Structure, Evolution, and Mitochondrial Genome Analysis of Mussel Species (Bivalvia, Mytilidae).

Based on the nucleotide sequences of the mitochondrial genome (mitogenome) of specimens taken from two mussel species (Arcuatula senhousia and Mytilus coruscus), an investigation was performed by means of the complex approaches of the genomics, molecular phylogenetics, and evolutionary genetics. The mitogenome structure of studied mussels, like in many other invertebrates, appears to be much more variable than in vertebrates and includes changing gene order, duplications, and deletions, which were most frequent for tRNA genes; the mussel species' mitogenomes also have variable sizes. The results demonstrate some of the very important properties of protein polypeptides, such as hydrophobicity and its determination by the purine and pyrimidine nucleotide ratio. This fact might indirectly indicate the necessity of purifying natural selection for the support of polypeptide functionality. However, in accordance with the widely accepted and logical concept of natural cutoff selection for organisms living in nature, which explains its action against deleterious nucleotide substitutions in the nonsynonymous codons (mutations) and its holding of the active (effective) macromolecules of the polypeptides in a population, we were unable to get unambiguous evidence in favor of this concept in the current paper. Here, the phylogeny and systematics of mussel species from one of the largest taxons of bivalve mollusks are studied, the family known as Mytilidae. The phylogeny for Mytilidae (order Mytilida), which currently has no consensus in terms of systematics, is reconstructed using a data matrix of 26-27 mitogenomes. Initially, a set of 100 sequences from GenBank were downloaded and checked for their gender: whether they were female (F) or male (M) in origin. Our analysis of the new data confirms the known drastic differences between the F/M mitogenome lines in mussels. Phylogenetic reconstructions of the F-lines were performed using the combined set of genetic markers, reconstructing only protein-coding genes (PCGs), only rRNA + tRNA genes, and all genes. Additionally, the analysis includes the usage of nucleotide sequences composed of other data matrices, such as 20-68 mitogenome sequences. The time of divergence from MRCA, estimated via BEAST2, for Mytilidae is close to 293 Mya, suggesting that they originate in the Silurian Period. From all these data, a consensus for the phylogeny of the subfamily of Mytilinae and its systematics is suggested. In particular, the long-debated argument on mussel systematics was resolved as to whether Mytilidae, and the subfamily of Mytilinae, are monophyletic. The topology signal, which was strongly resolved in this paper and in the literature, has refuted the theory regarding the monophyly of Mytilinae.

Comparative analyses of mitogenomes in the social bees with insights into evolution of long inverted repeats in the Meliponini.

The insect mitogenome is typically a compact circular molecule with highly conserved gene contents. Nonetheless, mitogenome structural variations have been reported in specific taxa, and gene rearrangements, usually the tRNAs, occur in different lineages. Because synapomorphies of mitogenome organizations can provide information for phylogenetic inferences, comparative analyses of mitogenomes have been given increasing attention. However, most studies use a very few species to represent the whole genus, tribe, family, or even order, overlooking potential variations at lower taxonomic levels, which might lead to some incorrect inferences. To provide new insights into mitogenome organizations and their implications for phylogenetic inference, this study conducted comparative analyses for mitogenomes of three social bee tribes (Meliponini, Bombini, and Apini) based on the phylogenetic framework with denser taxonomic sampling at the species and population levels. Comparative analyses revealed that mitogenomes of Apini and Bombini are the typical type, while those of Meliponini show diverse variations in mitogenome sizes and organizations. Large inverted repeats (IRs) cause significant gene rearrangements of protein coding genes (PCGs) and rRNAs in Indo-Malay/Australian stingless bee species. Molecular evolution analyses showed that the lineage with IRs have lower d N/ d S ratios for PCGs than lineages without IRs, indicating potential effects of IRs on the evolution of mitochondrial genes. The finding of IRs and different patterns of gene rearrangements suggested that Meliponini is a hotspot in mitogenome evolution. Unlike conserved PCGs and rRNAs whose rearrangements were found only in the mentioned lineages within Meliponini, tRNA rearrangements are common across all three tribes of social bees, and are significant even at the species level, indicating that comprehensive sampling is needed to fully understand the patterns of tRNA rearrangements, and their implications for phylogenetic inference.

The complete mitogenome of Sokolov's Dwarf Hamster (Cricetulus sokolovi) and implication of phylogenetic status.

There is still an obvious lack of information on Sokolov's Dwarf Hamster (Cricetulus sokolovi) which belongs to subfamily Cricetinae because the species is only rarely found in Gobi desert. In this study, we obtained the complete mitochondrial genome sequences of C. sokolovi. The genome is 16,292bp in length and has a base composition of 33.5% A, 30.5% T, 22.9% C, and 13.1% G. The mitogenome structure, consisting of 13 protein-coding genes, two rRNA genes (12S rRNA and 16S rRNA), 22 tRNA genes, and one control region, is similar to that of typical vertebrate mitochondrial genomes of other rodents. We restructured a Bayesian phylogenetic tree by using 12 species belonging to subfamily Cricetinae. As indicated by the phylogenetic tree, genus Cricetulus is polyphyletic group, and C. Sokolovi is the closest relative of Cricetulus griseus. The mitochondrial genome can provide basic data for further study on the phylogenetic relationship of subfamily Cricetinae.

The complete mitochondrial genome of white-tailed mole (Parascaptor leucura).

The white-tailed mole (Parascaptor leucura) belongs to genus Parascaptor, which is a monotypic genus distributed across Southwestern China, Assam (India), Bengal, and Northern Burma, and Laos. In this study, we obtained the complete mitochondrial genome of Parascaptor leucura. The genome is total 16,875 bp in length, containing 13 protein-coding genes, 22 transfer RNA genes (tRNA), two ribosomal RNA genes (rRNA), and two non-coding regions, with a base composition of 33.5% A, 26.4% T, 25.7% C, and 14.3% G. The nucleotide sequence data of 13 protein-coding genes of P. leucura and other nine Eulipotyphla species were used to reconstruct a Bayesian phylogenetic tree. The tree shows that P. leucura belongs to subfamily Talpinae and is closely related to Scaptochirus moschatus.

The complete mitochondrial genome of pygmy red-toothed shrew (Chodsigoa parva).

The study of pygmy red-toothed shrew (Chodsigoa parva), which is the smallest species of geuns Chodsigoa, is extremely lacking. Also, it is classified as data deficient (DD) on The IUCN Red List. Here, we obtained a complete mitochondrial genome of Chodsigoa parva. The mitochondrial genome of C. parva is totally 17,216 bp in length and it is composed of 13 protein-coding genes, 22 transfer RNA genes (tRNA), 2 ribosomal RNA genes (rRNA), and 2 non-coding regions. We restructured Bayesian phylogenetic tree by using 19 species those belong to family Soricidae. The mitochondrial genome can provide basic data for further study about the phylogenetic relationship of family Soricidae.