title: Genetic variation and balancing selection at MHC class  II exon 2 in cultured stocks and wild populations of orange-spotted grouper (Epinephelus  coioides).
abstract: Major histocompatibility complex (MHC) molecules play  vital roles in triggering adaptive immune responses and are considered the most  variable molecules in vertebrates. Recently, many studies have focused on the  polymorphism and evolution mode of MHC in both model and non-model organisms.  Here, we analyzed the MHC class II exon 2-encoding β chain in comparison with the  mitochondrial Cytb gene and our previously published microsatellite data  set in three cultured stocks and four wild populations of the orange-spotted  grouper (Epinephelus coioides) in order to investigate its genetic  variation and mechanism of evolution. We detected one to four alleles in one  individual, suggesting that at least two loci exist in the orange-spotted  grouper, as well as a particularly high level of allelic diversity at the MHC  loci. Furthermore, the cultured stocks exhibited reduced allelic diversity  compared to the wild counterparts. We found evidence of balancing selection at  MHC class II exon 2, and codon sites under positive selection were largely  correspondent to the protein-binding region. In addition, MHC class II exon 2  revealed significant differences between population differentiation patterns  from the neutral mitochondrial Cytb and microsatellites, which may  indicate local adaptation at MHC loci in orange-spotted grouper originating  from the South China Sea and Southeast Asia.
authors.affiliation: State Key Laboratory of Biocontrol, Institute of Aquatic Economic Animals and the Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-Sen University, Guangzhou, China.
authors.forename: Z N
authors.initials: ZN
authors.lastname: Meng
authors.forename: S
authors.initials: S
authors.lastname: Yang
authors.forename: B
authors.initials: B
authors.lastname: Fan
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.forename: H R
authors.initials: HR
authors.lastname: Lin
mesh_terms: D000818:Animals; D000835:Animals, Wild / Q000235:genetics* / Q000254:growth & development; D001210:Asia, Southeastern; D001492:Bass / Q000235:genetics* / Q000254:growth & development*; D002681:China; D045303:Cytochromes b / Q000235:genetics; D005091:Exons / Q000235:genetics*; D005802:Genes, MHC Class II / Q000235:genetics*; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D000949:Histocompatibility Antigens Class II / Q000235:genetics; D016013:Likelihood Functions; D008928:Mitochondria / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D010858:Pigmentation / Q000235:genetics; D012641:Selection, Genetic
chemical_list: D000949:Histocompatibility Antigens Class II; D045303:Cytochromes b