The first mitochondrial genome of the sepsid fly Nemopoda mamaevi Ozerov, 1997 (Diptera: Sciomyzoidea: Sepsidae), with mitochondrial genome phylogeny of cyclorrhapha

The mitochondrial genome of Homoneura picta (Diptera: Lauxaniidae) and its phylogenetic analysis

Homoneura picta belongs to the Homoneurinae subfamily of Lauxaniidae, and it is widely distributed and common in China. This study reports the newly sequenced mitochondrial genome of H. picta. The sequence is 15,469 bp long and contains 37 genes (13 protein-coding, 22 tRNA, and 2 rRNA genes) and a control region. The overall base composition is 38.4% for A, 37.7% for T, 14.1% for C, and 9.8% for G, with a bias toward A + T (76.1%). Phylogenetic analysis show that Homoneura is a sister genus of Cestrotus. We have successfully sequenced the mitochondrial genome of H. picta, which can be useful in investigating the phylogenetic status of Homoneurinae. Our results provide data for further studies of phylogeny in Diptera.

Comparative Analysis of the Mitochondrial Genomes of Chloropidae and Their Implications for the Phylogeny of the Family

Chloropidae, commonly known as grass flies, represent the most taxonomically diverse family of Diptera Carnoidea, comprising over 3000 described species worldwide. Previous phylogenetic studies of this family have predominantly relied on morphological characters, with mitochondrial genomes being reported in a few species. This study presents 11 newly sequenced mitochondrial genomes (10 Chloropidae and 1 Milichiidae) and provides the first comprehensive comparative analysis of mitochondrial genomes for Chloropidae. Apart from 37 standard genes and the control region, three conserved intergenic sequences across Diptera Cyclorrhapha were identified in all available chloropid mitochondrial genomes. Evolutionary rates within Chloropidae exhibit significant variation across subfamilies, with Chloropinae displaying higher rates than the other three subfamilies. Phylogenetic relationships based on mitochondrial genomes were inferred using maximum likelihood and Bayesian methods. The monophyly of Chloropidae and all four subfamilies is consistently strongly supported, while subfamily relationships within Chloropidae remain poorly resolved, possibly due to rapid evolution.

Eighteen mitochondrial genomes of Syrphidae (Insecta: Diptera: Brachycera) with a phylogenetic analysis of Muscomorpha

In this study, 18 mitochondrial genomes (mitogenomes) of Syrphidae were sequenced. These mitogenomes ranged from 15,648 to 16,405 bp and contained 37 genes that were similar to those from other Syrphidae species. Most protein-coding genes (PCGs) started with a standard ATN codon and ended with TAA/G. All transfer RNAs (tRNAs) could be folded into the cloverleaf secondary structure except tRNA-Ser (AGN), which lacks a dihydrouridine arm. The secondary structures of ribosomal RNAs (rRNAs) were predicted. Six domains (III is absent in arthropods) and 44 helices were included in the 16S rRNA, and three domains and 24 helices were included in the 12S rRNA. We found three conserved fragments in all syrphid mitogenomes. Phylogenetic analyses were performed based on the nucleotide data of 13 PCGs and two rRNAs from 76 Muscomorpha and three outgroup species. In results the paraphyly of Aschiza and Schizophora were supported, the Acalyptratae was also paraphyletic but the relationships of its superfamilies were difficult to determine, the monophyly of Calyptratea was supported with the relationships of Oestroidea and Muscoidea need to be further reconsidered. Within Syrphidae the monophyly of family level was supported, the Syrphinae were clustered into one branch, while the paraphyly of Eristalinae was still well supported.

