First complete mitogenomes of Diamesinae, Orthocladiinae, Prodiamesinae, Tanypodinae (Diptera: Chironomidae) and their implication in phylogenetics

Comparative Mitogenomic Analyses of Psectrocladius (Diptera: Chironomidae)

Psectrocladius, a genus within the species-rich subfamily Orthocladiinae (Diptera: Chironomidae), remains poorly resolved in molecular phylogenetics due to limited available molecular data. Here, we sequenced and analyzed the complete mitogenomes of five Psectrocladius species, using two Rheocricotopus species as outgroups. Our results reveal that the mitogenomes of Psectrocladius are structurally conserved and retain a presumed ancestral gene order. The nucleotide composition of these newly generated mitogenomes exhibits a pronounced A + T bias, which is characteristic of typical insect mitogenomes. The substitution rates, estimated using Ka/Ks ratios, indicate that all protein-coding genes are under purifying selection. The strongest purifying selection pressure was observed in the CO1 gene, while the weakest was in the ND5 gene. Both the maximum likelihood and Bayesian inference trees consistently show the following topology: ((((P. schlienzi + P. bisetus) + P. barbimanus) + P. oligosetus) + P. aquatronus). This study provides key insights into chironomid mitogenomes and their gene properties, offering valuable reference data for future research.

First report of the complete mitochondrial genome of Glyptotendipes pallens (Meigen, 1804) (Diptera: Chironomidae) from Hebei Province, China

Glyptotendipes pallens (Meigen, 1804) serves as a significant bioindicator for monitoring freshwater ecosystems. Despite the performance of COI barcode analyses on G. pallens, the mitogenome of this taxon remains unassembled and unanalyzed. In this study, we provide one newly sequenced complete mitogenome of G. pallens for the first time. The mitogenome is 16,063 bp long with high A + T content, and consists of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a noncoding control region. The phylogenetic analysis strongly supports G. pallens and G. tokunagai as sister species.

Comparative Mitogenomic Analyses of Tanypodinae (Diptera: Chironomidae)

Tanypodinae, a highly diverse subfamily within Chironomidae (Diptera), has been poorly represented in mitochondrial genome (mitogenome) databases, with only a limited number of complete or partial sequences available. To address this gap, we present the first complete mitogenome sequences of 16 Tanypodinae species and 1 Podonominae species. By integrating these novel data with previously published chironomid mitogenomes, we conducted a comprehensive comparative mitogenomic analysis of 21 Tanypodinae species. Our results reveal that Tanypodinae mitogenomes maintain a conserved structural organization, preserving the ancestral insect gene arrangement. The nucleotide composition exhibits significant bias, with the control region demonstrating the highest A + T content among all genomic regions. Evolutionary analysis indicates that all protein-coding genes (PCGs) are subject to purifying selection, with ATP8 exhibiting the most rapid evolutionary rate. Phylogenetic reconstruction based on PCG amino acid sequences delineates seven well-supported clades within Tanypodinae, corresponding to the tribes Pentaneurini, Natarsiini, Procladiini, Tanypodini, Clinotanypodini, Macropelopiini, and Anatopyniini. These findings significantly advance our understanding of mitogenomic architecture and provide critical insights into the phylogenetic relationships within Tanypodinae.

COI Insights into Diversity and Species Delimitation of Immature Stages of Non-Biting Midges (Diptera: Chironomidae)

The diversity of non-biting midges (Chironomidae, Diptera) remains an unresolved topic, with estimates of species numbers ranging from 6000 to 15,000 according to various authors. To assess Chironomidae diversity in Lithuania, we evaluate the effectiveness of COI gene-based species delimitation methods for providing rapid diversity estimates. Nevertheless, differences between tree-based and distance-based approaches can result in varying group classifications, which may cause species numbers to be overestimated or underestimated. For our study, we analyzed a dataset of 109 specimens sampled from six Lithuanian streams. By applying multiple methods, such as Assemble Species by Automatic Partitioning (ASAP), Automatic Barcode Gap Discovery (ABGD), the generalized mixed Yule-coalescent (GMYC) model, and the Bayesian implementation of the Poisson Tree Processes (bPTP) model, we found that species estimates ranged from 28 to 58. Among these methods, ASAP proved to be the most effective for our dataset, identifying 58 putative species. These results reinforce our assumption that the current understanding of Chironomidae species diversity is incomplete.

