Many mammals can taste sweet, this only applies to birds in exceptional cases such as Kolibris and some songbirds - at least so far. A team led by Julia Cramer from the Max Planck Institute for Ornithology has now shown that woodpeckers have also regained the meaning of sweets. With one exception: for turning paste, a species specialized in ants, this has selectively reversed with a simple and unexpected change in the receptor. These results showed a new mechanism of sensory reversal and illustrate how the sense of taste can adapt to the nutritional needs of the different types, writes the research group in »Current Biology«.
Most woodpeckers are primarily insect eaters, but there are also several types that include sugar -rich juices, nectar and fruits among their menu. Using behavioral tests with wild birds, Cramer and Co, that woodpecker clearly preferred sugar and amino acids towards water. Wendenhals, on the other hand, showed a preference for amino acids, but not for sugar. Therefore, the researchers examined whether the partially observed preference for sugar is reflected in the receptors of the birds.
Functional analyses of the taste receptors confirmed that the receptors of the woodpeckers studied are sensitive to sugar, whereas those of turn-necks are not. The last common ancestor of wendehals and other woodpeckers already had a modified taste receptor that could react to sugar. "Our finding reveals a third case in birds in which the sense of sweetness has developed again independently of each other," says Cramer. "Even more exciting, however, was the fact that reversible necks lost the new function of the receptor again later." The reason for this is obviously a single altered amino acid in the receptor at the reversible neck, which selectively switched off sugar perception. However, these birds retained their ability to taste amino acids in the process. Since they specialize in protein-rich insects as food, this is probably important, the researchers write.