The complete mitochondrial genome of Simulium jisigouense (Diptera: Simuliidae) and phylogenetic analysis of Simuliidae

The family Simuliidae belongs to Diptera whose systematic position is still strongly debated. A few mitochondrial genomes (mitogenomes) of Simuliidae and none of the subgenus Montisimulium in the genus Simulium have previously been available. Therefore, the mitogenome of Simulium jisigouense Chen, Zhang and Liu, 2008 was sequenced to better understand the diversity of mitogenomes within this family. The complete mitogenome of S. jisigouense was 16,384 bp long. It contained 37 genes including 22 tRNAs, 13 protein-coding genes (PCGs), and 2 rRNAs, and an A + T-rich region, which was the same as the arrangement of mitogenomes of ancestral insects. Almost all PCGs used the typical ATN as start codons, except COI used TTG. Almost all tRNAs could be folded into cloverleaf structures except the dihydrouridine (DHU) arm of tRNASer(AGN), which formed a loop. The phylogenetic analysis revealed that Simuliidae was monophyletic and was the sister group to Thaumaleidae. Subgenus Simulium was recovered as paraphyletic and needs more comprehensive sampling in future studies. Divergence time estimation showed that Simuliidae diverged from Thaumaleidae at 239.24 Ma and the subgenera of Simulium diverged from each other from 162.46 to 75.08 Ma.

Characterization of the mitochondrial genomes of Bradysia hygida, Phytosciara flavipes and Trichosia splendens (Diptera: Sciaridae) and novel insights on the control region of sciarid mitogenomes

Sciarids, also called "fungus gnats" are small, almost entirely dark-coloured insects. Sciarid larvae feed on different substrates and can infest agricultural crops and mushroom nurseries, causing economic losses. Of the 2174 Diptera mitogenome sequences currently available in GenBank, only eight are from the Sciaridae family, none of which are complete circular molecules. Here we describe the mitogenome sequences of three sciarid species: Phytosciara flavipes, Trichosia splendens and Bradysia hygida and provide novel insights on the control region of sciarid mitogenomes. The assembled mitogenomes range from 16,062 bp in P. flavipes to 17,095 bp in B. hygida. All 13 protein coding genes, 22 tRNAs and 2 rRNAs characteristic of insect mitogenomes were identified, but the sequence of the control region could not be determined. Experimental results suggest that the B. hygida control region is about 21 kb long resulting in a 37 kb long mitogenome which constitutes the largest insect mitochondrial genome described so far. Phylogenetic analysis using all Bibionomorpha mitogenome sequences available in GenBank strongly supports the Sciaridae monophyly and led to the identification of species and subfamily specific gene rearrangements. Our study extends the knowledge of this large and diverse insect family that includes agricultural pest species.

Mitogenome-wise codon usage pattern from comparative analysis of the first mitogenome of Blepharipa sp. (Muga uzifly) with other Oestroid flies

Uziflies (Family: Tachinidae) are dipteran endoparasites of sericigenous insects which cause major economic loss in the silk industry globally. Here, we are presenting the first full mitogenome of Blepharipa sp. (Acc: KY644698, 15,080 bp, A + T = 78.41%), a dipteran parasitoid of Muga silkworm (Antheraea assamensis) found in the Indian states of Assam and Meghalaya. This study has confirmed that Blepharipa sp. mitogenome gene content and arrangement is similar to other Tachinidae and Sarcophagidae flies of Oestroidea superfamily, typical of ancestral Diptera. Although, Calliphoridae and Oestridae flies have undergone tRNA translocation and insertion, forming unique intergenic spacers (IGS) and overlapping regions (OL) and a few of them (IGS, OL) have been conserved across Oestroidea flies. The Tachinidae mitogenomes exhibit more AT content and AT biased codons in their protein-coding genes (PCGs) than the Oestroidea counterpart. About 92.07% of all (3722) codons in PCGs of this new species have A/T in their 3rd codon position. The high proportion of AT and repeats in the control region (CR) affects sequence coverage, resulting in a short CR (Blepharipa sp.: 168 bp) and a smaller tachinid mitogenome. Our research unveils those genes with a high AT content had a reduced effective number of codons, leading to high codon usage bias. The neutrality test shows that natural selection has a stronger influence on codon usage bias than directed mutational pressure. This study also reveals that longer PCGs (e.g., nad5, cox1) have a higher codon usage bias than shorter PCGs (e.g., atp8, nad4l). The divergence rates increase nonlinearly as AT content at the 3rd codon position increases and higher rate of synonymous divergence than nonsynonymous divergence causes strong purifying selection. The phylogenetic analysis explains that Blepharipa sp. is well suited in the family of insectivorous tachinid maggots. It's possible that biased codon usage in the Tachinidae family reduces the effective number of codons, and purifying selection retains the core functions in their mitogenome, which could help with efficient metabolism in their endo-parasitic life style and survival strategy.

