Use of mitogenomic information in teleostean molecular phylogenetics: a tree-based exploration under the maximum-parsimony optimality criterion

Comparative Analysis of the Complete Mitochondrial Genomes of Three Sisoridae (Osteichthyes, Siluriformes) and the Phylogenetic Relationships of Sisoridae

The family Sisoridae is one of the largest and most diverse Asiatic catfish families, with most species occurring in the water systems of the Qinhai-Tibetan Plateau and East Himalayas. At present, the phylogenetic relationship of the Sisoridae is relatively chaotic. In this study, the mitochondrial genomes (mitogenomes) of three species Creteuchiloglanis kamengensis, Glaridoglanis andersonii, and Exostoma sp. were systematically investigated, the phylogenetic relationships of the family were reconstructed and to determine the phylogenetic position of Exostoma sp. within Sisoridae. The lengths of the mitogenomes' sequences of C. kamengensis, G. andersonii, and Exostoma sp. were 16,589 bp, 16,531 bp, and 16,529 bp, respectively. They all contained one identical control region (D-loop), two ribosomal RNAs (rRNAs), 13 protein-coding genes (PCGs) and 22 transfer RNA (tRNA) genes. We applied two approaches, Bayesian Inference (BI) and Maximum Likelihood (ML), to construct phylogenetic trees. Our findings revealed that the topological structure of both ML and BI trees exhibited significant congruence. Specifically, the phylogenetic tree strongly supports the monophyly of Sisorinae and Glyptosternoids and provides new molecular biological data to support the reconstruction of phylogenetic relationships with Sisoridae. This study is of great scientific value for phylogenetic and genetic variation studies of the Sisoridae.

Comprehensive analysis of 111 Pleuronectiformes mitochondrial genomes: insights into structure, conservation, variation and evolution

BACKGROUND

Pleuronectiformes, also known as flatfish, are important model and economic animals. However, a comprehensive genome survey of their important organelles, mitochondria, has been limited. Therefore, we aim to analyze the genomic structure, codon preference, nucleotide diversity, selective pressure and repeat sequences, as well as reconstruct the phylogenetic relationship using the mitochondrial genomes of 111 flatfish species.

RESULTS

Our analysis revealed a conserved gene content of protein-coding genes and rRNA genes, but varying numbers of tRNA genes and control regions across species. Various gene rearrangements were found in flatfish species, especially for the rearrangement of nad5-nad6-cytb block in Samaridae family, the swapping rearrangement of nad6 and cytb gene in Bothidae family, as well as the control region translocation and tRNA-Gln gene inversion in the subfamily Cynoglossinae, suggesting their unique evolutionary history and/or functional benefit. Codon usage showed obvious biases, with adenine being the most frequent nucleotide at the third codon position. Nucleotide diversity and selective pressure analysis suggested that different protein-coding genes underwent varying degrees of evolutionary pressure, with cytb and cox genes being the most conserved ones. Phylogenetic analysis using both whole mitogenome information and concatenated independently aligned protein-coding genes largely mirrored the taxonomic classification of the species, but showed different phylogeny. The identification of simple sequence repeats and various long repetitive sequences provided additional complexity of genome organization and offered markers for evolutionary studies and breeding practices.

CONCLUSIONS

This study represents a significant step forward in our comprehension of the flatfish mitochondrial genomes, providing valuable insights into the structure, conservation and variation within flatfish mitogenomes, with implications for understanding their evolutionary history, functional genomics and fisheries management. Future research can delve deeper into conservation biology, evolutionary biology and functional usages of variations.

Paternal Mitochondrial DNA Leakage in Natural Populations of Large-Scale Loach, Paramisgurnus dabryanus

Animal mitochondrial DNA is usually considered to comply with strict maternal inheritance, and only one mitochondrial DNA haplotype exists in an individual. However, mitochondrial heteroplasmy, the occurrence of more than one mitochondrial haplotype, has recently been reported in some animals, such as mice, mussels, and birds. This study conducted extensive field surveys to obtain representative samples to investigate the existence of paternal inheritance of mitochondrial DNA (mtDNA) in natural fish populations. Evidence of paternal mitochondrial DNA leakage of P. dabryanus was discovered using high-throughput sequencing and bioinformatics methods. Two distinct mitochondrial haplotypes (16,569 bp for haplotype I and 16,646 bp for haplotype II) were observed, differing by 18.83% in nucleotide sequence. Phylogenetic analysis suggests divergence between these haplotypes and potential interspecific hybridization with M. anguillicaudatus, leading to paternal leakage. In natural populations of P. dabryanus along the Yangtze River, both haplotypes are present, with Type I being dominant (75% copy number). Expression analysis shows that Type I has higher expression levels of ND3 and ND6 genes compared to Type II, suggesting Type I's primary role. This discovery of a species with two mitochondrial types provides a model for studying paternal leakage heterogeneity and insights into mitochondrial genome evolution and inheritance.

Comparative Study of Two Himalayan Snow Trouts, Schizothorax esocinus and Schizothorax curvifrons Within the Schizothoracinae and Other Nearest Relatives of Cyprinidae, Inferred from Mitochondrial Sequences of Cytochrome b (Cyt-b) and Cytochrome Oxidase I (Co-I) Gene

The Himalayan region encompasses varied aquatic ecosystems, characterized by the presence of diverse ichthyofauna, particularly represented by members of the Schizothorax genus, commonly referred to as snow trout. The primary objective of this work was to examine the molecular phylogeny of Schizothoracinae, specifically focusing on the two species, Schizothorax esocinus and Schizothorax curvifrons, which are known to inhabit the northern and north-eastern regions of the Himalayas. This investigation was conducted by analyzing the entire mitochondrial Cyt-b and Co-I gene sequences. The aligned Cyt-b and Co-I sequences for S. esocinus, S. curvifrons, and related members within the subfamily Schizothoracinae, spanned 1130 to 1141 and 1536 to 1551 base pairs, respectively. Using these gene, phylogenetic trees were created to compare Schizothoracinae species to other subfamilies of the family Cyprinidae (Barbinae, Alburninae, Leuciscinae, Xenocyprinae, Cyprininae, and Cultrinae). Genetic distances for Cyt-b and Co-I sequence at three hierarchical levels shows significant disparities in their average score. For Cyt-b, average p-distances for intraspecies, intragenus, and intrafamily were 2.13%, 4.1%, and 15.23%, respectively. Similarly, for Co-I, average p-distances were 1.19%, 3.6%, and 13.8% for intraspecies, intragenus, and intrafamily, respectively. Total number of haplotypes (h) based on Cyt-b and Co-I gene were 6 and 12 within the target Schizothorax spp. In the present study, the observed range of haplotype diversity (hd) for the Cyt-b gene varied from 0.00 to 0.847, with an average haplotype diversity of 0.847 ± 0.034. Similarly, for the Co-I gene, the observed haplotype diversity ranged from 0.00 to 0.931, with an average value of haplotype diversity estimated to be 0.931 ± 0.024. The results of the present study clearly shows that the representative species exhibited close affinities with members of Barbinae and Cyprininae, while other subfamilies formed distinct groups. The findings of the study also indicated that the Cyt-b and Co-I gene exhibits polymorphism and has the potential to serve as a marker for identifying genetic differentiation among populations based on ecological habitats. Mitochondrial Cyt-b and Co-I have been established as a universally accepted and validated genetic marker within a comprehensive bio-identification system at the species level.

