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

Have female twisted-wing parasites (Insecta: Strepsiptera) evolved tolerance traits as response to traumatic penetration?

Traumatic insemination describes an unusual form of mating during which a male penetrates the body wall of its female partner to inject sperm. Females unable to prevent traumatic insemination have been predicted to develop either traits of tolerance or of resistance, both reducing the fitness costs associated with the male-inflicted injury. The evolution of tolerance traits has previously been suggested for the bed bug. Here we present data suggesting that tolerance traits also evolved in females of the twisted-wing parasite species Stylops ovinae and Xenos vesparum. Using micro-indentation experiments and confocal laser scanning microscopy, we found that females of both investigated species possess a uniform resilin-rich integument that is notably thicker at penetration sites than at control sites. As the thickened cuticle does not seem to hamper penetration by males, we hypothesise that thickening of the cuticle resulted in reduced penetration damage and loss of haemolymph and in improved wound sealing. To evaluate the evolutionary relevance of the Stylops-specific paragenital organ and penis shape variation in the context of inter- and intraspecific competition, we conducted attraction and interspecific mating experiments, as well as a geometric-morphometric analysis of S. ovinae and X. vesparum penises. We found that S. ovinae females indeed attract sympatrically distributed congeneric males. However, only conspecific males were able to mate. In contrast, we did not observe any heterospecific male attraction by Xenos females. We therefore hypothesise that the paragenital organ in the genus Stylops represents a prezygotic mating barrier that prevents heterospecific matings.

Xenos yangi sp. nov.: A new twisted-wing parasite species (Strepsiptera, Xenidae) from Gaoligong Mountains, Southwest China

Here we report a new twisted-wing parasite species of the family Xenidae based on both morphological and molecular evidence. By using nearly complete mitogenomes, we confirmed the twisted-wing parasites on two wasps (Vespavelutina and Vespabicolor) (China: Yunnan) as the same species, and associated its neotenic females and alate males. Combining the mitogenomic data (COI) and morphological traits, this species was identified to be a new species of the genus Xenos, namely Xenosyangi Dong, Liu & Li, sp. nov. Detailed descriptions and illustrations are provided for the new species.

Substantial rearrangements, single nucleotide frameshift deletion and low diversity in mitogenome of Wolbachia-infected strepsipteran endoparasitoid in comparison to its tephritid hosts

Insect mitogenome organisation is highly conserved, yet, some insects, especially with parasitic life cycles, have rearranged mitogenomes. Furthermore, intraspecific mitochondrial diversity can be reduced by fitness-affecting bacterial endosymbionts like Wolbachia due to their maternal coinheritance with mitochondria. We have sequenced mitogenomes of the Wolbachia-infected endoparasitoid Dipterophagus daci (Strepsiptera: Halictophagidae) and four of its 22 known tephritid fruit fly host species using total genomic extracts of parasitised flies collected across > 700 km in Australia. This halictophagid mitogenome revealed extensive rearrangements relative to the four fly mitogenomes which exhibited the ancestral insect mitogenome pattern. Compared to the only four available other strepsipteran mitogenomes, the D. daci mitogenome had additional transpositions of one rRNA and two tRNA genes, and a single nucleotide frameshift deletion in nad5 requiring translational frameshifting or, alternatively, resulting in a large protein truncation. Dipterophagus daci displays an almost completely endoparasitic life cycle when compared to Strepsiptera that have maintained the ancestral state of free-living adults. Our results support the hypothesis that the transition to extreme endoparasitism evolved together with increased levels of mitogenome changes. Furthermore, intraspecific mitogenome diversity was substantially smaller in D. daci than the parasitised flies suggesting Wolbachia reduced mitochondrial diversity because of a role in D. daci fitness.

The mitochondrial genome of one 'twisted-wing parasite' Xenos cf. moutoni (Insecta, Strepsiptera, Xenidae) from Gaoligong Mountains, Southwest of China

The nearly complete mitochondrial genome (mitogenome) of Xenos cf. moutoni, one twisted-wing parasite on wasp Vespa velutina from Southwest of China, is described in this study. The total length of this mitogenome is 16,717 bp, containing 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs) and an incomplete A + T-rich control region . All of the 13 PCGs are initiated with canonical ATN (N represents A, T, G, C) as start codons; 8 PCGs are terminated with a complete typical stop codon TAA, and the remaining five PCGs (cox2, cox3, nad3, nad4 and nad5) have an incomplete stop codon with just a T. The phylogenetic analysis based on the nucleotide sequences of PCGs and rRNAs indicates that Xenos cf. moutoni has a close relationship with Xenos vesparum, confirming its placement in the family Xenidae.

