Bamboo-eater seemingly has no genes for cellulose-digesting enzymes.
The complete genetic sequence of the giant panda has revealed that the iconic Chinese bear has all the genes required to digest meat — but not its staple food, bamboo.
The international team sequenced a three-year-old female panda called Jingjing, who was also a mascot of the 2008 Beijing Olympics, and found that she lacks any recognizable genes for cellulases — enzymes that break down the plant material cellulose. "The panda's bamboo diet may be dictated by its gut bacteria rather than by its own genetic composition," says Wang Jun, deputy director of the Beijing Genomics Institute in Shenzhen, Guangdong province, who led the sequencing project.
The researchers also discovered that the T1R1 gene, which encodes a key receptor for the savoury or 'umami' flavour of meat, has become an inactive 'pseudogene' due to two mutations. "This may explain why the panda diet is primarily herbivorous even though it is classified as a carnivore," says Wang.
The research, published in Nature1, shows that pandas have about 21,000 genes packed into 21 pairs of chromosomes, including one pair of sex chromosomes. Of all the mammals that have been sequenced, pandas are most similar to dogs — with 80% similarity — and are only 68% similar to humans.
But the bear's genome has undergone fewer genetic changes over time than those of dogs and humans, suggesting that it evolved more slowly. The panda is often regarded as a 'living fossil' because its ancestors are thought to have lived in China more than eight million years ago.
The study also shows pandas have a high degree of genetic diversity — about twice as much as humans. "This shows that the panda has a good chance of survival despite its small population size," says Wang.
"The study has laid the biological foundation to better understand pandas, and has the potential for improving conservation by controlling diseases and boosting reproduction of the species," says Jianguo Liu, a conservation biologist at Michigan State University in East Lansing, Missouri, who was not involved in the study.
But critics stress that protecting the panda's increasingly fragmented and shrinking habitat is a more pressing issue in their conservation. China is thought to be home to around 1,600 wild pandas — though the actual number is hotly debated. Another 300 or so live in captivity.
Some conservationists, such as Fan Zhiyong, director of the conservation group WWF's China species programme, believe that the panda genome will have little impact on conservation efforts. "Protecting pandas in the wild remains the top priority, but their habitats are becoming smaller and smaller," says Fan. "If we don't have any wild pandas one day, what can we do with their genes?"
Although China has set up several panda sanctuaries since the 1960s, economic development often takes precedence over conservation. Consequently, pandas' habitats are often invaded by construction projects such as dams and highways. Tourism is also a big threat because pandas are reclusive creatures. For example, Jiuzhaigou, a panda sanctuary in Sichuan, is visited by millions of tourists every year. "You don't see any pandas there anymore," says Fan. "This is hardly surprising."
There is "no doubt" that information from the genome and habitat protection are both crucial for conservation efforts, says Wang. The panda genome, the first in a string of sequencing efforts by the Shenzhen institute, will be a test of how such genetic information can help in the conservation of endangered species, he adds. The team has got a draft genome map of the polar bear, and has started sequencing the genome of the Tibetan antelope.
Li, R. et al. Nature doi:10.1038/nature08696 (2009).
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Qiu, J. Genome reveals panda's carnivorous side. Nature (2009). https://doi.org/10.1038/news.2009.1141