Confirmation of the first intronic sequence in the bivalvian mitochondrial genome of Macoma balthica (Linnaeus, 1758)

The absence of canonical respiratory complex I subunits in male-type mitogenomes of three Donax species

Bivalves are an extraordinary class of animals in which species with a doubly uniparental inheritance (DUI) of mitochondrial DNA have been described. DUI is characterized as a mitochondrial homoplasmy of females and heteroplasmy of male individuals where F-type mitogenomes are passed to the progeny with mother egg cells and divergent M-type mitogenomes are inherited with fathers sperm cells. However, in most cases only male individuals retain divergent mitogenome inherited with spermatozoa. Additionally, in many of bivalves, unique mitochondrial features, like additional genes, gene duplication, gene extensions, mitochondrial introns, and recombination, were observed. In this study, we sequenced and assembled male-type mitogenomes of three Donax species. Comparative analysis of mitochondrial sequences revealed a lack of all seven NADH dehydrogenase subunits as well as the presence of three long additional open reading frames lacking identifiable homology to any of the existing genes.

De novo assembly of the complete mitochondrial genome of Mycetophylax simplex Emery, 1888 through organelle targeting revels no substantial expansion of gene spacers, but rather some slightly shorter genes

Mitochondria play a key role in cell biology and have their own genome, residing in a highly oxidative environment that induces faster changes than the nuclear genome. Because of this, mitochondrial markers have been exploited to reconstruct phylogenetic and phylogeographic relationships in studies of adaptation and molecular evolution. In this study, we determined the complete mitogenome of the fungus-farming ant Mycetophylax simplex (Hymenoptera, Formicidae) and conducted a comparative analysis among 29 myrmicine ant mitogenomes. Mycetophylax simplex is an endemic ant that inhabits sand dunes along the southern Atlantic coast. Specifically, the species occur in the ecosystem known as "restinga", within the Atlantic Forest biome. Due to habitat degradation, land use and decline of restinga habitats, the species is considered locally extinct in extremely urban beaches and is listed as vulnerable on the Brazilian Red List (ICMBio). We employed a mitochondrion-targeting approach to obtain the complete mitogenome through high-throughput DNA sequencing technology. This method allowed us to determine the mitogenome with high performance, coverage and low cost. The circular mitogenome has a length of 16,367 base pairs enclosing 37 genes (13 protein-coding genes, 22 tRNAs and 2 rRNAs) along with one control region (CR). All the protein-coding genes begin with a typical ATN codon and end with the canonical stop codons. All tRNAs formed the fully paired acceptor stems and fold into the typical cloverleaf-shaped secondary structures. The gene order is consistent with the shared Myrmicinae structure, and the A + T content of the majority strand is 81.51%. Long intergenic spacers were not found but some gene are slightly shorter. The phylogenetic relationships based on concatenated nucleotide and amino acid sequences of the 13 protein-coding genes, using Maximum Likelihood and Bayesian Inference methods, indicated that mitogenome sequences were useful in resolving higher-level relationship within Formicidae.

Comparative mitogenomics of Brachiopods reveals conservatism in articulate species and unusualness in inarticulate species

BACKGROUND

Brachiopods are a phylum of marine invertebrates with over 10,000 fossil species. Today, there are fewer than 500 extant species assigned to the class Articulata or Inarticulata and for which knowledge of evolutionary genetics and genomics is still poor. Until now, complete mitogenome sequences of two inarticulate species and four articulate species were available.

METHODS AND RESULTS

The complete mitogenome of the inarticulate brachiopod species Lingula reevii (20,778 bp) was obtained by using next generation sequencing. It contains 12 protein-coding genes (the annotation of atp8 is unsure), two ribosomal RNA genes, 26 transfer RNA genes, and one supernumerary ORF that is also conserved in the inarticulate species Lingula anatina. It is hypothesized that this ORF could represent a Lingula-specific mtORFan gene (without obvious homology to other genes). Comparative mitogenomics indicate the mitochondrial gene order of L. reevii is unique among brachiopods, and that compared to articulate species, inarticulate species exhibit massive mitogenome rearrangements, deviant ATP8 protein sequences and supernumerary ORFs, possibly representing species- or lineage-specific mtORFan genes.

CONCLUSION

The results of this study enrich genetics knowledge of extant brachiopods, which may eventually help to test hypotheses about their decline.