Mitochondrial Genomics Reveals Shared Phylogeographic Patterns and Demographic History among Three Periodical Cicada Species Groups

Comparative Analysis of Mitogenomes in Leafhopper Tribe Deltocephalini (Hemiptera: Cicadellidae: Deltocephalinae): Structural Conservatism and Phylogeny

Previous studies on the gene order and composition of leafhopper mitochondrial genomes have revealed a high level of conservation in overall genome structure. Some members of Deltocephalinae, the largest subfamily, exhibit tRNA gene rearrangements; however, few mitogenomes have been sequenced in this group and the degree of structural variation within tribes remains unclear. In this study, we sequenced the complete mitogenomes of 14 species belonging to four genera of tribe Deltocephalini from China and compared them with the two previously reported mitogenomes for this tribe. The studied mitogenomes showed a high degree of similarity to most other leafhopper mitogenomes in overall structure, mostly varying in the total length (14,961-15,416 bp) and number of non-coding A + T-rich regions. Gene size, order, arrangement, base composition, codon usage, and secondary structure of tRNAs in the newly sequenced mitogenomes were highly conserved in Deltocephalini, and variations in start/stop codon usage and tRNA secondary structure mostly matched those of other leafhoppers. Phylogenetic analysis of different combinations of protein-coding and ribosomal genes using maximum likelihood and Bayesian inference under different models using either amino acid or nucleotide sequences were generally consistent and agreed with the previous nuclear and partial mitochondrial gene sequence data, indicating that complete mitochondrial genomes are phylogenetically informative at different levels of divergence within Deltocephalini and among different leafhoppers species. In addition to Deltocephalini, Deltocephalinae included members of Athysanini and Opsiini formed monophyletic groups. Maximum likelihood and Bayesian inference analyses consistently grouped Graminella nigrinota with Paralimnini, rendering Deltocephalini polyphyletic. The topology consistently divided Deltocephalini into two major branches, with Alobaldia tobae and Polyamia penistenuis forming a well-supported sister group to the remaining species of the tribe.

Sympatric diversity pattern driven by the secondary contact of two deeply divergent lineages of the soybean pod borer Leguminivora glycinivorella

The soybean pod borer, Leguminivora glycinivorella (Matsumura), is an important tortricid pest species widely distributed in most parts of China and its adjacent regions. Here, we analyzed the genetic diversity and population differentiation of L. glycinivorella using diverse genetic information including the standard cox1 barcode sequences, mitochondrial genomes (mitogenomes), and single-nucleotide polymorphisms (SNPs) from genotyping-by-sequencing. Based on a comprehensive sampling (including adults or larvae of L. glycinivorella newly collected at 22 of the total 30 localities examined) that covers most of the known distribution range of this pest, analyses of 543 cox1 barcode sequences and 60 mitogenomes revealed that the traditionally recognized and widely distributed L. glycinivorella contains two sympatric and widely distributed genetic lineages (A and B) that were estimated to have diverged ∼1.14 million years ago during the middle Pleistocene. Moreover, low but statistically significant correlations were recognized between genetic differentiation and geographic or environmental distances, indicating the existence of local adaptation to some extent. Based on SNPs, phylogenetic inference, principal component analysis, fixation index, and admixture analysis all confirm the two divergent sympatric lineages. Compared with the stable demographic history of Lineage B, the expansion of Lineage A had possibly made the secondary contact of the two lineages probable, and this process may be driven by the climate fluctuation during the late Pleistocene as revealed by ecological niche modeling.

Comparative Study of Potential Habitats for Two Endemic Grassland Caterpillars on the Qinghai-Tibet Plateau Based on BIOMOD2 and Land Use Data

This study has systematically investigated and compared the geographical distribution patterns and population density of G. menyuanensis (Gm) and G. qinghaiensis (Gq), which are endemic to the QTP region and inflict severe damage. Using a method combining the BIOMOD2 integration model (incorporating nine ecological niche models) and current species distribution data, this study has compared changes in potential habitats and distribution centers of these two species during ancient, present, and future climate periods and conducted a correlation test on the prediction results with land use types. The study results indicate that there are differences in geographical distribution patterns, distribution elevations, and population density of these two species. Compared with single models, the integration model exhibits prominent accuracy and stability with higher KAPPA, TSS, and AUC values. The distribution of suitable habitats for these two species is significantly affected by climatic temperature and precipitation. There is a significant difference between the potential habitats of these two species. Gm and Gq are distributed in the northeastern boundary area and the central and eastern areas of the QTP, respectively. The areas of their suitable habitats are significantly and positively correlated with the area of grassland among all land use types of QTP, with no correlations with the areas of other land use types of QTP. The potential habitats of both species during the paleoclimate period were located in the eastern and southeastern boundary areas of the QTP. During the paleoclimate period, their potential habitats expanded towards the Hengduan Mountains (low-latitude regions) in the south compared with their current suitable habitats. With the subsequent temperature rising, their distribution centers shifted towards the northeast (high-latitude) regions, which could validate the hypothesis that the Hengduan Mountains were refuges for these species during the glacial period. In the future, there will be more potential suitable habitats for these two species in the QTP. This study elucidates the ecological factors affecting the current distribution of these grass caterpillars, provides an important reference for designating the prevention and control areas for Gm and Gq, and helps protect the alpine meadow ecosystem in the region.

The impact of geographic isolation and host shifts on population divergence of the rare cicada Subpsaltria yangi

The contributions of divergent selection and spatial isolation to population divergence are among the main focuses of evolutionary biology. Here we employed integrated methods to explore genomic divergence, demographic history and calling-song differentiation in the cicada Subpsaltria yangi, and compared the genotype and calling-song phenotype of different populations occurring in distinct habitats. Our results indicate that this species comprises four main lineages with unique sets of haplotypes and calling-song structure, which are distinctly associated with geographic isolation and habitats. The populations occurring on the Loess Plateau underwent substantial expansion at ∼0.130-0.115 Ma during the Last Interglacial. Geographic distance and host shift between pairs of populations predict genomic divergence, with geographic distance and acoustical signal together explaining > 60% of the divergence among populations. Differences in calling songs could reflect adaptation of populations to novel environments with different host plants, habitats and predators, which may have resulted from neutral divergence at the molecular level followed by natural selection. Geomorphic barriers and climate oscillations associated with Pleistocene glaciation may have been primary factors in shaping the population genetic structure of this species. Ultimately this may couple with a host shift in leading toward allopatric speciation in S. yangi, i.e., isolation by distance. Our findings improve understanding of divergence in allopatry of herbivorous insects, and may inform future studies on the molecular mechanisms underlying the association between genetic/phenotypic changes and adaptation of insects to novel niches and host plants.

Four complete mitochondrial genomes of the subgenus Pterelachisus (Diptera, Tipulidae, Tipula) and implications for the higher phylogeny of the family Tipulidae

The complete mitochondrial genomes of Tipula (Pterelachisus) cinereocincta mesacantha Alexander, 1934, T. (P.) legalis Alexander, 1933, T. (P.) varipennis Meigen, 1818, and T. (P.) yasumatsuana Alexander, 1954 are reported, three of them being sequenced for the first time. The mitochondrial genome lengths of the four species are 15,907 bp, 15,625 bp, 15,772 bp, and 15,735 bp, respectively. All genomes exhibit a high AT base composition, with A + T content of 76.7%, 75.0%, 77.8%, and 75.4%, respectively. The newly reported mitogenomes herein show a general similarity in overall structure, gene order, base composition, and nucleotide content to those of the previously studied species within the family Tipulidae. Phylogenetic analyses were conducted to investigate the relationships within Tipulidae, using both Maximum Likelihood and Bayesian Inference approaches. The results show that the four target species of the subgenus T. (Pterelachisus) basically form a monophyletic group within Tipulidae, clustering with species of the Tipula subgenera T. (Lunatipula), T. (Vestiplex), and T. (Formotipula); however, the genus Tipula is not monophyletic. Moreover, neither the tipulid subfamily Tipulinae nor the family Limoniidae is supported to be a monophyletic group. The monophyly of the family Tipulidae, and the sister relationship between Tipulidae and Cylindrotomidae are reconfirmed. These research findings could contribute to deep insights into the systematic and evolutionary patterns of crane flies.

