A recent study led by University of Michigan shows that penguins lack three out of five basic tastes – sweet, bitter and savory, or umami taste. Researchers believe that somehow the birds were affected by a reduction in overall taste perception about 20 million years ago. The causes remain uncertain, but scientists have a hypothesis.
For their study, scientists sequenced the genome of several penguins to learn that important taste receptor genes were either missing or lacking functionality. The findings were a great surprise to everybody since no one had ever thought that a fish-eating animal may lack the umami, or meaty taste.
“Penguins eat fish, so you would guess that they need the umami receptor genes, but for some reason they don’t have them. These findings are surprising and puzzling, and we do not have a good explanation for them. But we have a few ideas,”
said Jianzhi Zhang, lead author of the study and researcher at the University of Michigan’s Department of Ecology and Evolutionary Biology.
The team speculates that the loss of the taste perception in penguins was triggered by the harsh climate-cooling events which had occurred many million years ago in the Antarctic.
Past studies had mapped the taste receptor genes in other vertebrates to reveal that they usually have all the five basic tastes: bitter, sweet, sour, salty, and umami. Scientists also learned that birds were poorer tasters than mammals.
Birds are deprived of several tastes because they have fewer taste buds on their tongues, and lack teeth to chew on their food. Previous genetic research revealed that all birds examined so far lacked the sweet receptor gene or it was non-functional.
Prof. Zhang started the study after one of his Chinese peers requested that he would help him learn whether penguins lack some of the taste genes, or an incomplete sequencing was to blame for this conclusion of a previous study on Adelie and emperor penguins.
Prof. Zhang and his team analyzed the data on Adelie and emperor penguins gathered by the Chinese researchers and compared it with fresh data collected from mapping the genomes of rockhopper, chinstrap, and king penguins, as well as of eight other closely related bird species.
The team found that all five penguin species lacked or had non-functional taste receptor genes for sweet, bitter, and umami tastes. In the Adelie and emperor species, the bitter and umami taste genes weren’t lacking, but had become “pseudo-genes,” i.e. genes that have lost the ability of encoding proteins.
Researchers believe that the main culprit may be the Trpm5 protein, which is needed to send the umami, bitter and sweet taste signals to the brain. Trpm5 is known for not working well in cold temperatures, so the team thinks that the protein may have been altered by the dramatic climate cooling in Antarctica 20 million years ago.
Image Source: Virtual Antarctica