title: Dietary specialization drives multiple independent losses and gains in the bitter taste gene repertoire of Laurasiatherian Mammals.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: 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.
authors.forename: Zhijin
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Key laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, 1-5 Beichen West Road, Chaoyang, Beijing, 100101 China.
authors.forename: Guangjian
authors.initials: G
authors.lastname: Liu
authors.affiliation: School of Biosciences, Cardiff University, Sir Martin Evans Building, Museum Avenue, Cardiff, CF10 3AX UK.
authors.forename: Frank
authors.initials: F
authors.lastname: Hailer
authors.affiliation: School of Biosciences, Cardiff University, Sir Martin Evans Building, Museum Avenue, Cardiff, CF10 3AX UK.
authors.forename: Pablo
authors.initials: P
authors.lastname: Orozco-terWengel
authors.affiliation: Key laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, 1-5 Beichen West Road, Chaoyang, Beijing, 100101 China.|Institute of Health Sciences, Anhui University, Hefei, 230601 Anhui China.
authors.forename: Xinxin
authors.initials: X
authors.lastname: Tan
authors.affiliation: School of Life Sciences, Zhengzhou University, Zhengzhou, 450001 Henan China.
authors.forename: Jundong
authors.initials: J
authors.lastname: Tian
authors.affiliation: Key laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, 1-5 Beichen West Road, Chaoyang, Beijing, 100101 China.|Institute of Health Sciences, Anhui University, Hefei, 230601 Anhui China.
authors.forename: Zhongze
authors.initials: Z
authors.lastname: Yan
authors.affiliation: School of Life Sciences, Anhui University, Hefei, 230601 Anhui China.
authors.forename: Baowei
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Key laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, 1-5 Beichen West Road, Chaoyang, Beijing, 100101 China.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
keywords: Bitter taste receptor; Dietary specialization; Gene gain and loss; Laurasiatheria; Mammal; TAS2R