Phylogenetic assessment within a species complex of a subterranean rodent (Geomys bursarius) with conservation implications for isolated subspecies

Range contraction and expansion from glaciation have led to genetic divergence that may be particularly pronounced in fossorial species with low dispersal. The plains pocket gopher (Geomys bursarius) is a fossorial species that ranges widely across North America but has a poorly understood phylogeny. We used mitogenomes (14,996 base pairs) from 56 individuals across seven subspecies, plus two outgroup species, to assess genetic divergence from minimum spanning trees, measure genetic distances, and infer phylogenetic trees using BEAST. We found G. b. wisconsinensis was monophyletic with recent divergence. Further assessment is needed for G. b. major because it was paraphyletic and exhibited inconsistent groupings with other clades. Importantly, we identified G. b. illinoensis as being genetically distinct and monophyletic likely due to a unique colonization event eastward across the Mississippi River. Because G. b. illinoensis faces continued pressures from niche reduction and habitat loss, we recommend that G. b. illinoensis be considered an evolutionary significant unit warranting conservation actions to promote connectivity and restore suitable habitat. Such conservation efforts should benefit other grassland species including those originating from clades west of the Mississippi River that may also be evolutionary significant units.

Phylogeographic Pattern of the Assassin Bug Sycanus bifidus Inferred from Mitochondrial Genomes and Nuclear Genes

The assassin bug Sycanus bifidus has a wide distribution across southern China. This study explored its distribution and evolution by analyzing mitochondrial and nuclear ribosomal RNA genes, revealing how Pleistocene climate and geological changes shaped its phylogeography. We identified two main clades, A and B, that diverged in the Middle Pleistocene. Hainan Island's populations form a unique group within Clade A, suggesting that the Qiongzhou Strait served as a dispersal corridor during glaciation. Rising sea levels likely separated the Hainan population afterward. Ecological niche modeling showed that both populations have been viable since the last interglacial period, with demographic analyses indicating possible expansions during the Middle and Late Pleistocene, driven by favorable climates. This study highlights the significant effects of Pleistocene sea-level and climatic changes on the distribution and evolution of S. bifidus in China.

Mitogenomic Analysis and Phylogenetic Implications for the Deltocephaline Tribe Chiasmini (Hemiptera: Cicadellidae: Deltocephalinae)

The grassland leafhopper tribe Chiasmini (Cicadellidae: Deltocephalinae) presently comprises 324 described species worldwide, with the highest species diversity occurring in the Nearctic region but a greater diversity of genera occurring in the Old World. In China, this tribe comprises 39 described species in 11 genera, but the fauna remains understudied. The complete mitogenomes of three species of this tribe have been sequenced previously. In order to better understand the phylogenetic position of Chiasmini within the subfamily Deltocephalinae and to investigate relationships among Chiasmini genera and species, we sequenced and analyzed the complete mitogenomes of 13 species belonging to seven genera from China. Comparison of the newly sequenced mitogenomes reveals a closed circular double-stranded structure containing 37 genes with a total length of 14,805 to 16,269 bp and a variable number of non-coding A + T-rich regions. The gene size, gene order, gene arrangement, base composition, codon usage, and secondary structure of tRNAs of the newly sequenced mitogenomes of these 13 species are highly conserved in Chiasmini. The ATN codon is commonly used as the start codon in protein-coding genes (PCGs), except for ND5 in Doratura sp. and ATP6 in Nephotettix nigropictus, which use the rare GTG start codon. Most protein-coding genes have TAA or TAG as the stop codon, but some genes have an incomplete T stop codon. Except for the tRNA for serine (trnS1(AGN)), the secondary structure of the other 21 tRNAs is a typical cloverleaf structure. In addition to the primary type of G-U mismatch, five other types of tRNA mismatches were observed: A-A, A-C, A-G, U-C, and U-U. Chiasmini mitochondrial genomes exhibit gene overlaps with three relatively stable regions: the overlapping sequence between trnW and trnC is AAGTCTTA, the overlapping sequence between ATP8 and ATP6 is generally ATGATTA, and the overlapping sequence between ND4 and ND4L is generally TTATCAT. The largest non-coding region is the control region, which exhibits significant length and compositional variation among species. Some Chiasmini have tandem repeat structures within their control regions. Unlike some other deltocephaline leafhoppers, the sequenced Chiasmini lack mitochondrial gene rearrangements. Phylogenetic analyses of different combinations of protein-coding and ribosomal genes using maximum likelihood and Bayesian methods under different models, using either amino acid or nucleotide sequences, are generally consistent and also agree with results of prior analyses of nuclear and partial mitochondrial gene sequence data, indicating that complete mitochondrial genomes are phylogenetically informative at different levels of divergence within Chiasmini and among leafhoppers in general. Apart from Athysanini and Opsiini, most of the deltocephaline tribes are recovered as monophyletic. The results of ML and BI analyses show that Chiasmini is a monophyletic group with seven monophyletic genera arranged as follows: ((Zahniserius + (Gurawa + (Doratura + Aconurella))) + (Leofa + (Exitianus + Nephotettix))).

Variation in Avian Predation Pressure as a Driver for the Diversification of Periodical Cicada Broods

AbstractPeriodical cicadas live 13 or 17 years underground as nymphs, then emerge in synchrony as adults to reproduce. Developmentally synchronized populations called broods rarely coexist, with one dominant brood locally excluding those that emerge in off years. Twelve modern 17-year cicada broods are believed to have descended from only three ancestral broods following the last glaciation. The mechanisms by which these daughter broods overcame exclusion by the ancestral brood to synchronously emerge in a different year, however, are elusive. Here, we demonstrate that temporal variation in the population density of generalist predators can allow intermittent opportunities for new broods to invade, even though a single brood remains dominant most of the time. We show that this mechanism is consistent, in terms of the type and frequency of brood replacements, with the distribution of periodical cicada broods throughout North America today. Although we investigate one particularly charismatic case study, the mechanisms involved (competitive exclusion, Allee effects, trait variation, predation, and temporal variability) are ubiquitous and could contribute to patterns of species diversity in a range of systems.

Mitogenomes Provide Insights into the Species Boundaries and Phylogenetic Relationships among Three Dolycoris Sloe Bugs (Hemiptera: Pentatomidae) from China

(1) Background: The three sloe bugs, Dolycoris baccarum, Dolycoris indicus, and Dolycoris penicillatus, are found in the Chinese mainland and are morphologically similar. The species boundaries and phylogenetic relationships of the three species remain uncertain; (2) Methods: In this study, we generated multiple mitochondrial genomes (mitogenomes) for each of the three species and conducted comparative mitogenomic analysis, species delimitation, and phylogenetic analysis based on these data; (3) Results: Mitogenomes of the three Dolycoris species are conserved in nucleotide composition, gene arrangement, and codon usage. All protein-coding genes (PCGs) were found to be under purifying selection, and the ND4 evolved at the fastest rate. Most species delimitation analyses based on the COI gene and the concatenated 13 PCGs retrieved three operational taxonomic units (OTUs), which corresponded well with the three Dolycoris species identified based on morphological characters. A clear-cut barcode gap was discovered between the interspecific and intraspecific genetic distances of the three Dolycoris species. Phylogenetic analyses strongly supported the monophyly of Dolycoris, with interspecific relationship inferred as (D. indicus + (D. baccarum + D. penicillatus)); (4) Conclusions: Our study provides the first insight into the species boundaries and phylogenetic relationships of the three Dolycoris species distributed across the Chinese mainland.

The First Two Complete Mitochondrial Genomes for the Subfamily Meligethinae (Coleoptera: Nitidulidae) and Implications for the Higher Phylogeny of Nitidulidae

The phylogenetic status of the family Nitidulidae and its sister group relationship remain controversial. Also, the status of the subfamily Meligethinae is not fully understood, and previous studies have been mainly based on morphology, molecular fragments, and biological habits, rather than the analysis of the complete mitochondrial genome. Up to now, there has been no complete mitochondrial genome report of Meligethinae. In this study, the complete mitochondrial genomes of Meligethinus tschungseni and Brassicogethes affinis (both from China) were provided, and they were compared with the existing complete mitochondrial genomes of Nitidulidae. The phylogenetic analysis among 20 species of Coleoptera was reconstructed via PhyloBayes analysis and Maximum likelihood (ML) analysis, respectively. The results showed that the full lengths of Meligethinus tschungseni and Brassicogethes affinis were 15,783 bp and 16,622 bp, and the AT contents were 77% and 76.7%, respectively. Each complete mitochondrial genome contains 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), 2 ribosomal RNA genes (rRNAs), and a control region (A + T-rich region). All the PCGs begin with the standard start codon ATN (ATA, ATT, ATG, ATC). All the PCGs terminate with a complete terminal codon, TAA or TAG, except cox1, cox2, nad4, and nad5, which terminate with a single T. Furthermore, all the tRNAs have a typical clover-leaf secondary structure except trnS1, whose DHU arm is missing in both species. The two newly sequenced species have different numbers and lengths of tandem repeat regions in their control regions. Based on the genetic distance and Ka/Ks analysis, nad6 showed a higher variability and faster evolutionary rate. Based on the available complete mitochondrial genomes, the results showed that the four subfamilies (Nitidulinae, Meligethinae, Carpophilinae, Epuraeinae) of Nitidulidae formed a monophyletic group and further supported the sister group relationship of Nitidulidae + Kateretidae. In addition, the taxonomic status of Meligethinae and the sister group relationship between Meligethinae and Nitidulinae (the latter as currently circumscribed) were also preliminarily explored.