Limited Variation in Codon Usage across Mitochondrial Genomes of Non-Biting Midges (Diptera: Chironomidae)

The codon usage patterns of mitochondrial genomes offer insights into the evolutionary and phylogenetic studies of species. Codon usage analysis has been conducted in a few Chironomidae species, and the codon usage patterns in other species remain ambiguous. We aim to reveal the codon usage differences in the mitochondrial genomes across this family. We sequenced the first mitochondrial genome of the genus Conchapelopia and the third mitochondrial genome of the subfamily Tanypodinae. Then, we analyzed its relative synonymous codon usage and effective number of codons with registered mitochondrial genomes from 28 other genera. The results indicated that there was limited variation in codon usage across five subfamilies, Chironominae, Orthocladiinae, Diamesinae, Prodiamesinae and Tanypodinae. While Parochlus steinenii from Podonominae presented a weaker codon bias, P. steinenii possessed the most genes experiencing natural selection. Additionally, ND1, ND2 and ND3 were found to be the most frequently selected genes across all species. Our findings contribute to further understanding the evolutionary and phylogenetic relationships of Chironomidae.

Phylogenetic and Comparative Analysis of Cryptochironomus, Demicryptochironomus and Harnischia Inferred from Mitogenomes (Diptera: Chironomidae)

(1) Background: Mitochondrial genomes have been extensively employed as a crucial marker in numerous dipteran families for understanding phylogenetics and systematics relations, thereby playing a pivotal role in molecular biology studies. The phylogenetic relationship of the Harnischia generic complex remains contentious due to the paucity of taxonomic and molecular data. Specifically, the evolutionary relationships among Cryptochironomus, Demicryptochironomus, and Harnischia are still unclear. (2) Methods: In this study, Polypedilum and Endochironomus were used as outgroups to analyze phylogenetic relationships among Cryptochironomus, Demicryptochironomus, and Harnischia, mitogenomes of four Cryptochironomus, two Demicryptochironomus, two Harnischia, and two Cladopelma were newly sequenced. Subsequently, we conducted a thorough analysis of the nucleotide composition, sequence length, and evolutionary rate. (3) Results: All mitogenomes exhibited structural conservation, with all genes consistently arranged in the identical order as that of the ancestral mitogenome. Nucleotide composition varied significantly among different genes, and the control region displayed the highest A + T content. All protein-coding genes undergo rigorous purification selection, with the ATP8 gene exhibiting the most rapid evolutionary rate among them. Utilizing Bayesian Inference (BI) and Maximum Likelihood (ML) methods across various databases, we reconstructed the phylogenetic relationships among the genera within the Harnischia generic complex, drawing insights from an analysis of 14 mitochondrial genomes. (4) Conclusions: Our results showed that the monophyly of the genera Harnischia was well supported in all topologies; Cryptochironomus is sister to Demicryptochironomus.

New mitogenomes from the genus Cricotopus (Diptera: Chironomidae, Orthocladiinae): Characterization and phylogenetic implications

Cricotopus is a large and diverse genus of non-biting midges composed of several subgenera. Complete mitogenome sequences are available for very few Cricotopus species. The subgenus Pseudocricotopus unites species with unusual morphological structures in adult male and pupal stages, however, molecular methods are needed to verify the placement of this subgenus within Cricotopus. We obtained mitogenomes of C. (Pseudocricotopus) cf. montanus and nine other Cricotopus species for phylogenetic analysis, coupled with two Rheocricotopus species and one Synorthocladius species as outgroups. The structure of the mitogenome was similar among these Cricotopus species, exhibiting A+T bias and retaining ancestral gene order. Mutation rate, estimated as Ka/Ks, varied among genes, and was highest for ATP8 and lowest for COI. The phylogenetic relationships among species of Cricotopus, Rheocricotopus and Synorthocladius was reconstructed using Bayesian inference and maximum likelihood estimation. The phylogenetic trees confirmed placement of subgenus Pseudocricotopus, represented by Cricotopus cf. montanus, within Cricotopus. Our study increases the library of chironomid mitogenomes and provides insight into the properties of their constituent genes.

New data on mitogenomes of Thienemanniella Kieffer, 1911 (Diptera: Chironomidae, Orthocladiinae)

The mitochondrial genome (mitogenome) has been widely used as a powerful marker in phylogenetic and evolutionary studies of various Dipteran groups. However, only a few mitogenomes from the Thienemanniella genus have been reported till now. Furthermore, there is still indeterminacy in the phylogenetic relationships of the genus Thienemanniella. In this study, mitogenomes of five Thienemanniella species were sequenced and analyzed newly. Combined with the published mitogenome of Thienemanniella nipponica, the obtained results showed that mitogenomes of Thienemanniella were conserved in structure, and all genes were observed to be arranged in the same gene order as the ancestral mitogenome. Nucleotide composition varied significantly among different genes, and the control region displayed the highest A + T content. All protein coding genes are subjected to purification selection, and the fastest evolving gene is ATP8. Maximum likelihood and Bayesian inference analyses showed the phylogeny of Thienemanniella which was supported in five topologies. Our present study provides valuable insight into the phylogenetic relationships of Thienemanniella species.

