Mitochondrial Genome Comparison and Phylogenetic Analysis of Four Species of Dung Beetles (Coleoptera: Scarabaeidae: Scarabaeinae)

Dung beetles, despite their well-documented ecological significance, remain surprisingly underrepresented in molecular biology research, with a notable paucity of genomic and molecular data available for this ecologically crucial insect group. We sequenced and analyzed the whole mitochondrial genomes of four species of dung beetles, including <i>Catharsius molossus</i>, <i>Liatongus bucerus</i>, <i>Copris magicus</i>, and <i>Onitis falcatus</i> from the Scarabaeinae subfamily. The results showed that the mitochondrial genome sizes of the four dung beetle species ranged from 14,977 bp to 18,425 bp. Among them, the mitochondrial genome structure, base composition, codon usage, and gene arrangement of <i>L. bucerus</i> and <i>C. magicus</i> were relatively conserved, consistent with other Coleoptera species. However, <i>C. magicus</i> exhibited a unique rearrangement, with the <i>trnT</i> and <i>trnP</i> genes undergoing positional swapping, resulting in the formation of a <i>trnP-trnT</i> tRNA gene block. In <i>L. bucerus</i>, a long-distance translocation of the <i>trnI</i> gene and rearrangement between the <i>trnS2</i> and <i>nad1</i> genes occurred, leading to the formation of a <i>trnS2-trnI</i> tRNA gene block. This represents the first identification of such rearrangements in Scarabaeidae. The phylogenetic reconstruction of mitochondrial protein-coding genes in 63 species of Scarabaeinae revealed significant insights into their evolutionary relationships. It supported multilineage for the tribes Coprini and Onthophagini, and monophyly for the tribes Onitini and Oniticellini. Coprini maintained close affinities with Deltochilini, Dichotomiini, Phanaeini, Ateuchini, and Eurysternini, with Phanaeini as a sister group to each other, and the phylogenetic relationships among the tribes supported the existing findings. It clarified the position of four dung beetles in their respective clades and genera. This study could enrich the genetic data of Scarabaeidae and establishes a foundation for further understanding of the evolutionary relationships of dung beetles.