The bitter and umami tastes were lost in the common ancestor of all penguins
Penguins love eating fish, but can’t taste them. A new study conducted by scientists in China and the U.S. reveals that penguins lost three of the five basic tastes more than 23 million years ago. The flightless birds have failed to regain them. Vertebrates possess five basic tastes: sweet, salty, bitter, sour, and the savory meaty taste called umami.
Some taste genes in penguins have turned into pseudogenes
A genetic study led by scientists at the University of Michigan suggests that penguins do not have the ability to taste sweet, bitter and umami. Jianzhi Zhang, the lead author of the study, said that the loss of umami taste was “perplexing” because penguins are fish eaters. Penguins love eating fish, so researchers initially believed that the birds need umami receptor genes. But they don’t have them.
Taste is important for survival in most animals, but they may not be important in the penguin. Zhang said they began studying the bird’s genetics after a colleague from a genomics institute in China sequenced genomes from emperor and Adelie penguins, but couldn’t find some of the taste genes. They sought Zhang’s help to determine whether the missing genes were a true evolutionary deletion or a result of incomplete sequencing.
In addition, researchers analyzed bird tissue samples (rockhopper, chinstrap, king penguins, and eight other non-penguin bird species). They further studied 14 other non-penguin bird species. They were surprised to find that all penguin species lacked receptor genes for sweet, bitter and umami tastes. In emperor and Adelie genomes, bitter and umami taste receptor genes have become “pseudo-genes,” that lack the ability to encode proteins.
How penguins lost their taste receptor genes
The genomes of all non-penguin species had genes for the bitter and umami tastes. But, as expected, lacked receptor genes for the sweet taste. The results indicate that bitter and umami tastes were lost in the common ancestor of all penguins. And the receptor for the sweet taste was lost much earlier. Zhang suspects that the genes were lost during ancient climate cooling events in Antarctica, where penguins originated.
The cold Antarctica temperatures likely interfered with taste perception. Penguins originated about 60 million years ago after their separation from tubenose seabirds. Major penguin groups separated from each other about 23 million years ago. Zhang says the taste loss occurred during that 37-million-year span.
Findings of the study were published in the latest issue of the journal Current Biology.