Evolution of Olfactory Receptor Genes in East Asian Loaches

Daryi Wang, Tzi-Yuan Wang, Li-Chuan Weng, Yasufumi Emori, Chyng-Shyan Tzeng, and Wen-Hsiung Li (2009) Evolution of olfactory receptor genes in East Asian loaches. Zoological Studies 48(2): 223-237. It is well known that fish have fewer olfactory receptor (OR) genes than mammals do. In order to investigate the divergence of and evolutionary changes in OR genes in fish, 2 loach OR gene families (D1/3 and D32) from Taiwanese and Chinese populations of 2 species (Misgurnus anguillicaudatus and Paramisgurnus dabryanus) were analyzed. We found duplications in both D1/3 and D32 that had accumulated after the separation of the island of Taiwan from the Asian mainland similar to 5 million yrs ago. The accumulation of duplicate copies in a relatively short time suggests that gaining extra copies of OR genes may have been selectively advantageous for adapting to local environments. On the other hand, the loss of some OR genes in the 2 species in Taiwan may reflect loss of selective constraints on some OR genes. Moreover, unlike the situation in mammals in which pseudogenes are found in each family, pseudogenes are clustered in an expanding gene family in P dabryanus in Taiwan. The presence of pseudogenes and the limited number of functional OR genes in fish suggest that fish do not need a large number of OR genes. Finally, the dynamic changes in OR gene number and the possible explanation for a lower OR gene number in fish are discussed. http://zoolstud.sinica.edu.tw/Journals/48.2/223.pdf