Comparative mitogenomic analysis of mirid bugs (Hemiptera: Miridae) and evaluation of potential DNA barcoding markers

The family Miridae is one of the most species-rich families of insects. To better understand the diversity and evolution of mirids, we determined the mitogenome of Lygus pratenszs and re-sequenced the mitogenomes of four mirids (i.e., Apolygus lucorum, Adelphocoris suturalis, Ade. fasciaticollis and Ade. lineolatus). We performed a comparative analysis for 15 mitogenomic sequences representing 11 species of five genera within Miridae and evaluated the potential of these mitochondrial genes as molecular markers. Our results showed that the general mitogenomic features (gene content, gene arrangement, base composition and codon usage) were well conserved among these mirids. Four protein-coding genes (PCGs) (cox1, cox3, nad1 and nad3) had no length variability, where nad5 showed the largest size variation; no intraspecific length variation was found in PCGs. Two PCGs (nad4 and nad5) showed relatively high substitution rates at the nucleotide and amino acid levels, where cox1 had the lowest substitution rate. The Ka/Ks values for all PCGs were far lower than 1 (<0.59), but the Ka/Ks values of cox1-barcode sequences were always larger than 1 (1.34 -15.20), indicating that the 658 bp sequences of cox1 may be not the appropriate marker due to positive selection or selection relaxation. Phylogenetic analyses based on two concatenated mitogenomic datasets consistently supported the relationship of Nesidiocoris + (Trigonotylus + (Adelphocoris + (Apolygus + Lygus))), as revealed by nad4, nad5, rrnL and the combined 22 transfer RNA genes (tRNAs), respectively. Taken sequence length, substitution rate and phylogenetic signal together, the individual genes (nad4, nad5 and rrnL) and the combined 22 tRNAs could been used as potential molecular markers for Miridae at various taxonomic levels. Our results suggest that it is essential to evaluate and select suitable markers for different taxa groups when performing phylogenetic, population genetic and species identification studies.