Complete Mitochondrial Genomes of Nannostomus Pencilfish: Genome Characterization and Phylogenetic Analysis.

Although the pencilfish is a globally popular economic fish in the aquarium market, its taxonomic classification could be further refined. In order to understand the taxonomy of species of the genus Nannostomus (Characiformes, Lebiasinidae) and their phylogenetic position within the order Characiformes, in this study, we characterized mitochondrial genomes (mitogenomes) from four Nannostomus species for the first time. The four mitogenomes exhibited the typical circular structure, with overall sizes varying from 16,661 bp to 16,690 bp. They contained 13 protein-coding genes (PCGs), 2 ribosomal RNA genes (rRNAs), 22 transfer RNA genes (tRNAs), and 1 control region (CR). Nucleotide composition analysis suggested that the mitochondrial sequences were biased toward A and T. Bayesian inference and maximum likelihood analyses based on PCGs support the family Lebiasinidae classification, described using four Nannostomus species, clustering together with Lebiasina multimaculata from the same family. The results of this study support the current taxonomic classification of the family Lebiasinidae. Phylogenetic analysis also suggested that gene rearrangement would not significantly impact the phylogenetic relationships within the order Characiformes. These results might provide new data regarding the phylogeny and classification of the order Characiformes, thus providing a theoretical basis for the economic development of aquarium fish markets.

Characterization of the complete mitochondrial genome of Spirobolus grahami (Diplopoda: Spirobolidae) with phylogenetic analysis.

Diplopoda is one of the most diverse and important groups of soil arthropods, but little research has been done on their phylogenetic relationship and evolution. Here, we sequenced and annotated the complete mitochondrial genomes of Spirobolus grahami. The total mitogenome of S. grahami was typical circular, double-stranded molecules, with 14,875 bp in length, including 13 protein-coding genes, 22 tRNAs, two rRNAs, and one control region. Base composition analysis suggested that the mitochondrial sequences were biased toward A and T, with A + T content of 58.68%. The mitogenomes of S. grahami exhibited negative AT and positive GC skews. Most of the 13 PCGs had ATN as the start codon, except COX1 start with CGA, and most PCGs ended with the T stop codon. The dN/dS values for most PCGs were lower than 1, suggesting that purifying selection was likely the main driver of mitochondrial PCG evolution. Phylogenetic analyses based on 13 PCGs using BI and ML methods support the classification of genus Spirobolus and Tropostreptus. Glomeridesmus spelaeus is distantly related to the other Diplopoda species.

Comparison of seven complete mitochondrial genomes from Lamprologus and Neolamprologus (Chordata, Teleostei, Perciformes) and the phylogenetic implications for Cichlidae.

In this study, mitochondrial genomes (mitogenomes) of seven cichlid species (Lamprologuskungweensis, L.meleagris, L.ornatipinnis, Neolamprologusbrevis, N.caudopunctatus, N.leleupi, and N.similis) are characterized for the first time. The newly sequenced mitogenomes contained 37 typical genes [13 protein-coding genes (PCGs), two ribosomal RNA genes (rRNAs) and 22 transfer RNA genes (tRNAs)]. The mitogenomes were 16,562 ~ 16,587 bp in length with an A + T composition of 52.1~58.8%. The cichlid mitogenomes had a comparable nucleotide composition, A + T content was higher than the G + C content. The AT-skews of most mitogenomes were inconspicuously positive and the GC-skews were negative, indicating higher occurrences of C than G. Most PCGs started with the conventional start codon, ATN. There was no essential difference in the codon usage patterns of these seven species. Using Ka/Ks, we found the fastest-evolving gene were atp8. But the results of p-distance indicated that the fastest-evolving gene was nad6. Phylogenetic analysis revealed that L.meleagris did not cluster with Lamprologus species, but with species from the genus Neolamprologus. The novel information obtained about these mitogenomes will contribute to elucidating the complex relationships among cichlid species.