Taxonomic Status and Phylogenetic Relationship of the Charadriidae Family Based on Complete Mitogenomes

Background

The Charadriiformes provide a good source for researching evolution owing to their diverse distribution, behavior, morphology, and ecology. However, in the Charadrii, family-level relationships remain understudied, and the monophyly of Charadriidae is also a subject of controversy.

Methods

In the present study, we generated complete mitogenomes for two species, Charadrius leschenaultii and Charadrius mongolus, which were found to be 16,905 bp and 16,844 bp in length, respectively. Among the 13 protein codon genes, we observed variation in the rate of non-synonymous substitution rates, with the slowest rate found in COI and the fastest rate observed in ATP8. The Ka/Ks ratio for all Charadriidae species was significantly lower than one, which inferred that the protein-coding genes underwent purifying selection.

Results

Phylogenetic analysis based on the genes of Cyt b, 12S and ND2 revealed that the genus Pluvialis is the sister group of three families (Haematopodidae, Ibidorhynchidae, Recurvirostridae). However, the phylogenetic analysis based on complete mitogenomes indicated that the genus Pluvialis is within the Charadriidae family.

Conclusion

This study highlights the importance of carefully selecting the number of genes used to obtain accurate estimates of the species tree. It also suggests that relying on partial mtDNA genes with fast-evolving rates may lead to misleading results when resolving the Pluvialis sister group. Future research should focus on sequencing more mitogenomes at different taxonomic levels to gain a better understanding of the features and phylogenetic relationships within the Charadriiformes order.

Comparative and phylogenetic analyses of mitochondrial genomes in Elateridae (Coleoptera: Elateroidea)

The click-beetles (Elateridae) are a species-rich beetle family that is easily recognizable. They are distributed in all zoogeographical regions with over 11,000 species. Comparative studies of the structural characteristics of mitochondrial genomes (mitogenomes), as well as phylogenetic relationships of click-beetles, can improve our understanding of mitogenomic evolution. In this study, we determined four mitogenomes from Elateridae by next-generation sequencing. The four mitogenomes were 16,005 to 16,930 bp in length with 37 typical genes and a control region (A + T-rich region). Combined with previously reported elaterid mitogenomes, all PCGs initiate with either the standard start codon of ATN or TTG. According to the nonsynonymous/synonymous mutation ratio (Ka/Ks) of all PCGs, the highest and the lowest evolutionary rates were found for atp8 and cox1, respectively. Among the control regions of the four mitogenomes, several different patterns and numbers of tandem repeats were identified, which was the primary cause of the length variation in control regions. Phylogenetic analyses were conducted based on 13 protein-coding genes and two ribosomal RNA genes from 33 species of Elateridae and two outgroups. The Bayesian inference and maximum likelihood trees had an identical topological structure. The monophyly of Cardiophorinae, Agrypninae and Elaterinae was recovered with high support in all topologies, and the Tetralobinae was placed as the earliest branch in the Elateridae. Expanding the availability of mitogenomic and genomic data from a broader range of click-beetles could provide more clarity on the disputed relationships among subfamilies within Elateridae.

Novel tRNA Gene Rearrangements in the Mitochondrial Genomes of Poneroid Ants and Phylogenetic Implication of Paraponerinae (Hymenoptera: Formicidae)

Ants (Formicidae) are the most diverse eusocial insects in Hymenoptera, distributed across 17 extant subfamilies grouped into 3 major clades, the Formicoid, Leptanilloid, and Poneroid. While the mitogenomes of Formicoid ants have been well studied, there is a lack of published data on the mitogenomes of Poneroid ants, which requires further characterization. In this study, we first present three complete mitogenomes of Poneroid ants: Paraponera clavata, the only extant species from the subfamily Paraponerinae, and two species (Harpegnathos venator and Buniapone amblyops) from the Ponerinae subfamily. Notable novel gene rearrangements were observed in the new mitogenomes, located in the gene blocks CR-trnM-trnI-trnQ-ND2, COX1-trnK-trnD-ATP8, and ND3-trnA-trnR-trnN-trnS1-trnE-trnF-ND5. We reported the duplication of tRNA genes for the first time in Formicidae. An extra trnQ gene was identified in H. venator. These gene rearrangements could be explained by the tandem duplication/random loss (TDRL) model and the slipped-strand mispairing model. Additionally, one large duplicated region containing tandem repeats was identified in the control region of P. clavata. Phylogenetic analyses based on protein-coding genes and rRNA genes via maximum likelihood and Bayes methods supported the monophyly of the Poneroid clade and the sister group relationship between the subfamilies Paraponerinae and Amblyoponinae. However, caution is advised in interpreting the positions of Paraponerinae due to the potential artifact of long-branch attraction.

Comparative mitogenomic analysis of three bugs of the genus Hygia Uhler, 1861 (Hemiptera, Coreidae) and their phylogenetic position

Hygia Uhler, 1861 is the largest genus in the bug family Coreidae. Even though many species of this genus are economically important, the complete mitogenomes of Hygia species have not yet been reported. Therefore, in the present study, the complete mitogenomes of three Hygia species, H.lativentris (Motschulsky, 1866), H.bidentata Ren, 1987, and H.opaca (Uhler, 1860), are sequenced and characterized, and submitted in a phylogenetic analysis of the Coreidae. The results show that mitogenomes of the three species are highly conserved, typically with 37 genes plus its control region. The lengths are 16,313 bp, 17,023 bp, and 17,022 bp, respectively. Most protein-coding genes (PCGs) in all species start with the standard codon ATN and terminate with one of three stop codons: TAA, TAG, or T. The tRNAs secondary structures of all species have a typical clover structure, except for the trnS1 (AGC) in H.bidentata, which lacks dihydrouridine (DHU) arm that forms a simple loop. Variation in the length of the control region led to differences in mitochondrial genome sizes. The maximum-likelihood (ML) and Bayesian-inference (BI) phylogenetic analyses strongly supported the monophyly of Hygia and its position within Coreidae, and the relationships are ((H.bidentata + (H.opaca + (H.lativentris + Hygia sp.))). The results provide further understanding for future phylogenetic studies of Coreidae.

Evolutionary Rates, Divergence Rates, and Performance of Individual Mitochondrial Genes Based on Phylogenetic Analysis of Copepoda

Copepoda is a large and diverse group of crustaceans, which is widely distributed worldwide. It encompasses roughly 9 orders, whose phylogeny remains unresolved. We sequenced the complete mitochondrial genome (mitogenome) of Sinergasilus major (Markevich, 1940) and used it to explore the phylogeny and mitogenomic evolution of Copepoda. The mitogenome of S. major (14,588 bp) encodes the standard 37 genes as well as a putative control region, and molecular features are highly conserved compared to other Copepoda mitogenomes. Comparative analyses indicated that the nad2 gene has relatively high nucleotide diversity and evolutionary rate, as well as the largest amount of phylogenetic information. These results indicate that nad2 may be a better marker to investigate phylogenetic relationships among closely related species in Copepoda than the commonly used cox1 gene. The sister-group relationship of Siphonostomatoida and Cyclopoida was recovered with strong support in our study. The only topological ambiguity was found within Cyclopoida, which might be caused by the rapid evolution and sparse taxon sampling of this lineage. More taxa and genes should be used to reconstruct the Copepoda phylogeny in the future.

Geological events and climate change drive diversification and speciation of mute cicadas in eastern continental Asia

The poor mobility of nymphs living underground, usually for many years and the weak flying ability of adults make cicadas unique for evolutionary biology and bio-geographical study. Cicadas of the genus Karenia are unusual in Cicadidae in lacking the timbals that produce sound. Population differentiation, genetic structure, dispersal and evolutionary history of the eastern Asian mute cicada Karenia caelatata were investigated based on morphological, acoustic and molecular data. The results reveal a high level of genetic differentiation in this species. Six independent clades with nearly unique sets of haplotypes corresponding to geographically isolated populations are recognized. Genetic and geographic distances are significantly correlated among lineages. The phenotypic differentiation is generally consistent with the high levels of genetic divergence across populations. Results of ecological niche modeling suggest that the potential distribution range of this mountain-habitat specialist during the Last Glacial Maximum was broader than its current range, indicating this species had benefited from the climate change during the early Pleistocene in southern China. Geological events such as orogeny in Southwest China and Pleistocene climate oscillations have driven the differentiation and divergence of this species, and basins, plains and rivers function as natural "barriers" to block the gene flow. Besides significant genetic divergence being found among clades, the populations occurring in the Wuyi Mountains and the Hengduan Mountains are significantly different in the calling song structure from other populations. This may have resulted from significant population differentiation and subsequent adaptation of related populations. We conclude that ecological differences in habitats, coupled with geographical isolation, have driven population divergence and allopatric speciation. This study provides a plausible example of incipient speciation in Cicadidae and improves understanding of population differentiation, acoustic signal diversification and phylogeographic relationships of this unusual cicada species. It informs future studies on population differentiation, speciation and phylogeography of other mountain-habitat insects in the East Asian continent.

