Why penguins can't taste ice-cream: new study finds penguins' taste palate may be severely limited

Genetic researchers have found that penguins' taste palate may be severely limited to the point that they do not even have the receptor for their primary prey.

A University of Michigan-led study of penguin genetics has concluded that the flightless aquatic birds lost three of the five basic vertebrate tastes-sweet, bitter and the savory, meaty taste known as umami-more than 20 million years ago and never regained them.

Many other birds, such as chickens and finches, can't taste sweet things either. But they do have receptors for detecting bitter and umami (or meaty) flavors.

The study, led by Dr Huabin Zhao from Wuhan University, looked at the recently sequenced genomes of Adelie penguins (Pygoscelis adeliae) and emperor penguins (Aptenodytes forsteri) and 14 other bird species.

"Our results strongly suggest that the umami and bitter tastes were lost in the common ancestor of all penguins, whereas the sweet taste was lost earlier," explains study co-author Dr Jianzhi Zhang from the University of Michigan.

"Penguins eat fish, so you would guess that they need the umami receptor genes, but for some reason they don't have them."

Adding to the puzzle is that taste is a powerful indicator of whether a potential food item is good enough to eat.

"In general, a sour taste helps detect spoiled food and bitter taste helps detect toxic food," Zhang says. "Presumably, penguins cannot use taste to detect toxins ... but we don't know if penguins have other means of detecting toxins."

A protein known as Trpm5, essential for the recognition of sweet and bitter tastes, along with umami, functions poorly in cold temperatures, possibly leading to the changes seen in penguins. Future research will examine how well Trpm5 functions at temperatures similar to those experienced by penguins in the wild.

Analysis of the sense of taste in penguins was detailed in the journal Current Biology.