Structure, gene order, and nucleotide composition of mitochondrial genomes in parasitic lice from Amblycera

Parasitic lice have unique mitochondrial (mt) genomes characterized by rearranged gene orders, variable genome structures, and less AT content compared to most other insects. However, relatively little is known about the mt genomes of Amblycera, the suborder sister to all other parasitic lice. Comparing among nine different genera (including representative of all seven families), we show that Amblycera have variable and highly rearranged mt genomes. Some genera have fragmented genomes that vary considerably in length, whereas others have a single mt chromosome. Notably, these genomes are more AT-biased than most other lice. We also recover genus-level phylogenetic relationships among Amblycera that are consistent with those reported from large nuclear datasets, indicating that mt sequences are reliable for reconstructing evolutionary relationships in Amblycera. However, gene order data cannot reliably recover these same relationships. Overall, our results suggest that the mt genomes of lice, already know to be distinctive, are even more variable than previously thought.

Characteristics of the complete mitochondrial genome of Suhpalacsa longialata (Neuroptera, Ascalaphidae) and its phylogenetic implications

The owlflies (Family Ascalaphidae) belong to the Neuroptera but are often mistaken as dragonflies because of morphological characters. To date, only three mitochondrial genomes of Ascalaphidae, namely Libelloides macaronius; Ascaloptynx appendiculatus; Ascalohybris subjacens, are published in GenBank, meaning that they are greatly under-represented in comparison with the 430 described species reported in this family. In this study, we sequenced and described the complete mitochondrial genome of Suhpalacsa longialata (Neuroptera, Ascalaphidae). The total length of the S. longialata mitogenome was 15,911 bp, which is the longest known to date among the available family members of Ascalaphidae. However, the size of each gene was similar to the other three Ascalaphidae species. The S. longialata mitogenome included a transposition of tRNACys and tRNATrp genes and formed an unusual gene arrangement tRNACys-tRNATrp-tRNATyr (CWY). It is likely that the transposition occurred by a duplication of both genes followed by random loss of partial duplicated genes. The nucleotide composition of the S. longialata mitogenome was as follows: A = 41.0%, T = 33.8%, C = 15.5%, G = 9.7%. Both Bayesian inference and ML analyses strongly supported S. longialata as a sister clade to (Ascalohybris subjacens + L. macaronius), and indicated that Ascalaphidae is not monophyletic.

The first mitochondrial genome from Scopuridae (Insecta: Plecoptera) reveals structural features and phylogenetic implications

This study determined the first complete mitochondrial genome (mitogenome) of a stonefly, Scopura longa (Plecoptera: Scopuridae), and reconstructed a phylogeny based on two datasets of mitogenomes in eighteen available stoneflies to examine the relationships among Plecoptera. The complete mitogenome of S. longa is a circular molecule of 15,798bp in size. It contains 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs) and a control region (CR). Most PCGs used standard ATN start codons and TAN stop codons. All tRNAs could be folded as typical cloverleaf secondary structures except tRNA^Ser(AGN), with the dihydrouridine (DHU) arm missing. Tandem repeat regions, two potential stem-loop (SL) structures, Poly T structures and G+C-rich regions are detected in the control region. Finally, the phylogenetic relationships among the families within the Arctoperlaria were reconstructed. The topological structures of the two trees were almost identical. The present phylogenetic analysis shows that S. longa belongs to the infraorder Euholognatha. The monophyly of each family is generally well supported based on nucleotide sequences. The Pteronarcyidae is sister to ((Peltoperlidae+Styloperlidae)+(Perlidae+(Perlodidae+Chloroperlidae))).

