The mitochondrial genome of Protohermes concolorus Yang et Yang 1988 (Insecta: Megaloptera: Corydalidae)

Increasing 28 mitogenomes of Ephemeroptera, Odonata and Plecoptera support the Chiastomyaria hypothesis with three different outgroup combinations

BACKGROUND

The phylogenetic relationships of Odonata (dragonflies and damselflies) and Ephemeroptera (mayflies) remain unresolved. Different researchers have supported one of three hypotheses (Palaeoptera, Chiastomyaria or Metapterygota) based on data from different morphological characters and molecular markers, sometimes even re-assessing the same transcriptomes or mitochondrial genomes. The appropriate choice of outgroups and more taxon sampling is thought to eliminate artificial phylogenetic relationships and obtain an accurate phylogeny. Hence, in the current study, we sequenced 28 mt genomes from Ephemeroptera, Odonata and Plecoptera to further investigate phylogenetic relationships, the probability of each of the three hypotheses, and to examine mt gene arrangements in these species. We selected three different combinations of outgroups to analyze how outgroup choice affected the phylogenetic relationships of Odonata and Ephemeroptera.

METHODS

Mitochondrial genomes from 28 species of mayflies, dragonflies, damselflies and stoneflies were sequenced. We used Bayesian inference (BI) and Maximum likelihood (ML) analyses for each dataset to reconstruct an accurate phylogeny of these winged insect orders. The effect of outgroup choice was assessed by separate analyses using three outgroups combinations: (a) four bristletails and three silverfish as outgroups, (b) five bristletails and three silverfish as outgroups, or (c) five diplurans as outgroups.

RESULTS

Among these sequenced mitogenomes we found the gene arrangement IMQM in Heptageniidae (Ephemeroptera), and an inverted and translocated tRNA-Ile between the 12S RNA gene and the control region in Ephemerellidae (Ephemeroptera). The IMQM gene arrangement in Heptageniidae (Ephemeroptera) can be explained via the tandem-duplication and random loss model, and the transposition and inversion of tRNA-Ile genes in Ephemerellidae can be explained through the recombination and tandem duplication-random loss (TDRL) model. Our phylogenetic analysis strongly supported the Chiastomyaria hypothesis in three different outgroup combinations in BI analyses. The results also show that suitable outgroups are very important to determining phylogenetic relationships in the rapid evolution of insects especially among Ephemeroptera and Odonata. The mt genome is a suitable marker to investigate the phylogeny of inter-order and inter-family relationships of insects but outgroup choice is very important for deriving these relationships among winged insects. Hence, we must carefully choose the correct outgroup in order to discuss the relationships of Ephemeroptera and Odonata.

Phylogenetic relationships among tribes of the green lacewing subfamily Chrysopinae recovered based on mitochondrial phylogenomics

Chrysopidae (green lacewings) is the second largest family in Neuroptera, and it includes medium-size lacewings largely recognized by the presence of golden-colored eyes, bright green bodies and delicate wings with dense venation patterns. The subfamily Chrysopinae includes 97% of the species diversity in the family and it is currently divided into four tribes: Ankylopterygini, Belonopterygini, Chrysopini and Leucochrysini. Here we sequenced and annotated the nearly complete mitochondrial genomes of four species of each these tribes: Abachrysa eureka, Italochrysa insignis, Leucochrysa pretiosa, Parankyloteryx sp. We then reconstructed the phylogenetic relationships with estimated divergence times among tribes of Chrysopinae based on the mt genomic data. Our results suggest that Chrysopinae sans Nothancyla verreauxi evolved as two reciprocally monophyletic lineages formed by stem members of the tribes Leucochrysini plus Belonopterygini on one hand, and the stem members of Ankylopterygini plus Chrysopini on the other. Our estimations of divergence times place the diversification of stem Chrysopinae into the extant tribes during the Middle Jurassic to Late Cretaceous. The relatively young ages previously estimated for the green lacewing divergences were probably underestimated due to false inferences of homology between non-sister taxa that are later correctly identified as homoplasy after more taxa are added.

