Humans can easily and happily identify sweet-tasting foods. However, many carnivores lack this ability, and it was previously unclear whether birds, descendants of carnivorous dinosaurs, could taste sweet. A team of international researchers led by Mode Baldwin of the Maxplank Institute for Ornithology has shown that songbirds, a group of more than 4.000 species, can feel sweet regardless of their staple food. This study focuses on specific events of songbird ancestry that enabled umami (fragrant) taste receptors to recognize sugar. This ability is conserved in the songbird lineage and affects the diet of nearly half of all birds alive today.
Bitterness, saltiness, sweetness, sourness, and umami are the five basic tastes we humans feel. Taste has a great influence on our eating habits. What we find delicious often ends up on our plate. The rest of the animal kingdom is no exception, as taste helps ensure a distinction between nutritious and toxic. But what exactly do other animals taste?
It is well known that sweet receptors are widespread in mammals. However, birds are descendants of carnivorous dinosaurs and lack the essential subunits of this receptor. Perhaps most birds cannot detect sugar. The only known exception is the umami-reused hummingbird. Taste receptor To recognize carbohydrates.
But can’t all other birds taste sugar? An international team led by evolutionary biologist Maud Baldwin of the German Maxplanck Institute for Ornithology and Yasuka Toda of Meiji University in Japan investigated this question.
Nectar in the diet
First, researchers systematically studied bird food. Certain songbird strains, such as sunbirds, cape sugarbirds, and honey creepers, are known to consume large amounts of nectar on a regular basis.
However, Baldwin and colleagues have found that above average numbers of other songbird species consume nectar and fruit from time to time across radiation. “This was the first hint that when looking for the origin of the sweet taste of birds, we need to focus on a variety of songbirds, not just those that specialize in nectar,” explains Baldwin. Indeed, their behavioral experiments have shown that both nectar experts and grain-eating songbirds prefer sugar water to normal water.
Umami receptors respond to sugar
Toda and Baldwin dig deep and find umami Receptor Honeyeaters, honey experts, and other songbird honeyeaters with different diets also respond to sugar. They conclude that songbirds have a really sweet sensation and, like hummingbirds, do so using umami receptors.
To identify the origin of this ability, researchers have reconstructed ancestral umami receptors at various locations in the songbird family tree. Early ancestors of songbirds were found to have evolved their ability to detect sugar, even before they were radiated from Australia and spread throughout the globe. “We were very surprised at this result. The sweet perception appeared very early in the songbird’s radiation and then persisted in predominantly sugar-rich food-independent species,” Baldwin said. I will.
In addition to the timing of sensory changes, researchers were able to elucidate their molecular basis. They identified modifications that allowed sweet perception by comparing sugar-indifferent receptor sequences with sugar-responsive receptor sequences. “lots of people Amino acid residues Being involved in sugar detection, we needed to analyze more than 100 receptor mutants to elucidate the molecular mechanisms underlying the sugar response, “says Toda. Similar regions of the receptor are altered (although the subunits are different). Therefore, in the process of evolution, these distant groups of birds have converged on the same solution of reusing them. Umami taste A receptor that senses sugar. However, each group modified the receptor in different ways to achieve the same result.
Based on their findings, scientists suspect that the new sensory perceptions of ancestral songbirds may have had widespread influence on their subsequent evolution.In Australia, where songbirds have evolved, there are many sugar Sources such as insect secretions and sap are common.Sugar-rich food sources may have helped Songbird Spread over other continents and successfully occupy different ecological niches.
Researchers from Japan, Germany, Hong Kong, the United States and Australia participated in this study. Future research is now aimed at learning how sweet perception co-evolved with other physiological properties such as digestive and metabolic changes throughout the evolution of birds.
Yasuka Toda et al., The early origins of sweet perception in the radiation of songbirds, Science (2021). DOI: 10.1126 / science.abf6505
Max Planck Society
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Songbird’s ancestors have evolved a new way to taste sugar
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