Comparative Analysis of Metopograpsus quadridentatus (Crustacea: Decapoda: Grapsidae) Mitochondrial Genome Reveals Gene Rearrangement and Phylogeny

The taxonomy of the genus <i>Metopograpsus</i> is still a matter of debate because its species have limited morphological differences. Mitochondrial genomes, which are highly informative and easily accessible genetic markers, have been widely used to study molecular evolution and clarify relationships among species. This study aims to investigate the mitochondrial genome of <i>Metopograpsus quadridentatus</i>, a species with unique ecological and evolutionary significance. By analyzing the mitochondrial genome, we seek to address taxonomic uncertainties and provide insights into the evolutionary history of this species. In this study, we sequenced and analyzed the mitochondrial genome of <i>M. quadridentatus</i> to investigate its gene rearrangement patterns and its place within Brachyura. We compared the gene order of <i>M. quadridentatus</i> with that of 40 other Brachyuran species and created phylogenetic trees based on the nucleotide and amino acid sequences of 13 protein-coding genes (PCGs). We found that the mitochondrial gene arrangement of <i>M. quadridentatus</i> is mostly unchanged, similar to the original crustacean pattern, except for the movement of the <i>trnH</i> gene. Notably, the gene orders of several families, such as Eriphiidae, Grapsidae, Camptandriidae, Dotillidae, Plagusiidae, Ocypodidae, and Gecarcinidae, are the same. Phylogenetic analyses consistently placed <i>M. quadridentatus</i> within the genus <i>Metopograpsus</i> and the family Grapsidae, confirming its current taxonomic classification. These results offer important insights into evolutionary relationships and gene order conservation within Brachyura. Our study highlights the significance of mitochondrial genomes in resolving taxonomic uncertainties within the genus <i>Metopograpsus</i>.