The evolution of taste perception is usually associated with the ecology and dietary changes of organisms. However, the association between feeding ecology and taste receptor evolution is unclear in some lineages of vertebrate animals. One example is the sweet taste receptor gene Tas1r2. Previous analysis of partial sequences has revealed that Tas1r2 has undergone equally strong purifying selection between insectivorous and frugivorous bats. To test whether the sweet taste function is also important in bats with contrasting diets, we examined the complete coding sequences of both sweet taste receptor genes (Tas1r2 and Tas1r3) in 34 representative bat species. Although these two genes are highly conserved between frugivorous and insectivorous bats at the sequence level, our behavioral experiments revealed that an insectivorous bat (Myotis ricketti) showed no preference for natural sugars, whereas the frugivorous species (Rousettus leschenaultii) showed strong preferences for sucrose and fructose. Furthermore, while both sweet taste receptor genes are expressed in the taste tissue of insectivorous and frugivorous bats, our cell-based assays revealed striking functional divergence: the sweet taste receptors of frugivorous bats are able to respond to natural sugars whereas those of insectivorous bats are not, which is consistent with the behavioral preference tests, suggesting that functional evolution of sweet taste receptors is closely related to diet. This comprehensive study suggests that using sequence conservation alone could be misleading in inferring protein and physiological function and highlights the power of combining behavioral experiments, expression analysis, and functional assays in molecular evolutionary studies.

味觉的进化通常与生物的生态和饮食变化有关。然而，在脊椎动物的一些谱系中，摄食生态学和味觉受体进化之间的关联尚不清楚。一个例子是甜味受体基因Tas1r2。先前对部分序列的分析表明，Tas1r2在食虫蝙蝠和食果蝙蝠之间经历了同样强烈的纯化选择。为了测试甜味功能在具有对比饮食的蝙蝠中是否也很重要，我们检查了两种甜味受体基因（Tas1r2和Tas1r3) 在 34 种有代表性的蝙蝠物种中。尽管这两个基因在食果蝙蝠和食虫蝙蝠之间在序列水平上高度保守，但我们的行为实验表明，食虫蝙蝠 ( Myotis ricketti ) 对天然糖没有偏好，而食果蝙蝠 ( Rousettus leschenaultii) 表现出对蔗糖和果糖的强烈偏好。此外，虽然这两种甜味受体基因都在食虫蝙蝠和食果蝙蝠的味觉组织中表达，但我们基于细胞的分析揭示了惊人的功能差异：食果蝙蝠的甜味受体能够对天然糖做出反应，而食虫蝙蝠的甜味受体则不是，这与行为偏好测试一致，表明甜味受体的功能进化与饮食密切相关。这项综合研究表明，单独使用序列保守可能会在推断蛋白质和生理功能时产生误导，并突出了在分子进化研究中结合行为实验、表达分析和功能测定的力量。