The findings suggest whereas global changes in climate were the primary drivers in panda population fluctuation for millions of years, human activities were likely to underlie population divergence and serious decline.
The latest study led by Institute of Zoology of Chinese Academy of Sciences and Beijing Genomics Institute (BGI) and published in Nature Genetics reveals a good example for assessing and establishing the best conservation method for other endangered species.
Looked upon as the ambassador for all endangered species, giant panda is a well-recognised symbol of international wildlife conservation.
The giant panda is currently threatened by continued habitat loss, human persecution, among others. Its dietary specialisation, habitat isolation, and reproductive constraints have led to a perception that this is a species at an "evolutionary dead end", destined for deterministic extinction in the modern world.
Researchers carried out whole genome re-sequencing of 34 wild giant pandas and found the current six geographic populations of giant panda could be divided into three genetic populations, including Qinling (QIN), Minshan (MIN) and Qionglai-Daxiangling-Xiaoxiangling-Liangshan (QXL).
They found several important evolutionary events such as two population expansions, two bottlenecks and two population divergences.
The giant panda has a very special bamboo diet, while its ancestor was omnivorous or carnivores. As early as about 3 million years ago, they probably had already completed their dietary swift and pygmy panda emerged with bamboo as its primary diet.
The warm and wet weather at that time provided ideal conditions for the spread of bamboo forests that further led to the first population expansion of giant panda.
However, about 0.7 million years ago, the panda population began to decline due to the two largest Pleistocene glaciations happened in China, and its first population bottleneck occurred at about 0.3 million years ago. During that period, pygmy panda was gradually replaced by another subspecies - baconi panda that has larger body size.
After the retreat of the Penultimate Glaciations, giant panda's second population expansion happened and it reached its population peak between 30 to 50 thousand years ago.
Researchers also 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.
