An early sensory shift in the evolution of songbirds conferred the ability to detect sugars and may have played a critical role in the radiation of this large and diverse group of avian species, a new study finds. While a taste for sugars is conserved and widespread among mammals, the ability to detect sugars is not ancestral in the bird lineage, where most species were carnivorous. The entire avian clade was shaped by the early loss of T1R2, a gene encoding a sweet receptor. However, despite this loss, several divergent lineages of birds, including hummingbirds and parrots, regularly consume sugar-rich fruits and nectar. How these thousands of sweet-eating species evolved to perceive sugars without the T1R2 gene remains unknown. Yasuka Toda and colleagues investigated taste receptor function within the largest group of birds - the passerines, or songbirds - an order which comprises more than half of all bird species. They found that the emergence of sweet detection in these birds involved a single shift in a receptor for umami perception early in their evolutionary history. According to Toda et al., this early shift shaped the sensory biology of the entire radiation and in a different, yet convergent, way than that in nectar-feeding hummingbirds. This change highlights how new functions can emerge from existing sensory receptors. "The early evolution of sweet perception likely played an important role in the diversification of this lineage, which is now a numerically and ecologically dominant component of terrestrial avifaunas the world over," writes F. Keith Barker in a related Perspective.
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Journal
Science