The 2021 emergence of Brood X periodical cicadas Magicicada spp. (Hemiptera: Cicadidae) in Georgia, United States of America

The US state of Georgia includes the range of several periodical cicada broods and is the southernmost state in which Brood X periodical cicadas emerge; however, no research has focused on this brood in this state. We used reports of sightings on social media, communication with the public, and our own searches to determine the geographic range in Georgia and timing of biological events. Both adults and exuviae were identified to species to determine the species makeup at those locations. The first Brood X adult was photographed on April 26 in Lumpkin County, and Magicicada septendecim L. was the most common species. Online records and site visits led to distribution records in nine counties, including six that provided no records in the 2004 emergence. Driving surveys revealed patchy distributions of chorusing adults and species distribution modeling further predicted locations where Brood X can be found in future surveys. We observed cicada oviposition scars at two locations and found no effect of host plant on presence or density of scars. Lastly, collections of dead adults showed female remains were less common and more likely to be dismembered. Further investigations of the periodical cicadas in Georgia are recommended to better understand the phenology, evolution, and ecology of these remarkable insects.

Complete Mitochondrial Genome of Piophila casei (Diptera: Piophilidae): Genome Description and Phylogenetic Implications

Piophila casei is a flesh-feeding Diptera insect that adversely affects foodstuffs, such as dry-cured ham and cheese, and decaying human and animal carcasses. However, the unknown mitochondrial genome of P. casei can provide information on its genetic structure and phylogenetic position, which is of great significance to the research on its prevention and control. Therefore, we sequenced, annotated, and analyzed the previously unknown complete mitochondrial genome of P. casei. The complete mt genome of P. casei is a typical circular DNA, 15,785 bp in length, with a high A + T content of 76.6%. It contains 13 protein-coding genes (PCG), 2 ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and 1 control region. Phylogenetic analysis of 25 Diptera species was conducted using Bayesian and maximum likelihood methods, and their divergence times were inferred. The comparison of the mt genomes from two morphologically similar insects P. casei and Piophila megastigmata indicates a divergence time of 7.28 MYA between these species. The study provides a reference for understanding the forensic medicine, taxonomy, and genetics of P. casei.

Climatic oscillation promoted diversification of spinous assassin bugs during Pleistocene glaciation

Insect speciation is among the most fascinating topics in evolutionary biology; however, its underlying mechanisms remain unclear. Allopatric speciation represents one of the major types of speciation and is believed to have frequently occurred during glaciation periods, when climatic oscillation may have caused suitable habitats to be fragmented repeatedly, creating geographical isolation among populations. However, supporting evidence for allopatric speciation of insects in East Asia during the Pleistocene glaciation remains lacking. We aim to investigate the effect of climatic oscillation during the Pleistocene glaciation on the diversification pattern and evolutionary history of hemipteran insects and to test the hypothesis of Pleistocene species stability using spinous assassin bugs Sclomina (Hemiptera: Reduviidae), a small genus widely distributed in southern China but was later found to have cryptic species diversity. Here, using the whole mitochondrial genome (mitogenome) and nuclear ribosomal RNA genes, we investigated both interspecific and intraspecific diversification patterns of spinous assassin bugs. Approximate Bayesian computation, ecological niche modeling, and demographic history analyses were also applied to understand the diversification process and driven factors. Our data suggest that the five species of Sclomina are highly diverged, despite three of them currently being cryptic. Speciation occurred during the Pleistocene when suitable distribution areas were possibly fragmented. Six phylogeographic groups in the type species S. erinacea were identified, among which two groups underwent expansion during the early Last Glacial Period and after Last Glacier Maximum. Our analyses suggest that this genus may have experienced climate-driven habitat fragmentation and postglacial expansion in the Pleistocene, promoting allopatric speciation and intraspecific diversification. Our results reveal underestimated species diversity in a small insect group and illustrate a remarkable example of allopatric speciation of insects in East Asia promoted by Pleistocene climatic oscillations. These findings provide important insights into the speciation processes and aid the conservation of insect species diversity.

Weak genetic structure of flower thrips Frankliniella intonsa in China revealed by mitochondrial genomes

Human activities facilitate long-distance dispersal of insects beyond their native range. In particular, the transportation of live plants offers diffusion opportunities for some insects with weak flight abilities. The increase in urban afforestation also help insect reside in urban habitats. The flower thrips, Frankliniella intonsa, is a widespread pest that causes serious damage to many economically important plants. Human activities are likely to facilitate the dispersal of this pest, however, the population genetic structure of this pest remains unclear. Herein, high-throughput sequencing was used to obtain 149 whole mitochondrial genomes of flower thrips from 28 geographic populations in China. Population genetic analyses, phylogenetic reconstruction, and inference of demographic history were then performed. A weak genetic structure was found among all populations across large geographic distance in China, in which five mitochondrial haplotype lineages were resolved. One of the lineages was identified to be shared among most samples collected from central city areas, which may be derived from the surrounding areas. Demographic history analyses suggested a recent population expansion of F. intonsa. Overall, the present population genetic structure of flower thrips in China may be promoted by human-mediated urban afforestation across the country.

Features and evolution of control regions in leafroller moths (Lepidoptera: Tortricidae) inferred from mitochondrial genomes and phylogeny

The control region (CR) of the mitochondrial genome (mitogenome) represents a major noncoding fragment with several special structural features that are thought to be responsible for the initiation of mitogenome transcription and replication. However, few studies have revealed the evolutionary patterns of CR in the phylogenetic context. Here, we explain the characteristics and evolution of CR in Tortricidae, inferred from a mitogenome-based phylogeny. The first complete mitogenomes of the genera Meiligma and Matsumuraeses were sequenced. Both mitogenomes are double-stranded circular DNA molecules with lengths of 15,675 bp and 15,330 bp, respectively. Phylogenetic analyses derived from 13 protein-coding genes and two ribosomal RNAs showed that most tribes, including subfamilies Olethreutinae and Tortricinae, were recovered as monophyletic clades, similar to previous studies based on morphological or nuclear data. Moreover, comprehensive comparative analyses of the structural organization and role of tandem replications on the length variation and high AT content of CR sequences were conducted. The results reveal a significant positive correlation between the total length and AT content of tandem repeats and whole CR sequences in Tortricidae. The structural organization in CR sequences is diverse, even between closely related tribes, which demonstrates the plasticity of the mitochondrial DNA molecule in Tortricidae.

The mitochondrial genome of Binodoxys acalephae (Hymenoptera: Braconidae) with unique gene rearrangement and phylogenetic implications

BACKGROUND

Species in the subfamily Aphidiinae from the Braconidae of Hymenoptera are endoparasitic wasps that exclusively utilize aphids as hosts. Some Aphidiinae species are widely used as biological agents. However, there were only one species with determined complete mitochondrial genome from this subfamily.

METHODS AND RESULTS

In this study, we sequenced and annotated the mitochondrial genome (mitogenome) of Binodoxys acalephae, which was 15,116 bp in size and contained 37 genes. The start codon of 13 protein-coding genes was ATN, and the complete stop codon TAA and TAG was widely assigned to 11 protein-coding genes. The lrRNA contains 43 stem-loop structures, and srRNA contains 25 stem-loop structures. Translocation and inversion of tRNA genes was found to be dominant in B. acalephae. In contrast to Aphidius gifuensis from the same subfamily Aphidiinae, inverted tRNALeu1 was translocated to the gene cluster between tRNALeu2 and COX2, and the control region between tRNAIle and tRNAMet was deleted in the mitogenome of B. acalephae. Within Braconidae, gene clusters tRNATrp-tRNACys-tRNATyr and CR-tRNAIle-tRNAGln-tRNAMet were hotspots for gene rearrangement. Phylogenetic analysis showed that both Bayesian and maximum-likelihood methods recovered the monophyly of Aphidiinae and suggested that Aphidiinae formed sister clades with the remaining subfamilies. The phylogenetic analyses of nine subfamilies supported the monophyly of Cyclostomes and Noncyclostomes in Braconidae.