Comparative mitogenomic analysis reveals sexual dimorphism in a rare Montane lacewing (Insecta: Neuroptera: Ithonidae)

Rapisma McLachlan, 1866 (Neuroptera: Ithonidae) is a rarely encountered genus of lacewings found inmontane tropical or subtropical forests in Oriental Asia. In Xizang Autonomous Region (Tibet) of China there are two sympatrically distributed species of Rapisma, i.e. Rapisma xizangense Yang, 1993 and Rapisma zayuanum Yang, 1993, in which R. xizangense is only known as male and has dull brownish body and wing coloration, while R. zayuanum is only known as female and has bright green body and wing coloration. In order to clarify the relationship between these two species, we determined the complete mitochondrial (mt) genomes of R. xizangense and R. zayuanum for the first time. The mt genomes are 15,961 and 15,984 bp in size, respectively, and comprised 37 genes (13 protein coding genes, 22 tRNA genes and 2 rRNA genes). A major noncoding (control) region was 1,167 bp in R. xizangense and 1,193 bp in R. zayuanum with structural organizations simpler than that reported in other Neuropterida species, notably lacking conserved blocks or long tandem repeats. Besides similar mitogenomic structure, the genetic distance between R. xizangense and R. zayuanum based on two rRNAs and 13 protein coding genes (PCGs) as well as the genetic distance between each of these two Tibetan Rapisma species and a Thai Rapisma species (R. cryptunum) based on partial rrnL show that R. xizangense and R. zayuanum are most likely conspecific. Thus, R. zayuanumsyn. nov. is herein treated as a junior synonym of R. xizangense. The present finding represents a rare example of distinct sexual dimorphism in lacewings. This comparative mitogenomic analysis sheds new light on the identification of rare species with sexual dimorphism and the biology of Neuroptera.

Ancestral gene organization in the mitochondrial genome of Thyridosmylus langii (McLachlan, 1870) (Neuroptera: Osmylidae) and implications for lacewing evolution

The first complete mitochondrial genome of the lacewing family Osmylidae (Thyridosmylus langii (McLachlan, 1870)) (Neuroptera) was sequenced in this study. The genome is a circular molecule of 16,221 bp containing the typical 37 genes but is arranged in the same order as that of the putative ancestor of hexapod and lacks translocation of trnC as shared by all previously sequenced neuropteran mtDNAs. This reveals that trnC translocation does not represent an organizational synapomorphy in the mitochondrion for the entire Neuroptera clade. Comparative analysis of neuropteran tRNA genes reveals a relatively slow and conserved evolution of the mitochondrion throughout the order. Secondary structure models of the ribosomal RNA genes of T. langii largely agree with those proposed for other insect orders. Nevertheless, domain I of T. langii rrnL is consisted of nine helices rather than eight helices which is typical for neuropteran rrnL. Protein-coding genes have typical mitochondrial start codons, with the exception of COI, which uses the TCG start codon also found in Ithonidae and Chrysopidae. Like other neuropteran insects, the control region is the most AT-rich region and comparatively simple, with little evidence of conserved blocks or long tandem repeats. Considering the issues of base-compositional and branch length heterogeneity, we used a range of phylogenetic approaches to recover neuropteridan relationships and explored the effect of method choice on recovery of monophyly of Neuropterida: ((Neuroptera + Megaloptera) + Raphidioptera). The monophyly of Neuroptera and the more basal position of Osmylidae were also recovered by different datasets and phylogenetic methods.

The first mitochondrial genome for the fishfly subfamily Chauliodinae and implications for the higher phylogeny of Megaloptera

Megaloptera are a basal holometabolous insect order with larvae exclusively predacious and aquatic. The evolutionary history of Megaloptera attracts great interest because of its antiquity and important systematic status in Holometabola. However, due to the difficulties identifying morphological apomorphies for the group, controversial hypotheses on the monophyly and higher phylogeny of Megaloptera have been proposed. Herein, we describe the complete mitochondrial (mt) genome of a fishfly species, Neochauliodes punctatolosus Liu & Yang, 2006, representing the first mt genome of the subfamily Chauliodinae. A phylogenomic analysis was carried out based on the mt genomic sequences of 13 mt protein-coding genes (PCGs) and two rRNA genes of nine Neuropterida species, comprising all three orders of Neuropterida and all families and subfamilies of Megaloptera. Both maximum likelihood and Bayesian inference analyses highly support the monophyly of Megaloptera, which was recovered as the sister of Neuroptera. Within Megaloptera, the sister relationship between Corydalinae and Chauliodinae was corroborated. The divergence time estimation suggests that stem lineage of Neuropterida and Coleoptera separated in the Early Permian. The interordinal divergence within Neuropterida might have occurred in the Late Permian.

