Population Genetic Diversity And Mitochondrial Genome Of Ophiuroid In The Seamounts Of Western Pacific Ocean

Ophiuroid belong to echinoderms and is one of the most important fauna in the ocean.Seamount,as the habitat of fauna in the deep-sea,has become a unique ecosystem due to the abundance of biological communities.Mining and fishing become the major human activities in the seamount,which have caused considerable environmental damage to many benthic communities.By using the method of molecular marker,this paper study the genetic diversity and population structure of Ophiuroid in the seamounts of west Pacific ocean.The perspectives of habitat environment of population and the currents around seamount,was provided to interpret the connectivity of deep Ophiuroid populations.Moreover,the complete mitochondrial genome of Ophiuroid in seamount was obtained for revealing the basic characteristics of genetic diversity and constructing phylogenetic trees to trace the genetic classification and evolution.The potential gene rearrangement,and the adaptive evolutionary mechanism of Ophiuroid to the deep-sea environment was also discussed by using positive selection analysis of the protein coding genes.The achivevement of this research was expected to enhance our current understanding of the growth and historical evolution of seamount biome,and providing supporting data for the protection and management of the fragile seamount biome and ecosystem,as well as other seamount resources.The results of the study on the genetic diversity of Ophioplinthaca defensor populations and mitochondrial genome in the western Pacific Ocean showed that :(1)The relative high haplotype diversity(Hd)and low nucleotide diversity(?)of O.defensor populations were found in Weijia guyot and RC seamount.From the perspective of spatial distribution,the sample number and haplotype number on the south and southwest sides of Weijia guyot were higher than that on the north and east sides.The highest Hd and ? was detected in samples of ROV01 and the lowest in smaples of ROV06.(2)Within a single seamount,Weijia guyot did not show significant genetic differentiation,indicating a strong gene flow.Among multiple seamounts,TCS diagram also showed mixing uniformity of haplotypes and few stepsof mutation.The gene flow is strong with no significant population differentiation.By comparison,haplotypes between the southwest and the northwest Pacific Ocean had the most mutation steps(9 steps),indicating the furthest genetic distance between two O.defensor populations with the lowest gene exchange,and resulting in significant population differentiation.(3)The mismatch distribution curves of Weijia guyot conforms to the population expansion model,indicating that Ophiuroid population in this region has experienced a large-scale population expansion event in history.(4)The mitochondrial genome length of the four Ophiuroid studied in this paper is15,457 bp-16,907 bp.UUA,AGA,AGG,GGA,GUU and CCU were the highly frequent codons for amino acids of Leu,Ile,Phe and Ser.(5)The phylogenetic analysis results showed the latest four mitochondrial genome sequences and 19 published reference sequences of mitochondrial genome can be divided into four monophyletic orders.The topological structure is stable.The phylogenetic structure supports the existing phylogeny of the Ophiuroid.(6)The gene sequence of cox1-nad5 is conservative.There was only one positive selection site in Ophiomusium sp.,while other three Ophiuroids had more than eight positive selection sites.Pearson correlation analysis showed that a moderately significant positive correlation was found between water depths and positive selection sites of all samples of Ophiuroid.