Complete mtDNA sequences of two millipedes suggest a new model for mitochondrial gene rearrangements: duplication and nonrandom loss

Quantification of rearrangements and evolution of mitochondrial gene order of Acari (Chelicerata: Arachnida)

Invertebrate mitogenomes are generally fixed with formal 37 genes: 13 PCGs encoded subunits of OXPHOS, 2 ribosomal RNA (rRNA) functional in the translation of these PCGs and 22 transfer RNA (tRNA) genes. The order of these genes varies greatly among organisms and named rearrangement. Rearrangement patterns of mitochondrial genomes may shed light on mutation processes and evolutionary relationships of organisms. Mitochondrial gene organization is highly variable among Acari, so rearrangement is a very common mitogenomic pattern in this group. In this study, 258 unique Acari (Acariformes + Parasitiformes) mitogenomes were downloaded from NCBI and studied about rearrangement patterns. Sixty-seven mitotypes were determined among Acari and the most rearranged genes were trnL1 and nad2. Following that, trnI, trnS1, trnN, trnE, trnT, and trnP genes are remarkably mobile (RF > 95%). Conversely, atp6, cox3, trnG, and cytb genes also appears to be quite stable (RF < 20%). Within Acari, mean distance calculations are varied from 1.210 in atp8 to 0.155 in rrnS. Contrary to expectations, among Acari mobile tRNA genes appear to be conserved in sequences, whereas PCGs have higher distance values and seem to be mutated. Consistently, tRNA genes seem saturated, but some PCGs (atp6, cox genes, cytb, nad1, and nad6) are not saturated. These values do not correlate with each other (p > 0.005). This discrepancy may indicate that the genes were rearranged after mutation load; consistent with this, DAMBE saturation values are also not correlated with RF values. Parasitiformes mitogenomes are more mobile than Acariformes mitogenomes and may be under the effect of selective sweeping.

The complete mitochondrial DNA of the carnivorous sponge Lycopodina hypogea is putatively complemented by microDNAs

Carnivorous sponges (Porifera, Demospongiae, Cladorhizidae), contrary to the usual filter-feeding mechanism of sponges, are specialized in catching larger prey through adhesive surfaces or hook-like spicules. The mitochondrial DNA of sponges overall present several divergences from other metazoans, and while presenting unique features among major transitions, such as in calcarean and glass sponges, poriferan mitogenomes are relatively stable within their groups. Here, we report and discuss the mitogenome of Lycopodina hypogea (Vacelet & Boury-Esnault, 1996), which greatly vary from its subordinal counterparts in both structure and gene order. This mitogenome is seemingly multipartite into three chromosomes, two of them as microDNAs. The main chromosome, chrM1, is unusually large, 31,099 bp in length, has a unique gene order within Poecilosclerida, and presents two rRNA, 13 protein and 19 tRNA coding genes. Intergenic regions comprise approximately 40% of chrM1, bearing several terminal direct and inverted repeats (TDRr and TIRs) but holding no vestiges of former mitochondrial sequences, pseudogenes, or transposable elements. The nd4l and trnI(gau) genes are likely located in microDNAs thus comprising putative mitochondrial chromosomes chrM2, 291 bp, and chrM3, 140 bp, respectively. It is unclear which processes are responsible for the remarkable features of the of L. hypogea mitogenome, including a generalized gene rearrangement, long IGRs, and putative extrachromosomal genes in microDNAs.

Sequence comparison of the mitochondrial genomes of five caridean shrimps of the infraorder Caridea: phylogenetic implications and divergence time estimation

BACKGROUND

The Caridea, affiliated with Malacostraca, Decapoda, and Pleocyemata, constitute one of the most significant shrimp groups. They are widely distributed across diverse aquatic habitats worldwide, enriching their evolutionary history. In recent years, considerable attention has been focused on the classification and systematic evolution of Caridea, yet controversies still exist regarding the phylogenetic relationships among families.

METHODS

Here, the complete mitochondrial genome (mitogenome) sequences of five caridean species, namely Heterocarpus sibogae, Procletes levicarina, Macrobrachium sp., Latreutes anoplonyx, and Atya gabonensis, were determined using second-generation high-throughput sequencing technology. The basic structural characteristics, nucleotide composition, amino acid content, and codon usage bias of their mitogenomes were analyzed. Selection pressure values of protein-coding genes (PCGs) in species within the families Pandalidae, Palaemonidae, and Atyidae were also computed. Phylogenetic trees based on the nucleotide and amino acid sequences of 13 PCGs from 103 caridean species were constructed, and divergence times for various families within Caridea were estimated.

RESULTS

The mitogenome of these five caridean species vary in length from 15,782 to 16,420 base pairs, encoding a total of 37 or 38 genes, including 13 PCGs, 2 rRNA genes, and 22 or 23 tRNA genes. Specifically, L. anoplonyx encodes an additional tRNA gene, bringing its total gene count to 38. The base composition of the mitogenomes of these five species exhibited a higher proportion of adenine-thymine (AT) bases. Six start codons and four stop codons were identified across the five species. Analysis of amino acid content and codon usage revealed variations among the five species. Analysis of selective pressure in Pandalidae, Palaemonidae, and Atyidae showed that the Ka/Ks values of PCGs in all three families were less than 1, indicating that purifying selection is influencing on their evolution. Phylogenetic analysis revealed that each family within Caridea is monophyletic. The results of gene rearrangement and phylogenetic analysis demonstrated correlations between these two aspects. Divergence time estimation, supported by fossil records, indicated that the divergence of Caridea species occurred in the Triassic period of the Mesozoic era, with subsequent differentiation into two major lineages during the Jurassic period.

CONCLUSIONS

This study explored the fundamental characteristics and phylogenetic relationships of mitogenomes within the infraorder Caridea, providing valuable insights into their classification, interspecific evolutionary patterns, and the evolutionary status of various Caridea families. The findings provide essential references for identifying shrimp species and detecting significant gene rearrangements within the Caridea infraorder.

Full-Length Transcriptome Profiling of the Complete Mitochondrial Genome of Sericothrips houjii (Thysanoptera: Thripidae: Sericothripinae) Featuring Extensive Gene Rearrangement and Duplicated Control Regions

The mitochondrial genome (mitogenome) of Thysanoptera has extensive gene rearrangement, and some species have repeatable control regions. To investigate the characteristics of the gene expression, transcription and post-transcriptional processes in such extensively gene-rearranged mitogenomes, we sequenced the mitogenome and mitochondrial transcriptome of Sericothrips houjii to analyze. The mitogenome was 14,965 bp in length and included two CRs contains 140 bp repeats between COIII-trnN (CR1) and trnT-trnP (CR2). Unlike the putative ancestral arrangement of insects, S. houjii exhibited only six conserved gene blocks encompassing 14 genes (trnL2-COII, trnD-trnK, ND2-trnW, ATP8-ATP6, ND5-trnH-ND4-ND4L and trnV-lrRNA). A quantitative transcription map showed the gene with the highest relative expression in the mitogenome was ND4-ND4L. Based on analyses of polycistronic transcripts, non-coding RNAs (ncRNAs) and antisense transcripts, we proposed a transcriptional model of this mitogenome. Both CRs contained the transcription initiation sites (TISs) and transcription termination sites (TTSs) of both strands, and an additional TIS for the majority strand (J-strand) was found within antisense lrRNA. The post-transcriptional cleavage processes followed the "tRNA punctuation" model. After the cleavage of transfer RNAs (tRNAs), COI and ND3 matured as bicistronic mRNA COI/ND3 due to the translocation of intervening tRNAs, and the 3' untranslated region (UTR) remained in the mRNAs for COII, COIII, CYTB and ND5. Additionally, isoform RNAs of ND2, srRNA and lrRNA were identified. In summary, the relative mitochondrial gene expression levels, transcriptional model and post-transcriptional cleavage process of S. houjii are notably different from those insects with typical mitochondrial gene arrangements. In addition, the phylogenetic tree of Thripidae including S. houjii was reconstructed. Our study provides insights into the phylogenetic status of Sericothripinae and the transcriptional and post-transcriptional regulation processes of extensively gene-rearranged insect mitogenomes.

Daphnia sp. (Branchiopoda: Cladocera) Mitochondrial Genome Gene Rearrangement and Phylogenetic Position Within Branchiopoda

In high-altitude (4500 m) freshwater lakes, Daphnia is the apex species and the dominant zooplankton. It frequently dwells in the same lake as the Gammarid. Branchiopoda, a class of Arthropoda, Crustacea, is a relatively primitive group in the subphylum Crustacea, which originated in the Cambrian period of the Paleozoic. The complete mitogenome sequence of Daphnia sp. (Branchiopoda: Cladocera) was sequenced and annotated in this study and deposited in GenBank. The sequence structure of this species was studied by comparing the original sequences with BLAST. In addition, we have also researched the mechanisms of their mitochondrial gene rearrangement by establishing a model. We have used the Bayesian inference [BI] and maximum likelihood [ML] methods to proceed with phylogenetic analysis inference, which generates identical phylogenetic topology that reveals the phylogenetic state of Daphnia. The complete mitogenome of Daphnia sp. shows that it was 15,254 bp in length and included two control regions (CRs) and 37 genes (13 protein-coding genes, 22 tRNAs and two ribosomal RNAs [16S and 12S]). In addition to tRNA-Ser (GCT), other tRNAs have a typical cloverleaf secondary structure. Meanwhile, the mitogenome of Daphnia sp. was clearly rearranged when compared to the mitogenome of typical Daphnia. In a word, we report a newly sequenced mitogenome of Daphnia sp. with a unique rearrangement phenomenon. These results will be helpful for further phylogenetic research and provide a foundation for future studies on the characteristics of the mitochondrial gene arrangement process in Daphnia.