Performance of tree-building methods using a morphological dataset and a well-supported Hexapoda phylogeny

Recently, many studies have addressed the performance of phylogenetic tree-building methods (maximum parsimony, maximum likelihood, and Bayesian inference), focusing primarily on simulated data. However, for discrete morphological data, there is no consensus yet on which methods recover the phylogeny with better performance. To address this lack of consensus, we investigate the performance of different methods using an empirical dataset for hexapods as a model. As an empirical test of performance, we applied normalized indices to effectively measure accuracy (normalized Robinson-Foulds metric, nRF) and precision, which are measured via resolution, one minus Colless' consensus fork index (1-CFI). Additionally, to further explore phylogenetic accuracy and support measures, we calculated other statistics, such as the true positive rate (statistical power) and the false positive rate (type I error), and constructed receiver operating characteristic plots to visualize the relationship between these statistics. We applied the normalized indices to the reconstructed trees from the reanalyses of an empirical discrete morphological dataset from extant Hexapoda using a well-supported phylogenomic tree as a reference. Maximum likelihood and Bayesian inference applying the k-state Markov (Mk) model (without or with a discrete gamma distribution) performed better, showing higher precision (resolution). Additionally, our results suggest that most available tree topology tests are reliable estimators of the performance measures applied in this study. Thus, we suggest that likelihood-based methods and tree topology tests should be used more often in phylogenetic tree studies based on discrete morphological characters. Our study provides a fair indication that morphological datasets have robust phylogenetic signal.

A comprehensive phylogenomic study unveils evolutionary patterns and challenges in the mitochondrial genomes of Carcharhiniformes: A focus on Triakidae

The complex evolutionary patterns in the mitochondrial genome (mitogenome) of the most species-rich shark order, the Carcharhiniformes (ground sharks) has led to challenges in the phylogenomic reconstruction of the families and genera belonging to the order, particularly the family Triakidae (houndsharks). The current state of Triakidae phylogeny remains controversial, with arguments for both monophyly and paraphyly within the family. We hypothesize that this variability is triggered by the selection of different a priori partitioning schemes to account for site and gene heterogeneity within the mitogenome. Here we used an extensive statistical framework to select the a priori partitioning scheme for inference of the mitochondrial phylogenomic relationships within Carcharhiniformes, tested site heterogeneous CAT + GTR + G4 models and incorporated the multi-species coalescent model (MSCM) into our analyses to account for the influence of gene tree discordance on species tree inference. We included five newly assembled houndshark mitogenomes to increase resolution of Triakidae. During the assembly procedure, we uncovered a 714 bp-duplication in the mitogenome of Galeorhinus galeus. Phylogenetic reconstruction confirmed monophyly within Triakidae and the existence of two distinct clades of the expanded Mustelus genus. The latter alludes to potential evolutionary reversal of reproductive mode from placental to aplacental, suggesting that reproductive mode has played a role in the trajectory of adaptive divergence. These new sequences have the potential to contribute to population genomic investigations, species phylogeography delineation, environmental DNA metabarcoding databases and, ultimately, improved conservation strategies for these ecologically and economically important species.

Chryseobacterium pyrolae sp. nov., isolated from the rhizosphere soil of Pyrola calliantha H

A novel Gram-stain-negative, aerobic, non-motile, rod-shaped bacterium, designated pc2-12T, was isolated from the rhizosphere soil of the herb Pyrola calliantha collected from arid areas of Tibet. The strain grew most vigorously with 1 % (w/v) NaCl, at pH 7.0 and at 25 °C. According to the results of 16S rRNA gene sequence analysis, pc2-12T was closely related to the members of the genus Chryseobacterium, with highest levels of sequence similarity to Chryseobacterium viscerum 687B-08T (98.42 %), Chryseobacterium oncorhynchi 701B-08T (98.11 %) and Chryseobacterium ureilyticum DSM 18017T (97.98 %). The average nucleotide identity values between pc2-12T and C. viscerum 687B-08T, C. oncorhynchi 701B-08T and C. ureilyticum DSM 18017T were 79.71, 79.49 and 79.26 %, respectively. The in silico DNA-DNA hybridisation values between pc2-12T and C. viscerum 687B-08T, C. oncorhynchi 701B-08T and C. ureilyticum DSM 18017T were 23.30, 23.00 and 22.90 %, respectively. The draft genome sequence of pc2-12T was 4.64 Mb long, with DNA G+C content of 37.0 mol%. The fatty acids contained in the cells of pc2-12T were mainly composed of iso-C15 : 0, iso-C17 : 0 3-OH and summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c). The main polar lipid was phosphatidylethanolamine. MK-6 was the sole respiratory quinone. On the basis of the results of analysis of all the data described, pc2-12T is considered to represent a novel species of the genus Chryseobacterium, for which the name Chryseobacterium pyrolae sp. nov., is proposed. The type strain is pc2-12T (=GDMCC 1.3256T= JCM 35712T).

Endophytic Bacterium Flexivirga meconopsidis sp. nov. with Plant Growth-Promoting Function, Isolated from the Seeds of Meconopsis integrifolia

Strain Q11T of an irregular coccoid Gram-positive bacterium, aerobic and non-motile, was isolated from Meconopsis integrifolia seeds. Strain Q11T grew optimally in 1% (w/v) NaCl, pH 7, at 30 °C. Strain Q11T is most closely related to Flexivirga, as evidenced by 16S rRNA gene analysis, and shares the highest similarity with Flexivirga aerilata ID2601ST (99.24%). Based on genome sequence analysis, the average nucleotide identity and digital DNA-DNA hybridization values of strains Q11T and D2601ST were 88.82% and 36.20%, respectively. Additionally, strain Q11T showed the abilities of nitrogen fixation and indole acetic acid production and was shown to promote maize growth under laboratory conditions. Its genome contains antibiotic resistance genes (the vanY gene in the vanB cluster and the vanW gene in the vanI cluster) and extreme environment tolerance genes (ectoine biosynthetic gene cluster). Shotgun proteomics also detected antibiotic resistance proteins (class A beta-lactamases, D-alanine ligase family proteins) and proteins that improve plant cold tolerance (multispecies cold shock proteins). Strain Q11T was determined to be a novel species of the genus Flexivirga, for which the name Flexivirga meconopsidis sp. nov. is proposed. The strain type is Q11T (GDMCC 1.3002T = JCM 36020 T).

