The complete mitochondrial genomes of two ghost moths, Thitarodes renzhiensis and Thitarodes yunnanensis: the ancestral gene arrangement in Lepidoptera

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Abstract
Background: Lepidoptera encompasses more than 160,000 described species that have been classified into 45–48 superfamilies. The previously determined Lepidoptera mitochondrial genomes (mitogenomes) are limited to six superfamilies of the lineage Ditrysia. Compared with the ancestral insect gene order, these mitogenomes all contain a tRNA rearrangement. To gain new insights into Lepidoptera mitogenome evolution, we sequenced the mitogenomes of two ghost moths that belong to the non-ditrysian lineage Hepialoidea and conducted a comparative mitogenomic analysis across Lepidoptera.Results: The mitogenomes ofThitarodes renzhiensisandT.yunnanensisare 16,173 bp and 15,816 bp long with an A + T content of 81.28 % and 82.34 %, respectively. Both mitogenomes include 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and the A + T-rich region. Different tandem repeats in the A + T-rich region mainly account for the size difference between the two mitogenomes. All the protein-coding genes start with typical mitochondrial initiation codons, except forcox1(CGA) andnad1(TTG) in both mitogenomes. The anticodon oftrnS(AGN)inT. renzhiensisandT. yunnanensisis UCU instead of the mostly used GCU in other sequenced Lepidoptera mitogenomes. The 1,584-bp sequence fromrrnStonad2was also determined for an unspecified ghost moth (Thitarodessp.), which has no repetitive sequence in the A + T-rich region. All threeThitarodesspecies possess the ancestral gene order withtrnI-trnQ-trnMlocated between the A + T-rich region andnad2, which is different from the gene ordertrnM-trnI-trnQin all previously sequenced Lepidoptera species. The formerly identified conserved elements of Lepidoptera mitogenomes (i.e. the motif ‘ATAGA’ and poly-T stretch in the A + T-rich region and the long intergenic spacer upstream ofnad2) are absent in theThitarodesmitogenomes.Conclusion: The mitogenomes ofT. renzhiensisandT. yunnanensisexhibit unusual features compared with the previously determined Lepidoptera mitogenomes. Their ancestral gene order indicates that the tRNA rearrangement event(s) likely occurred after Hepialoidea diverged from other lepidopteran lineages. Characterization of the two ghost moth mitogenomes has enriched our knowledge of Lepidoptera mitogenomes and contributed to our understanding of the mechanisms underlying mitogenome evolution, especially gene rearrangements.

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