The complete mitochondrial genomes of five critical phytopathogenic Bipolaris species: features, evolution, and phylogeny

In the present study, three mitogenomes from the Bipolaris genus (Bipolaris maydis, B. zeicola, and B. oryzae) were assembled and compared with the other two reported Bipolaris mitogenomes (B. oryzae and B. sorokiniana). The five mitogenomes were all circular DNA molecules, with lengths ranging from 106,403 bp to 135,790 bp. The mitogenomes of the five Bipolaris species mainly comprised the same set of 13 core protein-coding genes (PCGs), two rRNAs, and a certain number of tRNAs and unidentified open reading frames (ORFs). The PCG length, AT skew and GC skew showed large variability among the 13 PCGs in the five mitogenomes. Across the 13 core PCGs tested, nad6 had the least genetic distance among the 16 Pleosporales species we investigated, indicating that this gene was highly conserved. In addition, the Ka/Ks values for all 12 core PCGs (excluding rps3) were < 1, suggesting that these genes were subject to purifying selection. Comparative mitogenomic analyses indicate that introns were the main factor contributing to the size variation of Bipolaris mitogenomes. The introns of the cox1 gene experienced frequent gain/loss events in Pleosporales species. The gene arrangement and collinearity in the mitogenomes of the five Bipolaris species were almost highly conserved within the genus. Phylogenetic analysis based on combined mitochondrial gene datasets showed that the five Bipolaris species formed well-supported topologies. This study is the first report on the mitogenomes of B. maydis and B. zeicola, as well as the first comparison of mitogenomes among Bipolaris species. The findings of this study will further advance investigations into the population genetics, evolution, and genomics of Bipolaris species.

Comparative mitogenomic analysis provides evolutionary insights into Formica (Hymenoptera: Formicidae)

Formica is a large genus in the family Formicidae with high diversity in its distribution, morphology, and physiology. To better understand evolutionary characteristics of Formica, the complete mitochondrial genomes (mitogenomes) of two Formica species were determined and a comparative mitogenomic analysis for this genus was performed. The two newly sequenced Formica mitogenomes each included 37 typical mitochondrial genes and a large non-coding region (putative control region), as observed in other Formica mitogenomes. Base composition, gene order, codon usage, and tRNA secondary structure were well conserved among Formica species, whereas diversity in sequence size and structural characteristics was observed in control regions. We also observed several conserved motifs in the intergenic spacer regions. These conserved genomic features may be related to mitochondrial function and their highly conserved physiological constraints, while the diversity of the control regions may be associated with adaptive evolution among heterogenous habitats. A negative AT-skew value on the majority chain was presented in each of Formica mitogenomes, indicating a reversal of strand asymmetry in base composition. Strong codon usage bias was observed in Formica mitogenomes, which was predominantly determined by nucleotide composition. All 13 mitochondrial protein-coding genes of Formica species exhibited molecular signatures of purifying selection, as indicated by the ratio of non-synonymous substitutions to synonymous substitutions being less than 1 for each protein-coding gene. Phylogenetic analyses based on mitogenomic data obtained fairly consistent phylogenetic relationships, except for two Formica species that had unstable phylogenetic positions, indicating mitogenomic data are useful for constructing phylogenies of ants. Beyond characterizing two additional Formica mitogenomes, this study also provided some key evolutionary insights into Formica.

Evolution of myxozoan mitochondrial genomes: insights from myxobolids

BACKGROUND

Myxozoa is a class of cnidarian parasites that encompasses over 2,400 species. Phylogenetic relationships among myxozoans remain highly debated, owing to both a lack of informative morphological characters and a shortage of molecular markers. Mitochondrial (mt) genomes are a common marker in phylogeny and biogeography. However, only five complete myxozoan mt genomes have been sequenced: four belonging to two closely related genera, Enteromyxum and Kudoa, and one from the genus Myxobolus. Interestingly, while cytochrome oxidase genes could be identified in Enteromyxum and Kudoa, no such genes were found in Myxobolus squamalis, and another member of the Myxobolidae (Henneguya salminicola) was found to have lost its entire mt genome. To evaluate the utility of mt genomes to reconstruct myxozoan relationships and to understand if the loss of cytochrome oxidase genes is a characteristic of myxobolids, we sequenced the mt genome of five myxozoans (Myxobolus wulii, M. honghuensis, M. shantungensis, Thelohanellus kitauei and, Sphaeromyxa zaharoni) using Illumina and Oxford Nanopore platforms.

RESULTS

Unlike Enteromyxum, which possesses a partitioned mt genome, the five mt genomes were encoded on single circular chromosomes. An mt plasmid was found in M. wulii, as described previously in Kudoa iwatai. In all new myxozoan genomes, five protein-coding genes (cob, cox1, cox2, nad1, and nad5) and two rRNAs (rnl and rns) were recognized, but no tRNA. We found that Myxobolus and Thelohanellus species shared unidentified reading frames, supporting the view that these mt open reading frames are functional. Our phylogenetic reconstructions based on the five conserved mt genes agree with previously published trees based on the 18S rRNA gene.

CONCLUSIONS

Our results suggest that the loss of cytochrome oxidase genes is not a characteristic of all myxobolids, the ancestral myxozoan mt genome was likely encoded on a single circular chromosome, and mt plasmids exist in a few lineages. Our findings indicate that myxozoan mt sequences are poor markers for reconstructing myxozoan phylogenetic relationships because of their fast-evolutionary rates and the abundance of repeated elements, which complicates assembly.

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.

The First Complete Mitochondrial Genome of the Genus Litostrophus: Insights into the Rearrangement and Evolution of Mitochondrial Genomes in Diplopoda

This study presents the complete mitochondrial genome (mitogenome) of Litostrophus scaber, which is the first mitogenome of the genus Litostrophus. The mitogenome is a circular molecule with a length of 15,081 bp. The proportion of adenine and thymine (A + T) was 69.25%. The gene ND4L used TGA as the initiation codon, while the other PCGs utilized ATN (A, T, G, C) as the initiation codons. More than half of the PCGs used T as an incomplete termination codon. The transcription direction of the L. scaber mitogenome matched Spirobolus bungii, in contrast to most millipedes. Novel rearrangements were found in the L. scaber mitogenome: trnQ -trnC and trnL1- trnP underwent short-distance translocations and the gene block rrnS-rrnL-ND1 moved to a position between ND4 and ND5, resulting in the formation of a novel gene order. The phylogenetic analysis showed that L. scaber is most closely related to S. bungii, followed by Narceus magnum. These findings enhance our understanding of the rearrangement and evolution of Diplopoda mitogenomes.

Comparative mitochondrial genome brings insights to slight variation in gene proportion and large intergenic spacer and phylogenetic relationship of mudskipper species

Fish mitochondrial genome have been largely studied worldwide for evolutionary and other genetic purposes and the structure and gene organization are commonly conservative. However, several studies have demonstrated that this scenario may present variations in some taxa, showing differentiation on the gene rearrangement. In this study, the complete mitogenome of terrestrial fish Boleophthalmus dussumieri was generated and compared with other species of the Exudercidae fishes. The newly complete mitogenome generated is circular and 16,685 bp of length, and it contained 13 protein-coding genes (PCGs), two ribosomal RNA (rRNAs), 22 transfer RNA genes (tRNAs), and one control region (CR), with high conservative structure, like other Mudskippers. Most of the PCG showed similar codon usage bias. The gene length was found to be different specially for the CR, 12S rRNA gene and ND5 gene in some taxon. All the Boleophthalmus species showed a gene duplication in the CR, except for B. dussumieri, and they presented a long intergenic spacer specially on the tRNA-Pro/ OH Tandem duplication/random loss (TDRL) and dimer-mitogenome and nonrandom loss (DMNL) are suitable to explain the mitogenome rearrangement observed in this study. The phylogenetic analysis well supported the monophyly of all mudskipper species and the analysis positioned the Periophthalmus clade as the most basal of the terrestrial fishes. This finding provides basis and brings insights for gene variation, gene rearrangements and replications showing evidence for variety of mitochondrial structure diversity within mudskippers.

Relaxed purifying selection pressure drives accelerated and dynamic gene rearrangements in thrips (Insecta: Thysanoptera) mitochondrial genomes

Insect mitochondrial genomes (mitogenome) generally present a typical gene order, which is considered as the ancestral arrangement. All sequenced mitogenomes in the Thysanoptera display high levels of gene rearrangement. Due to limited number of thrips mitogenomes sequenced, how gene rearrangement may be shaped by evolution remain unclear. Here, we analyzed 33 thrips mitogenomes, including 14 newly sequenced. These mitogenomes were diverse in organization, nucleotides substitution and gene arrangements. We found 28 highly rearranged gene orders with the breakpoints of gene rearrangements from 25 to 33. Reconstruction of the ancestors mitochondrial gene arrangements states indicated that Tubulifera have more complex pathways than Terebrantia in the gene order evolution. Molecular calibration estimated that divergence of two suborders occurred in the middle Triassic while the radiation of thrips was associated with the arose and flourish of angiosperm. Our evolutionary hypothesis testing suggests that relaxation of selection pressure enabled the early phase of Thysanoptera evolution, followed by a stronger selective pressure fixed diversification. Our analyses found gene inversion increases the nonsynonymous substitution rates and provide an evolutionary hypothesis driving the diverse gene orders.