The complete mitochondrial genome of the Asiatic cavity-nesting honeybee Apis cerana (Hymenoptera: Apidae)

In the present study, we determined the complete mitochondrial DNA (mtDNA) sequence of Apis cerana, the Asiatic cavity-nesting honeybee. We present here an analysis of features of its gene content and genome organization in comparison with Apis mellifera to assess the variation within the genus Apis and among main groups of Hymenoptera. The size of the entire mt genome of A. cerana is 15,895 bp, containing 2 ribosomal RNA genes, 13 protein-coding genes, 22 transfer RNA (tRNA) genes and one control region. These genes are transcribed from both strands and have a nucleotide composition high in A and T. The contents of A+T of the complete genomes are 83.96% for A. cerana. The AT bias had a significant effect on both the codon usage pattern and amino acid composition of proteins. There are a total of 3672 codons in all 13 protein-coding genes, excluding termination codons. The most frequently used amino acid is Leu (15.52%), followed by Ile (12.85%), Phe (10.10%), Ser (9.15%) and Met (8.96%). Intergenic regions in the mt genome of A. cerana are 705 bp in total. The order and orientation of the gene arrangement pattern is identical to that of A. mellifera, except for the position of the tRNA-Ser(AGN) gene. Phylogenetic analyses using concatenated amino acid sequences of 13 protein-coding genes, with three different computational algorithms (NJ, MP and ML), all revealed two distinct groups with high statistical support, indicating that A. cerana and A. mellifera are two separate species, consistent with results of previous morphological and molecular studies. The complete mtDNA sequence of A. cerana provides additional genetic markers for studying population genetics, systematics and phylogeographics of honeybees.

The complete mitochondrial genome of the Asiatic cavity-nesting honeybee Apis cerana (Hymenoptera: Apidae)

In the present study, we determined the complete mitochondrial DNA (mtDNA) sequence of Apis cerana, the Asiatic cavity-nesting honeybee. We present here an analysis of features of its gene content and genome organization in comparison with Apis mellifera to assess the variation within the genus Apis and among main groups of Hymenoptera. The size of the entire mt genome of A. cerana is 15,895 bp, containing 2 ribosomal RNA genes, 13 protein-coding genes, 22 transfer RNA (tRNA) genes and one control region. These genes are transcribed from both strands and have a nucleotide composition high in A and T. The contents of A+T of the complete genomes are 83.96% for A. cerana. The AT bias had a significant effect on both the codon usage pattern and amino acid composition of proteins. There are a total of 3672 codons in all 13 protein-coding genes, excluding termination codons. The most frequently used amino acid is Leu (15.52%), followed by Ile (12.85%), Phe (10.10%), Ser (9.15%) and Met (8.96%). Intergenic regions in the mt genome of A. cerana are 705 bp in total. The order and orientation of the gene arrangement pattern is identical to that of A. mellifera, except for the position of the tRNA-Ser(AGN) gene. Phylogenetic analyses using concatenated amino acid sequences of 13 protein-coding genes, with three different computational algorithms (NJ, MP and ML), all revealed two distinct groups with high statistical support, indicating that A. cerana and A. mellifera are two separate species, consistent with results of previous morphological and molecular studies. The complete mtDNA sequence of A. cerana provides additional genetic markers for studying population genetics, systematics and phylogeographics of honeybees.

The mitochondrial genome of the ascalaphid owlfly Libelloides macaronius and comparative evolutionary mitochondriomics of neuropterid insects

Background

The insect order Neuroptera encompasses more than 5,700 described species. To date, only three neuropteran mitochondrial genomes have been fully and one partly sequenced. Current knowledge on neuropteran mitochondrial genomes is limited, and new data are strongly required. In the present work, the mitochondrial genome of the ascalaphid owlfly Libelloides macaronius is described and compared with the known neuropterid mitochondrial genomes: Megaloptera, Neuroptera and Raphidioptera. These analyses are further extended to other endopterygotan orders.