Complete mitochondrial genome of the non-biting midge Polypedilum henicurum Wang, 1995 (Diptera: Chironomidae)

The complete mitochondrial genome of Polypedilum henicurum was sequenced and analyzed. The whole mitogenome is 15,964 bp in length and contains 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), and two ribosomal RNAs (rRNAs). The overall nucleotide composition is 39.5% A, 39.0% T, 13.1% C, and 8.4% G. Most PCGs start with ATN codon excluding COX1 (TTG) and all PCGs end with TAA codon. Gene arrangement stays the same with the ancestral mitochondrial genome. Bayesian inference phylogenetic tree supports its close relationship with P. unifascium. This work enriches the library of Chironomidae mitochondrial genomes and provides a valuable resource for understanding the evolutionary history of Polypedilum.

Contribution to the Knowledge of Dicranoptychini (Diptera, Tipuloidea, Limoniidae) in China, with the First Mitochondrial Genome of the Tribe and Its Phylogenetic Implications

Dicranoptychini is a tribe in the subfamily Limoniinae (Diptera, Tipuloidea, and Limoniidae) and includes only the genus Dicranoptycha Osten Sacken, 1860. However, the species diversity of the tribe in China was seriously underestimated, and the taxonomic status of Dicranoptycha has long been controversial. In this study, types of Chinese Dicranoptycha species and specimens collected from several localities in China were examined, and the first mitochondrial (mt) genome of the tribe Dicranoptychini is presented. Two Dicranoptycha species, D. jiufengshana sp. nov. and D. shandongensis sp. nov., from China, are described and illustrated as new to science. A Palaearctic species, D. prolongata Alexander, 1938, is recorded in China for the first time. In addition, the complete mt genome of D. shandongensis sp. nov. is sequenced and annotated, indicating that it is a typical circular DNA molecule with a length of 16,157 bp and shows a similar gene order, nucleotide composition, and codon usage to mt genomes of other Tipuloidea species. The two pairs of repeat elements are found in its control region. Phylogenetic results confirm the sister-group relationship between Cylindrotomidae and Tipulidae, question the position of the genus Epiphragma Osten Sacken, 1860 in Limoniidae, and indicate that Dicranoptychini may be a basal lineage within Limoniinae.

Comparative mitogenome analyses of twelve non-biting flies and provide insights into the phylogeny of Chironomidae (Diptera: Culicomorpha)

The family Chironomidae is represented by seven subfamilies in China, among which Chironominae and Orthocladiinae are the most diverse. To gain a better understanding of the architecture and evolution of the mitogenomes of Chironomidae, we sequenced mitogenomes of twelve species (including two published species) of the two subfamilies Chironominae and Orthocladiinae, and comparative mitogenomic analyses were performed. Thus, we identified highly conserved genome organization of twelve species with regard to genome content, nucleotide and amino acid composition, codon usage, and gene characteristics. The K_a/K_s values of most protein-coding genes were far smaller than 1, indicating that these genes were evolving under purifying selection. Phylogenetic relationships between the family Chironomidae were reconstructed using 23 species representing six subfamilies, based on protein-coding genes and rRNAs using Bayesian Inference and Maximum Likelihood. Our results suggested the following relationship within the Chironomidae: (Podonominae + Tanypodinae) + (Diamesinae + (Prodiamesinae + (Orthocladiinae + Chironominae))). This study contributes to the mitogenomic database of Chironomidae, which will be significant for studing the mitogenome evolution of Chironomidae.

Comparative Analysis of Mitogenomes of Chironomus (Diptera: Chironomidae)

(1) Background: Chironomids are biological indicators, playing an important role in monitoring and assessing the changes in water ecosystems. Mitochondrial genomes have been widely applied as a molecular marker to analyze the taxonomy and phylogeny of insects. However, knowledge of the mitogenomes of Chironomus species is scarce at present, which limits our understanding of the evolutionary relationships among Chironomus. (2) Methods: In our study, the mitogenomes and their basic structure of 12 Chironomus species and one Microchironomus species were newly sequenced. Combined with reported mitogenomes, a total of 15 mitogenomes of Chironomus were selected for a comparative mitogenomic analysis and phylogenetic reconstruction of Chironomus. (3) Results: Each mitogenome of the Chironomus species has the typical 37 genes and a control region. The basic structure of the whole mitogenomes of Chironomus species is relatively conservative, and the genetic arrangements stay the same as the ancestral mitogenome. (4) Conclusions: Our study enriches the library of mitogenomes of chironomids and provides a valuable resource for understanding the evolutionary history of Chironomus.

