Evolution of MHC class IIB in the genome of wild and ornamental guppies, Poecilia reticulata

被引:38
作者
van Oosterhout, C. [1 ]
Joyce, D. A. [1 ]
Cummings, S. M. [1 ]
机构
[1] Univ Hull, Sch Biol Sci, Kingston Upon Hull HU6 7RX, N Humberside, England
关键词
Poecilia reticulata; major histocompatibility complex; multigene evolution; gene duplication; gene conversion; teleost;
D O I
10.1038/sj.hdy.6800843
中图分类号
Q14 [生态学(生物生态学)];
学科分类号
071012 ; 0713 ;
摘要
This is the first study to quantify genomic sequence variation of the major histocompatibility complex (MHC) in wild and ornamental guppies, Poecilia reticulata. We sequenced 196 219 bp of exon 2 MHC class IIB (DAB) in 56 wild Trinidadian guppies and 14 ornamental strain guppies. Each of two natural populations possessed high allelic richness (15 - 16 alleles), whereas only three or fewer DAB alleles were amplified from ornamental guppies. The disparity in allelic richness between wild and ornamental fish cannot be fully explained by fixation of alleles by inbreeding, nor by the presence of non-amplified sequences (ie null alleles). Rather, we suggest that the same allele is fixed at duplicated MHC DAB loci owing to gene conversion. Alternatively, the number of loci in the ornamental strains has contracted during 4100 generations in captivity, a hypothesis consistent with the accordion model of MHC evolution. We furthermore analysed the substitution patterns by making pairwise comparisons of sequence variation at the putative peptide binding region (PBR). The rate of non-synonymous substitutions (dN) only marginally exceeded synonymous substitutions (dS) in PBR codons. Highly diverged sequences showed no evidence for diversifying selection, possibly because synonymous substitutions have accumulated since their divergence. Also, the substitution pattern of similar alleles did not show evidence for diversifying selection, plausibly because advantageous non-synonymous substitutions have not yet accumulated. Intermediately diverged sequences showed the highest relative rate of non-synonymous substitutions, with dN/dS > 14 in some pairwise comparisons. Consequently, a curvilinear relationship was observed between the dN/dS ratio and the level of sequence divergence.
引用
收藏
页码:111 / 118
页数:8
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