# Comparative Analysis of the Mitochondrial Genomes of Three Species of Elmidae (Coleoptera: Dryopoidea)

## TL;DR

This study compares the mitochondrial genomes of three elm beetle species to better understand their evolutionary relationships and taxonomy.

## Contribution

The paper provides new mitogenomic data for Elmidae and highlights ambiguities in their taxonomic classification.

## Key findings

- The three Elmidae species have similar mitochondrial genome structures but differ from typical Coleoptera gene arrangements.
- Phylogenetic analysis shows Elmidae is monophyletic within Dryopoidea but suggests taxonomic revisions at lower levels.
- COX1 and nad4L are the most conserved protein-coding genes in the studied species.

## Abstract

Elmidae (Coleoptera: Dryopoidea) is a widespread family of aquatic beetles that currently contains about 151 genera with approximately 1500 species. The phylogenetic positions of the intrafamilial taxonomic groups remain ambiguous. To further understand the position of Elmidae within Coleoptera and the relationships among the subfamily, tribe, and genus levels, three complete mitochondrial genomes of Elmidae (Cuspidevia jaechi, Grouvellinus longiusculus, and Stenelmis punctulata) were sequenced, annotated, analyzed, and compared. The nucleotide composition, genome organization, and codon usage of the three species were highly similar. However, their gene arrangement differed from that of typical mitochondrial genomes in Coleoptera. Phylogenetic analysis indicates that the higher taxonomic groups within Elmidae require further supplementation. This study contributes to the mitogenomic library of Elmidae, providing a scientific basis for an understanding of the evolution of Elmidae species.

The mitochondrial genomes of three species of Elmidae were sequenced. The sizes were 16,309 bp (C. jaechi), 16,291 bp (G. longiusculus), and 15,480 bp (S. punctulata). Each genome includes 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and a control region (CR). All three mitogenomes show AT bias. Except for trnS1, lacking the dihydrouridine (DHU) arm, all tRNA genes had a typical cloverleaf structure. The codon usage preferences of the three species showed high similarity. The arrangement of the genes in the three mitogenomes was consistent among them but differed from that in the typical mitogenomes of Coleoptera. The Ka/Ks ratio indicated that COX1 and nad4L had a lower evolutionary rate, being relatively conserved genes among 13 PCGs. The phylogenetic analysis revealed that Elmidae belongs to the superfamily Dryopoidea within the suborder Polyphaga and is monophyletic. The results preliminarily indicate that the taxonomic groups at the subfamily, tribe, and genus levels within Elmidae are ambiguous, and further revisions may be required in the future.