Penguins Fishing

P-p-p-poor penguins. It turns out that they are unable not only to fly but also to taste very much either. And they certainly wouldn’t be able to enjoy their eponymous chocolate biscuits

New research suggests that penguins don’t have three of the five basic tastes and for them food comes in only two flavours: salty and sour.

The team of scientists from the University of Michigan who made the discovery admits they are puzzled by the findings, which were published in Current Biology.

Most birds can’t taste sweet foods, although there are a few notable exceptions such as hummingbirds, but they can detect bitter and umami flavours.

Penguins, however, can’t enjoy or even detect the savoury taste of fish, squid and crustaceans that make up the bulk of their diet.

Jianzhi "George" Zhang a professor in the Department of Ecology and Evolutionary Biology who led the study said, “These findings are surprising and puzzling, and we do not have a good explanation for them. But we have a few ideas."

It was Zhang's colleagues at the Beijing Genomics Institute who prompted him to make the discovery after they realized they were unable to find some of the taste genes in the newly sequenced genomes of Adelie and emperor penguins.

Zhang took a closer look at penguin DNA to find that all species lack the functional genes for the receptors of sweet, umami, and bitter tastes.

And unlike many genes which have been lost over evolutionary time because they weren’t useful, Zhang thinks that the taste receptors in penguins may have been lost because of the extremely cold environments in which penguins originated from.

Although some penguins have made their homes in warmer environments they can all trace their roots back to Antarctica after they separated from tubenose seabirds, which include albatrosses, shearwaters and petrels, about 60 million years ago.

Unlike receptors for sour and salty, the taste receptors required for detecting sweet, umami, and bitter tastes are temperature sensitive and they don’t work when they get really cold.

This is the reason ice cream appears to get sweeter as it gets warmer. While frozen ice cream is delicious, as it melts it becomes sickly sweet and unpleasant. It’s also the reason we order a cold beer because as beer gets warmer it tastes more bitter.

What this means is that even if penguins had taste receptors for sweet, umami and bitter tastes they wouldn’t be much use to them anyway.

Previous anatomical studies have also suggested that some penguins lack taste buds altogether. Instead, stiff, sharp papillae cover their tongues with a thick, horny layer on top. It seems that penguins use their tongues not so much to taste food but to catch and hold onto it.

Penguins also tend to swallow their food whole, which might mean they aren’t that concerned about what their food tastes like.

But Zhang questions whether this is the right way of thinking.

He says, "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.”

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