Summary
Sensory systems evolve to enable organisms to detect cues pertinent to survival. The diversification of these systems is a critical aspect of the adaptative radiation of animals—that is, how an ancestral species rapidly diversifies into a large number of morphologically diverse descendant species. Birds are the most diverse clade of terrestrial vertebrates, at more than 10,000 currently recognized species. Curiously, the entire avian clade was shaped by the early loss of a gene encoding a sweet receptor. How then, did thousands of bird species that rely on nectar and fruit evolve to perceive sugars? On page 226 of this issue, Toda et al. (1) report a shift from savory to sweet perception in the early evolution of songbirds. The change may have played a critical role in the radiation of this diverse group.