Therefore, most woodpeckers love sweets – but not cuckoos –

Birds, which are descended from carnivorous dinosaurs, lack a portion of the sugar receptor in mammals. This should make them insensitive to sugars. However, recent studies have shown that both hummingbirds and songbirds regain their ability to sense sugar by altering taste cells (receptors) for the fifth primary taste, umami, so that they also respond to carbohydrates in fruit and nectar.

However, it is unclear how other birds feel about drunkenness, and to what extent its taste receptors reflect the huge diversity of diets in the bird world. To investigate this question, the research team chose to focus on the woodpecker family. Although woodpeckers are primarily insectivores, the family also includes many species that also feed on sugary sap, nectar, and fruit.

Taste adapts to nutritional needs

By studying the behavior of wild birds, researchers were able to show that woodpeckers clearly prefer sugar and amino acids (which make up proteins) over pure water. Surprisingly, it turned out that the cuckoo – a member of the woodpecker family that feeds almost exclusively on ants – had a taste for amino acids, but not for sugars.

This discovery highlights how the sense of taste adapts to the nutritional needs of different species.

Our next question was whether the response to sugar we saw was reflected in the birds’ taste receptors, says Maud Baldwin, a researcher at the Max Planck Institute for Ornithology in Germany.

Your taste buds have changed

Taste receptor analyzes confirmed that woodpecker receptors are sensitive to sugars, while cuckoo receptors are not. Interestingly, reconstruction of the evolutionary history of the woodpecker family suggests that the common ancestor of the cuckoo and woodpecker did indeed have a modified taste receptor that sensed sugars.

The discovery revealed a third independent case where the umami receptor in birds was modified so that it also responds to sugar, says Julia Kramer, a researcher at the Max Planck Institute for Ornithology in Germany.

But even more interesting is the conclusion that the new function of the future was subsequently lost in the cuckoo.

Prefer umami taste

Julia Kramer’s careful studies of the differences between cuckoo and woodpecker receptors unexpectedly revealed that changes to a single amino acid in the cuckoo’s receptor prevented sugar sensing: the birds retained their ability to taste umami, which is likely important to entomologists eating a high-protein diet. .

The findings trace an evolutionary history followed by a reversal of the early acquired ability to sense sweetness in woodpeckers – which may have originated in an early ancestor and therefore older than woodpeckers themselves – when cuckoo receptors changed later.

change in amino acid

“We were very surprised that this reversal is caused by changes in a single amino acid, which acts as a molecular switch for the selective regulation of sugar sensitivity in cuckoo surfaces,” Kramer explains. The unexpected consequence of this small change was that cuckoo flankers again lacked the ability to detect sugar in food, but retained the ability of the receptors to gather information about amino acid content. This makes a lot of sense when most of your diet consists of ants.

The representative of SLU in the group is Max Cardinale, whose research deals primarily with marine fish stock analyzes. However, he is also involved in research on bird migration, and since 2002 has been Director of the Bird Migration Research Center on the island of Ponza in Italy.

– Part of the study of woodpeckers was carried out in Ponza, because it is one of the few places in Europe where you can hunt many cuckoos in a short time, which was one of the keys to the success of the experiment, says Max Cardinale.

Further studies will be needed to describe how changes in taste receptors, and in other physiological and sensory systems, relate to the great diversity of food specialization in the avian world.

Scientific material:

A single residue confers a selective loss of sugar sensing in sparrows. current biology.

Contact:

Max Cardinale, researcher. Department of Water Resources, Swedish University of Agriculture, [email protected]