How would you feel if you lost the ability to taste your favorite meal? An awful lot like a penguin, it turns out.
New evidence, published in Current Biology, shows that Adélie and emperor penguins penguins are able to recognize only two of the five basic tastes.
While decoding genomes of the two Antarctic penguin species, a research team led by University of Michigan professor Jianzhi Zhang found something rather surprising: some genes related to taste were missing. Ultimately, they found that three other penguin species – the rockhopper, the chinstrap, and the king penguins – also lacked functioning receptor genes for sweet, bitter, and umami tastes, and can taste only sour and salty flavors.
Vertebrate animals have five basic taste senses – sweet, sour, bitter, salty, and umami. The fifth and lesser-known of the basic tastes, umami, includes savory or "brothy" flavors found in cured meats, MSG, shitake mushrooms, and fish.
“Penguins eat fish, so you would guess that they need the umami receptor genes, but for some reason they don’t have them,” Dr. Zhang said in a statement. “These findings are surprising and puzzling, and we do not have a good explanation for them. But we have a few ideas.”
The protein responsible for sending sweet, umami and bitter taste signals to the nervous system is called Trpm5. In separate studies on mice, Trpm5 appeared to function poorly in cold temperatures. Zhang suggests that this protein could explain why, after 60 million years of evolution near the South Pole, natural selection did away with certain tastes in penguins.
Co-author Huabin Zhao is planning follow up experiments to determine how Trpm5 functions in the Antarctic seawater most penguins hunt in.
Most carnivorous animals retain the ability to taste umami, but since penguins swallow their food whole, the sense probably isn’t missed all that sorely.
"Their behavior of swallowing food whole, and their tongue structure and function, suggest that penguins need no taste perception,” Zhang said in a statement, “although it is unclear whether these traits are a cause or a consequence of their major taste loss.”