Sequence Polymorphism and Geographical Variation at a Positively Selected MHC-DRB Gene in the Finless Porpoise (Neophocaena phocaenoides): Implication for Recent Differentiation of the Yangtze Finless Porpoise? |
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Authors: | Shixia Xu Wenhua Ren Xuming Zhou Kaiya Zhou Guang Yang |
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Affiliation: | (1) Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210046, China; |
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Abstract: | Sequence polymorphism at the MHC class II DRB locus was investigated in three finless porpoise (Neophocaena phocaenoides) populations in Chinese waters. Intragenic recombination and strong positive selection were the main forces in generating
sequence diversity in the DRB gene. MHC sequence diversity changed significantly along the study period. Significant decrease in heterozygosity and lost
alleles have been detected in the Yangtze River population and South China Sea population since 1990. Furthermore, there is
a trend of increasing population differentiation over time. Especially, the genetic differentiation between the Yangtze River
population and the Yellow Sea population was very low prior to 1990 (F
ST = 0.036, P = 0.009), but became very significant after 1990 (F
ST = 0.134, P < 0.001), suggesting a recent augmentation of genetic differentiation between both populations probably in a relatively short-term
period. Porpoises from the Yangtze River displayed divergent frequencies of shared and private alleles from those displayed
by two marine populations, which suggest that the former riverine population has been under a different selection regime (characteristic
of a fresh water environment) than that of its marine counterparts. |
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Keywords: | |
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