It is known that humans and animals distinguish between four basic tastes: bitter, sweet, sour and salty. There is also umami, the feeling of high-protein foods associated with glutamate.
The taste of bitterness should make animals aware that the food they are tasting may be spoiled or toxic. This is the evolutionary role of bitter. But when did living beings learn to feel it and at what point did the necessary receptors appear on the tongue? A group of scientists from Germany found this out.
Researchers work, published in PNAS, drew attention to genes necessary for taste perception in cartilaginous fish. This ancient group of underwater inhabitants is now represented by sharks, rays and chimeras.
The authors received detailed information. information about the DNA of many cartilaginous species, including sharks and rays. In 12 of them, it was possible to detect genes for the so-called type 2 taste receptors, which are necessary to sense bitterness. Further research made it clear that for the first time the necessary proteins appeared in some primitive creatures, the ancestors of many vertebrates. This happened about 460 million years ago, during the Paleozoic era.
Next, experts checked the functionality of the receptors. To do this, they used the cells of two sharks: the common cat and the white-spotted cat. The samples were exposed to 94 compounds that cause a bitter sensation in the human mouth. Eleven of them (including colchicine and bile acids) caused a reaction in the cells – therefore, the predators themselves were also adapted to recognize them.