Studies On Molecular Phylogeny Of Sesarmid Crabs From The Coast Of China And Molecular Phylogeography Of Two Mangrove Crabs

There are many problems in the classification of Chinese coastal Sesarmidae crabs.In order to clarify the systematic relationship between species and genera,mitochondrial DNA COI and 16S r RNA genes were used to conduct molecular systematic analysis on Chinese coastal sesarmid crabs.Mitochondrial COI gene as molecular marker,for two important mangrove crabs that are Uca arcuata and Parasesarma affine from the coast of China,different geographical populations to their systematic geographic pattern,population genetic structure,and larval diffusion how to affect its genetic structure were analyzed;the history and evolution of the existing population distribution pattern formation process,the comparison of evolution between Uca arcuata and Parasesarma affine and the Pleistocene glacial geology and climate influence on the population evolution history were known,then the historical factors,environmental factors and ecological habits of crab itself how to affect the population genetic structure and distribution pattern were illustrated.The results are as follows:The species in the family of Sesarmidae are among the species mostly difficult to be differentiated taxonomically in the Superfamily Grapsoidea because of their morphological similarity.The analysis of partial sequences of mitochondrial COI gene and 16S r RNA gene of 14 species in 8 genera of Sesarmidae for their molecular phylogenetics revealed that the percentages of sequence divergences of 14 species of Sesarmidae were from 5.7%to 14.5%and from 1.5%to 12.1%,both indicating that the species difference were significant.The phylogenetic trees illustrated show that the 14 species are separate and valid species and four species of Parasesarma and three species of Perisesarma are not two independent clades but clustered into one clade.Chiromantes dehaani and Sesarmops sinensis are clustered into one clade and then clustered with C.haematocheir into another clade,inconsistent with their morphological classification.The complicated molecular phylogenetic relationship among the species of Sesarmidae suggested that the species in the family of Sesarmidae might have polyphyletic origin,and their interspecific relationship or intergenus relationship need to be clarified.The mitochondrial COI gene fragment of Uca arcuata was 642 bp.A total of 293 individuals were collected from 14 locations and 121 different haplotypes were obtained.Mean haplotype diversity and nucleotide diversity were 0.8879±0.1045 and 0.0428±0.0234 respectivly,showing a high level of genetic diversity.The haplotype NJ tree and network diagram identified two distinct lineages?A and B?in the distribution range of the Yellow Sea,the East China Sea and the South China Sea.The 95 haplotypes of lineage A are all distributed in the East China Sea and the South China Sea except for one haplotype,while the haplotypes of lineage B are all distributed in the Yellow Sea,the East China Sea and the South China Sea.The divergence time of lineage A and lineage B was about 504 thousand years before present.The results of AMOVA analysis and F_STvalue analysis showed that there was a certain genetic differentiation in the distribution range of U.arcuata populations,but significant genetic difference was between the Yellow Sea group and the East China Sea-South China Sea group,which showed that there was a significant genetic differentiation between the two groups,forming a significant population genetic structure;this may be due to these facts that?1?the larvae of U.arcuata have habits of liking high salt water and prefering to stay in the tidal flat of its habitat;?2?the Yangtze River outflow as a geographical barrier might limit the gene connectivity between the two groups.The results of nucleotide mismatch distribution and neutral test revealed that U.arcuata?lineage A and lineage B?had undergone population expansion.The mitochondrial COI gene fragment of Parasesarma affine was 612 bp.A total of 222 individuals were collected from 12 locations and 40 different haplotypes were obtained.Mean haplotype diversity and nucleotide diversity were 0.5089±0.0419 and 0.0203±0.0171 respectivly,showing a moderate level of haplotype diversity.The topological structure of haplotype NJ tree showed that there was no obvious haplotype group and no forming significant branch pedigree;the network diagram of haplotype showed“star-like”structure,the main haplotype being the center and the other haplotypes arranged around it in a star shape.The results of AMOVA analysis?genetic variation mainly comes from within populations rather than among populations?and F_ST value analysis(the statistical test of F_ST value between every populations to another was not significant)showed that there was no significant genetic structure,no geographical isolation mode and low level of genetic differentiation among populations.The results of nucleotide mismatched distribution and neutral test revealed that the population expansion of P.affine had occurred about 51 000 years ago.