The first mitochondrial genomes of antlion (Neuroptera: Myrmeleontidae) and split-footed lacewing (Neuroptera: Nymphidae), with phylogenetic implications of Myrmeleontiformia

In the holometabolous insect order Neuroptera (lacewings), the cosmopolitan Myrmeleontidae (antlions) are the most species-rich family, while the closely related Nymphidae (split-footed lacewings) are a small endemic family from the Australian-Malesian region. Both families belong to the suborder Myrmeleontiformia, within which controversial hypotheses on the interfamilial phylogenetic relationships exist. Herein, we describe the complete mitochondrial (mt) genomes of an antlion (Myrmeleon immanis Walker, 1853) and a split-footed lacewing (Nymphes myrmeleonoides Leach, 1814), representing the first mt genomes for both families. These mt genomes are relatively small (respectively composed of 15,799 and 15,713 bp) compared to other lacewing mt genomes, and comprise 37 genes (13 protein coding genes, 22 tRNA genes and two rRNA genes). The arrangement of these two mt genomes is the same as in most derived Neuroptera mt genomes previously sequenced, specifically with a translocation of trnC. The start codons of all PCGs are started by ATN, with an exception of cox1, which is ACG in the M. immanis mt genome and TCG in N. myrmeleonoides. All tRNA genes have a typical clover-leaf structure of mitochondrial tRNA, with the exception of trnS1(AGN). The secondary structures of rrnL and rrnS are similar with those proposed insects and the domain I contains nine helices rather than eight helices, which is common within Neuroptera. A phylogenetic analysis based on the mt genomic data for all Neuropterida sequenced thus far, supports the monophyly of Myrmeleontiformia and the sister relationship between Ascalaphidae and Myrmeleontidae.

Complete mitochondrial genome sequences of two parasitic/commensal nemerteans, Gononemertes parasita and Nemertopsis tetraclitophila (Nemertea: Hoplonemertea)

BACKGROUND

Most nemerteans (phylum Nemertea) are free-living, but about 50 species are known to be firmly associated with other marine invertebrates. For example, Gononemertes parasita is associated with ascidians, and Nemertopsis tetraclitophila with barnacles. There are 12 complete or near-complete mitochondrial genome (mitogenome) sequences of nemerteans available in GenBank, but no mitogenomes of none free-living nemerteans have been determined so far. In the present paper complete mitogenomes of the above two parasitic/commensal nemerteans are reported.

METHODS

The complete mitochondrial genomes (mitogenome) of G. parasita and N. tetraclitophila were amplified by conventional and long PCR. Phylogenetic analyses of maximum likelihood (ML) and Bayesian inference (BI) were performed with both concatenated nucleotide and amino acid sequences.

RESULTS

Complete mitogenomes of G. parasita and N. tetraclitophila are 14742 bp and 14597 bp in size, respectively, which are within the range of published Hoplonemertea mitogenomes. Their gene orders are identical to that of published Hoplonemertea mitogenomes, but different from those of Palaeo- and Heteronemertea species. All the coding genes, as well as major non-coding regions (mNCRs), are AT rich, which is especially pronounced at the third codon position. The AT/GC skew pattern of the coding strand is the same among nemertean mitogenomes, but is variable in the mNCRs. Some slight differences are found between mitogenomes of the present species and other hoplonemerteans: in G. parasita the mNCR is biased toward T and C (contrary to other hoplonemerteans) and the rrnS gene has a unique 58-bp insertion at the 5' end; in N. tetraclitophila the nad3 gene starts with the ATT codon (ATG in other hoplonemerteans). Phylogenetic analyses of the nucleotide and amino acid datasets show early divergent positions of G. parasita and N. tetraclitophila within the analyzed Distromatonemertea species, and provide strong support for the close relationship between Hoplonemertea and Heteronemertea.

CONCLUSION

Gene order is highly conserved within the order Monostilifera, particularly within the Distromatonemertea, and the special lifestyle of G. parasita and N. tetraclitophila does not bring significant variations to the overall structures of their mitogenomes in comparison with free-living hoplonemerteans.

Insect mitochondrial genomics: implications for evolution and phylogeny

The mitochondrial (mt) genome is, to date, the most extensively studied genomic system in insects, outnumbering nuclear genomes tenfold and representing all orders versus very few. Phylogenomic analysis methods have been tested extensively, identifying compositional bias and rate variation, both within and between lineages, as the principal issues confronting accurate analyses. Major studies at both inter- and intraordinal levels have contributed to our understanding of phylogenetic relationships within many groups. Genome rearrangements are an additional data type for defining relationships, with rearrangement synapomorphies identified across multiple orders and at many different taxonomic levels. Hymenoptera and Psocodea have greatly elevated rates of rearrangement offering both opportunities and pitfalls for identifying rearrangement synapomorphies in each group. Finally, insects are model systems for studying aberrant mt genomes, including truncated tRNAs and multichromosomal genomes. Greater integration of nuclear and mt genomic studies is necessary to further our understanding of insect genomic evolution.

