Genetic Diversity And Structure Of Euphausia Superba In Antarctic(Subarea 48.1)

Euphausia superba is regarded as not only a key species in Antarctic but also the most abundant economic animal on the planet.In this study,mitochondrial COI gene 、 ND6 gene as well as genomic microsatellite markers were used to analyze the genetic diversity,genetic structure,and population history of E.superba in subarea 48.1(2013: 4 swarms;2016:12swarms).Our study will provide more scientific information on fisheries resources exploitation,biodiversity conservation and ecological balance maintenance.1.Population genetic of E.superba using the mitochondrial sequenceA total of 480 COI-ND6 sequence were obtainedfrom 12 sampling sites in 2016.The length is 1024 bp and no In-Del(insertion-deletion)was observed.The average base composition is A(26.2%)、T(39.8%)、G(15.0%)and C(19.0%),respectively.A total of 400 haplotypes were detected;the nucleotide diversity(π),haplotype diversity(Hd)and average number of nucleotide differences is 0.01218,0.9961 and 12.474,respectively.Genetic distances within and between 12 sites were very similar(variedfrom 0.011 to 0.014).NJ tree identified significant Phylogeographic structures.UPGMA tree,AMOVE analysis,PCoA analysis Fst and Nm suggest that E.superba lack of genetic structure.UPGMA tree and PCoA analysis showed that the same differentiation occurred within all swarms.Demographic history analysis suggest the expansion occurred in about0.0413 million years ago,is in the late Pleistocene.593 COI sequences(113 sequences in 2013;480 sequences in 2016)were obtained,and the length is 491 bp.The average G+C composition is39.9% both in 2013 and 2016.The haplotype diversity(Hd)(0.963 in 2013 and 0.9686 in 2016),nucleotide diversity(π)(2013 in 0.0115,2016 in0.01044)and pairwise nucleotide differences(2013 in 5.647 and 2016 in5.124)were all higher but not significantly different.The genetic distance between 2013 and 2016 was 0.011.The NJ tree and PCoA analysis showed that Antarctic krill samples did not form a separate branch in 2013 and2016,respectively.Molecular variance analysis showed that 0.35% genetic variations is between in two years,but the Fst was only 0.00351.Pairwise Fst between 2013 and 2016 was also small and not significant.But the PCoA analysis showed that the same differentiation occurred within all swarms.2.Solation and characterization of ten polymorphic microsatellites markers for E.superba and polymorphism verificationUsing 5’ end anchoring PCR and reduced-representation sequencing,10 polymorphic microsatellite markers were developed.After polymorphism verification,a total of 46 alleles were obtained.At per locus,the number of alleles(Na)ranged from 2 to 9;the observed heterozygosity(Ho)ranged from 0.033 to 1;the polymorphism information content(PIC)differed from 0.032863485 to 0.71939702.ES1,ES2,ES3,ES6,ES8,ES9 showed high polymorphism,ES10 was at a moderate polymorphism,ES4,ES5 and ES7 showed low polymorphism.The Shannon’s information index in ES5 is 0.085,in the remaining markers were very high.Only 2 locus showed significant deviation from Hardy-Weinberg equilibrium.All 10 microsatellite locus can be used as the candidate molecular markers for the population genetic of Antarctic krill.3.Genetic diversity and structure of E.superba based on microsatellite markers10 polymorphic microsatellite markers were used to analyze the genetic diversity and structure of Antarctic krill in 8 swarms.A total of 79 alleles were detected.At per locus,the number of alleles(Na)differed from 3 to 20;the observed heterozygosity(Ho)was between 0.0375 and0.9833 and the average observed heterozygosity(Ho)was 0.5562 higher than the expected heterozygosity(He)of 0.4928.Most combinations werehighly or moderate polymorphic.In a total of 80 combinations,48 units kept the Hardy-Weinberg equilibrium.Molecular variance analysis showed that 2.95% of genetic differences occurred among swarms,the Fst was 0.02953.The pairwise Fst ranged from-0.00162 to 0.05847.The Nei’s genetic distance is differed from 0.0140 to 0.1078.The Nei’s genetic identity in all swarms was more than 0.89.UPGMA analysis,Principal Coordinate Analysis(PCoA)and Bayesian analysis showed non-significant phylogeographic structures.Bayesian analysis identified that the same differentiation occurred within all swarms.