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

## TL;DR

This study uses the mitochondrial genome of a marine crab to clarify its evolutionary relationships and gene arrangement patterns.

## Contribution

The study reveals a conserved gene order with a unique trnH translocation in Metopograpsus quadridentatus, aiding taxonomic classification.

## Key findings

- The mitochondrial gene arrangement of M. quadridentatus is mostly unchanged, similar to ancient crustaceans.
- Phylogenetic analysis confirms M. quadridentatus belongs to the genus Metopograpsus and family Grapsidae.
- Gene order conservation is observed in several Brachyura families, including Grapsidae.

## Abstract

The marine crab Metopograpsus quadridentatus is categorized in the family Grapsidae, but its classification remains unclear because of limited differences in appearance among species. In this research, we examined its mitochondrial genome, which showed a gene order similar to that of ancient crustaceans, with the exception of the translocated trnH gene. Analysis of 13 protein-coding genes from 40 Brachyura species indicated that it belongs to the genus Metopograpsus and family Grapsidae, clarifying its evolutionary relationships and demonstrating the importance of mitochondrial genomes in taxonomic classification.

The taxonomy of the genus Metopograpsus 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 Metopograpsus quadridentatus, 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 M. quadridentatus to investigate its gene rearrangement patterns and its place within Brachyura. We compared the gene order of M. quadridentatus 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 M. quadridentatus is mostly unchanged, similar to the original crustacean pattern, except for the movement of the trnH 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 M. quadridentatus within the genus Metopograpsus 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 Metopograpsus.