New Mitogenome Features of Philopotamidae (Insecta: Trichoptera) with Two New Species of Gunungiella

A total of 14 individuals of Philopotamidae, from China, were examined. Six species in four genera, including two new species of the genus Gunungiella, were recognized. Their COI barcode sequences were extracted, mitogenomes were sequenced, assembled and analyzed. All of these sequences were used to further reveal the phylogenetic relationships of the family Philopotamidae. In addition, two new species: Gunungiella wangi n. sp., Gunungiella flabellata n. sp. were described and illustrated.

Characterization of Seventeen Complete Mitochondrial Genomes: Structural Features and Phylogenetic Implications of the Lepidopteran Insects

Lepidoptera (moths and butterflies) are widely distributed in the world, but high-level phylogeny in Lepidoptera remains uncertain. More mitochondrial genome (mitogenome) data can help to conduct comprehensive analysis and construct a robust phylogenetic tree. Here, we sequenced and annotated 17 complete moth mitogenomes and made comparative analysis with other moths. The gene order of trnM-trnI-trnQ in 17 moths was different from trnI-trnQ-trnM of ancestral insects. The number, type, and order of genes were consistent with reported moths. The length of newly sequenced complete mitogenomes ranged from 14,231 bp of Rhagastis albomarginatus to 15,756 bp of Numenes albofascia. These moth mitogenomes were typically with high A+T contents varied from 76.0% to 81.7% and exhibited negative GC skews. Among 13 protein coding genes (PCGs), some unusual initiations and terminations were found in part of newly sequenced moth mitogenomes. Three conserved gene-overlapping regions and one conserved intergenic region were detected among 17 mitogenomes. The phylogenetic relationship of major superfamilies in Macroheterocera was as follows: (Bombycoidea + Lasiocampoidea) + ((Drepanoidea + Geometroidea) + Noctuoidea)), which was different from previous studies. Moreover, the topology of Noctuoidea as (Notodontidae + (Erebidae + Noctuidae)) was supported by high Bayesian posterior probabilities (BPP = 1.0) and bootstrapping values (BSV = 100). This study greatly enriched the mitogenome database of moth and strengthened the high-level phylogenetic relationships of Lepidoptera.

First complete mitogenome of Axarus fungorum (Albu, 1980) from Guizhou Province, China (Diptera, Chironomidae)

Axarus fungorum (Albu, 1980) exhibits certain adaptations to different aquatic environments, appearing as an important evaluation element for freshwater quality monitoring. In this study, complete mitogenome of A. fungorum was provided for the first time to define the systematic and phylogenetic history of this taxon. The whole mitogenome is 15,696 bp long with high A + T content that consists of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a noncoding control region. ML analysis showed support for monophyly of Chironominae and close relationship between A. fungorum and Chironomus generic genera.

Mitogenomes provide new insights of evolutionary history of Boreheptagyiini and Diamesini (Diptera: Chironomidae: Diamesinae)

Mitogenomes have been widely used for phylogenetic reconstruction of various Dipteran groups, but specifically for chironomid, they have not been carried out to resolve the relationships. Diamesinae (Diptera: Chironomidae) are important bioindicators for freshwater ecosystem monitoring, but its evolutionary history remains uncertain for lack of information. Here, coupled with one previously published and 30 new mitogenomes of Diamesinae, we carried out comparative mitogenomic analysis and phylogenetic analysis. Mitogenomes of Diamesinae were conserved in structure, and all genes arranged in the same order as the ancestral insect mitogenome. All protein-coding genes in Diamesinae were under stronger purifying selection than those of other nonbiting midge species, which may exhibit signs of adaptation to life at cold living conditions. Phylogenetic analyses strongly supported the monophyly of Diamesinae, with Boreheptagyiini deeply nested within Diamesini. In addition, phylogenetic relationship of selected six genera was resolved, except Sympotthastia remained unstable. Our study revealed that the mitogenomes of Diamesinae are highly conserved, and they are practically useful for phylogenetic inference.