CONCLUSION

The arrangement of mitochondrial genes and the phylogenetic relationships among nine Braconidae subfamilies were constructed better to understand the diversity and evolution of Aphidiinae mitogenomes.

The mitochondrial genomes of the Geometroidea (Lepidoptera) and their phylogenetic implications

The Geometroidea is a large superfamily of Lepidoptera in species composition and contains numerous economically important pest species that cause great loss in crop and forest production. However, understanding of mitogenomes remains limited due to relatively fewer mitogenomes previously reported for this megadiverse group. Here, we sequenced and annotated nine mitogenomes for Geometridae and further analyzed the mitogenomic evolution and phylogeny of the whole superfamily. All nine mitogenomes contained 37 mitochondrial genes typical in insects, and gene organization was conserved except for Somatina indicataria. In S. indicataria, the positions of two tRNAs were rearranged. The trnR was located before trnA instead of after trnA typical in Lepidoptera, whereas the trnE was detected rarely on the minority strand (N-strand). This trnR-trnA-trnN-trnS1-trnE-trnF newly recognized in S. indicataria represents the first gene rearrangement reported for Geometroidea and is also unique in Lepidoptera. Besides, nucleotide composition analyses showed little heterogeneity among the four geometrid subfamilies involved herein, and overall, nad6 and atp8 have higher nucleotide diversity and Ka/Ks rate in Geometridae. In addition, the taxonomic assignments of the nine species, historically defined by morphological studies, were confirmed by various phylogenetic analyses based on the hitherto most extensive mitogenomic sampling in Geometroidea.

Revisiting the Phylogenetic Relationship and Evolution of Gargarini with Mitochondrial Genome (Hemiptera: Membracidae: Centrotinae)

In this study, we newly sequenced and analyzed the complete mitochondrial genomes of five genera and six species in Gargarini: Antialcidas floripennae, Centrotoscelus davidi, Kotogargara minuta, Machaerotypus stigmosus, Tricentrus fulgidus, and Tricentrus gammamaculatus. The mitochondrial genomes contain 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, and a control region. The lengths of the mitochondrial genomes are 15,253 bp to 15,812 bp, and the AT contents of the obtained mitogenomes indicate a strong AT bias, ranging from 75.8% to 78.5%. The start codons of all PCGs show that most start with a typical ATN (ATA/T/G/C) codon and less start with T/GTG; the stop codon TAA is frequently used, and TAG and a single T are less used. In Gargarini mitogenomes, all tRNA genes can be folded into the canonical cloverleaf secondary structure, except for trnaS1, which lacks a stable dihydrouridine (DHU) stem and is replaced by a simple loop. At the same time, the phylogenetic analysis of the tribe Gargarini based on sequence data of 13 PCGs from 18 treehopper species and four outgroups revealed that the 10 Gargarini species form a steady group with strong support and form a sister group with Leptocentrini, Hypsauchenini, Centrotini, and Leptobelini. Diversification within Gargarini is distinguished by a Later Cretaceous divergence that led to the rapid diversification of the species. Moreover, the ancestral state reconstructions analysis showed the absence of the suprahumeral horn, which was confirmed as the ancestor characteristic of the treehopper, which has evolved from simple to complex. Our results shed new light specifically on the molecular and phylogenetic evolution of the pronotum in Gargarini.

Complete Mitogenome Analysis of Five Leafhopper Species of Idiocerini (Hemiptera: Cicadellidae)

Insect mitochondrial genomes (mitogenomes) are of great interest in exploring molecular evolution, phylogenetics, and biogeography. So far, only 12 mitogenomes of the leafhopper tribe Idiocerini have been released in GenBank, although the tribe comprises 488 known species including some agricultural, forestry, and horticultural pests. In order to compare and analyze the mitochondrial genome structure of Idiocerini and even the selective pressure of 13 protein-coding genes (PCGs) of the family Cicadellidae, the complete mitogenomes of five species including Nabicerus dentimus, Sahlbergotettix salicicola, Podulmorinus opacus, Podulmorinus consimilis, and a new species of a new genus were determined by next-generation sequencing. The size of the newly determined mitogenomes ranged from 14,733 bp to 15,044 bp, comprising the standard set of 13 PCGs, 22 transfer RNA genes, two ribosomal RNA genes, and a long non-coding control region (CR). The extent of purifying selection presented different pictures in the tribe and the family. The less pronounced genes (0.5 < dN/dS < 1) were nad5 and nad4l in Idiocerin, whereas in the family Cicadellidae including the sequences of Idiocerin, nad1-nad6 and cox1 genes were less pronounced. The codon encoding leucine was the most common in all species, and the codon encoding serine 1 was the most common in all species except for P. opacus. Interestingly, in P. opacus, another of the most common codons is that encoding serine 2. Among the 17 examined species of the Idiocerini, 14 species contained the tandem repeats, and 11 species of them contained the motif "TTATA". These findings will promote research on the structure and evolution of the mitochondrial genome and highlight the need for more mitogenomes in Cicadellidae.

Complete mitochondrial genome analysis and molecular phylogenetic implications of Kennelia xylinana (Lepidoptera: Tortricidae)

Kennelia is a small genus in Tortricidae that is distributed in the Oriental and Palaearctic regions, and its taxonomic position within the subfamily Olethreutinae is controversial. For a comprehensive understanding of the genus, we sequenced the mitogenome of Kennelia xylinana, the type species of Kennelia, and Ancylis unculana, a species of Enarmoniini; analyzed the mitogenome characteristics of K. xylinana; and explored its phylogenetic position. Similar to other members of Lepidoptera, the mitogenome of K. xylinana is 15,762-bp long and consists of 13 protein-coding genes (PCGs), two ribosomal RNA genes, 22 transfer RNA genes, and a noncoding control region. In particular, we found a structure (TATAATTAATAA)₁₁ in the middle of the AT-rich region. Based on the Bayesian inference and maximum likelihood analyses of the 13 PCGs of 40 tortricid species, representing 8 tribes of 2 subfamilies, K. xylinana was clustered with two members of Enarmoniini, A. unculana and Loboschiza koenigiana, and formed highly supported monophyly. The results indicate that Kennelia should be placed in the tribe Enarmoniini.

Comparison of mitogenomes of three Petalocephala species (Hemiptera: Cicadellidae: Ledrinae) and their phylogenetic analysis

Ledrinae is a unique group of leafhoppers with a distinct appearance. Petalocephala is the largest Ledrinae genus that is difficult to identify except by dissecting the male genitals. To date, research on Ledrinae is relatively less compared with other leafhoppers. Therefore, to better understand this group, we sequenced and analyzed three complete Petalocephala mitochondrial genomes. We comparatively analyzed these general Petalocephala genomic features (including size, AT content, AT/GC skew, 13 protein-coding gene nucleotide compositions, etc.), and predicted 22 transfer RNA secondary structures. We obtained highly consistent phylogenetic results within Cicadellidae based on mitogenomic data using the maximum likelihood and Bayesian methods. Our results showed that all subfamilies were monophyletic and had a high node support rate, and there was a sister group relationship between Ledrinae and all other leafhopper groups. Furthermore, treehoppers were found to originate from leafhoppers and showed sister group relationships with Megophthalminae. Within Ledrinae, all phylogenetic trees supporting phylogenetic relationships were as follows: ([P. dicondylica + P. gongshanensis] + [Tituria pyramidata + [Ledra auditura + P. gongshanensis]]) Based on the complete mitogenome phylogenetic analysis and the comparison of morphological characteristics, we propose that Petalocephala is not monophyletic.

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.

Comparative Mitogenomics of Flesh Flies: Implications for Phylogeny

Flesh flies (Diptera: Sarcophagidae) represent a rapid radiation belonging to the Calyptratae. With more than 3000 known species, they are extraordinarily diverse in terms of their breeding habits and are therefore of particular importance in human and veterinary medicine, forensics, and ecology. To better comprehend the phylogenetic relationships and evolutionary characteristics of the Sarcophagidae, we sequenced the complete mitochondrial genomes of five species of flesh flies and performed mitogenomic comparisons amongst the three subfamilies. The mitochondrial genomes match the hypothetical condition of the insect ancestor in terms of gene content and gene arrangement. The evolutionary rates of the subfamilies of Sarcophagidae differ significantly, with Miltogramminae exhibiting a higher rate than the other two subfamilies. The monophyly of the Sarcophagidae and each subfamily is strongly supported by phylogenetic analysis, with the subfamily-level relationship inferred as (Sarcophaginae, (Miltogramminae, Paramacronychiinae)). This study suggests that phylogenetic analysis based on mitochondrial genomes may not be appropriate for rapidly evolving groups such as Miltogramminae and that the third-codon positions could play a considerable role in reconstructing the phylogeny of Sarcophagidae. The protein-coding genes ND2 and ND6 have the potential to be employed as DNA markers for species identification and delimitation in flesh flies.

