs of black pandas, the hairs of brown ones seem to have fewer and smaller melanosomes — organelles responsible for pigmentation of the hair and skin.
“The breakthrough of this paper is the finding that the missing of a gene or genetic segment could also lead to the change of colour,” says Shi Peng, an evolutionary geneticist at the CAS Kunming Institute of Zoology. “From a genetics perspective, this is a brand-new discovery.”
Hu and his colleagues plan now to investigate how the 25-base-pair deletion leads to changes in the size and number of melanosomes in brown pandas.
This article is reproduced with permission and was first published on March 4, 2024.