Addressing the complex phylogenetic relationship of the Gempylidae fishes using mitogenome data

The Gempylidae (snake mackerels) family, belonging to the order Perciformes, consists of about 24 species described in 16 genera primarily distributed in tropical, subtropical, and temperate seas worldwide. Despite substantial research on this family utilizing morphological and molecular approaches, taxonomy categorization in this group has remained puzzling for decades prompting the need for further investigation into the underlying evolutionary history among the gempylids using molecular tools. In this study, we assembled eight complete novel mitochondrial genomes for five Gempylidae species (Neoepinnula minetomai, Neoepinnula orientalis, Rexea antefurcata, Rexea prometheoides, and Thyrsites atun) using Ion Torrent sequencing to supplement publicly available mitogenome data for gempylids. Using Bayesian inference and maximum-likelihood tree search methods, we investigated the evolutionary relationships of 17 Gempylidae species using mitogenome data. In addition, we estimated divergence times for extant gempylids. We identified two major clades that formed approximately 48.05 (35.89-52.04) million years ago: Gempylidae 1 (Thyrsites atun, Promethichthys prometheus, Nealotus tripes, Diplospinus multistriatus, Paradiplospinus antarcticus, Rexea antefurcata, Rexea nakamurai, Rexea prometheoides, Rexea solandri, Thyrsitoides marleyi, Gempylus serpens, and Nesiarchus nasutus) and Gempylidae 2 (Lepidocybium flavobrunneum, Ruvettus pretiosus, Neoepinnula minetomai, Neoepinnula orientalis, and Epinnula magistralis). The present study demonstrated the superior performance of complete mitogenome data compared with individual genes in phylogenetic reconstruction. By including T. atun individuals from different regions, we demonstrated the potential for the application of mitogenomes in species phylogeography.

Characterization of the complete mitochondrial genome of the brazilian cownose ray Rhinoptera brasiliensis (Myliobatiformes, Rhinopteridae) in the western Atlantic and its phylogenetic implications

BACKGROUND

The Brazilian cownose ray, Rhinoptera brasiliensis has undergone a global population reduction and is currently classified by IUCN as Vulnerable. This species is sometimes confused with Rhinoptera bonasus, the only external diagnostic characteristic to distinguish between both species is the number of rows of tooth plates. Both cownose rays overlap geographically from Rio de Janeiro to the western North Atlantic. This calls for a more comprehensive phylogenetic assessment using mitochondria DNA genomes to better understand the relationships and delimitation of these two species.

METHODS AND RESULTS

The mitochondrial genome sequences of R. brasiliensis was obtained by next-generation sequencing. The length of the mitochondrial genome was 17,759 bp containing 13 protein-coding genes (PCGs), two ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and a non-coding control region (D-loop). Each PCG was initiated by an authoritative ATG codon, except for COX1 initiated by a GTG codon. Most of the PCGs were terminated by a complete codon (TAA/TAG), while an incomplete termination codon (TA/T) was found in five out of the 13 PCGs. The phylogenetic analysis showed that R. brasiliensis was closely related to R. steindachneri whereas the reported mitogenome as R. steindachneri (GenBank accession number KM364982), differs from multiple mitocondrial DNA sequences of R. steindachneri and is nearly identical to that of R. javanica.

CONCLUSION

The new mitogenome determined in this study provides new insight into the phylogenetic relationships in Rhinoptera, while providing new molecular data that can be applied to population genetic studies.

Characterization of the Complete Mitochondrial Genome of the Spotted Catfish Arius maculatus (Thunberg, 1792) and Its Phylogenetic Implications

The spotted catfish, Arius maculatus (Siluriformes), is an important economical aquaculture species inhabiting the Indian Ocean, as well as the western Pacific Ocean. The bioinformatics data in previous studies about the phylogenetic reconstruction of Siluriformes were insufficient and incomplete. In the present study, we presented a newly sequenced A. maculatus mitochondrial genome (mtDNA). The A. maculatus mtDNA was 16,710 bp in length and contained two ribosomal RNA (rRNA) genes, thirteen protein-coding genes (PCGs), twenty-two transfer RNA (tRNA) genes, and one D-loop region. The composition and order of these above genes were similar to those found in most other vertebrates. The relative synonymous codon usage (RSCU) of the 13 PCGs in A. maculatus mtDNA was consistent with that of PCGs in other published Siluriformes mtDNA. Furthermore, the average non-synonymous/synonymous mutation ratio (Ka/Ks) analysis, based on the 13 PCGs of the four Ariidae species, showed a strong purifying selection. Additionally, phylogenetic analysis, according to 13 concatenated PCG nucleotide and amino acid datasets, showed that A. maculatus and Netuma thalassina (Netuma), Occidentarius platypogon (Occidentarius), and Bagre panamensis (Bagre) were clustered as sister clade. The complete mtDNA of A. maculatus provides a helpful dataset for research on the population structure and genetic diversity of Ariidae species.

Ancient DNA from the extinct New Zealand grayling (Prototroctes oxyrhynchus) reveals evidence for Miocene marine dispersal

The evolutionary history of Southern Hemisphere graylings (Retropinnidae) in New Zealand (NZ), including their relationship to the Australian grayling, is poorly understood. The NZ grayling (Prototroctes oxyrhynchus) is the only known fish in NZ to have gone extinct since human arrival there. Despite its historical abundance, only 23 wet and dried, formalin-fixed specimens exist in museums. We used high-throughput DNA sequencing to generate mitogenomes from formalin-fixed P. oxyrhynchus specimens, and analysed these in a temporal phylogenetic framework of retropinnids and osmerids. We recovered a strong sister-relationship between NZ and Australian grayling (P. mareana), with a common ancestor ~13.8 Mya [95% highest posterior density (HPD): 6.1–23.2 Mya], after the height of Oligocene marine inundation in NZ. Our temporal phylogenetic analysis suggests a single marine dispersal between NZ and Australia, although the direction of dispersal is equivocal, followed by divergence into genetically and morphologically distinguishable species through isolation by distance. This study provides further insights into the possible extinction drivers of the NZ grayling, informs discussion regarding reintroduction of Prototroctes to NZ and highlights how advances in palaeogenetics can be used to test evolutionary hypotheses in fish, which, until relatively recently, have been comparatively neglected in ancient-DNA research.

Characterization of the complete mitochondrial genome of Glyptothorax minimaculatus and phylogenetic studies of Sisoridae

The entire mitochondrial genome (mitogenome) of Glyptothorax minimaculatus was sequenced; it spanned 16,536 bp in length and contained 13 protein-coding genes (PCGs), 2 ribosomal RNAs, and 22 transfer RNA genes. A total of 37 genes formed a typical vertebrate mitochondrial gene arrangement. The phylogenetic tree of Sisoridae based on 13 PCGs was constructed and supported that G. minimaculatus was closely related to Glyptothorax sinensis, Glyptothorax zanaensis, Glyptothorax longinema, Glyptothorax granosus and Glyptothorax lanceatus. The mitogenome of G. minimaculatus described in this study provided molecular evidence for its current taxonomic status and laid a groundwork for further study concerning phylogenetics within Sisoridae.