The analyses of the complete mitochondrial genomes of three crabs revealed novel gene rearrangements and phylogenetic relationships of Brachyura

BACKGROUND

Brachyura crab is the largest branch of Decapoda crustacean. Phylogenetic relationships within Brachyura remain controversial to be investigated. The mitochondrial genome (mitogenome) is an important molecular marker for studying the phylogenetic relationships of Brachyura.

METHODS AND RESULTS

To understand the phylogeny of Brachyura, the three complete mitogenomes from Charybdis annulata, Leptodius exaratus, and Spider crab were sequenced and annotated. Their full length was 15,747, 15,716, and 16,608 bp long, respectively. The first two crabs both contained 13 protein-coding genes (PCGs), two rRNA genes, 22 tRNA genes and a control region. However, Spider crab contained 13 PCGs, two rRNA genes, 25 tRNA genes and a control region. The mitogenomes of each of the three crabs exhibited high AT content (67.8%, 69.1%, and 70.8%), with negative AT skews (-0.014, - 0.028, and - 0.017) and GC skews (-0.269, - 0.286, and - 0.341). The gene order of C. annulata was identical to the ancestor of Brachyura. Compared with the ancestor of Brachyura, L. exaratus exhibited the gene rearrangements of Val (V)-rrnS-control region, and Spider crab had the four copies of Lys (K). Phylogenetic analyses indicated that C. annulata belonged to Portunidae family, Portunoidea superfamilies, L. exaratus belonged to Xanthidae family, Xanthoidea superfamilies, and Spider crab belonged to Mithracidae family, Majoidea superfamilies. Phylogenetic analyses showed that the two species (Somanniathelphusa boyangensis and Huananpotamon lichuanense) belonging to the Potamoidea were sister groups to the Thoracotremata, thus supporting the conclusion that Heterotremata is polyphyletic.

CONCLUSION

The results of this study enriched the crab mitogenome database and enabled us to better understand the phylogenetic relationships of Brachyura.

ORFans in Mitochondrial Genomes of Marine Polychaete Polydora

Most characterized metazoan mitochondrial genomes are compact and encode a small set of proteins that are essential for oxidative phosphorylation, as well as rRNA and tRNA for their expression. However, in rare cases, invertebrate taxa have additional open reading frames (ORFs) in their mtDNA sequences. Here, we sequenced and analyzed the mitochondrial genome of a polychaete worm, Polydora cf. ciliata, part of whose life cycle takes place in low-oxygen conditions. In the mitogenome, we found three "ORFan" regions (544, 1,060, and 427 bp) that have no resemblance to any standard metazoan mtDNA gene but lack stop codons in one of the reading frames. Similar regions are found in the mitochondrial genomes of three other Polydora species and Bocardiella hamata. All five species share the same gene order in their mitogenomes, which differ from that of other known Spionidae mitogenomes. By analyzing the ORFan sequences, we found that they are under purifying selection pressure and contain conservative regions. The codon adaptation indices (CAIs) of the ORFan genes were in the same range of values as the CAI of conventional protein-coding genes in corresponding mitochondrial genomes. The analysis of the P. cf. ciliata mitochondrial transcriptome showed that ORFan-544, ORFan-427, and a portion of the ORFan-1060 are transcribed. Together, this suggests that ORFan-544 and ORFan-427 encode functional proteins. It is likely that the ORFans originated when the Polydora/Bocardiella species complex separated from the rest of the Spionidae, and this event coincided with massive gene rearrangements in their mitochondrial genomes and tRNA-Met duplication.

Mitogenome of the stink bug Aelia fieberi (Hemiptera: Pentatomidae) and a comparative genomic analysis between phytophagous and predatory members of Pentatomidae

Aelia fieberi Scott, 1874 is a pest of crops. The mitogenome of A. fieberi (OL631608) was decoded by next-generation sequencing. The mitogenome, with 41.89% A, 31.70% T, 15.44% C and 10.97% G, is 15,471 bp in size. The phylogenetic tree showed that Asopinae and Phyllocephalinae were monophyletic; however, Pentatominae and Podopinae were not monophyletic, suggesting that the phylogenetic relationships of Pentatomoidae are complex and need revaluation and revision. Phytophagous bugs had a ~20-nucleotide longer in nad2 than predatory bugs. There were differences in amino acid sequence at six sites between phytophagous bugs and predatory bugs. The codon usage analysis indicated that frequently used codons used either A or T at the third position of the codon. The analysis of amino acid usage showed that leucine, isoleucine, serine, methionine, and phenylalanine were the most abundant in 53 species of Pentatomoidae. Thirteen protein-coding genes were evolving under purifying selection, cox1, and atp8 had the strongest and weakest purifying selection stress, respectively. Phytophagous bugs and predatory bugs had different evolutionary rates for eight genes. The mitogenomic information of A. fieberi could fill the knowledge gap for this important crop pest. The differences between phytophagous bugs and predatory bugs deepen our understanding of the effect of feeding habit on mitogenome.

Two-Fold ND5 Genes, Three-Fold Control Regions, lncRNA, and the "Missing" ATP8 Found in the Mitogenomes of Polypedates megacephalus (Rhacophridae: Polypedates)

In prior research on the mitochondrial genome (mitogenome) of Polypedates megacephalus, the one copy of ND5 gene was translocated to the control region (CR) and the ATP8 gene was not found. Gene loss is uncommon among vertebrates. However, in this study, we resequenced the mitogenomes of P. megacephalus from different regions using a "primer bridging" approach with Sanger sequencing technologies, which revealed the "missing" ATP8 gene in P. megacephalus as well as three other previously published Polypedates. The mitogenome of this species was found to contain two copies of the ND5 genes and three copies of the control regions. Furthermore, multiple tandem repeats were identified in the control regions. Notably, we observed that there was no correlation between genetic divergence and geographic distance. However, using the mitogenome, gene expression analysis was performed via RT-qPCR of liver samples and it was thus determined that COIII, ND2, ND4, and ND6 were reduced to 0.64 ± 0.24, 0.55 ± 0.34, 0.44 ± 0.21 and 0.65 ± 0.17, respectively, under low-temperature stress (8 °C) as compared with controls (p < 0.05). Remarkably, the transcript of long non-coding RNA (lncRNA) between positions 8029 and 8612 decreased significantly with exposure to low-temperature stress (8 °C). Antisense ND6 gene expression showed a downward trend, but this was not significant. These results reveal that modulations of protein-coding mitochondrial genes and lncRNAs of P. megacephalus play a crucial role in the molecular response to cold stress.

The First Five Mitochondrial Genomes for the Family Nidulariaceae Reveal Novel Gene Rearrangements, Intron Dynamics, and Phylogeny of Agaricales

The family Nidulariaceae, consisting of five genera including Cyathus, is a unique group of mushrooms commonly referred to as bird's nest fungi due to their striking resemblance to bird's nests. These mushrooms are considered medicinal mushrooms in Chinese medicine and have received attention in recent years for their anti-neurodegenerative properties. However, despite the interest in these mushrooms, very little is known about their mitochondrial genomes (mitogenomes). This study is the first comprehensive investigation of the mitogenomes of five Nidulariaceae species with circular genome structures ranging in size from 114,236 bp to 129,263 bp. Comparative analyses based on gene content, gene length, tRNA, and codon usage indicate convergence within the family Nidulariaceae and heterogeneity within the order Agaricales. Phylogenetic analysis based on a combined mitochondrial conserved protein dataset provides a well-supported phylogenetic tree for the Basidiomycetes, which clearly demonstrates the evolutionary relationships between Nidulariaceae and other members of Agaricales. Furthermore, phylogenetic inferences based on four different gene sets reveal the stability and proximity of evolutionary relationships within Agaricales. These results reveal the uniqueness of the family Nidulariaceae and its similarity to other members of Agaricales; provide valuable insights into the origin, evolution, and genetics of Nidulariaceae species; and enrich the fungal mitogenome resource. This study will help to expand the knowledge and understanding of the mitogenomes in mushrooms.