Comparative analysis of four complete mitogenomes from hoverfly genus Eristalinus with phylogenetic implications

The genus Eristalinus is widely distributed globally. Four complete mitochondrial genomes (i.e., mitogenomes) of Eristalinus were sequenced and analyzed in this study: Eristalinus viridis (Coquillett, 1898), E. quinquestriatus (Fabricius, 1781), E. tarsalis (Macquart, 1855), and E. sp. Within these four sequenced mitogenomes, most protein-coding genes (ND2, CO1, COX2, COX3, ND3, ND5, ND4, ND4L, ND6, and Cytb) began with a typical ATN (T/C/G/A) start codon and ended with a stop codon TAA or incomplete T, whereas ND1 began with the start codon TTG. ND3 ended with TAG. The secondary tRNA structure was that of a typical cloverleaf, and only the tRNA-Ser1 lacked a DHU arm. Three and five domains appeared in the 12S and 16S rRNA secondary structures, respectively. The phylogenetic relationships among the four Eristalinus species combined with the published mitogenomes of Syrphidae were reconstructed using the maximum likelihood and Bayesian inference methods, which support the monophyly of the subfamily Syrphinae but do not support that of the subfamily Eristalinae. Of note, Eristalini and Syrphini are monophyletic groups. The mitogenomes of E. viridis, E. quinquestriatus, E. sp., and E. tarsalis are useful for determining the phylogenetic relationships and evolution of Syrphidae.

The first mitochondrial genome of Sepsis monostigma (Diptera: Sepsidae)

The sepsid fly Sepsis monostigma belongs to the genus Sepsis of Sepsidae. We sequenced and annotated the mitogenome of S. monostigma which as the first representative of genus Sepsis with nearly complete mitochondrial data. This mitogenome is 14,887bp long, which contains of 22 transfer RNA genes, 13 protein coding genes (PCGs) and 2 ribosomal RNA genes and a part of the AT control region. ML phylogenetic outcome strongly supported the monophyly of Sepsidae, and the family Sepsidae is more close to the family Heleomyzidae. It also indicated that the genus Sepsis is the sister group to Nemopoda, and the genus Archisepsis is the sister group to Microsepsis.

Middle Jurassic origin in India: a new look at evolution of Vermileonidae and time-scaled relationships of lower brachyceran flies

Vermileonidae (wormlions) comprises 61 described species in 12 genera and is one of the oddest and most rarely collected dipteran families. Larvae of Vermileonidae are famous for their pitfall prey behaviour, whereas the adults are rarely seen. Here we report, for the first time, the complete mitochondrial genome from members of Vermileonidae. Phylogenetic reconstruction based on a representative sampling of the order reveals new insights into relationships between the Vermileonidae and other members of lower brachyceran flies. A sister-group relationship between Vermileonidae and Xylophagidae is supported, and the higher-level clade relationships are Tabanomorpha + (Muscomorpha + (Xylophagomorpha + Stratiomyomorpha)). Combining mitochondrial genome data with a morphological phylogeny, geographical distribution and geological history, we propose that the Vermileonidae originated in India during the Middle Jurassic, spreading to Africa via land bridges during the Late Jurassic, to the Palaearctic after the collision of India with Laurasia in the Late Oligocene, and to the Nearctic in the Early Miocene, via either North Atlantic or Beringian land bridges. Wet forested regions have proved to be barriers to their dispersal, explaining their absence from Central Africa, South America and eastern North America.