Genetic Diversity and Population Differentiation of Naked Carp (Gymnocypris przewalskii) Revealed by Cytochrome Oxidase Subunit I and D-Loop

The genetic diversity in the naked carp (Gymnocypris przewalskii) of China is threatened by climate change, human activities, as well as natural factors, eliciting conservation concerns. To explore the genetic aspects of G. przewalskii, the genetic diversity, genetic structure, population differentiation, and historical demography of 566 representative individuals from seven geographically distinct ranges of Qinghai Lake were evaluated by mitochondrial DNA cytochrome oxidase subunit I (COI) and D-loop sequences. Estimates of genetic parameters showed that the seven populations of G. przewalskii had high levels of haplotype diversity (0.50243–0.94620) and low levels of nucleotide diversity (0.00079–0.00624). Haplotype genealogy indicated there was no obvious phylogenetic pattern between haplotypes. Both markers denoted the absence of population genetic structure [the genetic differentiation coefficient F-statistics (Fst) < 0] and the presence of high genetic flow (COI: 0.9731–1.0441; D-loop: 0.9480–1.0398). The mismatch between the distribution and neutrality tests supported the evidence of population expansion, which occurred during the late middle Pleistocene [COI: 0.36–0.108 MYA (Million Years Ago); D-loop: 0.497–0.165 MYA]. Furthermore, this work illustrated two simple, reliable, and inexpensive molecular markers for analysis of genetic diversity, while the sensitivity of the mitochondrial D-loop region as a reflection of genetic diversity in G. przewalskii is higher than that of the COI gene.

Complete mitogenomes of four Trichiurus species: A taxonomic review of the T.lepturus species complex

Four Trichiurus species, T.japonicus, T.lepturus, T.nanhaiensis, and T.brevis, from the coasts of the China Seas, have been identified and their entire mitochondrial genomes (mitogenomes) have been sequenced by next-generation sequencing technology. A comparative analysis of five mitogenomes was conducted, including the mitogenome of T.gangeticus. The mitogenomes contained 16.568-16.840 bp and encoded 36 typical mitochondrial genes (13 protein-coding, 2 ribosomal RNA-coding, and 21 transfer RNA-coding genes) and two typical noncoding control regions. Although tRNAPro is absent from Trichiurus mitogenomes, when compared with the 22 tRNAs reported in other vertebrates, the gene arrangements in the mitogenomes of the studied species are consistent with those in most teleost mitogenomes. The full-length sequences and protein-coding genes (PCGs) in the mitogenomes of the five species had obvious AT biases and negative GC skew values. Our study indicate that the specimens in the Indian Ocean are neither T.lepturus nor T.nanhaiensis but they are T.gangeticus; the Trichiurus species composition in the Indian Ocean is totally different from that in Pacific and Atlantic oceans; there are at least two Trichiurus species in Indian Ocean; and the worldwide systematics and diversity of the genus Trichiurus need to be reviewed.

The complete mitochondrial genome of an endemic cichlid Etroplus canarensis from Western Ghats, India (Perciformes: Cichlidae) and molecular phylogenetic analysis

BACKGROUND

The Indian endemic cichlid Etroplus canarensis (Canara pearl spot) is an endangered fish and is one among the three Indian cichlids (Etroplinae) that had a restricted distribution in the South Canara region of Karnataka, India. Despite considerable investigations, the phylogeny of Indian Cichlids and its biogeographical origin is still ambiguous and remains a question under discussion which is scrutinized based on whole mitogenomes in the present study.

METHODS AND RESULTS

We report the 16,339 bp complete mitochondrial genome of E. canarensis for the first time using the next-generation sequencing methods. Comparison of gene arrangement and genome characterization was found to commensurate with the previous reports on two Indian cichlid fishes, E. suratensis and E. maculatus. ND6 has been identified as a gene with the highest evolutionary rate and COI and COII is the most conserved gene based on p-genetic distance calculation. Substitution rate (ka/ks) was found to be very low indicating a reduced rate of evolution among subfamily Etroplinae accounting for its subsided species divergence of Indian cichlids. Phylogenetic analysis of Indian cichlids based on a combined dataset of 12 protein-coding genes representing cichlids generated high posterior probability values pillaring paraphyletic nature of Indian Malagasy lineage and monophyletic Indian genus Etroplus.

CONCLUSION

The mitogenome sequence of E. canarensis may provide fundamental molecular data useful for further researches on genetic diversity, endemicity and the conservation of this endangered freshwater fish.

Evidence of dispersal between the Yenisei and the Lena river basins during the late Pleistocene within the whitefish (Coregonus lavaretus pidschian) complex

The Coregonus lavaretus (Linnaeus, 1758) complex is a morphologically and genetically diverse group of whitefish. Its taxonomic structure has been controversial for almost a century. At least 25 forms of C. lavaretus have been described in Siberia, but there is still no consensus on their intraspecific structure and taxonomy. Coregonus lavaretus pidschian (Gmelin, 1789) was described as a subspecies of C. lavaretus. Recently, it was assumed that this subspecies is also a complex. The purpose of this study was to compare the distributions of pidschian-like whitefish haplotypes in two basins of large Siberian rivers, Yenisei and Lena, and to assess the gene flow between basins of these rivers, which were connected after the last glaciation. The sequence of the following mitochondrial DNA genes, 16S rRNA (partial), tRNA-Leu (full), NADH dehydrogenase subunit 1 (full), tRNA-Ile (full), and tRNA-Gln (partial), were used for the inference of intraspecific genetic structure of C. l. pidschian. Whitefish haplotypes were clustered into two groups according to their distribution between two large Siberian river basins; however, there were shared haplotypes indicating events of migration and hybridization, which could occur when Bolshoi Yenisei and Lena river systems were connected after the last glaciation (the Late Pleistocene).

Comprehensive Draft Genome Analyses of Three Rockfishes (Scorpaeniformes, Sebastiscus) via Genome Survey Sequencing

Sebastiscus species, marine rockfishes, are of essential economic value. However, the genomic data of this genus is lacking and incomplete. Here, whole genome sequencing of all species of Sebastiscus was conducted to provide fundamental genomic information. The genome sizes were estimated to be 802.49 Mb (S. albofasciatus), 786.79 Mb (S. tertius), and 776.00 Mb (S. marmoratus) by using k-mer analyses. The draft genome sequences were initially assembled, and genome-wide microsatellite motifs were identified. The heterozygosity, repeat ratios, and numbers of microsatellite motifs all suggested possibly that S. tertius is more closely related to S. albofasciatus than S. marmoratus at the genetic level. Moreover, the complete mitochondrial genome sequences were assembled from the whole genome data and the phylogenetic analyses genetically supported the validation of Sebastiscus species. This study provides an important genome resource for further studies of Sebastiscus species.

The complete mitochondrial genome of Microphysogobioelongatus (Teleostei, Cyprinidae) and its phylogenetic implications

Mitochondria are important organelles with independent genetic material of eukaryotic organisms. In this study, we sequenced and analyzed the complete mitogenome of a small cyprinid fish, Microphysogobioelongatus (Yao & Yang, 1977). The mitogenome of M.elongatus is a typical circular molecule of 16,612 bp in length containing 13 protein-coding genes (PCGs), 22 transfer RNA genes, two ribosomal RNA genes, and a 930 bp control region. The base composition of the M.elongatus mitogenome is 30.8% A, 26.1% T, 16.7% G, and 26.4% C. All PCGs used the standard ATG start codon with the exception of COI. Six PCGs terminate with complete stop codons, whereas seven PCGs (ND2, COII, ATPase 6, COIII, ND3, ND4, and Cyt b) terminate with incomplete (T or TA) stop codons. All tRNA genes exhibited typical cloverleaf secondary structures with the exception of tRNA^Ser(AGY), for which the dihydrouridine arm forms a simple loop. The phylogenetic analysis divided the subfamily Gobioninae in three clades with relatively robust support, and that Microphysogobio is not a monophyletic group. The complete mitogenome of M.elongatus provides a valuable resource for future studies about molecular phylogeny and/or population genetics of Microphysogobio.