Characterization of two new Pylorgus mitogenomes (Hemiptera, Lygaeidae, Ischnorhynchinae) and a mitochondrial phylogeny of Lygaeoidea

Lygaeidae is a large family of Hemiptera (Heteroptera) currently separated into three subfamilies, Ischnorhynchinae, Lygaeinae, and Orsillinae. In this research, the complete mitogenomes of the iscnorhynchines Pylorgusporrectus Zheng, Zou & Hsiao, 1979 and Pylorgussordidus Zheng, Zou & Hsiao, 1979 were sequenced, and the phylogeny of Pylorgus and the Lygaeidae with known complete mitogenomes were examined. The mitogenomes are 15,174 bp and 15,399 bp in size, respectively, and comprised of 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and a control region (D-loop). Nucleotide composition is biased toward A and T, and the gene order is identical to that of the putative ancestral arrangement of insects. Eleven PCGs begin with a typical ATN, and the remaining two PCGs begin with TTG (cox1 and nad4l). All tRNAs had a typical cloverleaf secondary structure, but some of them had individual base mismatches. The phylogenetic analyses based on the concatenated nucleotide sequences of the 13 PCGs, using Bayesian inference and maximum likelihood, support the monophyly of Lygaeidae. The results show that P.porrectus and P.sordidus clustered with nine other Lygaeidae. This study includes the first complete sequencing of the mitochondrial genomes of two Pylorgus species, which will provide important data for studying the phylogenetic position of Lygaeidae in Lygaeoidea and reconstructing the phylogenetic relationships within Pentatomomorpha.

Nine Mitochondrial Genomes of Phasmatodea with Two Novel Mitochondrial Gene Rearrangements and Phylogeny

The classification of stick and leaf insects (Order Phasmatodea) is flawed at various taxonomic ranks due to a lack of robust phylogenetic relationships and convergent morphological characteristics. In this study, we sequenced nine new mitogenomes that ranged from 15,011 bp to 17,761 bp in length. In the mitogenome of Carausis sp., we found a translocation of trnR and trnA, which can be explained by the tandem duplication/random loss (TDRL) model. In the Stheneboea repudiosa Brunner von Wattenwyl, 1907, a novel mitochondrial structure of 12S rRNA-CR1-trnI-CR2-trnQ-trnM was found for the first time in Phasmatodea. Due to the low homology of CR1 and CR2, we hypothesized that trnI was inverted through recombination and then translocated into the middle of the control region. Control region repeats were frequently detected in the newly sequenced mitogenomes. To explore phylogenetic relationships in Phasmatodea, mtPCGs from 56 Phasmatodean species (composed of 9 stick insects from this study, 31 GenBank data, and 16 data derived from transcriptome splicing) were used for Bayesian inference (BI), and maximum likelihood (ML) analyses. Both analyses supported the monophyly of Lonchodinae and Necrosciinae, but Lonchodidae was polyphyletic. Phasmatidae was monophyletic, and Clitumninae was paraphyletic. Phyllidae was located at the base of Neophasmatodea and formed a sister group with the remaining Neophasmatodea. Bacillidae and Pseudophasmatidae were recovered as a sister group. Heteroptergidae was monophyletic, and the Heteropteryginae sister to the clade (Obriminae + Dataminae) was supported by BI analysis and ML analysis.

The Complete Mitochondrial Genome of Mytilisepta virgata (Mollusca: Bivalvia), Novel Gene Rearrangements, and the Phylogenetic Relationships of Mytilidae

The circular mitochondrial genome of Mytilisepta virgata spans 14,713 bp, which contains 13 protein-coding genes (PCGs), 2 ribosomal RNA genes, and 22 transfer RNA genes. Analysis of the 13 PCGs reveals that the mitochondrial gene arrangement of Mytilisepta is relatively conserved at the genus level. The location of the atp8 gene in Mytilisepta keenae differs from that of other species. However, compared with the putative molluscan ancestral gene order, M. virgata exhibits a high level of rearrangement. We constructed phylogenetic trees based on concatenated 12 PCGs from Mytilidae. As a result, we found that M. virgata is in the same clade as other Mytilisepta spp. The result of estimated divergence times revealed that M. virgata and M. keenae diverged around the early Paleogene period, although the oldest Mytilisepta fossil was from the late or upper Eocene period. Our results provide robust statistical evidence for a sister-group relationship within Mytilida. The findings not only confirm previous results, but also provide valuable insights into the evolutionary history of Mytilidae.

The first two mitochondrial genomes from Apiotrichum reveal mitochondrial evolution and different taxonomic assignment of Trichosporonales

Apiotrichum is a diverse anamorphic basidiomycetous yeast genus, and its mitogenome characterization has not been revealed. In this study, we assembled two Apiotrichum mitogenomes and compared them with mitogenomes from Agaricomycotina, Pucciniomycotina and Ustilaginomycotina. The mitogenomes of Apiotrichum gracile and A. gamsii comprised circular DNA molecules, with sizes of 34,648 bp and 38,096 bp, respectively. Intronic regions were found contributed the most to the size expansion of A. gamsii mitogenome. Comparative mitogenomic analysis revealed that 6.85-38.89% of nucleotides varied between tRNAs shared by the two Apiotrichum mitogenomes. The GC content of all core PCGs in A. gamsii was lower than that of A. gracile, with an average low value of 4.97%. The rps3 gene differentiated the most among Agaricomycotina, Pucciniomycotina and Ustilaginomycotina species, while nad4L gene was the most conserved in evolution. The Ka/Ks values for cob and rps3 genes were > 1, indicating the two genes may be subjected to positive selection in Agaricomycotina, Pucciniomycotina and Ustilaginomycotina. Frequent intron loss/gain events and potential intron transfer events have been detected in evolution of Agaricomycotina, Pucciniomycotina and Ustilaginomycotina. We further detected large-scale gene rearrangements between the 19 mitogenomes from Agaricomycotina, Pucciniomycotina and Ustilaginomycotina, and fifteen of the 17 mitochondrial genes shared by Apiotrichum varied in gene arrangements. Phylogenetic analyses based on maximum likelihood and Bayesian inference methods using a combined mitochondrial gene dataset revealed different taxonomic assignment of two Apiotrichum species, wherein A. gamsii had a more closely relationship with Trichosporon asahii. This study served as the first report on mitogenomes from the genus Apiotrichum, which promotes the understanding of evolution, genomics, and phylogeny of Apiotrichum.

Comparative genome and phylogenetic analysis revealed the complex mitochondrial genome and phylogenetic position of Conopomorpha sinensis Bradley

Conopomorpha sinensis Bradley is a destructive pest that causes severe economic damage to litchi and longan. Previous C. sinensis research has focused on population life tables, oviposition selectivity, pest population prediction, and control technology. However, there are few studies on its mitogenome and phylogenetic evolution. In this study, we sequenced the whole mitogenome of C. sinensis by the third-generation sequencing, and analyzed the characteristics of its mitogenome by comparative genome. The complete mitogenome of C. sinensis is a typical circular and double-stranded structure. The ENC-plot analyses revealed that natural selection could affect the information of codon bias of the protein-coding genes in the mitogenome of C. sinensis in the evolutionary process. Compared with 12 other Tineoidea species, the trnA-trnF gene cluster of tRNA in the C. sinensis mitogenome appears to have a new arrangement pattern. This new arrangement has not been found in other Tineoidea or other Lepidoptera, which needs further exploration. Meanwhile, a long AT repeated sequence was inserted between trnR and trnA, trnE and trnF, ND1 and trnS in the mitogenome of C. sinensis, and the reason for this sequence remains to be further studied. Furthermore, the results of phylogenetic analysis showed that the litchi fruit borer belonged to Gracillariidae, and Gracillariidae was monophyletic. The results will contribute to an improved understanding of the complex mitogenome and phylogeny of C. sinensis. It also will provide a molecular basis for further research on the genetic diversity and population differentiation of C. sinensis.

Mitochondrial genomic characterization of two endemic Chinese freshwater crabs of the genus Sinopotamon (Brachyura: Potamidae) and implications for biogeography analysis of Potamidae

As an endemic freshwater crab group in China, the phylogenetic relationships within Sinopotamon are still controversial because of the limited taxon samples. In this study, the complete mitogenomes of Sinopotamon chishuiense with 17,311 bp and the nearly complete mitogenomes of S. wushanense with 16,785 bp were firstly sequenced and analyzed. Compared with other reported mitogenomes of Potamidae, some novel patterns of gene rearrangement were detected in these two Sinopotamon mitogenomes, which could be illuminated by the mechanisms of tandem duplication-random loss, recombination, and translocation. Phylogenetic analyses showed the nonmonophyly of the Sinopotamon and a sister group relationship with Tenuilapotamon. These crabs from the eastern and southern of the Yangtze River basin were more closely related while other crabs form the plateau areas formed a separate clade. Divergence time indicated that the Sinopotamon and its sister group Tenuilapotamon diverged from other potamiscine freshwater crabs approximately 42.65 Mya, which belongs to the recent main uplifts period of the Tibetan Plateau in the Late Miocene. Combined with the similar evolutionary rates and relatively stable habitat altitude of these Sinopotamon species, these results implied that the ecological environment may be relatively stable during the speciation. Overall, our study yielded worthy perceptions for the evolutionary and taxonomic relationship of Sinopotamon and will help to better clarify the gene rearrangement events of the invertebrate mitogenome and lay the foundation for further phylogenetic study of Sinopotamon. Overall, our study yielded valuable insights into the evolutionary history and taxonomic relationship of Sinopotamon and these results will help to better explain the gene rearrangement events of the invertebrate mitogenome and lay the foundation for further phylogenetic study of Sinopotamon.

