The emperor penguin chases its prey through nearly freezing waters. Once it locates food, usually a fish or squid, it catches the animal in its powerful jaws and devours it.
But after all that work, the penguin can't actually taste the savory flavor of its meal.
Researcher Jianzhi Zhang, a molecular and genomic evolution professor at the University of Michigan, recently examined the emperor penguin's genome. But he says he couldn't find the bird's genes to taste umami, the savory flavor of meat or fish.
"We took a closer look and were able to confirm that those genes were truly lost," Zhang tells The Salt. So he tried another penguin species, and noticed serious mutations preventing the genes from functioning normally.
All in all, Zhang and his colleagues tested five species that represent all the lineages of penguin. Not one has the ability to taste the savoriness of its marine meals, the researchers report in the journal Current Biology.
Researchers started linking genes to tastes about 15 years ago. The thinking is that each taste has an evolutionary reason — each taste signals something to the eater. For example, bitterness indicates a toxin in the food. Herbivores tend to have a lot of bitter taste receptors, because they needed to be able to detect poisonous plants. Most vertebrate species can taste sourness, which indicates the food may be spoiled or rancid.
Researchers are still debating why an animal needs to taste umami, but Zhang says they think it has something to do with assessing the nutritional value of the food. The stronger the umami flavor, the more nutrient-dense the food is.
But depending on what an animal eats, some species lose the ability to taste certain foods. As Zhang explains, the giant panda used to be a carnivore, but a few million years ago, it switched over to bamboo. Around that time, the giant panda's umami-sensing genes developed serious mutations. The changes in the genome line up with the changes in panda teeth fossils, which lose their sharpness and become better suited for gnashing plants.
But that's obviously not the case with penguins, who live off of savory food. So what gives? Zhang has a few hypotheses for why the penguins lost their umami genes while other birds species got to keep theirs.
First, one of the umami genes doesn't work as well at cold temperatures. Even though the emperor penguin's body remains at a toasty 39 degrees Celsius, its mouth can get pretty cold in Antarctica.
"It's about zero degrees when you eat cold fish," says Zhang, so even if the penguins had a functional gene, it might not work when they needed it.
Plus, penguins have extremely spiky tongues — better for holding slippery fish than tasting them. One study showed that four species of penguin don't even have taste buds.
By the way, most birds, penguins included, are already missing two of the five tastes: bitter and sweet. That leaves penguins with just two options — sour and salty — for dinner.
Nonetheless, the penguin seems to be managing just fine. Zhang thinks that penguins don't need to taste their food to know it's nutritious, because they watch it swim moments before eating it. And it's unlikely that they will start tasting umami any time soon.
"It's not easy to gain those genes," he tells The Salt. Taste started evolving some 500 million years ago, so even if an animal were to evolve a new way to taste, "it will take a very long time, and it will look completely different."