A multi-locus approach to elucidating the evolutionary history of the clingfish Tomicodon petersii (Gobiesocidae) in the Tropical Eastern Pacific

Marine species that are widely distributed in the Tropical Eastern Pacific (TEP) has served as a model for studying biogeographic patterns resulting from the effects of intraregional habitat discontinuities and oceanographic processes on the diversification and evolution of cryptobenthic reef fishes. Tomicodon petersii, a clingfish (Gobiesocidae) endemic to the TEP, is found on very shallow rocky reefs from central Mexico to northern Peru, and in the Cocos and Galapagos islands. We evaluated the effect of likely biogeographic barriers in different parts of the TEP on the diversification process of this species. We used one mitochondrial and three nuclear DNA markers from 112 individuals collected across the distribution range of T. petersii. Our phylogenetic results showed the samples constituted a monophyletic group, with three well-supported, allopatric subgroups: in the Mexican province, the Panamic province (from El Salvador to Ecuador), and the Galapagos Islands. The split between the Mexican and more southerly clades was estimated to occur at the end of the Miocene ca. 5.74 Mya, and the subsequent cladogenetic event separating the Galapagos population from the Panamic population at the junction of the Pliocene and Pleistocene, ca. 2.85 Mya. The species tree, Bayesian species delimitation tests (BPP), STACEY, and substantial genetic distances separating these three populations indicate that these three independent evolutionary units likely include two unnamed species. The cladogenetic events that promoted the formation of those genetically differentiated groups are consistent with disruptive effects on gene flow of habitat discontinuities and oceanographic processes along the mainland shoreline in the TEP and of ocean-island isolation, in conjunction with the species intrinsic life-history characteristics.

Complete Mitochondrial Genome of Pseudocaranx dentex (Carangidae, Perciformes) Provides Insight into Phylogenetic and Evolutionary Relationship among Carangidae Family

Pseudocaranx dentex (white trevally) which belongs to the Carangidae family, is an important commercial fishery and aquaculture resource in Asia. However, its evolution and population genetics have received little attention which was limited by the mitogenome information absence. Here, we sequenced and annotated the complete mitochondrial genome of P. dentex which was 16,569 bp in length, containing twenty-two tRNAs (transfer RNAs), thirteen PCGs (protein-coding genes), two rRNAs (ribosomal RNAs), and one non-coding region with conservative gene arrangement. The Ka/Ks ratio analysis among Carangidae fishes indicated the PCGs were suffering purify selection and the values were related to the taxonomic status and further influenced by their living habits. Phylogenetic analysis based on the PCGs sequences of mitogenomes among 36 species presented three major clades in Carangidae. According to the phylogenetic tree, we further analyzed the taxonomic confusion of Carangoides equula which was on the same branch with P. dentex but a different branch with Carangoides spp. We inferred Kaiwarinus equula should be the accepted name and belong to the independent Kaiwarinus genus which was the sister genus of Pseudocaranx. This work provides mitochondrial genetic information and verifies the taxonomic status of P. dentex, and further helps to recognize the phylogenetic relationship and evolutionary history of Carangidae.

The mitochondrial genome of Stereolepis doederleini (Pempheriformes: Polyprionidae) and mitogenomic phylogeny of Pempheriformes

The complete mitochondrial (mt) genome of Stereolepis doederleini was sequenced from a specimen collected in a commercial aquarium in Jeju Island. The sequence was 16,513 base pairs in length and, similar to other vertebrate mt genomes, included 37 mt genes and a noncoding control region; the gene order was identical to that of typical vertebrate mt genome. Mitochondrial genome sequences of 17 species from 12 families were used to reconstruct phylogenetic relationships within the order Pempheriformes. The phylogenetic trees were constructed with three methods (neighbor joining [NJ], maximum likelihood [ML], and Bayesian method) using 12 protein coding genes, but not ND6. In all phylogenetic trees, Pempheriformes were clustered into three strongly supported clades. Two Acropomatidae species (Synagrops japonicus in clade-Ⅰ and Doederleinia berycoides in clade-Ⅲ) were polyphyletic; S. japonicus was close to Lateolabracidae and was the sister of Glaucosomatidae + (Pempheridae/(Percophidae+Creediidae)), and D. berycoides was sister to Howellidae + Epigonidae. All phylogenetic trees supported a sister relationship between Creediidae and Percophidae in clade-Ⅰ. Glaucosomatidae formed a sister clade with Pempheridae. The relationships within clade-Ⅱ, which was composed of four families (Pentacerotidae, Polyprionidae, Banjosidae, and Bathyclupeidae), slightly differed between NJ/ML and BI tree topologies. In clade-Ⅲ, the relationships among Howellidae, Epigonidae, and Acropomatidae were strongly supported.

The paedomorphic lateral line system in Pseudamiops and Gymnapogon (Percomorpha, Apogonidae), with morphological and molecular-based phylogenetic considerations

The lateral line system and its innervation were examined in two paedomorphic species of Apogonidae, Gymnapogon japonicus and Pseudamiops cf. springeri, both of which have been included in Gymnapogonini (Apogoninae) characterized by a small translucent body lacking canalized lateral line scales, but with many superficial neuromasts (total SNs: 2,691 and 2,197 in G. japonicus and Pseudamiops cf. springeri, respectively). Although scales are entirely absent in G. japonicus, the innervation pattern of the trunk lateral line system is basically similar to that in other apogonids having a single lateral line scale series. In comparison, Pseudamiops cf. springeri (and P. gracilicauda) have three series of inconspicuous lateral line scales with a distinct innervation pattern, implying a phylogenetic affinity with Pseudamia (Pseudamiinae). The monophyly of Pseudamiops and Pseudamia was also supported strongly by a molecular phylogenetic analysis, thus the paedomorphic nature is considered homoplasy between Pseudamiops and Gymnapogon. The innervation of head lateral line system in G. japonicus and Pseudamiops cf. springeri is basically the same with that of other apogonids, supporting homology of the presence of many head SNs among the species. The SN pattern and head canals of adult Pseudamiops cf. springeri are similar to those in juvenile Pseudamia gelatinosa, implying a paedomorphic truncation of lateral line system development in Pseudamiops cf. springeri.

Methodology of fish eDNA and its applications in ecology and environment

Fish environmental DNA (eDNA) studies have made substantial progress during the past decade, and significant advances in monitoring fishes have been gained by taking advantage of this technology. Although a number of reviews concerning eDNA are available and some recent fish eDNA reviews focused on fisheries or standard method have been published, a systematic review of methodology of fish eDNA and its applications in ecology and environment has not yet been published. To our knowledge, this is the first review of fish eDNA for solving ecological and environmental issues. First, the most comprehensive literature analysis of fish eDNA was presented and analyzed. Then, we systematically discuss the relevant experiments and analyses of fish eDNA, and infers that standard workflow is on the way to consensus. We additionally provide reference sequence databases and the primers used to amplify the reference sequences or detecting fish eDNA. The abiotic and biotic conditions affecting fish eDNA persistence are also summarized in a schematic diagram. Subsequently, we focus on the major achievements of fish eDNA in ecology and environment. We additionally highlight the exciting new tools, including in situ autonomous monitoring devices, CRISPR nucleic acid detection technology, and meta-omics technology for fish eDNA detection in future. Ultimately, methodology of fish eDNA will provide a wholly new paradigm for conservation actions of fishes, ecological and environmental management at a global scale.