Novel gene re-arrangement in the mitochondrial genome of Pisidiaserratifrons (Anomura, Galatheoidea, Porcellanidae) and phylogenetic associations in Anomura

To improve the taxonomy and systematics of Porcellanidae within the evolution of Anomura, we describe the complete mitochondrial genomes (mitogenomes) sequence of Pisidiaserratifrons, which is 15,344 bp in size, contains the entire set of 37 genes and has an AT-rich region. Compared with the pancrustacean ground pattern, at least five gene clusters (or genes) are significantly different with the typical genes, involving eleven tRNA genes and four PCGs and the tandem duplication/random loss and recombination models were used to explain the observed large-scale gene re-arrangements. The phylogenetic results showed that all Porcellanidae species clustered together as a group with well nodal support. Most Anomura superfamilies were found to be monophyletic, except Paguroidea. Divergence time estimation implies that the age of Anomura is over 225 MYA, dating back to at least the late Triassic. Most of the extant superfamilies and families arose during the late Cretaceous to early Tertiary. In general, the results obtained in this study will contribute to a better understanding of gene re-arrangements in Porcellanidae mitogenomes and provide new insights into the phylogeny of Anomura.

The complete mitochondrial genome and novel gene arrangement in Nesodiprion zhejiangensis Zhou & Xiao (Hymenoptera: Diprionidae)

The complete mitochondrial genome (mitogenome) of the sawfly, Nesodiprion zhejiangensis Zhou & Xiao, was sequenced, assembled, and deposited in GenBank (Accession Number: OM501121). The 15,660 bp N. zhejiangensis mitogenome encodes for 2 ribosomal RNAs (rrnL and rrnS), 22 transfer RNAs (tRNAs), 13 protein-coding genes (PCGs), and an AT-rich region of 450 bp in length. The nucleotide composition is biased toward adenine and thymine (A + T = 81.8%). Each PCG is initiated by an ATN codon, except for cox2, which starts with a TTG. Of 13 PCGs, 9 have a TAA termination codon, while the remainder terminate with a TAG or a single T. All tRNAs have the classic cloverleaf structure, except for the dihydrouridine (DHU) arm of tRNA^val, which forms a simple loop. There are 49 helices belonging to 6 domains in rrnL and 30 helices belonging to 4 domains in rrnS. In comparison to the ancestral architecture, N. zhejiangensis has the most rearranged mitogenome in Symphyta, in which rearrangement events of local inversion and transposition are identified in three gene clusters. Specifically, the main hotspot of gene rearrangement occurred between rrnS and trnY, and rearranged from rrnS-(AT-rich region)-I-Q-M-nd2-W-C-Y to rrnS-Q-W-C-nd2-I-M-(AT-rich region)-Y, involving a local inversion event of a large gene cluster and transposition events of some tRNAs. Transposition of trnA and trnR (rearranged from A-R to R-A) was observed at the nd3-nd5 gene junction while shuffling of trnP and trnT (rearranged from T-P to P-T) occurred at the nd4l-nd6 gene junction. While illegitimate inter-mtDNA recombination might explain the opposite orientations of transcription between rrnS and trnY, transposition events of tRNA in some gene blocks can be accounted for by the tandem duplication/random loss (TDRL) model. Our phylogenetic analysis suggests that N. zhejiangensis is closely related to congeneric species N. biremis and N. japonicus, which together form a sister lineage with the European pine sawfly, Neodiprion sertifer.

Complete mitochondrial genome of Distenia punctulatoides (Coleoptera: Chrysomeloidea: Disteniinae) and its phylogenetic implications

The family Disteniidae is a moderately large and widely distributed lineage. Distenia punctulatoides belongs to the family Disteniidae from the cerambycoid assemblage. Here, we report the complete mitogenome of D. punctulatoides, which is 15,675 bp in length. It contains 37 genes and a noncoding control region, which are arranged in the same order as that of the putative ancestor of beetles. The total base composition of the new mitogenome is 40.2% for A, 17.1% for C, 10.0% for G, and 32.7% for T. The new mitogenomic organization, nucleotide composition, and codon usage do not differ significantly from other beetles. Using available complete mitogenomes, the high-level phylogeny of the family Disteniidae was explored. The phylogenetic analyses showed that Disteniidae were monophyletic, and the genus Distenia grouped with the genus Clytomelegena as sister groups. Combining the morphological and molecular data, Typodryas Thomson, 1864 is suggested to be a junior synonym of Distenia Lepeletier and Audinet-Serville, 1828.

Complete mitochondrial genome of little ringed plover Charadrius dubius (Charadriiformes, Charadriidae)

This study encoded the complete mitochondrial genomic sequence of the little ringed plover Charadrius dubius. The mitochondrial genome has a total length of 16,864 bp, consisting of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a control region. The nucleotide composition was 23.8% T, 31.6% A, 30.8% C, and 13.8% G. This study provides the basic information on the mitogenome of C. dubius and supports the understanding of mitogenomic information and its phylogenetic relationship within Charadriiformes.

The Complete Mitochondrial Genome of Pilumnopeus Makianus (Brachyura: Pilumnidae), Novel Gene Rearrangements, and Phylogenetic Relationships of Brachyura

Pilumnopeus makianus is a crab that belongs to Pilumnidae, Brachyura. Although many recent studies have focused on the phylogeny of Brachyura, the internal relationships in this clade are far from settled. In this study, the complete mitogenome of P. makianus was sequenced and annotated for the first time. The length of the mitogenome is 15,863 bp, and includes 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNA), and 2 ribosomal RNA genes (rRNA). The mitogenome exhibits a high AT content (72.26%), with a negative AT-skew (-0.01) and a GC-skew (-0.256). In the mitogenome of P. makianus, all the tRNA genes are folded into the typical cloverleaf secondary structure, except trnS1 (TCT). A comparison with the ancestors of Brachyura reveals that gene rearrangement occurred in P. makianus. In addition, phylogenetic analyses based on thirteen PCGs indicated that P. makianus, Pilumnus vespertilio, and Echinoecus nipponicus clustered into a well-supported clade that supports the monophyly of the family Pilumnidae. These findings enabled a better understanding of phylogenetic relationships within Brachyura.

Evolution of Gene Arrangements in the Mitogenomes of Ensifera and Characterization of the Complete Mitogenome of Schizodactylus jimo

Gene arrangement (relative location of genes) is another evolutionary marker of the mitogenome that can provide extensive information on the evolutionary mechanism. To explore the evolution of gene arrangements in the mitogenome of diversified Ensifera, we sequenced the mitogenome of the unique dune cricket species found in China and used it for phylogenetic analysis, in combination with 84 known Ensiferan mitogenomes. The mitogenome of Schizodactylus jimo is a 16,428-bp circular molecule that contains 37 genes. We identified eight types of gene arrangement in the 85 ensiferan mitogenomes. The gene location changes (i.e., gene translocation and duplication) were in three gene blocks: I-Q-M-ND2, rrnl-rns-V, and ND3-A-R-N-S-E-F. From the phylogenetic tree, we found that Schizodactylus jimo and most other species share a typical and ancient gene arrangement type (Type I), while Grylloidea has two types (Types II and III), and the other five types are rare and scattered in the phylogenetic tree. We deduced that the tandem replication–random loss model is the evolutionary mechanism of gene arrangements in Ensifera. Selection pressure analysis revealed that purifying selection dominated the evolution of the ensiferan mitochondrial genome. This study suggests that most gene rearrangements in the ensiferan mitogenome are rare accidental events.

A Rearrangement of the Mitochondrial Genes of Centipedes (Arthropoda, Myriapoda) with a Phylogenetic Analysis

Due to the limitations of taxon sampling and differences in results from the available data, the phylogenetic relationships of the Myriapoda remain contentious. Therefore, we try to reconstruct and analyze the phylogenetic relationships within the Myriapoda by examining mitochondrial genomes (the mitogenome). In this study, typical circular mitogenomes of Mecistocephalus marmoratus and Scolopendra subspinipes were sequenced by Sanger sequencing; they were 15,279 bp and 14,637 bp in length, respectively, and a control region and 37 typical mitochondrial genes were annotated in the sequences. The results showed that all 13 PCGs started with ATN codons and ended with TAR codons or a single T; what is interesting is that the gene orders of M. marmoratus have been extensively rearranged compared with most Myriapoda. Thus, we propose a simple duplication/loss model to explain the extensively rearranged genes of M. marmoratus, hoping to provide insights into mitogenome rearrangement events in Myriapoda. In addition, our mitogenomic phylogenetic analyses showed that the main myriapod groups are monophyletic and supported the combination of the Pauropoda and Diplopoda to form the Dignatha. Within the Chilopoda, we suggest that Scutigeromorpha is a sister group to the Lithobiomorpha, Geophilomorpha, and Scolopendromorpha. We also identified a close relationship between the Lithobiomorpha and Geophilomorpha. The results also indicate that the mitogenome can be used as an effective mechanism to understand the phylogenetic relationships within Myriapoda.

