Mei Xiang, female giant panda, Smithsonian's National Zoological Park.
Credit: Smithsonian National Zoo
Bamboo isn't the only food pandas crave — the furry giants also have a sweet tooth, a new study finds.
Studies of panda behavior and genetics suggest that pandas not only have taste receptors for sweet foods, but also show a strong preference for natural sweeteners such as fructose and sucrose.
"Pandas love sugar,"study leader Danielle Reed, a behavioral geneticist at the Monell Chemical Senses Center in Philadelphia, said in a statement. "Our results can explain why Bao Bao, the 6-month-old giant-panda cub at theNational Zoo in Washington, D.C., is apparently relishing sweet potato as a first food during weaning." [Baby Panda Pics: See a Cub Growing Up]
Giant pandas feed almost exclusively on bamboo, a plant that contains very little sugar and doesn't taste sweet to humans. Pandas belong to the same order as cats, which have lost the ability to taste sweet foods because of a genetic mutation that turns off sweet-taste receptors.
Reed and her team wondered if pandas, like their distant relatives cats, had also lost this ability.
To find out, the team studied eight 3- to 22-year-old giant pandas at the Shaanxi Wild Animal Rescue and Research Center in China for six months. They gave the animals two bowls of liquid: one that contained water, and one that contained water with one of six natural sugars (fructose, galactose, glucose, lactose, maltose and sucrose), at a low or a high concentration.
The pandas clearly preferred the sugar water to regular water, especially the fructose and sucrose solutions. "The animals avidly consumed a full liter of these sugary solutions within the respective five-minute test periods," according to the researchers.
The researchers also tested whether the pandas preferred the diet version — water flavored with artificial sweeteners — but the bears didn't seem as keen on it, suggesting they may not be able to taste these sweeteners, or at least not very well, the researchers said.
Meanwhile, scientists confirmed that pandas do, in fact, have sweet-taste receptors. They isolated genes for these receptors from DNA collected from pandas during routine health exams and inserted the genes into human host cells grown in a lab. The cells showed a strong response to sugars, but not to most artificial sweeteners.
"This is the first study to address taste perception in the giant panda as it relates to feeding behavior," study researcher Peihua Jiang, a molecular biologist at Monell, said in a statement. The researchers also hope to test whether pandas can taste bitter flavors.
"The results could have significant implications for the conservation of this endangered species as their natural habitats continue to be demolished," Jiang said.
The research, which is part of a long-term project to understand how taste-receptor genes influence food preferences and diet, was detailed today (March 26) in the journal PLOS ONE.