Characterization of the complete mitochondrial genome of Chrysochir aureus and phylogenetic studies of Sciaenidae

The complete mitochondrial genome of Chrysochir aureus was sequenced. The full length of the mitochondrial genome was 16,501 bp, including 13 protein-coding genes (PCGs), two ribosomal RNAs, 22 transfer RNA genes, a non-coding control region (CR) and one origin of replication on the light-strand (OL). The total nucleotide composition of mitochondrial DNA was 26.95% A, 29.99% C, 26.29% T, and 16.77% G. Twelve PCGs used the canonical ATG as their initiation codon, whereas COI gene started with an alternative start codon GTG. The mitochondrial genome of C. aureus described in this study could be a useful basis for management of this species and laid a foundation for further research involved with phylogenetic relationship within Sciaenidae.

Characterization of the complete mitochondrial genome of Ostorhinchus novemfasciatus and phylogenetic studies of Apogoninae

The complete mitochondrial genome of Ostorhinchus novemfasciatus was first presented in this study. The full length of the mitochondrial genome was 16,779 bp, including 13 protein-coding genes (PCGs), two ribosomal RNAs, 22 transfer RNA genes, a non-coding control region (CR) and one origin of replication on the light-strand (OL). The total nucleotide composition of mitochondrial DNA was 26.0% A, 30.2% C, 26.2% T and 17.5% G. 12 PCGs used the canonical ATG as their initiation codon, whereas COI gene started with an alternative start codon GTG. The mitochondrial genome of O. novemfasciatus described in this study could be a useful basis for the management of this species and laid a foundation for further research involved with phylogenetic relationship within Apogoninae.

Characterization and comparison of the complete mitochondrial genomes of two stingrays, Dasyatis pastinaca and Dasyatis tortonesei (Myliobatiformes: Dasyatidae) from the Mediterranean Sea

This work represents the complete mitochondrial genomes of two stingrays, Dasyatis pastinaca and Dasyatis tortonesei, from the Mediterranean Sea. The mitogenomes of these two species were obtained through whole generation sequencing and annotated. These mitogenomes were found to be 17,713 bp and 17,630 bp respectively and each contained 37 genes, that is 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes and two ribosomal RNA (rRNA) genes, a control region and the origin of L-strand replication (O_L). All PCGs begin with the codon ATG, except for cytochrome c oxidase subunit 1 (COX1) gene, while two PCGs end with an incomplete termination codon. All tRNA genes are able to fold into their typical cloverleaf secondary structures, except for tRNA-Ser1^AGY which lacks the dihydrouracil arm. The control region was 1982 bp and 1889 bp for D. pastinaca and D. tortonesei respectively. Phylogenetic analysis using Bayesian Inference confirmed the occurrence of the genus Dasyatis within the monophyletic subfamily Dasyatinae. This study adds on genetic resources available for these two stingray species.

Comparative analysis of the complete mitochondrial genomes of three rockfishes (Scorpaeniformes, Sebastiscus) and insights into the phylogenetic relationships of Sebastidae

Mitochondrial genome is a powerful molecule marker to provide information for phylogenetic relationships and revealing molecular evolution in ichthyological studies. Sebastiscus species, a marine rockfish, are of essential economic value. However, the taxonomic status and phylogenetic relationships of Sebastidae have been controversial so far. Here, the mitochondrial genomes (mitogenomes) of three species, S. tertius, S. albofasciatus, and S. marmoratus, were systemically investigated. The lengths of the mitogenomes' sequences of S. tertius, S. albofasciatus, and S. marmoratus were 16910, 17056, and 17580 bp, respectively. It contained 13 protein-coding genes (PCGs), two ribosomal RNAs (rRNAs), 22 transfer RNA (tRNA) genes, and one identical control region (D-loop) among the three species. The genetic distance and Ka/Ks ratio analyses indicated 13 PCGs were suffering purifying selection and the selection pressures were different from certain deep-sea fishes, which were most likely due to the difference in their living environment. The phylogenetic tree was constructed by Bayesian Inference (BI) and Maximum Likelihood (ML). Most interestingly, the results indicated that Sebastidae and Scorpaenidae were grouped into a separate branch, so the taxonomic status of Sebastidae should be classified into subfamily Sebastinae. Our results may lead to a taxonomic revision of Scorpaenoidei.

Fingerprinting of hatchery haplotypes and acquisition of genetic information by whole-mitogenome sequencing of masu salmon, Oncorhynchus masou masou, in the Kase River system, Japan

Stocking hatchery fish can lead to disturbance and extinction of the local indigenous population. Masu salmon Oncorhynchus masou masou, which is endemic across Japan, is a commonly stocked fish for recreational fishing in Japan. To conserve the indigenous resource, their genetic information is required, however, especially on Kyushu Island, the paucity of genetic information for this species has hindered proper resource management. Here, to identify hatchery mitogenome haplotypes of this species, stocked in the Kase River system, Kyushu Island, Japan, and to provide mitogenomic information for the resource management of this species, we analyzed the whole-mitogenome of masu salmon in this river system and several hatcheries potentially used for stocking. Whole-mitogenome sequencing clearly identified hatchery haplotypes, like fingerprints: among the 21 whole-mitogenome haplotypes obtained, six were determined to be hatchery haplotypes. These hatchery haplotypes were distributed in 13 out of 17 sites, suggesting that informal stocking of O. m. masou has been performed widely across this river system. The population of no hatchery haplotypes mainly belonged to clade I, a clade not found in Hokkaido Island in previous studies. Sites without hatchery haplotypes, and the non-hatchery haplotypes in clade I might be candidates for conservation as putative indigenous resources. The whole-mitogenome haplotype analysis also clarified that the same reared strain was used in multiple hatcheries. Analysis of molecular variance suggested that stocked hatchery haplotypes reduce the genetic variation among populations in this river system. It will be necessary to pay attention to genetic fluctuations so that the resources of this river system will not deteriorate further. The single nucleotide polymorphism data obtained here could be used for resource management in this and other rivers: e.g., for monitoring of informal stocking and stocked hatchery fishes, and/or putative indigenous resources.

A new gene order in the mitochondrial genome of the deep-sea diaphanous hatchet fish Sternoptyx diaphana Hermann, 1781 (Stomiiformes: Sternoptychidae)

Species of the Sternoptychidae teleost family display an impressive morphology, including their extreme reduced size. Here, we report the first mitochondrial genome of the diaphanous hatchet fish Sternoptyx diaphana. By using short-read sequencing Illumina HiSeq, we generated two mitochondrial contigs which were later physically assembled by PCR. The mitochondrial genome of S. diaphana was 17,224 bp in length (excluding the control region) and is composed of 13 PCGs and 2 ribosomal RNA genes. Strikingly, we could not identify the tRNA-Phe and two copies of tRNA-Met were differently positioned. Additionally, the mitogenome displays a completely new gene rearrangement among vertebrates. We expect that the study presented here will pave the way for further molecular studies with this underrepresented group of illusive teleost fish.

