تنوع گسترده ژنوم میتوکتدریایی سخت‌بالپوشان به سمت افزایش عدم تقارن رشته‌ها

Beetles (Insecta: Coleoptera) are the most diverse group of animals with more than 387,000 species in nearly all terrestrial and freshwater ecosystems. The significant increase in the number of deposited sequences of beetle mitochondrial DNA (mtDNA) in GeneBank allow a comprehensive analysis of the direction and intensity of changes in base composition and DNA sequence using a large reliable database. Here, we played with numbers and proportions in a large source (6409 gene sequences belonging to 493 beetle species) of beetle mtDNA to explore the extent and direction of base compositional changes in this diverse group. Sequence edition and accuracy was checked by AliView software (vr. 1.17.1) and calculations were performed using Mega 6 software. In addition, a total of 832 sequences of protein coding genes (PCGs) and ribosomal RNA genes (rRNA) genes belonging to 64 species of the closely related orders in the group Neuropterida (i.e. Megaloptera, Raphidioptera, and Neuroptera) as well as 489 complete genomes belonging to other orders within the superorder Endopterygota were used as reference. Almost all PCGs, rRNA genes, and the whole protein coding region of the majority strand in Coleoptera showed increase in C, and to a lesser extent, A, and G content, besides significant decrease in T and A+T content when compared with the closely related orders within Neuropterida. We detected extensive unidirectional diversification of beetle mtDNA in comparison with all other holometabolous insects, a diversification in favor of C and at expense of T on the majority strand. These patterns of substitution are likely to increase AT skew and decrease GC skew of beetle mtDNA. Therefore, beetle mtDNA seems to diversify towards higher strand asymmetry, which results probably from direct conversion of A to G and T to C on the minority strand. The patterns of molecular evolution are homogenous across a given DNA strand, regardless of bearing or lacking the protein coding region.