Results

The mitochondrial genome of L. macaronius is a circular molecule 15,890 bp long. It includes the entire set of 37 genes usually present in animal mitochondrial genomes. The gene order of this newly sequenced genome is unique among Neuroptera and differs from the ancestral type of insects in the translocation of trnC. The L. macaronius genome shows the lowest A+T content (74.50%) among known neuropterid genomes. Protein-coding genes possess the typical mitochondrial start codons, except for cox1, which has an unusual ACG. Comparisons among endopterygotan mitochondrial genomes showed that A+T content and AT/GC-skews exhibit a broad range of variation among 84 analyzed taxa. Comparative analyses showed that neuropterid mitochondrial protein-coding genes experienced complex evolutionary histories, involving features ranging from codon usage to rate of substitution, that make them potential markers for population genetics/phylogenetics studies at different taxonomic ranks. The 22 tRNAs show variable substitution patterns in Neuropterida, with higher sequence conservation in genes located on the α strand. Inferred secondary structures for neuropterid rrnS and rrnL genes largely agree with those known for other insects. For the first time, a model is provided for domain I of an insect rrnL. The control region in Neuropterida, as in other insects, is fast-evolving genomic region, characterized by AT-rich motifs.

Conclusions

The new genome shares many features with known neuropteran genomes but differs in its low A+T content. Comparative analysis of neuropterid mitochondrial genes showed that they experienced distinct evolutionary patterns. Both tRNA families and ribosomal RNAs show composite substitution pathways. The neuropterid mitochondrial genome is characterized by a complex evolutionary history.

The complete mitochondrial genomes of three cestode species of Taenia infecting animals and humans

Mitochondrial (mt) genome sequences provide useful markers for investigating population genetic structures, systematics and phylogenetics of organisms. Although Taenia multiceps, T. hydatigena, and T. taeniaeformis are common taeniid tapeworms of ruminants, pigs, dogs, or cats, causing significant economic losses, no published study on their mt genomes is available. The complete mt genomes of T. multiceps, T. hydatigena, and T. taeniaeformis were amplified in two overlapping fragments and then sequenced. The sizes of the entire mt genome were 13700 bp for T. multiceps, 13489 bp for T. hydatigena, and 13647 bp for T. taeniaeformis. Each of the three genomes contains 36 genes, consisting of 12 genes for proteins, 2 genes for rRNA, and 22 genes for tRNA, which are the same as the mt genomes of all other cestode species studied to date. All genes are transcribed in the same direction and have a nucleotide composition high in A and T. The contents of A+T of the complete genomes are 71.3% for T. multiceps, 70.8% for T. hydatigena, and 73.0% for T. taeniaeformis. The AT bias had a significant effect on both the codon usage pattern and amino acid composition of proteins. T. multiceps and T. hydatigena had two noncoding regions, but T. taeniaeformis had only one. Phylogenetic analyses based on concatenated amino acid sequences of 12 protein-coding genes revealed that T. multiceps, T. hydatigena, and T. taeniaeformis were more closely related to the other members of the Taenia genus, consistent with results of previous morphological and molecular studies. The present study determined the complete mt genome sequences for three Taenia species of animal and human health significance, providing useful markers for studying the systematics, population genetics, and molecular epidemiology of these cestode parasites of animals and humans.

Complete mitochondrial genome of the Chinese spiny lobster Panulirus stimpsoni (Crustacea: Decapoda): genome characterization and phylogenetic considerations

The genetics and molecular biology of the commercially important Chinese spiny lobster, Panulirus stimpsoni are little known. Here, we present the complete mitochondrial genome sequence of P. stimpsoni, determined by the long polymerase chain reaction and primer walking sequencing method. The entire genome is 15,677 bp in length, encoding the standard set of 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes. The overall A+T content of the genome is 65.6%, lower than most malacostracan species. The gene order is consistent with the pancrustacean ground pattern. Several conserved elements were identified from P. stimpsoni control region, viz. one [TA(A)]n-block, two GA-blocks and three hairpin structures. However, the position of [TA(A)]n-block and number of hairpin structure are different from those in the congeneric P. japonicus and other decapods. Phylogenetic analyses using the concatenated nucleotide and amino acid sequences of 13 protein-coding genes do not support the monophyly of suborder Pleocyemata, which is in contrast to most morphological and molecular results. However, the position of Palinura and Astacidea is unstable, as represented by the basal or sister branches to other Reptantia species. P. stimpsoni, as the second species of Palinura with complete mitochondrial genome available, will provide important information on both genomics and conservation biology of the group.