Phylogeny of caucasian rock lizards (Darevskia) and other true lizards based on mitogenome analysis: Optimisation of the algorithms and gene selection

We generated a phylogeny for Caucasian rock lizards (Darevskia), and included six other families of true lizards (Lacertini), based on complete mitochondrial genome analysis. Next-generation sequencing (NGS) of genomic DNA was used to obtain 16 new mitogenomes of Darevskia. These, along with 35 sequences downloaded from GenBank: genera Darevskia, Zootoca, Podarcis, Phoenicolacerta, Takydromus, Lacerta, and Eremias-were used in the analysis. All four analytical methods (Bayesian Inference, BI; Maximum Likelihood, ML; Maximum Parsimony, MP; and Neighbor-Joining, NJ) showed almost congruent intra-generic topologies for Darevskia and other lizard genera. However, ML and NJ methods on one side, and BI and MP methods on the other harvested conflicting phylogenies. The ML/NJ topology supports earlier published separation of Darevskia into three mitochondrial clades (Murphy, Fu, Macculloch, Darevsky, and Kupinova, 2000), but BI and MP topologies support that the basal branching occurred between D. parvula from the western Lesser Caucasus and the rest of Darevskia. All topologies altered the phylogenetic position of some individual species, including D. daghestanica, D. derjugini, and D. chlorogaster. Reanalysis after excluding four saturated genes from the data set, and excluding genus Eremias gives fully convergent topologies. The most basal branching for true lizards was between Far Eastern Takydromus and the Western Eurasian genera (BI). Comparing phylogenetic performance of individual genes relative to whole mitogenome data, concatenated 16S RNA (the least saturated gene in our analyses) and Cytochrome b genes generate a robust phylogeny that is fully congruent with that based on the complete mitogenome.

The mitogenome of freshwater loach Homatula laxiclathra (Teleostei: Nemacheilidae) with phylogenetic analysis of Nemacheilidae

The complete mitogenome can provide valuable genetic information to reconstruct relationships between species. In this study, we sequenced a stone loach, Homatula laxiclathra (Teleostei: Nemacheilidae), which is found in the northern region of the Qinling Mountains in China. The size of the H. laxiclathra mitogenome is 16,570 bp, which contains 37 typical mitochondrial genes including 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs, and a control region (D-loop) with a total AT content of 55.8%. This is similar to other Nemacheilidae sequences published in GenBank. Furthermore, a mito-phylogenomic analysis of 46 Nemacheilidae species places H. laxiclathra in a robust monophyletic Homatula cluster with other Homatula species. Our results contribute toward a better understanding of a true phylogeny of these species based on large-scale taxonomic samplings as well as to help grasp the evolution of fish mitogenomes.

Sequencing and Characterisation of Complete Mitochondrial DNA Genome for Trigonopoma pauciperforatum (Cypriniformes: Cyprinidae: Danioninae) with Phylogenetic Consideration

The Trigonopoma pauciperforatum or the redstripe rasbora is a cyprinid commonly found in marshes and swampy areas with slight acidic tannin-stained water in the tropics. In this study, the complete mitogenome sequence of T. pauciperforatum was first amplified in two parts using two pairs of overlapping primers and then sequenced. The size of the mitogenome is 16,707 bp, encompassing 22 transfer RNA genes, 13 protein-coding genes, two ribosomal RNA genes and a putative control region. Identical gene organisation was detected between this species and other family members. The heavy strand accommodates 28 genes while the light strand houses the remaining nine genes. Most protein-coding genes utilise ATG as start codon except for COI gene which uses GTG instead. The terminal associated sequence (TAS), central conserved sequence block (CSB-F, CSB-D and CSB-E) as well as variable sequence block (CSB-1, CSB-2 and CSB-3) are conserved in the control region. The maximum likelihood phylogenetic tree revealed the divergence of T. pauciperforatum from the basal region of the major clade, where its evolutionary relationships with Boraras maculatus, Rasbora cephalotaenia and R. daniconius are poorly resolved as suggested by the low bootstrap values. This work contributes towards the genetic resource enrichment for peat swamp conservation and comprehensive in-depth comparisons across other phylogenetic researches done on the Rasbora-related genus.

Genetic analysis of wild Ancherythroculter nigrocauda in tributaries and the main stream of the upper Yangtze River basin of China

Biodiversity is threatened by several factors that are often associated with overfishing, water pollution and hydroelectric dams, among other environmental impacts. The present study aimed to evaluate the genetic aspects of wild groups of Ancherythroculter nigrocauda using the mitochondrial cytochrome c oxidase subunit I (coI) and cytochrome b (cytb) genes and the d-loop region. We collected 89 representative individuals from three geographically distinct ranges of the Upper Yangtze River, including the Longxi River (LOR), Laixi River (LAR), and Hejiang range of the Yangtze River (HJ). The genetic analysis results showed that the three populations of A. nigrocauda had high levels of haplotype diversity (0.3434-0.951) and low levels of nucleotide diversity (0.00074-0.00412) based on the single gene sequences and the combination of gene sequences. Haplotype genealogy showed that only one haplotype (Hap-2) was shared by these three geographic groups, and 2-3 were shared by two groups; the other haplotypes were group-specific. The genetic distance within and between the populations was low; however, most of the molecular variance came from within the populations. Furthermore, high gene flow (>1.0) was found in HJ vs LOR and HJ vs LAR based on the d-loop region sequence and combination. These results suggested that there was a decrease in the degree of A. nigrocauda genetic diversity in the upper Yangtze River, and the genetic protection of the populations should be highlighted in the future.

Resolving Phylogenetic Relationships within Passeriformes Based on Mitochondrial Genes and Inferring the Evolution of Their Mitogenomes in Terms of Duplications

Mitochondrial genes are placed on one molecule, which implies that they should carry consistent phylogenetic information. Following this advantage, we present a well-supported phylogeny based on mitochondrial genomes from almost 300 representatives of Passeriformes, the most numerous and differentiated Aves order. The analyses resolved the phylogenetic position of paraphyletic Basal and Transitional Oscines. Passerida occurred divided into two groups, one containing Paroidea and Sylvioidea, whereas the other, Passeroidea and Muscicapoidea. Analyses of mitogenomes showed four types of rearrangements including a duplicated control region (CR) with adjacent genes. Mapping the presence and absence of duplications onto the phylogenetic tree revealed that the duplication was the ancestral state for passerines and was maintained in early diverged lineages. Next, the duplication could be lost and occurred independently at least four times according to the most parsimonious scenario. In some lineages, two CR copies have been inherited from an ancient duplication and highly diverged, whereas in others, the second copy became similar to the first one due to concerted evolution. The second CR copies accumulated over twice as many substitutions as the first ones. However, the second CRs were not completely eliminated and were retained for a long time, which suggests that both regions can fulfill an important role in mitogenomes. Phylogenetic analyses based on CR sequences subjected to the complex evolution can produce tree topologies inconsistent with real evolutionary relationships between species. Passerines with two CRs showed a higher metabolic rate in relation to their body mass.

