Selection Pressure Analysis In Selective And Wild Common Carp (Cyprinus Carpio L.)

Selection pressures are the principle evolutionary forces for geneticdifferentiation of populations. Recent advances in selection pressures onmitochondrial DNA and microsatellite have been described in a range oforganisms. The common carp (Cyprinus carpio L.) has experienced strongselection pressure, in particular artificial selection, during itsdomestication process. However, the contribution and extent of artificialselection in driving genome-wide population differentiation remainsunclear. In this study, we employed three methods to analyze the selectionpressure between selective and wild common carp with genetic variation,genetic population structure and genetic differentiation.1、Analysis of selection pressure between wild and selected commoncarp using microsatellite genotypingWe investigated the genetic differentiation of four selected strains(Xingguo red common carp, Pursed red common carp, Glass red commoncarp, Jian common carp) and two wild populations (from Yangtze River)of common carp by genotyping ten microsatellite loci. It was found that the selected strains displayed lower genetic variability, higher inbreedingcoefficients, higher linkage disequilibrium (LD) within population, andhigher genetic differentiation between populations compared with the wildpopulations, indicating strong selection pressures in the process ofdomestication. Of the10loci,5appeared to be under positive directionalselection in the selective strains, and all ten loci in wild populations werepotentially under purifying selection. We conclude that strong selectionpressures, in particular artificial selection, have driven the populationgenetic differentiation of selective and wild common carp.2、Analysis of selection pressure between wild and selective commoncarp by mitochondrial DNA sequencingWe analyzed the selection pressure in wild and selective commoncarp by mitochondrial DNA sequencing. The selective common carppopulation presented lower genetic variation, higher genetic inbreedingcoefficients within population, and clearly genetic differentiation amongpopulations. Compared with wild common carp, selective common carphad less haplotypes. Most of haplotypes in selective common carp wereshared with wild common carp. And four selective populations presenteddifferent private haplotypes with high differentiation among distribution ofhaplotypes. These results indicated that the four selective populations experienced strong selection pressure during their domesticate history,with the different selection methods.3、Analysis of selection pressure between wild and selective commoncarp using MHC class II beta genesTo detect genetic differentiation resulted from the selection, we usedPCR amplification and cloning method in investigating MajorHistocompatibility Complex (MHC) class II beta genes between wild andselective common carp. The results indicated that the genetic diversitybetween wild and selective common carp populations had no significantdifferent, even if the selective population had small founder populationsize. There was no significantly genetic differentiation detected betweenpopulations except Purse red common carp. Most of sequence sites wereunder negative purifying selection, whereas the other sites were underpositive selection. It suggested that the MHC were strongly sensitive withthe antigen selection, which may have made high genetic diversity inMHC genes, and have driven different genetic variation in the selectivepopulations.