Comparative mitochondrial genome analysis and phylogenetic relationship among lepidopteran species

Lepidoptera has rich species including many agricultural pests and economical insects around the world. The mitochondrial genomes (mitogenomes) were utilized to explore the phylogenetic relationships between difference taxonomic levels in Lepidoptera. However, the knowledge of mitogenomic characteristics and phylogenetic position about superfamily-level in this order is unresolved. In this study, we integrated 794 mitogenomes consisting of 37 genes and a noncoding control region, which covered 26 lepidopteran superfamilies from newly sequenced and publicly available genomes for comparative genomic and phylogenetic analysis. In primitive taxon, putative start codon of cox1 gene was ATA or ATT instead of CGA, but stop codon of that showed four types, namely TAA, TAG, TA and T. The 7-bp overlap between atp8 and atp6 presented as "ATGATAA". Moreover, the most frequently utilized amino acids were leucine (UUA) in 13 PCGs. Phylogenetic analysis showed that the main backbone relationship in Lepidoptera was (Hepialoidea + (Nepticuloidea + (Adeloidea + (Tischerioidea + (Tineoidea + (Yponomeutoidea + (Gracillarioidea + (Papilionoidea + ((Zygaenoidea + Tortricoidea) + (Gelechioidea + (Pyraloidea + ((Geometroidea + Noctuoidea) + (Lasiocampoidea + Bombycoidea))))))))))))).

Detecting and removing sample contamination in phylogenomic data: an example and its implications for Cicadidae phylogeny (Insecta: Hemiptera)

Contamination of a genetic sample with DNA from one or more non-target species is a continuing concern of molecular phylogenetic studies, both Sanger sequencing studies and Next-Generation Sequencing (NGS) studies. We developed an automated pipeline for identifying and excluding likely cross-contaminated loci based on detection of bimodal distributions of patristic distances across gene trees. When the contamination occurs between samples within a dataset, comparisons between a contaminated sample and its contaminant taxon will yield bimodal distributions with one peak close to zero patristic distance. This new method does not rely on a priori knowledge of taxon relatedness nor does it determine the causes(s) of the contamination. Exclusion of putatively contaminated loci from a dataset generated for the insect family Cicadidae showed that these sequences were affecting some topological patterns and branch supports, although the effects were sometimes subtle, with some contamination-influenced relationships exhibiting strong bootstrap support. Long tip branches and outlier values for one anchored phylogenomic pipeline statistic (AvgNHomologs) were correlated with the presence of contamination. While the AHE markers used here, which target hemipteroid taxa, proved effective in resolving deep and shallow level Cicadidae relationships in aggregate, individual markers contained inadequate phylogenetic signal, in part probably due to short length. The cleaned dataset, consisting of 429 loci, from 90 genera representing 44 of 56 current Cicadidae tribes, supported three of the four sampled Cicadidae subfamilies in concatenated-matrix maximum likelihood (ML) and multispecies coalescent-based species tree analyses, with the fourth subfamily weakly supported in the ML trees. No well-supported patterns from previous family-level Sanger sequencing studies of Cicadidae phylogeny were contradicted. One taxon (Aragualna plenalinea) did not fall with its current subfamily in the genetic tree, and this genus and its tribe Aragualnini is reclassified to Tibicininae following morphological re-examination. Only subtle differences were observed in trees after removal of loci for which divergent base frequencies were detected. Greater success may be achieved by increased taxon sampling and developing a probe set targeting a more recent common ancestor and longer loci. Searches for contamination are an essential step in phylogenomic analyses of all kinds and our pipeline is an effective solution.

Mitochondrial composition of and diffusion limiting factors of three social wasp genera Polistes, Ropalidia, and parapolybia (Hymenoptera: Vespidae)

Background

Social wasps Polistes, Ropalidia, and Parapolybia, belonging to the subfamily Polistinae, have obviously different distribution patterns, yet the factors leading to this difference remain unknown.

Results

The 17 newly sequenced mitogenomes of Polistes, Ropalidia, and Parapolybia contain 37 genes, and there are obvious differences among the compositions of the three genera. The monophyly of the genus Polistes and a monophyletic Ropalidiini: (Ropalidia + Parapolybia) are concordant with previous morphological analysis of the subfamily Polistinae. Our inferred divergence time demonstrates Polistes (at around 69 Ma) was diverged earlier than Ropalidia and Parapolybia (at around 61 Ma). The rearrangement of both trnY and trnL1 are shared by all the Polistinae. In addition, the unique rearrangement of TDRL derived at 69 Ma is detected in Polistes, and Ropalidia contains a Reversal which may derive at 61 Ma. Hereafter, the possibility is elaborated that Polistes originated in Aisa and then dispersed from Africa to South America, and Polistes and Ropalidia spread from Southeast Asia to Australia. At last, continental drift and Quaternary Ice Ages are inferred to be two main limiting factors in the current distributions of the three genera.

Conclusions

Obvious differences occur in the mitochondrial composition of Polistes, Ropalidia, and Parapolybia. According to the reconstructed time-calibrated framework, it is inquired that the continental drifts and the climate are mainly diffusion limiting factors of the three genera.

Supplementary information

The online version contains supplementary material available at 10.1186/s12862-022-02017-6.

Comparative Mitogenomics of True Frogs (Ranidae, Anura), and Its Implications for the Phylogeny and Evolutionary History of Rana

Simple Summary

The true frogs of the genus Rana are a complex and diverse group. Many new species have been discovered with the help of molecular markers and morphological traits. However, the evolutionary history in Rana were not well understood. In this study, we sequenced and annotated the complete mitochondrial genome of R. longicrus and R. zhenhaiensis. In 13 protein codon genes, the COI was the most conserved, and ATP8 had a fast rate of evolution. The Ka/Ks ratio analysis among Rana indicated the protein-coding genes were suffering purify selection. There were three kinds of gene arrangement patterns found. This study provides mitochondrial genetic information, improving our understanding of mitogenomic structure and evolution, and recognizes the phylogenetic relationship and taxonomy among Rana.

Abstract

The true frogs of the genus Rana are a complex and diverse group, containing approximately 60 species with wide distribution across Eurasia and the Americas. Recently, many new species have been discovered with the help of molecular markers and morphological traits. However, the evolutionary history in Rana was not well understood and might be limited by the absence of mitogenome information. In this study, we sequenced and annotated the complete mitochondrial genome of R. longicrus and R. zhenhaiensis, containing 22 tRNAs, 13 protein-coding genes, two ribosomal RNAs, and a non-coding region, with 17,502 bp and 18,006 bp in length, respectively. In 13 protein codon genes, the COI was the most conserved, and ATP8 had a fast rate of evolution. The Ka/Ks ratio analysis among Rana indicated the protein-coding genes were suffering purify selection. There were three kinds of gene arrangement patterns found. The mitochondrial gene arrangement was not related to species diversification, and several independent shifts happened in evolutionary history. Climate fluctuation and environmental change may have played an essential role in species diversification in Rana. This study provides mitochondrial genetic information, improving our understanding of mitogenomic structure and evolution, and recognizes the phylogenetic relationship and taxonomy among Rana.

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.

African climate and geomorphology drive evolution and ghost introgression in sable antelope

The evolutionary history of African ungulates has been largely explained in the light of Pleistocene climatic oscillations and the way these influenced the distribution of vegetation types, leading to range expansions and/or isolation in refugia. In contrast, comparatively fewer studies have addressed the continent's environmental heterogeneity and the role played by its geomorphological barriers. In this study, we performed a range-wide analysis of complete mitogenomes of sable antelope (Hippotragus niger) to explore how these different factors may have contributed as drivers of evolution in South-Central Africa. Our results supported two sympatric and deeply divergent mitochondrial lineages in west Tanzanian sables, which can be explained as the result of introgressive hybridization of a mitochondrial ghost lineage from an archaic, as-yet-undefined, congener. Phylogeographic subdivisions into three main lineages suggest that sable diversification may not have been solely driven by climatic events affecting populations differently across a continental scale. Often in interplay with climate, geomorphological features have also clearly shaped the species' patterns of vicariance, where the East Africa Rift System and the Eastern Arc Mountains acted as geological barriers. Subsequent splits among southern populations may be linked to rearrangements in the Zambezi system, possibly framing the most recent time when the river attained its current drainage profile. This work underscores how the use of comprehensive mitogenomic datasets on a model species with a wide geographic distribution can contribute to a much-enhanced understanding of environmental, geomorphological, and evolutionary patterns in Africa throughout the Quaternary.