The complete mitochondrial genome of Rhynchocypris oxycephalus (Teleostei: Cyprinidae) and its phylogenetic implications

Rhynchocypris oxycephalus (Teleostei: Cyprinidae) is a typical small cold water fish, which is distributed widely and mainly inhabits in East Asia. Here, we sequenced and determined the complete mitochondrial genome of R. oxycephalus and studied its phylogenetic implication. R. oxycephalus mitogenome is 16,609 bp in length (GenBank accession no.: MH885043), and it contains 13 protein-coding genes (PCGs), two rRNA genes, 22 tRNA genes, and two noncoding regions (the control region and the putative origin of light-strand replication). 12 PCGs started with ATG, while COI used GTG as the start codon. The secondary structure of tRNA-Ser (AGN) lacks the dihydrouracil (DHU) arm. The control region is 943bp in length, with a termination-associated sequence, six conserved sequence blocks (CSB-1, CSB-2, CSB-3, CSB-D, CSB-E, CSB-F), and a repetitive sequence. Phylogenetic analysis was performed with maximum likelihood and Bayesian methods based on the concatenated nucleotide sequence of 13 PCGs and the complete sequence without control region, and the result revealed that the relationship between R. oxycephalus and R. percnurus is closest, while the relationship with R. kumgangensis is farthest. The genus Rhynchocypris is revealed as a polyphyletic group, and R. kumgangensis had distant relationship with other Rhynchocypris species. In addition, COI and ND2 genes are considered as the fittest DNA barcoding gene in genus Rhynchocypris. This work provides additional molecular information for studying R. oxycephalus conservation genetics and evolutionary relationships.

Comparison of mitochondrial DNA enrichment and sequencing methods from fish tissue

Sparid fish species have different commercial values related to their organoleptic features. Mitochondrial (mt) DNA provides a potential tool to distinguish species, but the enrichment of high-quality mtDNA from total genomic DNA is critical to obtain entire mtDNA sequences. Conventional mtDNA isolation is relatively low-cost and proficient. However, high numbers of PCR cycles can lead to artefacts (10^-6 mutations/bp). We describe a rapid protocol for mtDNA extraction and enrichment from fish tissues, based on conventional miniprep columns and paramagnetic bead-based purification, without the need to employ PCR amplification. This newly described method generates a substrate for next-generation sequencing (NGS) analysis and is likely to have wider applications for mitochondrial studies in other fish families to help ensure traceability and differentiation of fish with high commercial values.

Direct fishing and eDNA metabarcoding for biomonitoring during a 3-year survey significantly improves number of fish detected around a South East Asian reservoir

Biodiversity has to be accurately evaluated to assess more precisely possible dam effects on fish populations, in particular on the most biodiverse rivers such as the Mekong River. To improve tools for fish biodiversity assessment, a methodological survey was performed in the surroundings of a recent hydropower dam in the Mekong basin, the Nam Theun 2 project. Results of two different approaches, experimental surface gillnets capture and environmental DNA metabarcoding assays based on 12S ribosomal RNA and cytochrome b, were compared during 3 years (2014–2016). Pitfalls and benefits were identified for each method but the combined use of both approaches indisputably allows describing more accurately fish diversity around the reservoir. Importantly, striking convergent results were observed for biodiversity reports. 75% of the fish species caught by gillnets (62/82) were shown by the metabarcoding study performed on DNA extracted from water samples. eDNA approach also revealed to be sensitive by detecting 30 supplementary species known as present before the dam construction but never caught by gillnets during 3 years. Furthermore, potential of the marker-genes study might be underestimated since it was not possible to assign some sequences at lower taxonomic levels. Although 121 sequences were generated for this study, a third of species in the area, that exhibits high endemism, are still unknown in DNA databases. Efforts to complete local reference libraries must continue to improve the taxonomic assignment quality when using the non-invasive and promising eDNA approach. These results are of broader interest because of increasing number of hydropower projects in the Mekong Basin. They reveal the crucial importance to sample tissues/DNA of species before dam projects, i.e. before the species could become endangered and difficult to catch, to obtain more precise biomonitoring in the future as we believe eDNA metabarcoding will rapidly be integrated as a standard tool in such studies.

Complete mitochondrial DNA genomes for two northeast Pacific mesopelagic fishes, the Mexican lampfish (Triphoturus mexicanus) and black-belly dragonfish (Stomias atriventer)

Mesopelagic fishes are an important component of marine ecosystems, providing an important link between lower and higher trophic levels. This group of fishes is also highly abundant and make up a large portion of the marine vertebrate biomass. Here we report on the full mitochondrial sequences for two common mesopelagic fishes from the southern California bight: the Mexican lampfish Triphoturus mexicanus (Actinopterygii: Myctophidae) and the black-belly dragonfish Stomias atriventer (Actinopterygii: Stomiidae). Triphoturus mexicanus showed previously reported gene rearrangements for the Myctophidae. Phylogenetic analysis grouped S. atriventer with other Stomiiformes and T. mexicanus within the Myctophiformes.

Phylogenetic analysis of sooty grunter and other major freshwater fishes in the suborder Percoidei based on mitochondrial DNA

Perciformes is the largest order of fishes and vertebrates. Sooty grunter (Hephaestus fuliginosus) is an economic fish species in the Terapontidae family of Percoidei, a suborder within Perciformes. To conduct molecular-level analysis of the phylogenetic relationships between sooty grunter and major freshwater fishes in Percoidei, we analysed the entire sooty grunter mitochondrial genome sequence and obtained the mitochondrial genome information of 19 fishes from Terapontidae, Serranidae, and Centrarchidae families in Percoidei from GenBank. The complete length of the sooty grunter mitochondrial genome was 16,770 bp; it encoded 13 proteins, 2 rRNAs, 22 tRNAs, and a displacement loop (D-loop). Other than ND6 and eight tRNA genes that are encoded by the light strand, the majority of genes are encoded by the heavy strand. The sequence and distribution of sooty grunter mitochondrial-encoded genes and non-coding segment were similar to those of most vertebrates. The results of neighbour joining, maximum parsimony, and Bayesian inference analyses of the complete mitochondrial genome and six genes, including cytochrome oxidase I, cytochrome B, 12S rRNA, ND2, ND4, and ND5, were consistent. In the phylogenetic trees, fishes in Terapontidae and Centrarchidae formed monophyletic clades, whereas those in Serranidae were divided into two clades, each containing Lateolabrax and Siniperca species. Among the three freshwater fish species in Terapontidae, the freshwater Terapontidae were more closely related to jade perch than with silver perch, suggesting that freshwater Terapontidae fishes originate from marine fishes. In addition, the phylogenetic results indicated that Micropterus salmoides salmoides and Micropterus salmoides floridanus in Centrarchidae should be designated as two independent species, and Siniperca in Serranidae should be considered an independent family. The sooty grunter mitochondrial genome sequence obtained in this study could be used to conduct population genetic diversity and germplasm resource studies. Furthermore, the phylogenetic analysis results of freshwater fishes in Percoidei could provide a molecular basis for cross-breeding.