Bear
necessities: low metabolism lets pandas survive on bamboo
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[July 10, 2015]
By Will Dunham
WASHINGTON (Reuters) - Giant pandas eat
vegetables even though their bodies are better equipped to eat meat. So
how do these black-and-white bears from the remote, misty mountains of
central China survive on a diet almost exclusively of a low-nutrient
food like bamboo?
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Scientists on Thursday provided an answer. They found that the
giant panda is downright miserly in the amount of energy it expends
on a daily basis - a level similar to that of the famously sluggish
three-toed sloth - thanks to low levels of physical activity and low
levels of thyroid hormones.
The critically endangered panda is the only one of the world's eight
bear species with a vegetarian diet. Pandas, whose ancestors were
carnivores, possess a digestive system that evolved to handle a meat
diet even though bamboo now makes up about 99 percent of their food.
Bamboo is tough to digest and the pandas must devour lots of it to
survive.
The researchers studied three wild pandas at Foping Nature Reserve
in Shaanxi province and five captive pandas at the Beijing Zoo. They
found that the daily energy expenditure of these bears was only
about 38 percent of other similar-sized animals.
![](http://archives.lincolndailynews.com/2012/Jun/18/images/ads/current/ldn_sda_062409.png) A key to the panda's remarkably low metabolism is the fact that it
boasts extremely low levels of thyroid hormones, most likely due to
a mutation in a gene called DUOX2 involved in thyroid hormone
synthesis, the researchers said. The thyroid gland controls
metabolic processes including energy use.
"Giant pandas achieved this low metabolism through a suite of
morphological, behavioral, physiological and genetic adaptations
during their long evolutionary history," said biologist Fuwen Wei of
the Chinese Academy of Sciences' Institute of Zoology in Beijing,
who led the study published in the journal Science.
The researchers said the size of the panda's brain, liver and kidney
is relatively small compared to other bears.
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"These reduced organ sizes likely contribute to their low energy
demands," Wei said.
The researchers found that the wild pandas rested for more than half
of any given day and traveled only about 65 feet (20 meters) per
hour. With their low metabolism, the researchers said, the panda
needs its coat of thick fur to retain body heat in order to keep
warm.
There are only about 1,800 giant pandas left in the wild, according
to the World Wildlife Fund, citing Chinese government figures.
(Reporting by Will Dunham; Editing by Sandra Maler)
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