Why giant pandas would rather chomp on bamboo than eat meat

By Stephen Beech

Giant pandas don't eat meat because chemicals in the bamboo they chomp on changing their tastes, suggests new research.

Despite having digestive systems typical of carnivores, the diet of the iconic species consists almost entirely of the leaves, stems and shoots of various types of bamboo.

Now a new study, published in the journal Frontiers in Veterinary Science, indicates that molecules found in bamboo may be behind their plant-based diet.

Chinese researchers found miRNA – tiny bamboo molecules – could enter giant pandas’ bloodstream and enable the adaptation to a bamboo-based diet.

Giant pandas have evolved several features, including "pseudo thumbs" to grasp bamboo and flat teeth that are well suited for crushing it, which make it possible for them to live off plants.

The research team explained that all living organisms have DNA, which stores the genetic information in a cell, and RNA, which carries and transfers that information.

MicroRNAs (miRNA) are small non-coding RNAs that play an important role in gene expression, the process of turning the information encoded in a gene into a function.

MiRNA from plants can be absorbed through food.

The Chinse team explored if plant-derived miRNA can enter giant pandas’ systems and regulate gene expression and thereby aid adaptation to a bamboo-based diet.

Study senior author Professor Feng Li, a researcher at China West Normal University, said: “We showed that plant-derived miRNAs are present in the blood of giant pandas.

“Our study proved that bamboo used as food for giant pandas does affect the change of giant pandas’ feeding habits.”

The research team took blood samples from seven giant pandas: three adult females, three adult males, and one juvenile female. In those samples, they found 57 miRNAs that were likely derived from bamboo.

Li said: “MiRNA in bamboo can enter giant pandas’ bodies through diet, be absorbed by the intestine, enter the blood circulation, and then regulate when the giant panda’s RNA transfers information, thus playing a role in regulating the gene expression of giant pandas."

The researchers explained that the plant-derived miRNAs can regulate different physiological processes, including growth and development, biological rhythms, behavior, and immune responses.

Li said: “MiRNA in bamboo is also involved in the regulation of smell, taste, and dopamine pathways of giant pandas, all of which are related to their feeding habits."

The research team believes that as pandas eat more bamboo as they grow, certain miRNAs accumulate, modulate gene expression, and aid in the adaptation to the taste of bamboo.

They say the miRNAs might also influence giant pandas’ sense of smell and enable them to pick out the freshest and most nutritious pieces of bamboo plants.

Li believes miRNAs from bamboo may also enable the adaption of giant pandas from a meat- to a plant-based diet.

The researchers also found that pandas of different ages and sexes had different miRNA compositions in their blood.

Li said: “Only miRNAs that can specifically play a role in regulating gene expression can remain in the body, and those that do not play a role will be expelled."

For example, he said some miRNAs regulate reproductive processes and so can only be found in the blood of pandas of a certain sex or age.

Li believes the fact that miRNA could transmit signals from plants to animals, may open doors for studying the treatment and prevention of animal diseases.

He said: “Plant miRNAs may also participate in regulating the animal immune system, enhancing animals’ disease resistance."

The researchers believe that studying plant miRNA-induced changes could also help to assess and improve the safety of plant-based foods for animals and humans.

But they say, to draw definitive conclusions about the potential of miRNA in general and the effects it might have on giant pandas, more research is needed.

Li added: “The giant panda is a very precious national treasure in our country, and blood samples are not easy to get.

“If possible, we hope to collect blood samples of young pandas who have not yet eaten bamboo for research, and perhaps get more surprising results.”