WIKIMEDIA, MARCIAL4Birds lack the classical vertebrate sweet taste receptor, but evolution has fashioned a new one for hummingbirds from an ancestral savory, or umami, receptor, according to a report published in Science today (August 21). This repurposed receptor has enabled hummingbirds to glug plant nectar while their closest relatives eat insects.
“It’s long been a puzzle as to how hummingbirds detect sweetness and these investigators, using a whole bunch of different techniques, have pretty much . . . nailed the answer,” said Gary Beauchamp, director of the Monell Chemical Senses Center in Philadelphia, who was not involved in the work.
On the tongues of most vertebrates, the receptor that binds sugars and conveys the sense of sweet taste consists of two subunits called T1R2 and T1R3. When T1R3 is paired with the subunit T1R1, on the other hand, savory flavors from meat, cheese, and fish are sensed. The subunit T1R2 is therefore thought to be largely responsible for sweet taste perception. Indeed, mammals that are solely carnivorous have lost the gene encoding T1R2 and mice genetically ...
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