In an ongoing attempt to boost the dwindling number of pandas on the planet (currently tallying just under 2,000), scientists have discovered what appears to be a physiological roadblock to the bear's good health: they possess the wrong type of gut.
The daily life of a panda is fairly mundane. They spend about 14 hours each day feeding, the rest of their time sleeping, with a bit of time set aside for the occasional copulation. But researchers at the Chengdu Research Base of Giant Panda Breeding in China may have figured out why the bears lead such a monotonous existence. It turns out these giant herbivores never evolved the digestive system to support such roughage. Instead, their gut biota is more akin to a carnivore.
"Unlike other plant-eating animals that have successfully evolved anatomically-specialized digestive systems to efficiently deconstruct fibrous plant matter, the giant panda still retains a gastrointestinal tract typical of carnivores," said Zhihe Zhang, director of the Research Base and lead author of the paper that appears in the American Society for Microbiology journal, mBio. "The animals also do not have the genes for plant-digesting enzymes in their own genome. This combined scenario may have increased their risk for extinction."
To explore the digestive biome of the panda, researchers collected 121 fecal samples from 45 giant pandas living at the Research Base. They sequenced the bacteria from the samples and discovered that normal plant-digesting bacteria, such as Ruminococcaceae and Bacteriodes, were absent. Instead, the bears' guts were dominated by bacteria normally found in the guts of carnivores, such as Escherichia/Shigella and Streptococcus.
"This result is unexpected and quite interesting, because it implies the giant panda's gut microbiota may not have well adapted to its unique diet, and places pandas at an evolutionary dilemma," said Xiaoyan Pang, of Shanghai Jiao Tong University and a co-author of the new study.
Giant pandas began their evolutionary journey as omnivorous bears. They switched to the bamboo-exclusive diet around two million years ago, but somehow their guts never got the memo, for they have not only retained the gut flora of a carnivore, but they also retained the simple stomach and short intestines common to their meat-eating ancestors.
Researchers now believe that this mismatch in gut apparatus may explain why so little of the bamboo is actually digested. Although a giant panda will consume around 30 pounds of stems and leaves each day, they only digest a paltry 17% of it. Which may also explain why they are forced to sleep the remainder of the day, to conserve their precious energy.
The scientists at Research Base hope this new insight into the panda's gut flora will help resolve some of the digestive issues they suffer from in captivity - a type of colic that causes stomach cramps and malaise.
Iain Valentine, Director of Giant Pandas at Edinburgh Zoo where the colic research is being conducted, described the findings as "hugely interesting and an important piece of the panda's evolutionary jigsaw."
"The upside is they've got a digestive system that deals with very large volumes of material very quickly," Valentine says. "You have to remember there aren't many predators around so they've got the time on their hands to sit around eating all day."