Pandas need to be lazy to survive

Chuck Bednar for – @BednarChuck

A team of researchers from the Chinese Academy of Sciences, the University of Aberdeen and the Beijing Zoo have solved the mystery of why giant pandas are able to survive even though they eat nothing but bamboo – it’s because, for all intents and purposes, they’re lazy.

To be more accurate, the creatures are able to sustain themselves on a diet of shoots and leaves because they expend extremely minute amounts of energy during the course of a day, according to BBC News reports published on Friday. In fact, the study authors found that pandas burn approximately 38 percent of the calories used by other animals of similar size.

Reporting in the July 10 edition of the journal Science, they explain that the average panda energy expenditure is around 5.2 megajoules per day, or just 37.7 percent of the expected 13.8 MJ/day for mammals. Among only wild pandas, the mean amount of calories consumed was 6.2 MJ/day, or 45 percent of the predicted value.

“Pandas achieve this exceptionally low expenditure in part by reduced sizes of several vital organs and low physical activity,” lead authors Yonggang Nie, John R. Speakman and Qi Wu wrote. “A combination of morphological, behavioral, physiological, and genetic adaptations, leading to low energy expenditure, likely enables giant pandas to survive on a bamboo diet.”

Low thyroid hormone levels play a key role

According to the researchers, the animals’ lack of energy expenditure was associated with low levels of the thyroid hormones thyroxine and triiodothyronine, which averaged 46.9 percent and 64 percent the amounts expected for mammals of similarly size, respectively. One reason for this may be a mutation unique to giant pandas in a gene essential to thyroid hormone synthesis.

The BBC explained pandas are only active 49 percent of the time, and when they were actually moving, they traveled only 20 meters per hour (just over 0.01 miles per hour). Pandas in captivity were even less active, getting up and moving only about one-third of the time that they were monitored, the British news agency added.

Speakman explained that while pandas “save a lot of energy by being frugal with the energy they spend on physical activity,” but their low activity isn’t the only thing that contributes to their low metabolism. Even the metabolic rate of an active panda is lower than stationary human.

“We found that their low metabolism is correlated with very low levels of thyroid hormones, which was linked to a genetic mutation in the thyroid hormone synthesis pathway that is unique to the panda,” he added. In fact, the hormone levels of a giant panda were said to be similar to those of hibernating black bears, and the creatures were also found to have brains, kidneys and livers that were relatively small in comparison to other bears, BBC News added.


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