Characteristics and phylogenetic implications of the mitochondrial genome of a rare species, Libellula melli

This study sequenced and assembled the mitochondrial genome of the rare dragonfly species Libellula melli, and submitted the results to the NCBI GenBank database, obtaining the accession number PP588458. The mitochondrial genome spans a total length of 15,149 bp, encompassing 13 protein-coding genes (PCGs), 22 tRNA genes, 2 rRNA genes, and a control region or D-loop. Of these, 25 genes and segments are located on the heavy strand (H-strand), while the remaining 13 reside on the light strand (L-strand). The nucleotide composition of the L. melli mitochondrial genome exhibits a prominent AT bias (AT = 73.3 %), with T, C, A, and G bases comprising 34.5 %, 15.6 %, 38.8 %, and 11.1 % respectively, displaying a positive AT skew of 0.059. Among the 13 PCGs, the primary start codons are ATT, ATG, and TTG, while the primary stop codons are TAA, with instances of TA(C) and T(AT) also observed. RSCU analysis reveals that the most frequently used codon is UUA, with an RSCU value of 3.75, encoding leucine (Leu). The secondary structures of the proteins encoded by the 13 PCGs generally exhibit a trend of α-helix > random coil > extended strand > β-turn. Phylogenetic analysis uncovers the phylogenetic relationships of L. melli within the reported Libellulidae species, revealing (((((((L. melli + L. quadrimaculata) + L. angelina) + ((O. chrysis + O. glaucum) + O. albistylum)) + ((C. servilia servilia + T. virginia) + N. fulvia) + (L. albifrons + S. eroticum)) + (P. flavescens + T. aurora)) + (D. phaon + H. croceus)) + (B. contaminate + P. zonata)). This study provides insights into the mitochondrial genome and its characteristics of this rare dragonfly species, contributing to our understanding of the intricate evolutionary relationships within the Odonata order. The data obtained serve as a foundation for further exploration of the complex phylogenetic relationships among dragonfly insects.