The complete mitochondrial genome of Syrphus ribesii (Diptera: Syrphoidea: Syrphidae)

The complete mitochondrial genome of Syrphus ribesii was determined in this study. The double-stranded circular DNA molecule was 16,530 bp in length, containing 37 typical genes: 13 protein-coding genes (PCGs), 2 rRNA genes, 22 tRNA genes, and an A + T-rich region. Thirteen PCGs were 11,196 bp in size, encoding 3720 amino acids in total. All the PCGs started with ATN, except the COI used TTG as its initiation codon. Most PCGs terminated with standard codon TAA, while the COI ended with T and the ND5 ended with TA. The lrRNA and srRNA genes were 1341 bp and 793 bp in length, respectively. The A + T-rich region harbored some typical structures characteristic of the dipterans. The phylogenetic tree showed that Syrphus ribesii was closely related to Eupeodes corollae, and the Syrphidae and Pipunculidae constituted a monophyletic group within the Syrphoidea.

A phylogenomic study of Steganinae fruit flies (Diptera: Drosophilidae): strong gene tree heterogeneity and evidence for monophyly

BACKGROUND

The Drosophilidae family is traditionally divided into two subfamilies: Drosophilinae and Steganinae. This division is based on morphological characters, and the two subfamilies have been treated as monophyletic in most of the literature, but some molecular phylogenies have suggested Steganinae to be paraphyletic. To test the paraphyletic-Steganinae hypothesis, here, we used genomic sequences of eight Drosophilidae (three Steganinae and five Drosophilinae) and two Ephydridae (outgroup) species and inferred the phylogeny for the group based on a dataset of 1,028 orthologous genes present in all species (> 1,000,000 bp). This dataset includes three genera that broke the monophyly of the subfamilies in previous works. To investigate possible biases introduced by small sample sizes and automatic gene annotation, we used the same methods to infer species trees from a set of 10 manually annotated genes that are commonly used in phylogenetics.

RESULTS

Most of the 1,028 gene trees depicted Steganinae as paraphyletic with distinct topologies, but the most common topology depicted it as monophyletic (43.7% of the gene trees). Despite the high levels of gene tree heterogeneity observed, species tree inference in ASTRAL, in PhyloNet, and with the concatenation approach strongly supported the monophyly of both subfamilies for the 1,028-gene dataset. However, when using the concatenation approach to infer a species tree from the smaller set of 10 genes, we recovered Steganinae as a paraphyletic group. The pattern of gene tree heterogeneity was asymmetrical and thus could not be explained solely by incomplete lineage sorting (ILS).

CONCLUSIONS

Steganinae was clearly a monophyletic group in the dataset that we analyzed. In addition to ILS, gene tree discordance was possibly the result of introgression, suggesting complex branching processes during the early evolution of Drosophilidae with short speciation intervals and gene flow. Our study highlights the importance of genomic data in elucidating contentious phylogenetic relationships and suggests that phylogenetic inference for drosophilids based on small molecular datasets should be performed cautiously. Finally, we suggest an approach for the correction and cleaning of BUSCO-derived genomic datasets that will be useful to other researchers planning to use this tool for phylogenomic studies.

Genome skimming is a low-cost and robust strategy to assemble complete mitochondrial genomes from ethanol preserved specimens in biodiversity studies

Global loss of biodiversity is an ongoing process that concerns both local and global authorities. Studies of biodiversity mainly involve traditional methods using morphological characters and molecular protocols. However, conventional methods are a time consuming and resource demanding task. The development of high-throughput sequencing (HTS) techniques has reshaped the way we explore biodiversity and opened a path to new questions and novel empirical approaches. With the emergence of HTS, sequencing the complete mitochondrial genome became more accessible, and the number of genome sequences published has increased exponentially during the last decades. Despite the current state of knowledge about the potential of mitogenomics in phylogenetics, this is still a relatively under-explored area for a multitude of taxonomic groups, especially for those without commercial relevance, non-models organisms and with preserved DNA. Here we take the first step to assemble and annotate the genomes from HTS data using a new protocol of genome skimming which will offer an opportunity to extend the field of mitogenomics to under-studied organisms. We extracted genomic DNA from specimens preserved in ethanol. We used Nextera XT DNA to prepare indexed paired-end libraries since it is a powerful tool for working with diverse samples, requiring a low amount of input DNA. We sequenced the samples in two different Illumina platform (MiSeq or NextSeq 550). We trimmed raw reads, filtered and had their quality tested accordingly. We performed the assembly using a baiting and iterative mapping strategy, and the annotated the putative mitochondrion through a semi-automatic procedure. We applied the contiguity index to access the completeness of each new mitogenome. Our results reveal the efficiency of the proposed method to recover the whole mitogenomes of preserved DNA from non-model organisms even if there are gene rearrangement in the specimens. Our findings suggest the potential of combining the adequate platform and library to the genome skimming as an innovative approach, which opens a new range of possibilities of its use to obtain molecular data from organisms with different levels of preservation.

