The complete mitochondrial genome of Thitarodes sejilaensis (Lepidoptera: Hepialidae), a host insect of Ophiocordyceps sinensis and its implication in taxonomic revision of Hepialus adopted in China

Abstract

The mitochondrial genome is widely used for phylogenetic analyses and evolutionary biology. The complete mitochondrial genome of Thitarodes sejilaensis (Lepidoptera: Hepialidae) was sequenced and analyzed in this study. This mitogenome is a typical circular molecule of 15,290bp, with the gene content, orientation and order identical to other insects in the family Hepialidae. The genome nucleotide composition is heavily biased towards As and Ts, accounting for 80.87% of total nucleotide content. The major strand shows a positive AT-skew and negative GC-skew. All 13 protein-coding genes (PCG) are initiated by the canonical putative start codons ATN, except for COI and ND1 that use the initiation codons CGA and TTG, respectively. Nine PCGs share the complete termination codons TAA, while the remaining PCGs use an incomplete termination codon T. Additionally, the codon distribution and Relative Synonymous Codon Usage of all PCGs in the T. sejilaensis mitogenome are consistent with other Hepialidae mitogenomes. Among 22 transfer RNAs, 21 have the typical clover-leaf structure, while tRNASer(AGN) does not possess the dihydrouridine (DHU) arm and could not form a stable stem-loop structure. The secondary structures of 2 ribosomal RNA genes broadly conform to the proposed models of these genes documented in other lepidopteran insects. T. sejilaensis AT-rich region exhibits three repetitive sequences of 118bp. Other regions contain 22-bp overlapping nucleotides and 72-bp intergenic nucleotides. The phylogenetic relationships were constructed by two datasets, the amino acid sequence derived from protein-coding genes and the nucleotide sequence of 13 PCGs and 2 rRNAs. Using Maximum Likelihood (ML), we reconstructed a phylogenetic tree which supported a more primitive taxa of Hepialoidea within Lepidoptera. Moreover, according to comparisons based on the CytB sequences and morphological characteristic, Hepialus species reported in China should be revised. Our taxonomic recommendations include assigning these species to the following genera: Thitarodes, Ahamus, Hepialus and Parahepialus.