Tasting opportunity

From oxygen-poor mountaintops to toxin-laced foods, animals repeatedly encounter ecological challenges that require transformative shifts in physiology and behavior (1–3). These innovations often evolve through just a few amino acid substitutions in otherwise conserved proteins (2, 3), raising central questions in evolutionary biology: How likely are such changes to evolve, and how often does evolution follow the same path in different species? The sense of taste, a deeply conserved interface between environment and behavior, offers a powerful lens to examine repeatability and how such changes arise (4). On page 1330 of this issue, Zhang et al. (5) trace the evolution of sour tolerance in birds by linking behavioral preference, receptor physiology, and molecular evolution. Their work shows how a small set of amino acid substitutions in a sour taste receptor (6) facilitated a sensory shift, enabling birds to exploit acidic fruits.