December 17, 2012
Genetic Research Uncovers Population History Of Giant Panda
redOrbit Staff & Wire Reports - Your Universe Online
By re-sequencing the genomes of nearly three dozen wild giant pandas, a team of Chinese scientists say that they have managed to construct a complete, continuous history of this rarest member of the bear family, from its origins to the current day.
The researchers, who were led by the Institute of Zoology at the Chinese Academy of Sciences (CAS) and the genome sequencing center BGI, completed whole genome re-sequencing of 34 members of the species. They discovered that the six modern-day geographic giant panda populations could be divided into three genetic populations: Qinling (QIN), Minshan (MIN), and Qionglai-Daxiangling-Xiaoxiangling-Liangshan (QXL).
"We have identified three genetic populations of giant panda for the current six geographic populations lived in western of China," Shancen Zhao, Project Manager from BGI, said in a statement on Sunday. Those three populations emerged after the giant pandas were impacted by several key evolutionary events over the years, including a pair of population expansions, two bottlenecks, and two population divergences, the researchers explained.
While the pandas we know today thrive on a diet of bamboo, their ancestors were omnivores or carnivores, with bamboo becoming the primary source of culinary sustenance for the creatures about three million years ago. It was then that the giant panda experienced its first population explosion, thanks largely to the warm and wet weather conditions that made bamboo more and more prevalent, the researchers said.
About 700,000 years ago, the population experienced a decline due to two Pleistocene glaciations in China. Following the retreat of those glaciations, the second population explosion occurred, with the bear species reaching their peak population between 30,000 to 50,000 years ago, the scientists explained.
More recently, the giant panda split into Qinling and non-Qinling populations about 300,000 years ago, and the non-Qinling split into the MIN and QXL populations approximately 2,800 years ago.
"Researchers identified the signals of panda's local adaptation. They found the largest group of selected genes in these populations was related to sensory system. However, the two genes, Tas2r49 and Tas2r3, were associated with bitter taste and were under directional selection between the QIN and non-QIN populations, showing no signal of directional selection between MIN and QXL populations," BGI representatives said.
"As a form of olfactory communication, odor perception is crucial for reproduction and survival of giant pandas in the dense forest. Researchers found the MIN and QXL populations had fewer directionally selected genes than QIN and non-QIN, suggesting less variation happens in the selection processes between MIN and QXL," they added. "They also found the evidence that population fluctuations were driven by global climate shifts, but recent human activities have likely caused population divergence and the serious recent decline."
Results of the study were recently published in Nature Genetics.