| Brachyura crabs,the largest clade of the decapod Crustacea,have undergone an extensive radiation and today are extremely diverse both morphologically and ecologically.They play a very important role in the ecology of marine environment,and occupy an important position in aquaculture.But the extreme morphological diversity and probable large scale convergence of adult features in the Brachyura has confounded consensus on phylogenetic relationships.Molecular approach was used to test hypotheses about the phylogeny of selected brachyuran crabs which were collected from the Taiwan Strait and Indian Ocean.Combining the morphological characters,brachyura were assessed for their phylogenetic position by using 18s ribosomal RNA,16S mitochondrial RNA and COâ… sequences(DNA sequence of the mitochondrial cytochrome oxidaseâ… ).And discussed the origin of the Brachyura crabs.The results as follows:1.Charybdis Feriatus,Portunus sanguinolentus,Charybdis vadorum,Charybdis variegata,Charybdis acuta,Charybdis truncata,Hemigrapsus sinensis,Parthenope validus,Macrophthalmus japonicus,Eriphiidae sp.,Macromedaeus distinguendus,Leptodius exaratus,Raninoides serratifrons and Dromia dehaani were identified from the specimens basis on the morphological characters.2.Established the 18S rRNA,16S rRNA and COâ… gene PCR reaction system. Amplifying and sequencing 18s rRNA,16S rRNA and COâ… sequences of the crab samples.And submitted 18 sequences to the international gene bank,the submissions are EU284139-EU284156.3.Through analysing the 18s rRNA,16S rRNA and COâ… sequences of the species,we find that 18s rRNA is 1785 bp and constantest,it is effictive at the infraorder level of brachyuran.DNA sequence of the mitochondrial cytochrome oxidaseâ… is 709bp,and has the highest variability.It is very useful in phylogenetic inference in the genus.Mitochondrial 16S rRNA is 530bp and also very conservative, but more variable than 18S rRNA,It is the most effective evolutionary marker in the brachyuran.4.Using those sequences of the samples and combining the related DNA sequences of brachyuran in GenBank,we built the molecular phylogentic tree of brachyurans.Combining the morphological characters,all the species gained their phylogenetic position.We also discussed the origin of Brachyura crab.The 18S rRNA molecue phylogenetic tree is composed by four families:Grapsioidea,Ocypodioidea, Potamoidea and Portunoidea.This suggested that the four families arose from a common marine ancestor,and the estimated divegence time are similar.In the 18S rRNA molecue phylogenetic tree five Charybdis grouped togather first.The genetic distance of them is small,this accords with the traditional classification.Through analysing the 18s DNA molecue phylogenetic tree we can find that the so called higher crabs grouped with Raninidae first,then grouped with the Dromiidae.This suggests that the so called higher crabs have a more close phylogenetic relationship with Raninidae.The COâ… gene phylogenetic tree shows the phylogenetic relationship of the five Chiarybdis. Through analysing the mitochondrial 16s rRNA molecue phylogenetic tree we can find that the samples from the Indian ocean grouped the Xanthidae.And this accords with the morphological analysis.So the samples of the Indian ocean should belong to the Xanthidae.In the 16s rRNA molecue phylogenetic tree,the higher crabs also grouped with Raninidae first,then grouped with the Dromiidae.Combin with the 18s DNA molecue phylogenetic tree,this experiment supports that the Raninidae demarcate the lower limit of the Brachyura and form a distinct lineage that diverged early from the lineage leading to other members of this infraorder. |
