February 19, 2015

Geneticists at the University of Michigan have discovered that penguins have lost the ability to taste sweet foods and, in fact, can barely taste any of the fish and seafood that makes up their diet in the wild. The scientists examined genes that regulate the sensation of taste among five different species of penguins from the Southern Hemisphere: Adélie, chinstrap, emperor, king, and rockhopper penguins. Most vertebrates (animals with backbones) can detect five distinct tastes: sweet, sour,  bitter, salty, and a meaty flavor called umami. But the Michigan scientists found that penguins can only detect salty and bitter flavors. Their findings were published this week in the journal Current Biology.

Scientists have discovered that penguins, such as these Emperor penguins, have lost the ability to taste certain types of foods. (Credit: © Shutterstock)

In all five penguin species, the scientists found that the genes that regulate the taste sensation of sweet and bitter were either broken or missing, meaning the penguins could not detect those flavors. They suspect the genes became nonfunctional millions of years ago. Surprisingly, they found that genes related to sensing umami were also not functional in all five species. Since umami is the dominant flavor in the taste profile of protein-rich foods, the scientists concluded that penguins cannot taste the fish and other seafoods they eat.

Taste is an important sense by which human beings and animals detect many chemicals in their environment. Many animals depend on their taste buds, located on the tongue, to find foods that are edible and avoid poisonous ones. Many carbohydrates, a good source of energy, taste sweet, while many poisonous substances are bitter. Most animals, including human beings, will readily accept sweet foods and reject bitter foods. The sensation of umami is caused by a chemical called glutamate. Glutamate is found in many protein-rich foods.

Scientists believe that penguins have little use for detecting sweet flavors, since fish, their main source of food, are mostly protein with little carbohydrate. Any long-ago mutation that disabled genes involving the detection of sweet tastes would not cause problems. The scientists were more puzzled by the lack of genes to detect umami. But, they observed that the penguin’s tongue is dotted with sharp protrusions. These may limit the number of taste buds, but they are useful for gripping fish, which the penguins quickly swallow whole without chewing. Since they do not chew their food, tasting it may not be that important. Other scientists suspect that other senses, especially vision and smell, may be more important for penguins in finding and identifying their favorite foods.

Tags: penguins, taste