Penguins really have bad taste - they can't detect the savory taste of the fish they eat, and they also can't enjoy fruits or sugar. Penguins have lost their ability to taste everything else other than salty and sour.
Humans (and most vertebrates) have five basic tastes: sweet, sour, salty, bitter and umami. In case you're wondering about the last one, umami is the savory meaty taste. While the loss of taste is very intriguing, the loss of the umami taste is especially perplexing because penguins are fish eaters. Study leader Jianzhi "George" Zhang, a professor in the U-M Department of Ecology and Evolutionary Biology said:
"Penguins eat fish, so you would guess that they need the umami receptor genes, but for some reason they don't have them," says Jianzhi "George" Zhang of the University of Michigan. "These findings are surprising and puzzling, and we do not have a good explanation for them. But we have a few ideas."
This is highly unusual. While no birds can taste sweet, most are capable of perceiving umami and bitter notes - especially the carnivorous ones... but not penguins. Since the loss of taste appeared in all penguin species, it seems likely that the change was actually done by the penguins' ancestors.
“Taken together, our results strongly suggest that the umami and bitter tastes were lost in the common ancestor of all penguins,” write Huabin Zhao and colleagues.
It's not clear why this happens, but it likely has a lot to do with the extremely cold environments in which the penguins live. The taste receptors for sweet, umami, and bitter tastes are temperature sensitive - they don't really work well when it's extremely cold. So even if penguins had them, they wouldn't perform adequately, so they likely faded away in time. Also, penguins tend to swallow their food whole, so they likely don't care that much how it tastes like.
"Their behavior of swallowing food whole, and their tongue structure and function, suggest that penguins need no taste perception, although it is unclear whether these traits are a cause or a consequence of their major taste loss," Zhang says.
Penguin tongues are also strange from other points of view, the study observes. Some penguins lack taste buds altogether; the tongues are instead covered with stiff, sharp papillae covered by a thick, horny layer. The tongue has lost its tasting potential, but instead, it became better at catching and trapping prey.
- Huabin Zhao, Jianwen Li, Jianzhi Zhang. Molecular evidence for the loss of three basic tastes in penguins. Current Biology, 2015; 25 (4): R141 DOI:10.1016/j.cub.2015.01.026