The Complete Mitochondrial Genome of the Chicken Body Louse, Menacanthus cornutus, and Evolutionary Patterns of Extensive Gene Rearrangements in the Mitochondrial Genomes of Amblycera (Psocodea: Phthiraptera)

Animal mitochondrial (mt) genomes are typically double-strand circular DNA molecules, but diverse structural variations have been widely found in multiple groups. In parasitic lice (Phthiraptera), the structure of mt genomes varies remarkably across all five suborders. In this study, we reported the complete mt genome of a chicken body louse, Menacanthus cornutus, which has a typical single circular mt chromosome and drastic mt gene rearrangements. This mt genome is 15,693 bp in length, consisting of 13 protein-coding genes, 23 tRNA genes, 2 rRNA genes, and a control region. A comparison with a typical insect mt genome suggested that two highly similar trnM are present in the mt genome of M. cornutus. Moreover, almost every single gene was rearranged, and over half of mt genes were inverted. Phylogenetic analyses inferred from the mt genome sequences supported the monophyly and position of Amblycera. Mapped over the phylogenetic relationships of Amblycera, we identified two inversion events for the conserved gene blocks in Boopidae and Menoponidae. The inverted ND4L-ND4 was likely a synapomorphic rearrangement in Menoponidae. Our study demonstrated the importance of sequencing mt genomes for additional taxa to uncover the mechanism underlying the structural evolution of the mt genome in parasitic lice.

Comparative Analysis of Mitochondrial Genomes among Twelve Sibling Species of the Genus Atkinsoniella Distant, 1908 (Hemiptera: Cicadellidae: Cicadellinae) and Phylogenetic Analysis

Simple Summary

Atkinsoniella is a large genus of 98 species across the world and 88 species recorded in China within the globally distributed subfamily Cicadellinae, which is phytophagous, and some of which have been reported as important agricultural pests. Some Atkinsoniella species are very similar in morphological characteristics, making accurate identification at species level confusing. To provide further evidence toward understanding the relationships within the genus Atkinsoniella and subfamily Cicadellinae, mitogenomes of 12 Atkinsoniella sibling species were obtained and annotated. Their characteristics were comparatively analyzed. In addition, the comprehensive phylogenetic relationship within the subfamily Cicadellinae was determined based on three mitochondrial datasets using both the maximum-likelihood (ML) and Bayesian inference (BI) methods. The results suggested that the genus Atkinsoniella was recovered as a monophyletic group. The branches of the 12 newly sequenced species were clearly separated, with most nodes receiving strong support in all analyses, indicating that mitogenomics is an effective method for identifying closely related species and understanding their phylogenetic and evolutionary relationships.

Abstract

The herbivorous leafhopper genus Atkinsoniella Distant, 1908 (Hemiptera: Cicadellidae: Cicadellinae), a large genus of subfamily Cicadellinae, consists of 98 valid species worldwide and 88 species recorded in China. Some species of the genus are very similar in morphological characteristics, so they are difficult to identify accurately. In this study, 12 mitochondrial genomes of Atkinsoniella species with similar morphological characteristics were first obtained through high-throughput sequencing, which featured a typical circular molecule of 15,034–15,988 bp in length. The arrangement and orientation of 37 genes were identical to those of typical Cicadellidae mitogenomes. The phylogenetic relationship within the subfamily Cicadellinae was reconstructed using maximum-likelihood (ML) and Bayesian inference (BI) methods based on three concatenated datasets. The topological structures of the six obtained phylogenetic trees were highly consistent. The results suggested that Atkinsoniella was recovered as a monophyletic group and emerged as a sister group with the monophyletic clade of Bothrogonia, Paracrocampsa (part), and Draeculacephala (part). The branches of the 12 newly sequenced species were clearly separated, with most nodes receiving strong support in all analyses. In addition, the key to the 12 Atkinsoniella species was provided to identify species according to morphological characteristics. This study further promotes research on the classification, genetics, evolution, and phylogeny of the genus Atkinsoniella and subfamily Cicadellinae.

Insights into the Divergence of Chinese Ips Bark Beetles during Evolutionary Adaptation

Simple Summary

Bark beetle species of the genus Ips are among the major pests of Chinese conifer forests. Based on mitochondrial genome and SNP, we investigated the phylogenetic relationships and evolutionary trends of 19 populations of six Ips species that had serious outbreaks in recent years. Our results demonstrated the relationships between Ips evolution and host plants, pheromones, and altitudinal differences, and provided new insights into the mechanism of adaptive evolution of Ips bark beetles.

Abstract

Many bark beetles of the genus Ips are economically important insect pests that cause severe damage to conifer forests worldwide. In this study, sequencing the mitochondrial genome and restriction site-associated DNA of Ips bark beetles helps us understand their phylogenetic relationships, biogeographic history, and evolution of ecological traits (e.g., pheromones and host plants). Our results show that the same topology in phylogenetic trees constructed in different ways (ML/MP/BI) and with different data (mtDNA/SNP) helps us to clarify the phylogenetic relationships between Chinese Ips bark beetle populations and Euramerican species and their higher order clades; Ips bark beetles are polyphyletic. The structure of the mitochondrial genome of Ips bark beetles is similar and conserved to some extent, especially in the sibling species Ips typographus and Ips nitidus. Genetic differences among Ips species are mainly related to their geographic distribution and different hosts. The evolutionary pattern of aggregation pheromones of Ips species reflects their adaptations to the environment and differences among hosts in their evolutionary process. The evolution of Ips species is closely related to the uplift of the Qinghai-Tibet Plateau and host switching. Our study addresses the evolutionary trend and phylogenetic relationships of Ips bark beetles in China, and also provides a new perspective on the evolution of bark beetles and their relationships with host plants and pheromones.

A Mitochondrial Genome Phylogeny of Cleridae (Coleoptera, Cleroidea)

The predaceous beetle family Cleridae includes a large and widely distributed rapid radiation, which is vital for the ecosystem. Despite its important role, a number of problems remain to be solved regarding the phylogenetic inter-relationships, the timing of divergence, and the mitochondrial biology. Mitochondrial genomes have been widely used to reconstruct phylogenies of various insect groups, but never introduced to Cleridae until now. Here, we generated 18 mitochondrial genomes to address these issues, which are all novel to the family. In addition to phylogenomic analysis, we have leveraged our new sources to study the mitochondrial biology in terms of nucleotide composition, codon usage and substitutional rate, to understand how these vital cellular components may have contributed to the divergence of the Cleridae. Our results recovered Korynetinae sister to the remaining clerids, and the calde of Clerinae+Hydnocerinae is indicated more related to Tillinae. A time-calibrated phylogeny estimated the earliest divergence time of Cleridae was soon after the origin of the family, not later than 160.18 Mya (95% HPD: 158.18–162.07 Mya) during the mid-Jurassic. This is the first mitochondrial genome-based phylogenetic study of the Cleridae that covers nearly all subfamily members, which provides an alternative evidence for reconstructing the phylogenetic relationships.

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.

Advances in the Evolution and Ecology of 13- and 17-Year Periodical Cicadas

Apart from model organisms, 13- and 17-year periodical cicadas (Hemiptera: Cicadidae: Magicicada) are among the most studied insects in evolution and ecology. They are attractive subjects because they predictably emerge in large numbers; have a complex biogeography shaped by both spatial and temporal isolation; and include three largely sympatric, parallel species groups that are, in a sense, evolutionary replicates. Magicicada are also relatively easy to capture and manipulate, and their spectacular, synchronized mass emergences facilitate outreach and citizen science opportunities. Since the last major review, studies of Magicicada have revealed insights into reproductive character displacement and the nature of species boundaries, provided additional examples of allochronic speciation, found evidence for repeated and parallel (but noncontemporaneous) evolution of 13- and 17-year life cycles, quantified the amount and direction of gene flow through time, revealed phylogeographic patterning resulting from paleoclimate change, examined the timing of juvenile development, and created hypotheses for the evolution of life-cycle control and the future effects of climate changeon Magicicada life cycles. New ecological studies have supported and questioned the role of prime numbers in Magicicada ecology and evolution, found bidirectional shifts in population size over generations, quantified the contribution of Magicicada to nutrient flow in forest ecosystems, and examined behavioral and biochemical interactions between Magicicada and their fungal parasites and bacterial endosymbionts.

