Department of Ecology, Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Wuhan University, Wuhan 430072, People's Republic of China.
Monell Chemical Senses Center, Philadelphia, PA 19104, USA.
Biol Lett. 2019 Sep 27;15(9):20190461. doi: 10.1098/rsbl.2019.0461. Epub 2019 Sep 25.
Nectar may contain many secondary metabolites that are commonly toxic and bitter-tasting. It has been hypothesized that such bitter-tasting secondary metabolites might keep the nectar exclusive to only a few pollinators. To test this hypothesis, we examined functional changes of bitter taste receptor genes (s) in a species of nectar-feeding bird (Anna's hummingbird) by comparing these genes with those from two closely related insect-feeding species (chimney swift and chuck-will's widow). We previously identified a larger number of s in the hummingbird than in its close insectivorous relatives. In the present study, we demonstrate higher sensitivity and new functions in the hummingbird gene copies generated by a lineage-specific duplication, which has been shaped by positive selection. These results suggest that the bitter taste may lead to increased sensitivities and specialized abilities of the hummingbird to detect bitter-tasting nectar. Moreover, this study potentially supports the hypothesis that bitter-tasting nectar may have been specialized for some pollinators, thus enforcing plant-pollinator mutualism.
花蜜可能含有许多通常有毒且味道苦涩的次生代谢物。人们假设，这些味道苦涩的次生代谢物可能会使花蜜只对少数传粉者具有吸引力。为了验证这一假设，我们通过比较一种花蜜鸟类（安娜蜂鸟）的苦味受体基因（s）与两种亲缘关系密切的食虫物种（烟囱 swift 和 chuck-will 的寡妇）的基因，来研究这些基因的功能变化。我们之前在蜂鸟中发现了比其近亲食虫动物更多的 s。在本研究中，我们证明了由谱系特异性复制产生的蜂鸟 基因拷贝具有更高的敏感性和新功能，这种复制受到了正选择的影响。这些结果表明，苦味可能导致蜂鸟对苦涩花蜜的检测敏感性和专门能力增强。此外，这项研究可能支持这样一种假设，即苦涩的花蜜可能已经专门为某些传粉者而存在，从而加强了植物与传粉者的共生关系。
