The joy of eating may be lost on the penguin, which, according to a new study, likely can’t taste its own food.
The report, published today in Current Biology, is the result of a genomic analysis suggesting that all penguin species lack functioning genes for the receptors of sweet, umami, and bitter tastes. The umami taste gives meat (like fish, the penguin’s primary food source) its savory qualities.
George Zhang at the University of Michigan led the research group, which located the genes for tasting bitter and umami flavors in 20 other kinds of birds (the gene for tasting sweet flavor is lacking in all bird species). But in the five penguin genomes they looked at, including Adélie and emperor penguins, the genes were either faulty or missing. This similarity led the researchers to believe that penguins lost these genes long ago in a common ancestor. And since penguins originated in Antarctica, penguins elsewhere shouldn’t have the capacity to taste sweet, umami, or bitter things, either.
Genes for the remaining two taste receptors—sour and salty—are still present in penguins’ DNA, but this doesn’t necessarily mean that they can taste all things sour and salty. The overall findings are preliminary and purely genetic, too, and will require further testing.
The researchers propose that the frigid Antarctic weather may have contributed to penguins’ gradual loss of taste, since taste receptors don’t send signals to the brain properly in extremely cold climates.
Here’s Jacob Kastrenakes, writing for The Verge:
Prior research has shown that the tongue’s receptor channels, which are what react to tastes, function poorly at lower temperatures when it comes to detecting sweet, bitter, and umami. The Michigan researchers speculate that the environment may have been so cold that this receptor was “effectively non-functional” in penguins’ ancestors. “Those three tastes … would not be useful any more because the channel is not functioning,” Zhang says. “So gradually mutations would accumulate in those genes and eventually they would become lost.”
Some experts say that beyond the cold weather hypothesis, penguins’ loss of certain taste receptors isn’t too surprising from an evolutionary standpoint. Their tongues are typically used to capture prey, and they’re able to swallow fish without chewing—so taste perception doesn’t seem necessary for survival. Still, the researchers don’t know if these behavioral traits are a cause or consequence of the absence of certain taste genes.
Either way, the study points to the way environment influences taste.
“It makes sense that different or extreme habitats can alter taste genes over time,” said John McQuaid, journalist and author of “Tasty: The Art and Science of What We Eat,” in an email to NOVA Next. “But the relationship between environment and taste is more complex than that—a lot more so than most scientists thought even a few years ago.
“The new wrinkle,” he wrote, “is that taste receptors are found all over the body, where many of the functions they perform are unknown. So what happens in the gut or the lungs, for instance, may also influence the taste receptors there and everywhere in the body—and with that taste genes and perceptions, over time.”