The mitochondrial genome of the butterfly Papilio xuthus (Lepidoptera: Papilionidae) and related phylogenetic analyses

The nearly complete mitochondrial genome of the butterfly Papilio xuthus (Lepidoptera: Papilionidae) was sequenced for its nucleotide sequence of 13,964 bp. The genome has a typical gene order identical to other lepidopteran species. All tRNAs showed same stable canonical clover-leaf structure as those of other insects, except for tRNA(Ser) (AGN), in which the dihydrouracil arm (DHU arm) could not form stable stem-loop structure. Anomalous initiation codons have been observed for the cox1 gene, where the ATTACG hexa-nucleotide was believed to be involved in the initiation signaling. Twelve mitochondrial protein-coding gene sequence data were used to infer the phylogenetic relationships among the insect orders. Even though the number of insect orders represented by complete mitochondrial genomes is still limited, several well-established relationships are evident in the phylogenetic analysis of the complete sequences. Monophyly of the Homometabola was not supported in this paper. Phylogenetic analyses of the available species of Bombycoidea, Pyraloidea, Papilionoidea and Tortricidea bolstered the current morphology-based hypothesis that Bombycoidea, Pyraloidea and Papilionoidea are monophyletic (Obtectomera). Bombycoidea (Bombyx mandarina and Antheraea pernyi) and Papilionoidea (P. xuthus and Coreana raphaelis) formed a sister group.

The mitochondrial genome of the 'twisted-wing parasite' Mengenilla australiensis (Insecta, Strepsiptera): a comparative study

BACKGROUND

Strepsiptera are an unusual group of sexually dimorphic, entomophagous parasitoids whose evolutionary origins remain elusive. The lineage leading to Mengenilla australiensis (Family Mengenillidae) is the sister group to all remaining extant strepsipterans. It is unique in that members of this family have retained a less derived condition, where females are free-living from pupation onwards, and are structurally much less simplified. We sequenced almost the entire mitochondrial genome of M. australiensis as an important comparative data point to the already available genome of its distant relative Xenos vesparum (Family Xenidae). This study represents the first in-depth comparative mitochondrial genomic analysis of Strepsiptera.

RESULTS

The partial genome of M. australiensis is presented as a 13421 bp fragment, across which all 13 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes and 18 transfer RNA (tRNA) sequences are identified. Two tRNA translocations disrupt an otherwise ancestral insect mitochondrial genome order. A+T content is measured at 84.3%, C-content is also very skewed. Compared with M. australiensis, codon bias in X. vesparum is more balanced. Interestingly, the size of the protein coding genome is truncated in both strepsipterans, especially in X. vesparum which, uniquely, has 4.3% fewer amino acids than the average holometabolan complement. A revised assessment of mitochondrial rRNA secondary structure based on comparative structural considerations is presented for M. australiensis and X. vesparum.

CONCLUSIONS

The mitochondrial genome of X. vesparum has undergone a series of alterations which are probably related to an extremely derived lifestyle. Although M. australiensis shares some of these attributes; it has retained greater signal from the hypothetical most recent common ancestor (MRCA) of Strepsiptera, inviting the possibility that a shift in the mitochondrial selective environment might be related to the specialization accompanying the evolution of a small, morphologically simplified completely host-dependent lifestyle. These results provide useful insights into the nature of the evolutionary transitions that accompanied the emergence of Strepsiptera, but we emphasize the need for adequate sampling across the order in future investigations concerning the extraordinary developmental and evolutionary origins of this group.

Complete mitochondrial genome of the Asian paddle crab Charybdis japonica (Crustacea: Decapoda: Portunidae): gene rearrangement of the marine brachyurans and phylogenetic considerations of the decapods

Given the commercial and ecological importance of the Asian paddle crab, Charybdis japonica, there is a clearly need for genetic and molecular research on this species. Here, we present the complete mitochondrial genome sequence of C. japonica, determined by the long-polymerase chain reaction and primer walking sequencing method. The entire genome is 15,738 bp in length, encoding a standard set of 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes, plus the putative control region, which is typical for metazoans. The total A+T content of the genome is 69.2%, lower than the other brachyuran crabs except for Callinectes sapidus. The gene order is identical to the published marine brachyurans and differs from the ancestral pancrustacean order by only the position of the tRNA ( His ) gene. Phylogenetic analyses using the concatenated nucleotide and amino acid sequences of 13 protein-coding genes strongly support the monophyly of Dendrobranchiata and Pleocyemata, which is consistent with the previous taxonomic classification. However, the systematic status of Charybdis within subfamily Thalamitinae of family Portunidae is not supported. C. japonica, as the first species of Charybdis with complete mitochondrial genome available, will provide important information on both genomics and molecular ecology of the group.