The mitochondrial genome of Protohermes concolorus Yang et Yang 1988 (Insecta: Megaloptera: Corydalidae).

The first complete mitochondrial genome of dobsonfly Protohermes concolorus Yang et Yang, 1988 (Megaloptera: Corydalidae) was sequenced in this study. The genome was a circular molecule of 15,851 bp containing the typical 37 genes that arranged in the same order as that of the putative ancestor of hexapods. Sequences overlaps were observed between several neighbor genes, which made the genome relatively compact. The tRNA-Ser (GCT) could not be folded into typical secondary structure because its DHU arm was replaced with a simple loop. Six of the 13 protein genes were terminated with a single T adjacent to a downstream tRNA gene in the same strand. The variation of GC content caused the different nucleotide substitution patterns of the protein genes. The genome was AT-biased with a total A + T content of 75.83% which was also demonstrated by the codon usage. The control region was the most AT-rich region with a sub-region of even higher A + T content. Protein genes of two strands presented opposite CG-skew trends which was also reflected by the codon usage. For most of the amino acids, the protein coding sequences did not prefer to use the cognate codons of corresponding tRNAs and the codon usage of the protein genes was not random. The variation of nucleotide substitution patterns of protein genes was significantly correlated with the GC content. The phylogenetic analyses based on all the 13 protein genes showed that Megaloptera was the sister group of other holometabolous insects except Coleoptera.