Characterization and Phylogenetic Implications of the Complete Mitochondrial Genome of Syrphidae

In this study, the complete mitochondrial genomes (mitogenomes) of two hoverfly species of Korinchia angustiabdomena (Huo, Ren, and Zheng) and Volucella nigricans Coquillett (Diptera: Syrphidae) were determined and analyzed. The circular mitogenomes were 16,473 bp in K. angustiabdomena (GenBank No. MK870078) and 15,724 bp in V. nigricans (GenBank No. MK870079). Two newly sequenced mitogenomes both contained 37 genes, and the gene order was similar with other syrphine species. All the protein-coding genes (PCGs) were started with the standard ATN codons; and most of PCGs were terminated with a TAA stop codon, while ND1 in K. angustiabdomena ended with a TAG codon, and ND5 terminated with truncated T stop codons in both species. The phylogenetic relationship between K. angustiabdomena and V. nigricans with related lineages was reconstructed using Bayesian inference and Maximum-likelihood analyses. The monophyly of each family considered within Muscomorpha was confirmed by the clades in the phylogenetic tree, and superfamily of the Oestroidea (Calliphoridae, Sarcophagidae, and Oestridae) was unexpectedly found to be a paraphyletic group based on our selected data. This mitogenome information for K. angustiabdomena and V. nigricans could facilitate future studies of evolutionarily related insects.

Mitochondrial Genomes Provide Insights into the Phylogeny of Lauxanioidea (Diptera: Cyclorrhapha)

The superfamily Lauxanioidea is a significant dipteran clade including over 2500 known species in three families: Lauxaniidae, Celyphidae and Chamaemyiidae. We sequenced the first five (three complete and two partial) lauxanioid mitochondrial (mt) genomes, and used them to reconstruct the phylogeny of this group. The lauxanioid mt genomes are typical of the Diptera, containing all 37 genes usually present in bilaterian animals. A total of three conserved intergenic sequences have been reported across the Cyclorrhapha. The inferred secondary structure of 22 tRNAs suggested five substitution patterns among the Cyclorrhapha. The control region in the Lauxanioidea has apparently evolved very fast, but four conserved structural elements were detected in all three complete mt genome sequences. Phylogenetic relationships based on the mt genome data were inferred by Maximum Likelihood and Bayesian methods. The traditional relationships between families within the Lauxanioidea, (Chamaemyiidae + (Lauxaniidae + Celyphidae)), were corroborated; however, the higher-level relationships between cyclorrhaphan superfamilies are mostly poorly supported.

Mitochondrial genomes of the hoverflies Episyrphus balteatus and Eupeodes corollae (Diptera: Syrphidae), with a phylogenetic analysis of Muscomorpha

The hoverflies Episyrphus balteatus and Eupeodes corollae (Diptera: Muscomorpha: Syrphidae) are important natural aphid predators. We obtained mitochondrial genome sequences from these two species using methods of PCR amplification and sequencing. The complete Episyrphus mitochondrial genome is 16,175 bp long while the incomplete one of Eupeodes is 15,326 bp long. All 37 typical mitochondrial genes are present in both species and arranged in ancestral positions and directions. The two mitochondrial genomes showed a biased A/T usage versus G/C. The cox1, cox2, cox3, cob and nad1 showed relatively low level of nucleotide diversity among protein-coding genes, while the trnM was the most conserved one without any nucleotide variation in stem regions within Muscomorpha. Phylogenetic relationships among the major lineages of Muscomorpha were reconstructed using a complete set of mitochondrial genes. Bayesian and maximum likelihood analyses generated congruent topologies. Our results supported the monophyly of five species within the Syrphidae (Syrphoidea). The Platypezoidea was sister to all other species of Muscomorpha in our phylogeny. Our study demonstrated the power of the complete mitochondrial gene set for phylogenetic analysis in Muscomorpha.

