The First Conserved Mitochondrial Genome of Polygraphus Poligraphus (Coleoptera: Curculionidae) and Its Phylogenetic Implications

Abstract

Background: Polygraphus poligraphus L., the four-eyed spruce bark beetle, belongs to the Curculionidae (Coleoptera), which mainly harms Picea asperata Mast and Pinus armandii Franch tree trunks. So far, there is no mitochondrial genome reported for P. poligraphus.Results: In this study, we sequenced and annotated the nearly complete mitogenome of P. poligraphus for the first time and predicted the secondary structures of its tRNAs. The results showed that the mitogenome of P. poligraphus was 15,302 bp (partial genome) in length with A + T content of 69.65% due to large-scale duplication. The nearly complete mitochondrial genome of P. Poligraphus contained a set of 36 genes typical of the insect mitogenome, including 13 protein-coding genes (PCGs), 2 ribosomal RNA genes (rRNAs), 21 transfer RNA genes (tRNAs) but lacked tRNA-Ile, as for the typical insect mitogenome. The results of nucleotide skew statistics showed that the AT-skews and GC-skew of P. poligraphus were positive and negative, respectively, which were similar to other Scolytinae insects. All PCGs were initiated with the standard start codon ATN. All tRNA genes had the typical cloverleaf structure, except for the trnS1, which lacked a dihydroxyuridine (DHU) arm. Furthermore, we reconstructed phylogenetic trees of P. poligraphus based on the data set of the mitogenome’s protein-coding gene sequences using the Bayesian inference (BI) method. Phylogenetic analysis indicated that the P. poligraphus mitogenome clustered with Gnathotrichus materiarius and Pityophthorus pubescens mitogenomes in a monophyletic manner. The phylogeny of these three genera of Scolytinae is presented as Polygraphus + (Gnathotrichus + Pityophthorus). Conclusions: The results presented herein will provide a reference for further molecular taxonomy, evolution and phylogenetic research of P. poligraphus. However, additional mitogenome samples are still needed to more satisfactorily resolve the phylogeny of the Scolytinae.