Insect phylogenomics: exploring the source of incongruence using new transcriptomic data

The evolution of the diverse insect lineages is one of the most fascinating issues in evolutionary biology. Despite extensive research in this area, the resolution of insect phylogeny especially of interordinal relationships has turned out to be still a great challenge. One of the challenges for insect systematics is the radiation of the polyneopteran lineages with several contradictory and/or unresolved relationships. Here, we provide the first transcriptomic data for three enigmatic polyneopteran orders (Dermaptera, Plecoptera, and Zoraptera) to clarify one of the most debated issues among higher insect systematics. We applied different approaches to generate 3 data sets comprising 78 species and 1,579 clusters of orthologous genes. Using these three matrices, we explored several key mechanistic problems of phylogenetic reconstruction including missing data, matrix selection, gene and taxa number/choice, and the biological function of the genes. Based on the first phylogenomic approach including these three ambiguous polyneopteran orders, we provide here conclusive support for monophyletic Polyneoptera, contesting the hypothesis of Zoraptera + Paraneoptera and Plecoptera + remaining Neoptera. In addition, we employ various approaches to evaluate data quality and highlight problematic nodes within the Insect Tree that still exist despite our phylogenomic approach. We further show how the support for these nodes or alternative hypotheses might depend on the taxon- and/or gene-sampling.

The architecture and complete sequence of mitochondrial genome of an assassin bug Agriosphodrus dohrni (Hemiptera: Reduviidae)

The 16, 470 bp nucleotide sequence of the mitochondrial genome (mitogenome) of an assassin bug from the reduviid subfamily Harpactorinae, Agriosphodrus dohrni, has been revealed. The entire genome encodes for two ribosomal RNA genes (rrnL and rrnS), 22 transfer RNA (tRNA) genes, 13 protein-coding genes, and a control region. The nucleotide composition is biased toward adenine and thymine (A+T = 72.2%). Comparative analysis with two other reduviid species Triatoma dimidiata and Valentia hoffmanni, exhibited highly conserved genome architectures including genome contents, gene order, nucleotide composition, codon usage, amino acid composition, as well as genome asymmetry. All protein-coding genes use standard mitochondrial initiation codons (methionine and isoleucine), except that nad1 starts with GTG. All tRNAs have the classic clover-leaf structure, except that the dihydrouridine (DHU) arm of tRNA(Ser(AGN)) forms a simple loop. Secondary structure comparisons of the two mitochondrial ribosomal subunits among sequenced assassin bugs show that the sequence and structure of rrnL is more conservative than that of rrnS. The presence of structural elements in the control region is also discussed, with emphasis on their implications in the regulation of replication and/or transcription of the reduviid mitogenome. The phylogenetic analyses indicated that within Reduviidae, Harpactorinae is a sister group to the Salyavatinae + Triatominae clade.

The first molecular phylogeny of Strepsiptera (Insecta) reveals an early burst of molecular evolution correlated with the transition to endoparasitism

A comprehensive model of evolution requires an understanding of the relationship between selection at the molecular and phenotypic level. We investigate this in Strepsiptera, an order of endoparasitic insects whose evolutionary biology is poorly studied. We present the first molecular phylogeny of Strepsiptera, and use this as a framework to investigate the association between parasitism and molecular evolution. We find evidence of a significant burst in the rate of molecular evolution in the early history of Strepsiptera. The evolution of morphological traits linked to parasitism is significantly correlated with the pattern in molecular rate. The correlated burst in genotypic-phenotypic evolution precedes the main phase of strepsipteran diversification, which is characterised by the return to a low and even molecular rate, and a period of relative morphological stability. These findings suggest that the transition to endoparasitism led to relaxation of selective constraint in the strepsipteran genome. Our results indicate that a parasitic lifestyle can affect the rate of molecular evolution, although other causal life-history traits correlated with parasitism may also play an important role.

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.