Comparative Mt Genomics of the Tipuloidea (Diptera: Nematocera: Tipulomorpha) and Its Implications for the Phylogeny of the Tipulomorpha

A traditionally controversial taxon, the Tipulomorpha has been frequently discussed with respect to both its familial composition and relationships with other Nematocera. The interpretation of internal relationships within the Tipuloidea, which include the Tipulidae sensu stricto, Cylindrotomidae, Pediciidae and Limoniidae, is also problematic. We sequenced the first complete mitochondrial (mt) genome of Symplecta hybrida (Meigen, 1804), which belongs to the subfamily Chioneinae of family Limoniidae, and another five nearly complete mt genomes from the Tipuloidea. We did a comparative analysis of these mt genomics and used them, along with some other representatives of the Nematocera to construct phylogenetic trees. Trees inferred by Bayesian methods strongly support a sister-group relationship between Trichoceridae and Tipuloidea. Tipulomorpha are not supported as the earliest branch of the Diptera. Furthermore, phylogenetic trees indicate that the family Limoniidae is a paraphyletic group.

The complete mitochondrial genome of the Atylotus miser (Diptera: Tabanomorpha: Tabanidae), with mitochondrial genome phylogeny of lower Brachycera (Orthorrhapha)

Brachycera is a clade with over 80,000 described species and originated from the Mesozoic, and its larvae employ comprehensive feeding strategies. The phylogeny of the lower Brachycera has been studied intensively over the past decades. In order to supplement the lack of genetic data in this important group, we sequenced the complete mitochondrial (mt) genome of Atylotus miser as well as the nearly complete mt genomes of another 11 orthorrhaphous flies. The mt genome of A. miser is 15,858bp, which is typical of Diptera, with 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a 993bp control region. The rest of the orthorrhaphous mt genomes in our study have the similar structure with A. miser. Additionally, we conducted a phylogenetic analysis of 20 mt genomes using Maximum-likelihood and Bayesian methods in order to reconstruct the evolutionary relationship of Orthorrhapha. The results show that all infraorders of Brachycera are monophyletic, and a relationship of Tabanomorpha+((Xylophagomorpha+Stratiomyomorpha)+Muscomorpha) has been proposed. Within Xylophagomorpha, Nemestrinoidae forms the sister group of Xylophagidae.

The Phylogeny and Evolutionary Timescale of Muscoidea (Diptera: Brachycera: Calyptratae) Inferred from Mitochondrial Genomes

Muscoidea is a significant dipteran clade that includes house flies (Family Muscidae), latrine flies (F. Fannidae), dung flies (F. Scathophagidae) and root maggot flies (F. Anthomyiidae). It is comprised of approximately 7000 described species. The monophyly of the Muscoidea and the precise relationships of muscoids to the closest superfamily the Oestroidea (blow flies, flesh flies etc) are both unresolved. Until now mitochondrial (mt) genomes were available for only two of the four muscoid families precluding a thorough test of phylogenetic relationships using this data source. Here we present the first two mt genomes for the families Fanniidae (Euryomma sp.) (family Fanniidae) and Anthomyiidae (Delia platura (Meigen, 1826)). We also conducted phylogenetic analyses containing of these newly sequenced mt genomes plus 15 other species representative of dipteran diversity to address the internal relationship of Muscoidea and its systematic position. Both maximum-likelihood and Bayesian analyses suggested that Muscoidea was not a monophyletic group with the relationship: (Fanniidae + Muscidae) + ((Anthomyiidae + Scathophagidae) + (Calliphoridae + Sarcophagidae)), supported by the majority of analysed datasets. This also infers that Oestroidea was paraphyletic in the majority of analyses. Divergence time estimation suggested that the earliest split within the Calyptratae, separating (Tachinidae + Oestridae) from the remaining families, occurred in the Early Eocene. The main divergence within the paraphyletic muscoidea grade was between Fanniidae + Muscidae and the lineage ((Anthomyiidae + Scathophagidae) + (Calliphoridae + Sarcophagidae)) which occurred in the Late Eocene.