Population Genetic Variation And Adaptive Evolution Of Ammodytes Personatus

Ammodytes personatus belongs to the family Ammodytoidae.As a kind of small pelagic fish,it is sensitive to temperature.It is one of the important economic fish in China and widely distributed in the north of the yellow sea,the coastal water of Japanese island and the sea areas of Korean peninsula.This study used the mitochondrial DNA molecular marker technology to analyze population genetic diversity and genetic structure of A.personatus in China and Japan.In this study,we assessed and compared the phylogeographical pattern of A.personatus in different ocean current system by mitochondrial DNA(mtDNA)Cyt b and ATP6 gene,and then evaluated the role of historical and present environment factors in shaping the genetic structure of marine species.We also conducted natural selection test for A.personatus.According to the habit of resistance to high temperature,the existence of HSP70 gene was tested in this species.Based on mitochondrial DNA,we analyzed the population genetic variation and adaptive evolution of A.personatus,the results were following:(1)A 1162-bp fragment(including a 21 bp fragment of the tRNA)of the Cyt b gene was sequenced in this species.A total of 174 individuals were collected from eight locations(Qingdao,Dalian,Fukuoka,Seto Naikai,Aichi Prefecture,Sendai Bay,Hachinohe and Cape Soya)in China and Japan.One hundred and seventy haplotypes were obtained.The total haplotype diversity and nucleotide diversity were 0.9997±0.0007 and0.0387±0.0186,respectively.Haplotype network and NJ tree identified two distinct lineages in this species(Lineage A and B).Significant genetic variation were found by AMOVA analysis and pairwise FST(FST=-0.0291-0.7869).Mismatch distribution and neutrality test revealed that A.personatus had undergone population expansion.Natural selection analysis showed that the selection pressure value of Lineage B(dN/dS)was0.0086,and the selection pressure value of Lineage A(dN/dS)was 0.0159.The ocean currents and the annual sea temperature showed that the surface sea temperature was heavily influenced by the Kuroshio and Oyashio currents,the annual sea temperature of Lineage A varied from 11.26℃ to 19.99℃,and the annual sea temperature in the Lineage B varied from 11.26℃ to 14.17℃.We found the frequency of Lineage B along the Pacific coast of Japan from Soya to Sendai Bay reduced gradually.The frequency of Lineage Aalong the Pacific coast of Japan from Fukuoka to Sendai Bay also reduced gradually,this trend indicated that Sendai Bay maybe the transition zone.Natural selection pressure test and amino acid mutation loci analysis showed that Lineage B had a stronger selection pressure than Lineage A.In conclusion we suggested that in the process of spreading from the high latitudes to low latitudes of A.personatus,with the increasing temperature,it suffered a new selection pressure that made the lineage A had more purified mutation loci.(2)A 644-bp fragment of the ATP6 gene was sequenced in this species.In total 185 individuals were collected from eight locations(Qingdao,Dalian,Fukuoka,Seto Naikai,Aichi Prefecture,Sendai Bay,Hachinohe and Cape Soya)in China and the coastal water of Japanese island.One hundred and seventy haplotypes were obtained.The total haplotype diversity and nucleotide diversity were 0.9865±0.0042 and 0.0415±0.0202.Haplotype network and NJ tree identified two distinct lineages in this species.Significant genetic variation were found by AMOVA analysis and pairwise FST(FST=-0.0259-0.8092).Mismatch distribution and neutrality test revealed that A.personatus had undergone population expansion.Natural selection analysis showed that the selection pressure value of Lineage B(dN/dS)was 0.0182,and the selection pressure value of Lineage A(dN/dS)was 0.0406,which indicated the Lineage B experienced the stronger environment selection pressure.Amino acid mutation site test for ATP6 had the same results with Cyt b.(3)As a cold-water species A.personatus was sensitive to sea temperature.It started aestivation when the water temperature exceeds the tolerance limitation.To test the existence of HSP70 gene in this species.we had a genomic sequencing for A.personatus,we used the Larimichthys crocea HSP70 gene sequence as the target to blast the local alignment,and then found the sequence of HSP70 gene in the config.We successfully got A.personatus HSP70 gene sequences.We used Hachinohe group and Qingdao group as for reference with 17 bony fishes of HSP70 gene sequence to conduct a homology comparison.A close genetic relationship were revealed between A.personatus and two species Larimichthys crocea and Miichthys miiuy.Combining with the characters of heat shock proteins,we speculated that in the process of spreading from high latitudes to low latitudes,the survival environment temperature of A.personatus rising,heat shock proteins within the cells produced stress reaction,and HSP70 gene expression level increased significantly,it protected the cell from the damage,thereby it reduced cell death.This enhanced the ability to adapt to the environment.Combined the change of historical geography,marine environmental factors and ecological habit of marine fish,we inferred that,Pleistocene glaciation was the major force of A.personatus population differentitation,and the change of environment temperature and ocean currents were also important factors for shaping the current population distribution.