Penguins apparently can't enjoy or even detect the savory taste of the fish they eat or the sweet taste of fruit. A new analysis of the DNA evidence, which is described in in the February 16, 2015 issue of Current Biology, suggests that the flightless, waddling birds have lost three of the five basic tastes over evolutionary time. For them, it appears, food comes in only two flavors, salty and sour. The Current Biology article is entitled "Molecular Evidence for the Loss of Three Basic Tastes in Penguins." 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. "Penguins eat fish, so you would guess that they need the umami receptor genes, but for some reason they don't have them," says Dr. 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." It was Dr. Zhang's colleagues in China who led him to this discovery after they realized that they couldn't find some of the taste genes in their newly sequenced genomes of Adelie and emperor penguins. Dr. Zhang took a closer look at the penguin DNA to find that all penguin species lack functional genes for the receptors of sweet, umami, and bitter tastes. The researchers suggest that the genes encoding those taste receptors may have been lost in penguins not because they weren't useful, but rather because of the extremely cold environments in which penguins live. [Note: While some penguins have since moved to warmer climes, all penguins trace their roots to Antarctica.] Unlike receptors for sour and salty tastes, the taste receptors required for detecting sweet, umami, and bitter tastes are temperature-sensitive. They don't work when they get really cold anyway.
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