First report of the complete mitogenome of Tanypus punctipennis Meigen, 1818 (Diptera, Chironomidae) from Hebei Province, China

Tanypus punctipennis Meigen, 1818 is an important bioindicator for freshwater ecosystems monitoring. Although COI barcode analyses have been performed on T. punctipennis, the mitogenome of this taxon has not been assembled and analyzed. Here, the complete mitogenome of T. punctipennis was sequenced and analyzed to confirm the systematic and phylogenetic history of this species. The mitogenome is 16,215 bp long with high A + T content, and consists of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a noncoding control region. The phylogenomic analysis supports monophyletic Tanypodinae and close relationship between T. punctipennis and Clinotanypus. Our results indicate that mitogenomes showed strong signals in phylogenetic reconstructions at the genus level of Tanypodinae.

First Report on Mitochondrial Gene Rearrangement in Non-Biting Midges, Revealing a Synapomorphy in Stenochironomus Kieffer (Diptera: Chironomidae)

Simple Summary

Gene rearrangement is an additional type of data to support relationships of taxa, with rearrangement synapomorphies identified across multiple orders and at many different taxonomic levels. The concept to use mitochondrial gene rearrangements as phylogenetic markers has been proposed since the mid-1980s, the synapomorphic gene rearrangements have been identified from many lineages. However, mitochondrial gene rearrangement has never been observed in the non-biting midges (Diptera: Chironomidae). Here, seven new mitogenomes of the genus Stenochironomus were sequenced and analyzed. Coupled with published data, phylogenetic analyses were performed within Chironominae. The present study showed that mitogenomes of Stenochironomus are showing a higher A+T bias than other chironomid species. A synapomorphic gene rearrangement that the gene order rearranges from trnI-trnQ-trnM to trnI-trnM-trnQ was identified within Stenochironomus, which is the first instance of mitochondrial gene rearrangement discovered in the Chironomidae. The monophyly of the genus Stenochironomus was strongly supported by mitogenomes. Our study provides new insights into the mitochondrial gene order of Chironomidae, and provides a valuable resource for understanding synapomorphic gene rearrangements.

Abstract

(1) Background: Gene rearrangement of mitochondrial genome, especially those with phylogenetic signals, has long fascinated evolutionary biologists. The synapomorphic gene rearrangements have been identified across multiple orders and at many different taxonomic levels, supporting the monophyletic or systematic relationships of related lineages. However, mitochondrial gene rearrangement has never been observed in the non-biting midges (Diptera: Chironomidae); (2) methods: in this study, the complete mitogenomes of seven Stenochironomus species were sequenced and analyzed for the first time; (3) results: each mitogenome of Stenochironomus contains 37 typical genes and a control region. The whole mitogenomes of Stenochironomus species exhibit a higher A+T bias than other published chironomid species. The gene order rearranges from trnI-trnQ-trnM to trnI-trnM-trnQ in all the seven mitogenomes of Stenochironomus, which might be act as a synapomorphy of the genus, supporting the monophyletic of Stenochironomus species. In addition, another derived gene cluster: trnA-trnG-ND3-trnR exists in Stenochironomus tobaduodecimus. The derived gene orders described above are the first case of mitochondrial gene rearrangement in Chironomidae. Coupled with published data, phylogenetic relationships were reconstructed within Chironominae, and strongly supported the monophyly of Stenochironomus; (4) conclusions: our study provides new insights into the mitochondrial gene order of Chironomidae, and provides a valuable resource for understanding the synapomorphic gene rearrangements.

The complete mitochondrial genome of the non-biting midge Chironomus yoshimatsui (Diptera: Chironomidae)

A non-biting midge Chironomus yoshimatsui has been widely used in ecotoxicology and chemical risk assessments. In this study, the complete mitochondrial genome (mitogenome) sequence of C. yoshimatsui was determined using short-read next-generation sequencing technologies. The mitogenome was 15,734 bp in length and consisted of 13 protein coding genes, 2 ribosomal RNAs, and 22 transfer RNAs. The A + T content was 77.8%. The gene order was identical to the pattern conserved across Diptera. The mitocgenome sequence obtained in this study provides a useful resource for further evolutionary and ecological studies.

First report of the complete mitogenome of Microchironomus tabarui Sasa, 1987 (Diptera, Chironomidae) from Hebei Province, China

Microchironomus tabarui Sasa, 1987 is an important bioindicator for freshwater ecosystem monitoring. Although COI barcode analyes have been performed on M. tabarui, the mitogenome of this taxon has not been assembled and analyzed. Here the complete mitogenome of M. tabarui was sequenced and analyzed to confirm the systematic and phylogenetic history of this species. The mitogenome is 15,667 bp long with high A + T content and consists of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a noncoding control region. The phylogenomic analysis support monophyletic Chironominae and close relationship between M. tabarui and Chironomus. Our results indicate that mitogenomes showed strong signals in phylogenetic reconstructions at the genus level of Chironominae.