Phylogenomic Analyses of the Tenthredinoidea Support the Familial Rank of Athaliidae (Insecta, Tenthredinoidea)

The systematic status of the genus Athalia and related genera is a perennial controversy in sawfly taxonomy. Several authors have hypothesized that the placement of Athalia within the Tenthredinidae is artificial, but no studies have focused on this topic. If the hypothesis that Athalia does not belong to Tenthredinidae can be supported, the taxonomic framework of Tenthredinoidea needs revision. We present a comprehensive phylogenomic study of Tenthredinoidae, focusing on the positions of Athalia and related genera by sampling 80 representatives mainly of the Tenthredinoidea, including Heptamelinae and Blasticotomidae. Our phylogenetic reconstructions based on nuclear genes and mitochondrial (mt) sequences support Athalia and related genera as a distinct clade sister to Tenthredinidae + (Cimbicidae + Diprionidae). A comparison of symphytan mitochondrial genomes reveals an innovative gene rearrangement pattern in Athaliidae, in which Dentathalia demonstrates a more ancestral pattern than Athalia and Hypsathalia. The lineage specificity of mt rRNA secondary structures also provides sufficient support to consider Athaliidae as a separate family. In summary, the phylogeny and genomic structural changes unanimously support the taxonomic treatment of Athaliidae as a family and the re-establishment of Dentathalia as a valid genus.

Gene rearrangements in the mitochondrial genome of ten ascaris species and phylogenetic implications for Ascaridoidea and Heterakoidea families

The Ascaridoidea family and Heterakoidea family are the most common and typical representative of large parasites. Although our understanding of these parasites' diversity has expanded by analyses of some mitochondrial genes, there is limited information on these species' evolutionary rates. Here we determined ten complete mitogenome sequences of five subfamilies of Ascaridoidea and one subfamily of Heterakoidea. The phylogenetic tree divided the Ascaridoidea into six monophyletic major clades, and the divergence time of Heterakoidea family and Ascaridoidea family can be placed during the early Carboniferous Period (300-360 Mya). The reconstruction of the ancestral state showed that the gene orders of all species in Ascaridoidea were conserved, and the Heterakoidea had obvious genome rearrangement. The conserved blocks between them were divided into five and the main types are tandem-duplication/random loss (TDRL). These results will help to better understand the gene rearrangements and evolutionary position of ascaris species.

Complete mitochondrial genomes from museum specimens clarify millipede evolution in the Eastern Arc Mountains

The Eastern Arc Mountains in Tanzania represent a hotspot for biological diversity of global importance. The level of endemism is high, and Eastern Arc biodiversity has been studied extensively in vertebrates and invertebrates, including millipedes. However, millipede evolution is vastly understudied at the molecular level. Therefore, we used next-generation ‘shotgun’ sequencing to obtain mitochondrial genome sequences of 26 museum specimens, representing six genera and 12 millipede species found across the Eastern Arc Mountains. Bayesian and maximum likelihood methods yielded consistent topologies with high node support, confirming a high level of congruence between molecular and morphological analyses. The only exception was a Tropostreptus sigmatospinus individual from Zanzibar, which was placed outside an otherwise monophyletic group consisting of mainland individuals of the same assumed species. For two species with a distribution across several mountain blocks (Tropostreptus sigmatospinus and Tropostreptus hamatus), each mountain population represents a distinct monophyletic lineage. In contrast, we also observe that distinct species exist sympatrically in the same montane forests, indicative of older speciation events that are not defined by current forest distribution. Our results are important for understanding speciation mechanisms in montane rain forests and highlight that ethanol-preserved invertebrates exhibit a tremendous potential for genomic analyses.

The Complete Mitochondrial Genome of Spirobolus bungii (Diplopoda, Spirobolidae): The First Sequence for the Genus Spirobolus

Millipedes (Diplopoda) comprise one of the most important groups of large soil arthropods in terrestrial ecosystems; however, their phylogenetic relationships are poorly understood. Herein, the mitochondrial genome (mitogenome) of Spirobolus bungii was sequenced and annotated, which was 14,879 bp in size and included 37 typical mitochondrial genes (13 protein-coding genes (PCGs), two ribosomal RNA genes (rRNAs), and 22 transfer RNA genes (tRNAs)). Most of the 13 PCGs had ATN (AT/A/T/G) as the start codon except for COX1, which used CGA, and most PCGs ended with the T end codon. By comparing the gene arrangements of the mitogenomes among Diplopoda species, rearrangement occurred between and within orders. In contrast to Narceus annularus, the mitogenome genes of S. bungii had consistent orders but were transcribed in completely opposite directions, which was a novel finding in Spirobolidae. Moreover, the phylogenetic relationships within Diplopoda, which were based on the sequences of 13 PCGs, showed that S. bungii was clustered with N. annularus, followed by Abacion magmun. This indicated that there might be a close relationship between Callipodida and Spirobolida. These results could contribute to further studies on the genetics and evolutionary processes of S. bungii and other Diplopoda species.

The first complete mitochondrial genome of Dufouriellini (Hemiptera: Anthocoridae) and implications for its phylogenetic position

The mitochondrial genome (mitogenome) is extensively used to better understand the phylogenetic relationships within the family level, but there are still limited representations at the tribe level of Anthocoridae. Here we describe the first complete mitogenome of Dufouriellini. The mitogenome of Cardiastethus sp. is 15,209 bp in size, containing 13 typical protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs, and a control region. All genes are arranged in the same gene order as the most other known cimicomorphan mitogenomes. The phylogenetic relationships based on mitogenomes using Bayesian inference and maximum likelihood methods show that Dufouriellini is sister to Anthocorini, and then both of them together form sister group with Oriini. The monophyly of each superfamily of Cimicomorpha is generally well supported. Reduvioidea is basal within Cimicomorpha. The topology of the remaining superfamily is as follows: (Miroidea + (Cimicoidea + (Velocipedoidea + Nabioidea))). This study will help to enhance our understanding of mitochondrial genomic evolution and phylogenetic relationships in the tribe level of Anthocoridae and also superfamily level of Cimicomorpha.

Comparative Mitogenomic Analyses of Hydropsychidae Revealing the Novel Rearrangement of Protein-Coding Gene and tRNA (Trichoptera: Annulipalpia)

Gene rearrangement of the mitochondrial genome of insects, especially the rearrangement of protein-coding genes, has long been a hot topic for entomologists. Although mitochondrial gene rearrangement is common within Annulipalpia, protein-coding gene rearrangement is relatively rare. As the largest family in Annulipalpia, the available mitogenomes from Hydropsychidae Curtis, 1835 are scarce, and thus restrict our interpretation of the mitogenome characteristic. In this study, we obtained 19 novel mitogenomes of Hydropsychidae, of which the mitogenomes of the genus Arctopsyche are published for the first time. Coupled with published hydropsychid mitogenome, we analyzed the nucleotide composition evolutionary rates and gene rearrangements of the mitogenomes among subfamilies. As a result, we found two novel gene rearrangement patterns within Hydropsychidae, including rearrangement of protein-coding genes. Meanwhile, our results consider that the protein-coding gene arrangement of Potamyia can be interpreted by the tandem duplication/random loss (TDRL) model. In addition, the phylogenetic relationships within Hydropsychidae constructed by two strategies (Bayesian inference and maximum likelihood) strongly support the monophyly of Arctopscychinae, Diplectroninae, Hydropsychinae, and Macronematinae. Our study provides new insights into the mechanisms and patterns of mitogenome rearrangements in Hydropsychidae.

Insights into the Evolution of Aphid Mitogenome Features from New Data and Comparative Analysis

The complete mitochondrial genomes and their rearrangement patterns can provide useful information for inferring evolutionary history of organisms. Aphids are one of the insect groups with some unique mitogenome features. In this study, to examine whether some features in aphid mitogenomes are independent species-specific evolutionary events or clade-specific events at certain taxonomic levels, we sequenced three new aphid mitogenomes (Hormaphidinae: Ceratovacuna keduensis, Pseudoregma panicola; Lachninae: Nippolachnus piri) and compared them with all known aphid mitogenomes. The three mitogenomes are 16,059–17,033 bp in length, with a set of 37 typical mitochondrial genes, a non-coding control region and a tandem repeat region. The gene orders of them are all highly rearranged. Within the subfamily Hormaphidinae, the presence of repeat region and mitogenome rearrangement in Cerataphidini species but not in the other two tribes indicate that these may be Cerataphidini-specific features. The same gene rearrangement pattern in the two Lachninae species, N. piri (Tuberolachnini) and Stomaphis sinisalicis (Stomaphidini), supports that this feature should be at least derived from the common ancestor of two tribes. Overall, our data and analyses provide new insights into the evolutionary patterns of gene rearrangement and repeat region in aphid mitogenomes, and further corroborate the potential role of gene rearrangement in elucidating the evolutionary history of different insect lineages.

Complete Mitochondrial Genome of Two Ectoparasitic Capsalids (Platyhelminthes: Monogenea: Monopisthocotylea): Gene Content, Composition, and Rearrangement

The capsalid monogeneans are important pathogens that generally infect marine fishes and have a substantial impact on fish welfare in aquaculture systems worldwide. However, the current mitogenome information on capsalids has received little attention, limiting the understanding of their evolution and phylogenetic relationships with other monogeneans. This paper reports the complete mitochondrial genomes of Capsala katsuwoni and Capsala martinieri for the first time, which we obtained using a next-generation sequencing method. The mitogenomes of C. katsuwoni and C. martinieri are 13,265 and 13,984 bp in length, respectively. Both species contain the typical 12 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and a control region. The genome compositions show a moderate A+T bias (66.5% and 63.9% for C. katsuwoni and C. martinieri, respectively) and exhibit a negative AT skew but a positive GC skew in both species. One gene block rearrangement was found in C. katsuwoni in comparison with other capsalid species. Instead of being basal to the Gyrodactylidea and Dactylogyridea or being clustered with Dactylogyridea, all species of Capsalidea are grouped into a monophyletic clade. Our results clarify the gene rearrangement process and evolutionary status of Capsalidae and lay a foundation for further phylogenetic studies of monogeneans.

