Giant pandas spend most of their days chomping on bamboo, but a new study finds that they have a sweet tooth too.
The discovery, published in the latest PLoS ONE, explains why a baby giant panda at a U.S. zoo craves a certain sweet food.
"Pandas love sugar," study author Danelle Reed of the Monell Chemical Senses Center said in a press release. "Our results can explain why Bao Bao, the 6-month-old giant panda cub at the National Zoo in Washington, D.C., is apparently relishing sweet potato as a first food during weaning."
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For the study, Reed and her colleagues presented eight giant pandas with two bowls of liquid. One contained plain water, while the other contained a solution of water mixed with one of six different natural sugars: fructose, galactose, glucose, lactose, maltose and sucrose. Each sugar was presented at a low and a high concentration.
There is no doubt as to what the pandas like. They preferred all of the sugar solutions to plain water. This was especially evident for fructose and sucrose, as the animals quickly gulped down these sugary solutions within the respective five-minute test periods.
Another series of preference tests explored the pandas' responses to five artificial sweeteners. There was little to no preference for most artificial sweetener solutions, suggesting that giant pandas cannot taste, or do not strongly perceive, these compounds as being sweet.
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It could also be that the pandas perceived an "off taste" to the artificial sweeteners and went for the plain water instead.
Earlier DNA studies on giant pandas identified genes that code for the sweet taste receptor. These genes were isolated and then inserted into human host cells grown in culture. The cells responded vigorously to sugars, but not to most artificial sweeteners.
Giant pandas therefore have a fully operational sweet taste receptor. This is surprising, given that bamboo contains very small amounts of sugars and doesn't taste sweet to humans. Researchers had therefore previously considered that giant pandas, which are in the taxonomic order Carnivora, had lost their sweet taste perception.
That's what happened to wild cats, which must eat meat in order to survive. At some point during their evolution, they lost the ability to taste sweets. This is due to a genetic defect that deactivates the sweet taste receptor. It's why cat food companies don't market desserts for felines! Cats could care less.
Giant pandas, with their sweet tooth, could be more flexible than previously thought about their food choices. They might be able to transition to other food sources in different habitats.
As lead author Peihua Jiang, a molecular biologist at Montell, concluded: "This is the first study to address taste perception in the giant panda as it relates to feeding behavior. We hope to extend this research further to examine bitter taste perception. The results could have significant implications for the conservation of this endangered species as their natural habitats continue to be demolished."
Photo: Wikimedia Commons