关键词: 蟹类, 18S rDNA, COl, 分子系统发育

Abstract: Using molecular phylogenetic methodology with gene sequence fragments of 18S rDNA and subunitl of C enzyme oxide of mitochondrial dell pigment(CO I) as the molecular mark and combined withmorphological character,evolutionary history of selected brachyuran crabs were discussed. Totally 10 18SrDNA sequnces and 5 CO I gene fragments were obtained by Polymerase Chain Reaction (PCR),andsummited to the Genebank. The length of 18S rDNA sequences from 10 crabs,ranges from 1 780 to l787 bp,in which the shortest one is Hemigrapsus sinensis, the longest one is Parthenope validus. In the 18S rDNAsequnces, the average content of base A,T,G and C is 23.72%,24.58%,24.52%,and 27.17% separately.Sequence alignment shows that 18S rDNA sequences are relatively conservative,containing only onehypervariable region of about 50 bp between 88 bp and 130 bp. The base distance of the species is very small,from 0.001 to 0.017.The phylogenetic trees of 18S rDNA give molecular biological proof for the same originof Grapsioidea,Ocypodioidea and Portunoidea, and also support moving the Helice crab from Sesarminae toVaruninae.The length of mitochondrial DNA sequence from 5 charybdis crabs is 709 bp,and the averagecontent of the base A,T,G and C is 26.88%,37.62%,17.50% and 18.00%separately.The fragment ofco I gene has high species variability,more suitable for the study of the interspecific evolutionary history.The base distance of the charybdis is long,from 0.016 to 0.138.The phylogenetic trees of CO I gene truereflect the evolutionary relations of different charybdis species and are concordant with traditional taxology.This provides a molecular method for the identification of charybdis species of similar morphologicalcharact ers.

Key words: crab, 18S rDNA, COl, phylogenesis