Feeding on nothing but fibrous bamboo, the giant panda manages to maintain a lusciously plump figure year-round, even in the off-season when there are only nutrient-poor leaves to munch on.
Publishing in Cell Reports, researchers can now reveal that the secret to stable chub lies in the panda’s gut. The study details the adaptable nature of this internal microbiome, showing how shifts in the composition of gut bacteria help pandas to lay down extra fat stores when highly nutritious bamboo shoots begin to emerge, preparing their bodies to make it through the lean seasons when only adult leaves remain.
“We’ve known for a long time that these pandas have a different set of gut microbiota during the shoot-eating season, and it’s very obvious that they are chubbier during this time of the year,” says first author Guangping Huang, at the Institute of Zoology, Chinese Academy of Sciences.
Though the link has previously been suspected, the study is the first to establish a causal pathway between these two observations, demonstrating a direct relationship between a panda’s gut microbiota and its phenotype.
The team, led by Fuwen Wei, has been studying wild giant pandas living in the Qinling Mountains in central China for decades. Throughout most of the year, these animals feed on fibrous bamboo leaves. It is only during late spring and early summer that they get to enjoy newly sprouted bamboo shoots that are rich in protein.
Wei says that these wild pandas have a significantly higher level of a bacterium called Clostridium butyricum in their gut during the shoot-eating season compared with during the leaf-eating season. To investigate whether the change in gut microbiota could affect a panda’s metabolism, the team performed a faecal transplant. Panda faeces were collected in the wild during both shoot-eating and leaf-eating season and transplanted to germ-free mice, before putting them on a simulated panda diet of bamboo.
They found that mice transplanted with panda faeces collected during shoot-eating season gained significantly more weight and had more fat than mice transplanted with faeces from leaf-eating season, despite consuming the same amount of food.
Further analysis completed the causal link. The elevated levels of C. butyricum associated with shoot-eating season resulted in a metabolic product known to upregulate the expression of a circadian rhythm gene, increasing lipid synthesis and storage. The seasonal changes of the gut microbiota of pandas help them to synchronise their lipid metabolism to the availability of nutrients.
As well as revealing the secrets to maintaining a fat-bear week winning figure when things are looking scarce, the team are excited about the possibilities offered by their innovative mouse-gut proxy.
“For endangered and vulnerable wild animals, we can’t really run tests on them directly. Our research created a mouse model for future faecal transplant experiments that can help study wild animals’ gut microbiota,” Huang says.
Next, the team plans to map out more microorganisms in the panda’s gut and find out about their roles in affecting the animal’s health.
“Causal research of host phenotype and gut microbiota in wild animals is just beginning. Identifying what bacteria are beneficial for animals is very important, because one day we may be able to treat some diseases with probiotics,” Huang says.