Comparative Mitogenomic Analysis of Heptageniid Mayflies (Insecta: Ephemeroptera): Conserved Intergenic Spacer and tRNA Gene Duplication

SIMPLE SUMMARY: Heptageniidae is one of the most abundant and widespread families of mayflies, with more than 600 described species and distributed mainly in the Holoarctic, Oriental, and Afrotropical regions. Previous phylogenetic analyses in this family mainly focused on morphological characters and were restricted to one or several genes. Ten complete mitochondrial genomes from this family are reported here. A conserved intergenic spacer and tRNA gene duplication in Heptageniidae mitogenomes may be regarded as ancient features and provide evidence for the phylogenic analysis within Ephemeroptera. ABSTRACT: Large intergenic spacers and tRNA gene duplications have been reported in several insect groups, although little is known about mitogenomes of mayflies. Here, we determined complete mitogenomes of ten heptageniid species and systemically analyzed their mitogenomic features. Both a conserved intergenic spacer (IGS) and trnM duplication were detected in those mitogenomes. The IGS, which was observed in heptageniids, could be further folded into a stable stem–loop structure. The tRNA gene duplication was found in almost all analyzed mitogenomes, and a unique gene block trnI-trnM-trnQ-trnM-ND2 was also discovered. Our analysis demonstrates that the heptageniid gene arrangement pattern can be explained by the tandem duplication-random loss (TDRL) model. Phylogenetic analyses using both Bayesian inference (BI) and maximum likelihood (ML) methods based on the nucleotide and amino acid sequence data recovered the genus Epeorus as monophyletic with strong support. Our results provide a better understanding of mitogenomic evolution in Heptageniidae, as well as novel molecular markers for species identification of mayflies.