Study On Mitochondrial Genome And Genetic Diversity Of Sipunculus Nudus In The Coasts Of China

As a small phylum,Sipuncula are seldom investigated by scientists.In recent years,the wild populations of S.nudus were overexploited.On the other hand,human activities have destroyed the environment that sustains them.It contributes to the falling numbers of wild populations.The protection of the sipuncula resources is imminent.Sipunculus nudus is the type species in genus Sipunculus and good sample for evolutionary and population genetic structure studies of phylum Sipuncula.In this paper,to investigate classification status and population genetic structure of the phylum Sipuncula,the molecular and morphological approach was used.The main results were as follows:1.Morphological analysis:1)Caecum rectum was tubular.2)The number of LMBs: average number of LMBs of Lingshui?Yantai?France S.nudus were 31.2?29 and 31,respectively.3)State of LMBs at the glans region: do not split in Lingshui populations,all split in Yantai populations,not all split in France populations.4)Degree of nephridia attachment from the body wall: average percentage of the length attached to the body wall of Lingshui?Yantai?France populations were 28.56%?33.5%and 15.67%,respectively.5)State of the origin of the retractor muscles: the origin of each ventral retractor muscle connected to average 6 LMBs in China and France populations.The origin of each dorsal retractor muscle connected to average 5.5 and 6 LMBs respectively in China and France populations.Accordding to the standards to identify to Sipuncula,morphological analysis showed three populations(Yantai,Lingshui,and France)all were Sipunculus nudus.And morphological characteristics were regional differences.2.The complete mitochondrial genome and the taxonomic status analysis of the phylum Sipuncula.1)Two complete mitochondrial genomes of S.nudus from Gulei and Yantai were obtained,15376 bp(FJ422961)and15303 bp(KP751904)in length respectively.The complete mitochondrial genome of Yantai and Concarneau S.nudus consisted of 37 genes,including 13 protein-coding genes,2 r RNA genes,23 t RNA genes.However,Gulei S.nudus consisted of 38 genes,one more threonine t RNA than that of which located between 16 S r RNA and ND3,the remaining 37 genes order were resembled.The mt DNA's homology between Yantai and Gulei was 79.10%.That of Concarneau with Gulei and Yantai were 71.00% and 70.8%,respectively.2)Phylogenetic analyses: instead of phylum mollusca,phylum sipuncula was together on a clade with phylum annelida.It supported phylum sipuncula had a more close relationship with phylum annelida.3.Genetic structure and population differentiation of S.nudus from 6 localities in the coasts of China were analyzed based on sequences of mitochondrial cytochrome b gene.The main results were as follows:1)Complete mitochondrial Cytb gene sequences(1138 bp)from 203 individuals of Sipunculus nudus were analyzed,299 polymorphic sites and 128 haplotypes were identifed,the nucleotide diversity and haplotypes diversity were 0.0488 and 0.9773,respectively.The genetic diversity of S.nudus was relatively high.The variation among populations accounting for 88.4% was main source of variation.2)According to differentiation index(Fst)and gene flow(Nm)in populations of S.nudus,5populations south of Yantai was no significant difference or low difference,Fst<0.15;There was high difference between Yantai and 5 populations south of Yantai,Fst>0.15.The genetic communication was frequently among the 5 populations south of Yantai,Nm>5;There was low gene flow between Yantai and 5 populations south of Yantai,Nm<0.05.3)Fu's Fs and Tajima's D were negative;The figures of mismatch distribution were unimodal;Haplotype network was radial structure centring on main haplotype;These results indicated S.nudus population had experienced a large-scale population expansion in history.