Comparative Mitogenomic Analysis Reveals Intraspecific, Interspecific Variations and Genetic Diversity of Medical Fungus Ganoderma

Ganoderma species are widely distributed in the world with high diversity. Some species are considered to be pathogenic fungi while others are used as traditional medicine in Asia. In this study, we sequenced and assembled four Ganoderma complete mitogenomes, including G. subamboinense s118, G. lucidum s37, G. lingzhi s62, and G. lingzhi s74. The sizes of the four mitogenomes ranged from 50,603 to 73,416 bp. All Ganoderma specimens had a full set of core protein-coding genes (PCGs), and the rps3 gene of Ganoderma species was detected to be under positive or relaxed selection. We found that the non-conserved PCGs, which encode RNA polymerases, DNA polymerases, homing endonucleases, and unknown functional proteins, are dynamic within and between Ganoderma species. Introns were thought to be the main contributing factor in Ganoderma mitogenome size variation (p < 0.01). Frequent intron loss/gain events were detected within and between Ganoderma species. The mitogenome of G. lucidum s26 gained intron P637 in the cox3 gene compared with the other two G. lucidum mitogenomes. In addition, some rare introns in Ganoderma were detected in distinct Basidiomycetes, indicating potential gene transfer events. Comparative mitogenomic analysis revealed that gene arrangements also varied within and between Ganoderma mitogenomes. Using maximum likelihood and Bayesian inference methods with a combined mitochondrial gene dataset, phylogenetic analyses generated identical, well-supported tree topologies for 71 Agaricomycetes species. This study reveals intraspecific and interspecific variations of the Ganoderma mitogenomes, which promotes the understanding of the origin, evolution, and genetic diversity of Ganoderma species.

Novel Gene Rearrangement in the Mitochondrial Genome of Three Garra and Insights Into the Phylogenetic Relationships of Labeoninae

Complete mitochondrial genomes (mitogenomes) can provide valuable information for phylogenetic relationships, gene rearrangement, and molecular evolution. Here, we report the mitochondrial whole genomes of three Garra species and explore the mechanisms of rearrangements that occur in their mitochondrial genomes. The lengths of the mitogenomes’ sequences of Garra dengba, Garra tibetana, and Garra yajiangensis were 16,876, 16,861, and 16,835, respectively. They contained 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNA genes, and two identical control regions (CRs). The mitochondrial genomes of three Garra species were rearranged compared to other fish mitochondrial genomes. The tRNA-Thr, tRNA-Pro and CR (T-P-CR) genes undergo replication followed by random loss of the tRNA-Thr and tRNA-Pro genes to form tRNA-Thr, CR1, tRNA-Pro and CR2 (T-CR-P-CR). Tandem duplication and random loss best explain this mitochondrial gene rearrangement. These results provide a foundation for future characterization of the mitochondrial gene arrangement of Labeoninae and further phylogenetic studies.

Positive Correlation of the Gene Rearrangements and Evolutionary Rates in the Mitochondrial Genomes of Thrips (Insecta: Thysanoptera)

Simple Summary

Aeolothrips, commonly known as banded thrips, is the largest genus of the family Aeolothripidae (predatory thrips). In the current study, we sequenced the mitochondrial genome (mitogenome) of the banded thrip species Aeolothrips xinjiangensis. We found a novel gene arrangement in this mitogenome that has not been reported in Thysanoptera. By comparing the gene order and rearrangement patterns, we found seven identical gene blocks and three identical rearrangement events in two mitogenomes of banded thrips. There was marked variation in the mitochondrial gene order across thrip species, with only two conserved gene blocks shared by all 14 thrips. In addition, we found a positive correlation between the degree of gene rearrangement and evolutionary rate. Our results suggested that the mitogenomes of thrips have tended to be stable since their massive rearrangement.

Abstract

Extensive gene rearrangement is characteristic in the mitogenomes of thrips (Thysanoptera), but the historical process giving rise to the contemporary gene rearrangement pattern remains unclear. To better understand the evolutionary processes of gene rearrangement in the mitogenomes of thrips, we sequenced the mitogenome of the banded thrip species Aeolothrips xinjiangensis. First, we found a novel mitochondrial gene order in this species. This mitogenome is 16,947 bp in length and encodes the typical 37 coding genes (13 protein-coding genes, 22 tRNA genes, and two rRNA genes) of insects. The gene arrangement was dramatically different from the putative ancestral mitogenome, with 26 genes being translocated, eight of which were inverted. Moreover, we found a novel, conserved gene block, trnC-trnY, which has not been previously reported in the mitogenomes of thrips. With this newly assembled mitogenome, we compared mitogenome sequences across Thysanoptera to assess the evolutionary processes giving rise to the current gene rearrangement pattern in thrips. Seven identical gene blocks were shared by two sequenced banded thrip mitogenomes, while the reversal of ND2 combined with TDRL events resulted in the different gene orders of these two species. In phylogenetic analysis, the monophyly of the suborders and families of Thysanoptera was well supported. Across the gene orders of 14 thrips, only two conserved gene blocks, ATP8-ATP6 and ND4-ND4L, could be found. Correlation analysis showed that the degree of gene rearrangement was positively correlated with the non-synonymous substitution rate in thrips. Our study suggests that the mitogenomes of thrips remain stable over long evolutionary timescales after massive rearrangement during early diversification.

First two mitochondrial genomes for the order Filobasidiales reveal novel gene rearrangements and intron dynamics of Tremellomycetes

In the present study, two mitogenomes from the Filobasidium genus were assembled and compared with other Tremellomycetes mitogenomes. The mitogenomes of F. wieringae and F. globisporum both comprised circular DNA molecules, with sizes of 27,861 bp and 71,783 bp, respectively. Comparative mitogenomic analysis revealed that the genetic contents, tRNAs, and codon usages of the two Filobasidium species differed greatly. The sizes of the two Filobasidium mitogenomes varied greatly with the introns being the main factor contributing to mitogenome expansion in F. globisporum. Positive selection was observed in several protein-coding genes (PCGs) in the Agaricomycotina, Pucciniomycotina, and Ustilaginomycotina species, including cob, cox2, nad2, and rps3 genes. Frequent intron loss/gain events were detected to have occurred during the evolution of the Tremellomycetes mitogenomes, and the mitogenomes of 17 species from Agaricomycotina, Pucciniomycotina, and Ustilaginomycotina have undergone large-scale gene rearrangements. Phylogenetic analyses based on Bayesian inference and the maximum likelihood methods using a combined mitochondrial gene set generated identical and well-supported phylogenetic trees, wherein Filobasidium species had close relationships with Trichosporonales species. This study, which is the first report on mitogenomes from the order Filobasidiales, provides a basis for understanding the genomics, evolution, and taxonomy of this important fungal group.

Five new mitogenomes sequences of Calidridine sandpipers (Aves: Charadriiformes) and comparative mitogenomics of genus Calidris

Background

The genus Calidris (Charadriiformes, Scolopacidae) includes shorebirds known as dunlin, knots, and sanderlings. The relationships between species nested within Calidris, including Eurynorynchus, Limicola and Aphriza, are not well-resolved.

Methods

Samples were collected from Xiaoyangkou, Rudong County, Jiangsu Province, China. Mitogenomes were sequenced using the Illumina Novaseq 6000 platform for PE 2 × 150 bp sequencing, and then checked for PCR products. Protein-coding genes were determined using an Open Reading Frame Finder. tRNAscan-SE, MITOS, and ARWEN were used to confirm tRNA and rRNA annotations. Bioinformatic analyses were conducted using DnaSP 5.1 and MEGA X. Phylogenic trees were constructed using maximum likelihood and Bayesian analyses.

Results

We sequenced and annotated the mitogenome of five species and obtained four complete mitogenomes and one nearly complete mitogenome. Circular mitogenomes displayed moderate size variation, with a mean length of 16,747 bp, ranging from 16,642 to 16,791 bp. The mitogenome encoded a control region and a typical set of 37 genes containing two rRNA genes, 13 protein-coding genes, and 22 tRNA genes. There were four start codons, four stop codons, and one incomplete stop codon (T-). The nucleotide composition was consistently AT-biased. The average uncorrected pairwise distances revealed heterogeneity in the evolutionary rate for each gene; the COIII had a slow evolutionary rate, whereas the ATP8 gene had a fast rate. dN/dS analysis indicated that the protein-coding genes were under purifying selection. The genetic distances between species showed that the greatest genetic distance was between Eurynorhynchus pygmeus and Limicola falcinellus (22.5%), and the shortest was between E. pygmeus and Calidris ruficollis (12.8%). Phylogenetic trees revealed that Calidris is not a monophyletic genus, as species from the genera Eurynorynchus and Limicola were nested within Calidris. The molecular data obtained in this study are valuable for research on the taxonomy, population genetics, and evolution of birds in the genus Calidris.

