In a blind taste test, eight out of eight pandas agree - sugar is delicious. In a study published today scientists put the panda taste receptors to the test, to uncover whether they would notice the difference between plain water and the sweet stuff. "Generally speaking, animals that eat plants have a sweet taste receptor because that enables them to detect in plants sugars that are sources of calories," - says Professor Gary Beauchamp, director of the Monell Centre that carried out the research.
But unlike most herbivores, pandas stick to one plant - bamboo - which is notoriously low on sugar. So the researchers wondered whether like many carnivorous animals, including cats, pandas had lost their ability to detect sweetness. Since carnivores "don't eat plants (and therefore) don't contact sugars, there's no longer a pressure for them to maintain the sweet receptor function", Beauchamp says. But it turned out pandas, like other herbivores, still have a fine-tuned sweet tooth.
In this study, published online in PLOS ONE, eight giant pandas between three and 22 years of age were studied at the Shaanxi Wild Animal Rescue and Research Centre in China over a six-month period. When given two bowls of liquid, one sweetened and one not, the eight pandas universally slurped down the sugary brew. The researchers tested a variety of sugars, including fructose, glucose, sucrose, lactose, maltose, and galactose. In all cases, the sweet drink was preferred, and especially the ones with fructose and sucrose, which humans perceive as the sweetest. The scientists also used cellular analysis to show how pandas responded to sugars at a DNA level.
Using DNA collected from the giant pandas during routine health examinations, genes that code for the panda sweet taste receptor were isolated and then inserted into human host cells grown in culture. These cells responded vigorously to sugars but not to most artificial sweeteners. This step helped investigators confirm pandas have a functional sweet taste receptor that underlies their ability to detect and respond to sugars.
The researchers speculate pandas may hold on to working sweet receptor cells because, beyond the taste factor, they may be used in places like the pancreas and the gut to help with plant digestion. "This is the first study to address taste perception in the giant panda as it relates to feeding behaviour," - says lead author Dr Peihua Jiang, a molecular biologist at Monell. "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", - says Dr.