Characterization, Comparison of Four New Mitogenomes of Centrotinae (Hemiptera: Membracidae) and Phylogenetic Implications Supports New Synonymy

To explore the phylogenetic relationships of the subfamily Centrotinae from the mitochondrial genome data, four complete mitogenomes (Anchon lineatus, Anchon yunnanensis, Gargara genistae and Tricentrus longivalvulatus) were sequenced and analyzed. All the newly sequenced mitogenomes contain 37 genes. Among the 13 protein-coding genes (PCGs) of the Centrotinae mitogenomes, a sliding window analysis and the ratio of Ka/Ks suggest that atp8 is a relatively fast evolving gene, while cox1 is the slowest. All PCGs start with ATN, except for nad5 (start with TTG), and stop with TAA or the incomplete stop codon T, except for nad2 and cytb (terminate with TAG). All tRNAs can fold into the typical cloverleaf secondary structure, except for trnS1, which lacks the dihydrouridine (DHU) arm. The BI and ML phylogenetic analyses of concatenated alignments of 13 mitochondrial PCGs among the major lineages produce a well-resolved framework. Phylogenetic analyses show that Membracoidea, Smiliinae and Centrotinae, together with tribes Centrotypini and Leptobelini are recovered as well-supported monophyletic groups. The tribe Gargarini (sensu Wallace et al.) and its monophyly are supported.

MEANGS: an efficient seed-free tool for de novo assembling animal mitochondrial genome using whole genome NGS data

Advances in next-generation sequencing (NGS) technologies have led to an exponential increase in the number of whole genome sequences (WGS) in databases. This wealth of WGS data has greatly facilitated the recovery of full mitochondrial genomes (mitogenomes), which are vital for phylogenetic, evolutionary and ecological studies. Unfortunately, most existing software cannot easily assemble mitogenome reference sequences conveniently or efficiently. Therefore, we developed a seed-free de novo assembly tool, MEANGS, which applies the trie-search method to extend contigs from self-discovery seeds and assemble a mitogenome from animal WGS data. We then used data from 16 species with different qualities to compare the performance of MEANGS with three other available programs. MEANGS exhibited the best overall performance since it was the only one that completed all tests, and it assembled full or partial mitogenomes for all of the tested samples while the others failed. Furthermore, MEANGS selects superior assembly sequences and annotates protein-coding genes. Thus, MEANGS can be one of the most efficient software for generating high-quality mitogenomes so far, the further use of it will benefit the study on mitogenome based on whole genome NGS data. MEANGS is available at https://github.com/YanCCscu/meangs.

The mitochondrial genomes of Tortricidae: nucleotide composition, gene variation and phylogenetic performance

BACKGROUND

Mitochondrial genomes (mitogenomes) have greatly improved our understanding of the backbone phylogeny of Lepidoptera, but few studies on comparative mitogenomics below the family level have been conducted. Here, we generated 13 mitogenomes of eight tortricid species, reannotated 27 previously reported mitogenomes, and systematically performed a comparative analysis of nucleotide composition, gene variation and phylogenetic performance.

RESULTS

The lengths of completely sequenced mitogenomes ranged from 15,440 bp to 15,778 bp, and the gene content and organization were conserved in Tortricidae and typical for Lepidoptera. Analyses of AT-skew and GC-skew, the effective number of codons and the codon bias index all show a base bias in Tortricidae, with little heterogeneity among the major tortricid groups. Variations in the divergence rates among 13 protein-coding genes of the same tortricid subgroup and of the same PCG among tortricid subgroups were detected. The secondary structures of 22 transfer RNA genes and two ribosomal RNA genes were predicted and comparatively illustrated, showing evolutionary heterogeneity among different RNAs or different regions of the same RNA. The phylogenetic uncertainty of Enarmoniini in Tortricidae was confirmed. The synonymy of Bactrini and Olethreutini was confirmed for the first time, with the representative Bactrini consistently nesting in the Olethreutini clade. Nad6 exhibits the highest phylogenetic informativeness from the root to the tip of the resulting tree, and the combination of the third coding positions of 13 protein-coding genes shows extremely high phylogenetic informativeness.

CONCLUSIONS

This study presents 13 mitogenomes of eight tortricid species and represents the first detailed comparative mitogenomics study of Tortricidae. The results further our understanding of the evolutionary architectures of tortricid mitogenomes and provide a basis for future studies of population genetics and phylogenetic investigations in this group.

Comparative Analysis of Eight Mitogenomes of Bark Beetles and Their Phylogenetic Implications

Simple Summary

Many bark beetles are destructive pests in coniferous forests and cause extensive ecological and economic losses worldwide. Comparative studies of the structural characteristics of mitogenomes and phylogenetic relationships of bark beetles can improve our understanding of mitogenome evolution. In this study, we sequenced eight mitogenomes of bark beetles. Our results show that the use of start and stop codons, the abundance of amino acids, and the relative frequency of codon use are conserved among the eight bark beetles. Different regions of tRNA exhibit different degrees of conservatism. Together with the analysis of evolutionary rates and genetic distance among bark beetle species, our results reveal phylogenetic relationships among bark beetles of the subfamily Scolytinae.

Abstract

Many bark beetles of the subfamily Scolytinae are the most economically important insect pests of coniferous forests worldwide. In this study, we sequenced the mitochondrial genomes of eight bark beetle species, including Dendroctonus micans, Orthotomicus erosus, Polygraphus poligraphus, Dryocoetes hectographus, Ips nitidus, Ips typographus, Ips subelongatus, and Ips hauseri, to examine their structural characteristics and determine their phylogenetic relationships. We also used previously published mitochondrial genome sequence data from other Scolytinae species to identify and localize the eight species studied within the bark beetle phylogeny. Their gene arrangement matched the presumed ancestral pattern of these bark beetles. Start and stop codon usage, amino acid abundance, and the relative codon usage frequencies were conserved among bark beetles. Genetic distances between species ranged from 0.037 to 0.418, and evolutionary rates of protein-coding genes ranged from 0.07 for COI to 0.69 for ND2. Our results shed light on the phylogenetic relationships and taxonomic status of several bark beetles in the subfamily Scolytinae and highlight the need for further sequencing analyses and taxonomic revisions in additional bark beetle species.

The Complete Mitochondrial Genome of One Breeding Strain of Asian Swamp Eel (Monopterus albus, Zuiew 1793) Using PacBio and Illumina Sequencing Technologies and Phylogenetic Analysis in Synbranchiformes

Asian swamp eel (Monopterus albus, Zuiew 1793) is a commercially important fish due to its nutritional value in Eastern and Southeastern Asia. One local strain of M. albus distributed in the Jianghan Plain of China has been subjected to a selection breeding program because of its preferred body color and superiority of growth and fecundity. Some members of the genus Monopterus have been reclassified into other genera recently. These classifications require further phylogenetic analyses. In this study, the complete mitochondrial genomes of the breeds of M. albus were decoded using both PacBio and Illumina sequencing technologies, then phylogenetic analyses were carried out, including sampling of M. albus at five different sites and 14 species of Synbranchiformes with complete mitochondrial genomes. The total length of the mitogenome is 16,621 bp, which is one nucleotide shorter than that of four mitogenomes of M. albus sampled from four provinces in China, as well as one with an unknown sampling site. The gene content, gene order, and overall base compositions are almost identical to the five reported ones. The results of maximum likelihood (ML) and Bayesian inference analyses of the complete mitochondrial genome and 13 protein-coding genes (PCGs) were consistent. The phylogenetic trees indicated that the selecting breed formed the deepest branch in the clade of all Asian swamp eels, confirmed the phylogenetic relationships of four genera of the family Synbranchidae, also providing systematic phylogenetic relationships for the order Synbranchiformes. The divergence time analyses showed that all Asian swamp eels diverged about 0.49 million years ago (MYA) and their common ancestor split from other species about 45.96 MYA in the middle of the Miocene epoch. Altogether, the complete mitogenome of this breed of M. albus would serve as an important dataset for germplasm identification and breeding programs for this species, in addition to providing great help in identifying the phylogenetic relationships of the order Synbranchiformes.

Population Genetic Structure of the Invasive Spotted Alfalfa Aphid Therioaphis trifolii (Hemiptera: Aphididae) in China Inferred From Complete Mitochondrial Genomes

Biological invasions represent a natural rapid evolutionary process in which invasive species may present a major threat to biodiversity and ecosystem integrity. Analyzing the genetic structure and demographic history of invaded populations is critical for the effective management of invasive species. The spotted alfalfa aphid (SAA) Therioaphis trifolii is indigenous in the Mediterranean region of Europe and Africa and has invaded China, causing severe damages to the alfalfa industry. However, little is known about its genetic structure and invasion history. In this study, we obtained 167 complete mitochondrial genome sequences from 23 SAA populations across China based on high-throughput sequencing and performed population genetic and phylogenomic analyses. High haplotype diversity and low nucleotide diversity were found in SAA populations in China with distinct genetic structures, i.e., all populations diverged into three phylogenetic lineages. Demographic history analyses showed a recent expansion of the SAA population, consistent with the recent invasion history. Our study indicated that SAA may have invaded through multiple introduction events during commercial trades of alfalfa, although this needs further validation by nuclear markers.