Comparative genomic analysis of vertebrate mitochondrial reveals a differential of rearrangements rate between taxonomic class

Vertebrate mitochondrial genomes have been extensively studied for genetic and evolutionary purposes, these are normally believed to be extremely conserved, however, different cases of gene rearrangements have been reported. To verify the level of rearrangement and the mitogenome evolution, we performed a comparative genomic analysis of the 2831 vertebrate mitochondrial genomes representing 12 classes available in the NCBI database. Using a combination of bioinformatics methods, we determined there is a high number of errors in the annotation of mitochondrial genes, especially in tRNAs. We determined there is a large variation in the proportion of rearrangements per gene and per taxonomic class, with higher values observed in Actinopteri, Amphibia and Reptilia. We highlight that these are results for currently available vertebrate sequences, so an increase in sequence representativeness in some groups may alter the rearrangement rates, so in a few years it would be interesting to see if these rates are maintained or altered with the new mitogenome sequences. In addition, within each vertebrate class, different patterns in rearrangement proportion with distinct hotspots in the mitochondrial genome were found. We also determined that there are eleven convergence events in gene rearrangement, nine of which are new reports to the scientific community.

Novel mitochondrial gene rearrangements pattern in the millipede Polydesmus sp. GZCS-2019 and phylogenetic analysis of the Myriapoda

The subphylum Myriapoda included four extant classes (Chilopoda, Symphyla, Diplopoda, and Pauropoda). Due to the limitation of taxon sampling, the phylogenetic relationships within Myriapoda remained contentious, especially for Diplopoda. Herein, we determined the complete mitochondrial genome of Polydesmus sp. GZCS-2019 (Myriapoda: Polydesmida) and the mitochondrial genomes are circular molecules of 15,036 bp, with all genes encoded on + strand. The A+T content is 66.1%, making the chain asymmetric, and exhibits negative AT-skew (-0.236). Several genes rearrangements were detected and we propose a new rearrangement model: "TD (N\R) L + C" based on the genome-scale duplication + (non-random/random) loss + recombination. Phylogenetic analyses demonstrated that Chilopoda and Symphyla both were monophyletic group, whereas Pauropoda was embedded in Diplopoda to form the Dignatha. Divergence time showed the first split of Myriapoda occurred between the Chilopoda and other classes (Wenlock period of Silurian). We combine phylogenetic analysis, divergence time, and gene arrangement to yield valuable insights into the evolutionary history and classification relationship of Myriapoda and these results support a monophyletic Progoneata and the relationship (Chilopoda + (Symphyla + (Diplopoda + Pauropoda))) within myriapod. Our results help to better explain the gene rearrangement events of the invertebrate mitogenome and lay the foundation for further phylogenetic study of Myriapoda.

Comparative Analysis of Mitochondrial Genomes in Two Subspecies of the Sunwatcher Toad-Headed Agama (Phrynocephalus helioscopus): Prevalent Intraspecific Gene Rearrangements in Phrynocephalus

Intraspecific rearrangements of mitochondrial genomes are rarely reported in reptiles, even in vertebrates. The sunwatcher toad-headed agama, Phryncoephalus helioscopus, can serve as an excellent model for investigating the dynamic mitogenome structure at intraspecific level. To date, seven subspecies of P. helioscopus are well recognized, but little is known about the mitogenomic evolution among different subspecies. In this study, complete mitogenomes of subspecies P. helioscopus varius II and P. helioscopus cameranoi were determined by next-generation sequencing, and another P. helioscopus varius I retrieved from GenBank was compiled for comparative analysis. The nucleotide composition and the codon usage are similar to those previously published from toad-headed agamas. P. helioscopus varius II and P. helioscopus cameranoi have 23 tRNA genes, including standard 22 tRNA genes and one extra tRNA-Phe (tRNA-Phe duplication). Gene order and phylogenetic analyses in the genus Phrynocephalus support prevalent intraspecific gene rearrangement in P. helioscopus and other congener species including P. erythrurus, P. vlangalii, and P. forsythii. Six different mitochondrial gene arrangements are observed in Phrynocephalus. Overall, the occurrence of rearrangements may result from multiple independent structural dynamic events. The split of the two subspecies in P. helioscopus was dated at approximately 2.34 million years ago (Ma). Two types of gene rearrangements are found in the three mitogenomes of P. helioscopus, and this intraspecific rearrangement phenomenon can be explained by the tandem duplication/random loss (TDRL) model. Post duplication, the alternative loss types can occur in 0.23–0.72 Ma, suggesting that the duplication and fixation of these rearrangements can occur quite quickly. These findings highlight the need for more mitogenomes at the population level in order to better understand the potentially rampant intraspecific mitogenomic reorganization in Phrynocephalus.

Different gene rearrangements of the genus Dardanus (Anomura: Diogenidae) and insights into the phylogeny of Paguroidea

Complete mitochondrial genomes (mitogenomes) can provide useful information for phylogenetic relationships, gene rearrangement, and molecular evolution. In this study, the complete mitogenomes of two hermit crabs, Dardanus arrosor and Dardanus aspersus, were sequenced for the first time and compared with other published mitogenomes of Paguroidea. Each of the two mitogenomes contains an entire set of 37 genes and a putative control region, but they display different gene arrangements. The different arrangements of the two mitogenomes might be the result of transposition, reversal, and tandem duplication/random loss events from the ancestral pancrustacean pattern. Genome sequence similarity analysis reveals the gene rearrangement in 15 Paguroidea mitogenomes. After synteny analysis between the 15 Paguroidea mitogenomes, an obvious rearranged region is found in D. aspersus mitogenome. Across the 13 protein-coding genes (PCGs) tested, COI has the least and ND6 has the largest genetic distances among the 15 hermit crabs, indicating varied evolution rates of PCGs. In addition, the dN/dS ratio analysis shows that all PCGs are evolving under purifying selection. The phylogenetic analyses based on both gene order and sequence data present the monophyly of three families (Paguridae, Coenobitidae, and Pylochelidae) and the paraphyly of the family Diogenidae. Meanwhile, the phylogenetic tree based on the nucleotide sequences of 13 PCGs shows that two Dardanus species formed a sister group with five Coenobitidae species. These findings help to better understand the gene rearrangement and phylogeny of Paguroidea, as well as provide new insights into the usefulness of mitochondrial gene order as a phylogenetic marker.

Sorting Signed Permutations by Inverse Tandem Duplication Random Losses

Gene order evolution of unichromosomal genomes, for example mitochondrial genomes, has been modelled mostly by four major types of genome rearrangements: inversions, transpositions, inverse transpositions, and tandem duplication random losses. Generalizing models that include all those rearrangements while admitting computational tractability are rare. In this paper, we study such a rearrangement model, namely the inverse tandem duplication random loss (iTDRL) model, where an iTDRL duplicates and inverts a continuous segment of a gene order followed by the random loss of one of the redundant copies of each gene. The iTDRL rearrangement has currently been proposed by several authors suggesting it to be a possible mechanisms of mitochondrial gene order evolution. We initiate the algorithmic study of this new model of genome rearrangement by proving that a shortest rearrangement scenario that transforms one given gene order into another given gene order can be obtained in quasilinear time. Furthermore, we show that the length of such a scenario, i.e., the minimum number of iTDRLs in the transformation, can be computed in linear time.

The first mitochondrial genome of the genus Exhippolysmata (Decapoda: Caridea: Lysmatidae), with gene rearrangements and phylogenetic associations in Caridea

The complete mitochondrial genome (mitogenome) of animals can provide useful information for evolutionary and phylogenetic analyses. The mitogenome of the genus Exhippolysmata (i.e., Exhippolysmata ensirostris) was sequenced and annotated for the first time, its phylogenetic relationship with selected members from the infraorder Caridea was investigated. The 16,350 bp mitogenome contains the entire set of 37 common genes. The mitogenome composition was highly A + T biased at 64.43% with positive AT skew (0.009) and negative GC skew (- 0.199). All tRNA genes in the E. ensirostris mitogenome had a typical cloverleaf secondary structure, except for trnS1 (AGN), which appeared to lack the dihydrouridine arm. The gene order in the E. ensirostris mitogenome was rearranged compared with those of ancestral decapod taxa, the gene order of trnL2-cox2 changed to cox2-trnL2. The tandem duplication-random loss model is the most likely mechanism for the observed gene rearrangement of E. ensirostris. The ML and BI phylogenetic analyses place all Caridea species into one group with strong bootstrap support. The family Lysmatidae is most closely related to Alpheidae and Palaemonidae. These results will help to better understand the gene rearrangements and evolutionary position of E. ensirostris and lay a foundation for further phylogenetic studies of Caridea.

Mitochondrial DNA duplication, recombination, and introgression during interspecific hybridization

mtDNA recombination events in yeasts are known, but altered mitochondrial genomes were not completed. Therefore, we analyzed recombined mtDNAs in six Saccharomyces cerevisiae × Saccharomyces paradoxus hybrids in detail. Assembled molecules contain mostly segments with variable length introgressed to other mtDNA. All recombination sites are in the vicinity of the mobile elements, introns in cox1, cob genes and free standing ORF1, ORF4. The transplaced regions involve co-converted proximal exon regions. Thus, these selfish elements are beneficial to the host if the mother molecule is challenged with another molecule for transmission to the progeny. They trigger mtDNA recombination ensuring the transfer of adjacent regions, into the progeny of recombinant molecules. The recombination of the large segments may result in mitotically stable duplication of several genes.