The Analysis Of Genetic Structure Of Liobagrus Marginatoides Endemic To The Upper Yangtze River

Liobagrus marginatoides belonging to the family Amblycipitidae of theSiluriformes, is one of the Liobagrus catfish species. It distributes only in the upperYangtze River basin in southwest China(Ding RH,1994). With the development ofCascade hydropower project in the upper Yangtze River basin basin, such as stemstream of the upper Yangtze River, Jinsha River, Minjiang River and Jialing River,the habitat of L. marginatoides is ecpected to change tremendously. In order to accessthe genetic diversity and population genetic differentiation of L. marginatoides, weused two kinds of molecular genetic markers, mitochondrial molecular marker andmicrosatellite molecular marker, to analyse the genetic information of L.marginatoides from four geographical populations which sampled from the upperYangtze River basin. The main results were as follows:1The genetic diversity of L. marginatoides based on mitochondrial genome(1) Based on the comparison of four kinds of mitogenome sequences from Liobagrusnigricauda, Liobagrus marginatus, Liobagrus kingi and Liobagrus marginatoides,16SRNA、D-loop and Cyt b were screened as genetic markers of L. Marginatoides.We analysised142sequences of L. marginatoides based on16SRNA，twenty-sixpolymorphic sites and eleven haplotypes were identified，the nucleotide diversity andthe haplotype diversity were0.00067and0.34112，respectively；Based on D-loop，134sequences were analysised,thirty-eight polymorphic sites and hirty-ninehaplotypes were identified，the nucleotide diversity and the haplotype diversity were0.00188and0.68230，respectively；134cyt b sequences of L. Marginatoides wereanalysised, twenty-one polymorphic sites and sixteen haplotypes were identified，thenucleotide diversity and the haplotype diversity were0.00087and0.26858，respectively；Compared with others fishes, such as Rhinogobio ventralis and Coreiusguichenoti, the genetic diversity of L. Marginatoides was low, relatively.(2) The network of haplotypes and neighbor-joining tree showed a preliminaryrelationship between the distribution of haplotype and geographical population. And based on16SRNA、D-loop and Cyt b, the single population.Gene flow and theAnalysis of Molecular variance (AMOVA) indicated that there are more gene flowsamong populations. the most genetic variation come from the withinpopulation.Though there was no sgnificant differentiation between populations, thepopulations distributed in main stream of upper Yangtze River has preliminarydifferentiation compared with others of tributary.(3) Based on16SRNA、D-loop、Cytb gene，Mismatch distribution pattern and theneutral test included indexes of Fu’s Fs and Tajima’s D, showed the L. Marginatoidespopulation may had experienced a population expansion in history, but the result wasnot sgnificant.2Isolation and characterization of microsatellite markers(1) Microsatellite markers were isolated from an enriched genomic library. Afterlibrary screening,86clones containing microsatellite sequence were selected tosequence. Thirty-nine pair primers were designed. There were twelve pair primerssuccessfully amplifing products were polymorphic, and the rest24weremiscellaneous or monomorphic.14pair microsatellite primers were used foraccessing population genetic differentiation of L. marginatoides. Totally, we identified275alleles, the number of alleles per locus varied from9(LM-11) to41(LM-17) andthe average of which was22.92.The value of polymorphism information content (PIC)ranged from0.38585(LM-11) to0.907583(LM-17). These were many locis deviatedfrom Hardy–Weinberg equilibrium in the population of L. Marginatoides, such asLM-17,which only krpt it in the population Jiangjin and Nancong. Because this maynot be enough samples of L. Marginatoides fou analysing.(2) The number of alleles of L. Marginatoides’ populations ranged from5.0(Jiangjin) to13.33(Zhuyangxi), the value of polymorphism information content (PIC)was from0.40484(Gaochang) to0.50950(Juexi). The observedheterozygosity(Ho)value ranged from0.6459(Zhuyangxi) to0.7854(Gaochang), andexpected heterozygosity (He) value ranged from0.7223(Nancong) to0.8031(Zhuyangxi). The result showed that genetic diversity of L. Marginatoides was rich.(3) Based on the mitochondrial marker and microsatellite marker, the reslut ofanalysis of molecular variation variance (AMOVA) indicated that the most geneticvariation was fr om within population. Though the genetic differentiation among sixpopulations of L. marginatoides was not significant,statistically.But there wasinitial genetic differentiation between the group which was in stem stream of Yangtze River and which in tributary, so we should built two evolutionarily significant unit,respectively. And the protection of endemic and rare allele of L. Marginatoidesshould be taken, such an the population of Gaochang or Jiangjin.