Giant pandas, the "teddy bears of the wild," are notorious for being bamboo munchers. This specialist diet is perplexing because the panda gut is poorly adapted to digesting bamboo, and it is so low in nutritional value that pandas basically need to omnomnom all day long. You might think that it would be tough for a panda to get on with daily life on this low energy diet, but researchers have started to figure out how the animal has adapted to cope with its bamboo grub.
Researchers from the University of Aberdeen and Beijing Zoo in China have published a paper in Science, identifying some of the giant pandas' energy-saving traits. They measured the giant panda's average daily energy expenditure (DEE) to be roughly 38% of that of other mammals with the same body mass. For example, giant pandas have a much lower DEE than other bears, and it is also substantially lower than that of koalas. In fact, their DEE is more comparable to that of the three-toed sloth.
This information came from a study of eight pandas: five of them were captive and three of them were wild. Radio collars with GPS and accelerometers monitored the wild pandas and sent information about their activity back to the researchers. The pandas' movements were split into four categories: lying and sitting (inactive) and eating and "other activities" (active). The researchers weighed and observed the amount of bamboo that the pandas ate, and then collected and measured the pandas' feces and urine to measure their energy expenditure.
They also investigated their internal architecture, which revealed that the panda's body has adapted to this low-energy lifestyle: its brain, liver, and kidneys are smaller than those of other bears, so they require less energy to operate. Pandas also have lower thyroid hormone levels compared with other bears. In fact, the giant panda's thyroid hormone levels are comparable to those of a hibernating black bear, which lower their thyroid levels to preserve energy while they sleep for the winter.
The researchers also compared the genome of the giant panda to the genomes of other mammals in order to ascertain the extent to which their genes are responsible for their low-energy adaptations. They identified that pandas have their own variant of the DUOX2 gene found in humans. In mankind, the absence of the DUOX2 gene is associated with an underactive thyroid, the gland that controls the body's metabolism. The modified gene is having an effect on pandas that is comparable to the gene's absence in humans.
Fortunately for the panda, its body has adapted to a life of low-energy bamboo. To see the panda's sedate way of life in action, check out this video. You know. For science.