An analysis of giant panda poop has revealed that when the bears switch to a leafy, less fibrous diet, they slough off the lining of their gastrointestinal tract. It then passes through their digestive system and comes out as a gooey mass. The findings, published in Frontiers in Microbiology this month, may help explain why these endangered animals are struggling to reproduce.
Recent work revealed that the digestive systems of giant pandas (Ailuropoda melanoleuca) resemble that of carnivores and omnivorous bears – even though their transition to a vegetarian diet happened some 2 million years ago. Their gut and gut microbes are built for breaking down meat and small amounts of plant matter, yet pandas eat up to a third of their body weight in bamboo every day.
A team led by Garret Suen from the University of Wisconsin-Madison and Ashli Brown of Mississippi State studied two giant pandas living at the Memphis Zoological Society in Tennessee: a female named YaYa and a male named LeLe (pictured above). The team observed the pandas’ bamboo consumption behavior, and they collected fresh feces (pictured to the right) as well as samples of mucous excretion.
Pandas undergo dramatic seasonal shifts in diet: Most of the time, they eat bamboo stalks, but in August and September, they shift to leaves. Shortly after this summertime shift from woody stalks to less fibrous leaves, the pandas experience episodes of gastrointestinal tract distress, with symptoms ranging from abdominal pain to the excretion of mucous stools containing gelatinous pellets called mucoids. And the pandas stop eating.
After sequencing DNA extracted from stool samples, the team found that microbial diversity is lower in samples collected immediately before mucoid episodes than in the mucoids. Additionally, mucoids contain microbes that are typically found in the gut lining. Together, these findings suggest that mucoids are the expulsion of the internal mucus lining driven by changes in diet.
“What we think might be happening is that their diet is causing a strong internal reaction, leading to an inflammatory response,” Suen explained in a statement. “Pandas are basically shedding their gastrointestinal lining to allow for the replacement of those microbes. It’s kind of like resetting the microbiome.”
The researchers aren’t sure why pandas experience this resetting, and furthermore, this summer shift in food – and the sickness that follows – coincides with the beginning of panda pregnancies. Mucoids are more prevalent following breeding season, and the reduction in nutrition may affect gestation, lactation, and cub development.
Image in the text: Fecal sample from a giant panda, showing a mix of bamboo stalk and leaves. Candace Williams