Molecular evolution of sour tolerance in birds.

Taste is crucial in shaping animal perception. Sourness, one of the primary tastes, is aversive in mammals, whereas many birds frequently consume acidic fruits, suggesting a potential tolerance. Our study uncovers a mechanism enabling avian sour tolerance that involves changes to the sour receptor [otopetrin 1 (OTOP1)]. We demonstrate that sour tolerance is a conserved trait in birds, with avian OTOP1 exhibiting acid-induced inhibition and OTOP1 modulation affecting sour perception and tolerance. Ancestral reconstruction reveals that the increase in acid tolerance may have evolved at the same point in the songbird phylogeny as the regain of sweet sensing in this clade. This shift might have enabled songbirds to feed on a wider range of fruits, affecting the evolution and diversification of the songbird radiation. Editor's summary: Many organisms find strongly sour flavors unappealing, likely due to their association with unripe or spoiled fruit. However, some bird species have developed a tolerance for highly acidic, sour flavors. Zhang et al. examined the genetic basis of sour taste perception in birds, finding that canary and pigeon alleles of the OTOP1 gene react to acid differently than mammalian alleles (see the Perspective by Rowland and Schneider). Indeed, gene knock-ins of the canary allele of OTOP1 into mice induced sour tolerance without otherwise affecting taste perception. A mutation shared by all songbirds seems to improve on the sour tolerance seen across other birds and may have contributed to the radiation of songbird species by diversifying dietary options. —Corinne Simonti [ABSTRACT FROM AUTHOR]