This study aims to know the efficiency of the partial sequence of COI and 16S rRNA genes for the identification of crab species and to determine their phylogenetic relationships. A total of 36 sequences of 14 different species of crab were generated, belonging to 9 genera and 7 families. The average %GC content was higher in the sequences of the COI gene compared to the 16S rRNA. A large variation of the GC content was found at the 3rd codon position of the COI sequences. All the species were discriminated by COI and 16S rRNA when an intraspecific threshold of 2% K2P was used. The mean congeneric divergence was 72 and 94-fold higher than mean conspecific divergence for the COI and 16S rRNA markers, respectively. However, K2P% between closely related species was higher in COI compared to 16S rRNA. The Maximum Likelihood (ML) phylogenetic tree constructed based on COI and 16S rRNA gene sequences showed that the same species were clustered together under a single clade, supporting that both the markers were efficient in discriminating crab species. The ML tree of the COI sequences showed long-branch attraction and clustering of the species from different genus together. Such incongruence was not found in the tree topology of the 16S rRNA, providing phylogenetic relationships among species with a true divergence rate. The study revealed that the COI gene would be much efficient in discriminating closely related species, and 16S rRNA would be superior to COI in phylogenetic analysis.

这项研究旨在了解COI和16S rRNA基因部分序列对蟹类物种鉴定的效率，并确定它们的系统发生关系。总共产生了14个不同种类的蟹的36个序列，分别属于9属7科。与16S rRNA相比，COI基因序列中的平均％GC含量更高。在COI序列的第3个密码子位置发现GC含量有很大变化。当使用2％K2P的种内阈值时，所有物种均由COI和16S rRNA区分。平均同系差异分别比COI和16S rRNA标记的平均同种差异高72倍和94倍。但是，与16S rRNA相比，密切相关物种之间的K2P％在COI中更高。基于COI和16S rRNA基因序列构建的最大似然（ML）系统发育树表明，同一物种在单个进化枝下聚集在一起，这表明这两种标记物均能有效区分蟹类。COI序列的ML树显示了长期分支吸引并将不同属的物种聚集在一起。在16S rRNA的树形拓扑中未发现这种不一致，这为物种之间的系统发育关系提供了真实的发散率。研究表明，COI基因在区分密切相关物种方面将非常有效，在系统发育分析中16S rRNA将优于COI。支持这两种标记物在区分蟹类物种方面是有效的。COI序列的ML树显示了长期分支吸引并将不同属的物种聚集在一起。在16S rRNA的树形拓扑中未发现这种不一致，这为物种之间的系统发育关系提供了真实的发散率。研究表明，COI基因在区分密切相关物种方面将非常有效，在系统发育分析中16S rRNA将优于COI。支持这两种标记物在区分蟹类物种方面是有效的。COI序列的ML树显示了长期分支吸引并将不同属的物种聚集在一起。在16S rRNA的树形拓扑中未发现这种不一致，这为物种之间的系统发育关系提供了真实的发散率。研究表明，COI基因在区分密切相关物种方面将非常有效，在系统发育分析中16S rRNA将优于COI。