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article imagePenguins love to eat fish, but they probably can't taste them

By Karen Graham     Feb 16, 2015 in Science
Penguins love fish, krill, squid and other sea life they catch while swimming underwater in the cold Antarctic oceans. But did you know they probably can't taste what they are gulping down their throats?
As far as diets go, penguins are way ahead of us landlubbers when it comes to getting enough omega threes. Their diet, rich in fatty fish keeps them far ahead of the curve. But when it comes to enjoying the taste of fish or any of the other sea life they eat, these flightless birds are clueless, say researchers at the University of Michigan.
Sensing environmental cues is essential to the survival and reproduction of any organism, say researchers, and one of the most important is the sense of taste, because it lets us know what food is safe and what could harm us. Generally, vertebrates can detect five different tastes, sweet, sour, bitter, salty, and umami, a "pleasantly savory taste," like the taste of tomatoes fresh from a summer garden.
Using genome and gene sequencing, scientists are inferring that penguins have lost the ability to discern sweet, umami, and bitter tastes. The findings were published today in the journal Current Biology. They say that only two tastes, sour and salty may still be present.
"Penguins eat fish, so you would guess that they need the umami receptor genes, but for some reason they don't have them," Jianzhi 'George' Zhang, a professor in ecology, and evolutionary biology at Michigan, explained in a press release. "These findings are surprising and puzzling, and we do not have a good explanation for them. But we have a few ideas."
So the big question is what led to the loss of some of the taste receptors? Zhang says he has a hypothesis, and he told The Verge it is only a hypothesis, but he thinks that it's too cold in Antarctica for the taste receptors to matter. Zhang went on to say that previous research has shown the tongue's receptor channels, which react to taste, don't function very well at lower temperatures when it comes to detecting sweet, cour and umami.
The research team believes that the environment may have been so cold that the receptors became essentially "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."
While the study was based entirely on genetic findings, Zhang says additional research will have to be done confirming penguins can't actually taste these foods. The team is sure another study will prove them correct. "It's very clear," Zhang says. If the genes aren't there, he says, then the animals don't have those tastes."
More about Penguins, sense of taste, Evolution, sweet and bitter, to cold to matter
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