Liu Zhijin, Liu Guangjian, Hailer Frank, Orozco-terWengel Pablo, Tan Xinxin, Tian Jundong, Yan Zhongze, Zhang Baowei, Li Ming
Key laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, 1-5 Beichen West Road, Chaoyang, Beijing, 100101 China.
School of Biosciences, Cardiff University, Sir Martin Evans Building, Museum Avenue, Cardiff, CF10 3AX UK.
Front Zool. 2016 Jun 29;13:28. doi: 10.1186/s12983-016-0161-1. eCollection 2016.
Bitter taste perception is essential for species with selective food intake, enabling them to avoid unpalatable or toxic items. Previous studies noted a marked variation in the number of TAS2R genes among various vertebrate species, but the underlying causes are not well understood. Laurasiatherian mammals have highly diversified dietary niche, showing repeated evolution of specialized feeding preferences in multiple lineages and offering a unique chance to investigate how various feeding niches are associated with copy number variation for bitter taste receptor genes.
Here we investigated the evolutionary trajectories of TAS2Rs and their implications on bitter taste perception in whole-genome assemblies of 41 Laurasiatherian species. The number of intact TAS2Rs copies varied considerably, ranging from 0 to 52. As an extreme example of a narrow dietary niche, the Chinese pangolin possessed the lowest number of intact TAS2Rs (n = 2) among studied terrestrial vertebrates. Marine mammals (cetacea and pinnipedia), which swallow prey whole, presented a reduced copy number of TAS2Rs (n = 0-5). In contrast, independent insectivorous lineages, such as the shrew and insectivorous bats possessed a higher TAS2R diversity (n = 52 and n = 20-32, respectively), exceeding that in herbivores (n = 9-22) and omnivores (n = 18-22).
Besides herbivores, insectivores in Laurasiatheria tend to have more functional TAS2Rs in comparison to carnivores and omnivores. Furthermore, animals swallowing food whole (cetacean, pinnipedia and pangolin) have lost most functional TAS2Rs. These findings provide the most comprehensive view of the bitter taste gene repertoire in Laurasiatherian mammals to date, casting new light on the relationship between losses and gains of TAS2Rs and dietary specialization in mammals.
苦味感知对于具有选择性食物摄取的物种至关重要，使它们能够避免难吃或有毒的食物。先前的研究指出，各种脊椎动物物种中TAS2R基因的数量存在显著差异，但其潜在原因尚不清楚。劳亚兽类哺乳动物具有高度多样化的饮食生态位，在多个谱系中显示出专门进食偏好的反复进化，并提供了一个独特的机会来研究各种进食生态位如何与苦味受体基因的拷贝数变异相关联。
在这里，我们研究了41种劳亚兽类物种全基因组组装中TAS2R的进化轨迹及其对苦味感知的影响。完整的TAS2R拷贝数差异很大，范围从0到52。作为狭窄饮食生态位的一个极端例子，中国穿山甲在所研究的陆生脊椎动物中拥有的完整TAS2R数量最少（n = 2）。整个吞下猎物的海洋哺乳动物（鲸目和鳍足目）的TAS2R拷贝数减少（n = 0 - 5）。相比之下，独立的食虫谱系，如鼩鼱和食虫蝙蝠具有更高的TAS2R多样性（分别为n = 52和n = 20 - 32），超过了食草动物（n = 9 - 22）和杂食动物（n = 18 - 22）。
除了食草动物外，与食肉动物和杂食动物相比，劳亚兽类中的食虫动物往往具有更多功能性TAS2R。此外，整个吞下食物的动物（鲸类、鳍足类和穿山甲）已经失去了大多数功能性TAS2R。这些发现提供了迄今为止劳亚兽类哺乳动物苦味基因库最全面的观点，为TAS2R的得失与哺乳动物饮食特化之间的关系提供了新的线索。
