Abstract
Simple SummaryBristletails (Insecta: Microcoryphia) are primarily wingless insects, some of which have been found to exhibit parthenogenesis. In the genus Coreamachilis, parthenogenesis occurs in C. coreanus, whereas sexual reproduction is found in C. songi. Therefore, after obtaining mitochondrial genome sequences of these two species, we analyzed their selection pressure, based on phylogenetic trees of Microcoryphia. However, no positive selection was found in the mitochondrial protein coding genes of either C. coreanus or C. songi. In addition, a long hairpin structure was found between ND1 and 16S rRNA genes in Machilinae and Petrobiinae, which was highly consistent with the phylogenetic results.The order Microcoryphia, commonly known as bristletails, is considered as the most primitive one among living insects. Within this order, two species, Coreamachilis coreanus and C. songi (Machilidae: Machilinae), display the following contrasting reproductive strategies: parthenogenesis occurs in C. coreanus, whereas sexual reproduction is found in C. songi. In the present study, the complete mitogenomes of C. coreanus and C. songi were sequenced to compare their mitogenome structure, analyze relationships within the Microcoryphia, and assess adaptive evolution. The length of the mitogenomes of C. coreanus and C. songi were 15,578 bp and 15,570 bp, respectively, and the gene orders were those of typical insects. A long hairpin structure was found between the ND1 and 16S rRNA genes of both species that seem to be characteristic of Machilinae and Petrobiinae species. Phylogenetic assessment of Coreamachilis was conducted using BI and ML analyses with concatenated nucleotide sequences of the 13 protein-coding genes. The results showed that the monophyly of Machilidae, Machilinae, and Petrobiinae was not supported. The genus Coreamachilis (C. coreanus and C. songi) was a sister clade to Allopsontus helanensis, and then the clade of ((C. coreanus + C. songi) + A. helanensis) was a sister clade to A. baii, which suggests that the monophyly of Allopsontus was not supported. Positive selection analysis of the 13 protein-coding genes failed to reveal any positive selection in C. coreanus or C. songi. The long hairpin structures found in Machilinae and Petrobiinae were highly consistent with the phylogenetic results and could potentially be used as an additional molecular characteristic to further discuss relationships within the Microcoryphia.
Highlights
Bristletails (Insecta: Microcoryphia) are primarily wingless insects, living in places such as under fallen leaves, the bark of trees, moss on wet logs, etc
The locations of the 13 protein-coding genes (PCGs) and two ribosomal RNAs (rRNAs) genes were determined by comparing with homologous sequences of other Microcoryphia mitogenomes [44,47], and the 13 PCGs were translated into amino acids by MEGA 7.0 [48]
We combined all mitogenomes of Microcoryphia as the ingroup including C. coreanus and C. songi along with the two outgroups in order to discuss the phylogenetic relationships in Microcoryphia
Summary
Bristletails (Insecta: Microcoryphia) are primarily wingless insects, living in places such as under fallen leaves, the bark of trees, moss on wet logs, etc. Insect mitogenomes are usually double-stranded circular molecules with a length of 14–20 kb, encoding 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), two ribosomal RNAs (rRNAs), and a control region (CR; or the AT-rich region) [12,13]. Because of their characteristics of fast evolution rates, small genome sizes, and low sequence recombination, mitogenomes have been used widely as molecular markers for phylogenetic analyses [13,14,15]. A positive selection analysis was used to assess whether C. coreanus, with parthenogenic reproduction, and C. songi, with sexual reproduction, were under positive selection at the mitogenome level
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