Analysis of the RNA virome of basal hexapods.

The diversity and evolution of RNA viruses has been well studied in arthropods and especially in insects. However, the diversity of RNA viruses in the basal hexapods has not been analysed yet. To better understand their diversity, evolutionary histories and genome organizations, we searched for RNA viruses in transcriptome and genome databases of basal hexapods. We discovered  40 novel RNA viruses, some of which are also present as endogenous viral elements derived from RNA viruses. Here, we demonstrated that basal hexapods host 14 RNA viral clades that have been recently identified in invertebrates. The following RNA viral clades are associated with basal hexapods: Reo, Partiti-Picobirna, Toti-Chryso, Mono-Chu, Bunya-Arena, Orthomyxo, Qinvirus, Picorna-Calici, Hepe-Virga, Narna-Levi, Tombus-Noda, Luteo-Sobemo, Permutotetra and Flavi. We have found representatives of the nine RNA viral clades that are present as endogenous genomic copies in the genomes of Machilis (Monocondylia) and Catajapyx (Diplura). Our study provided a first insight into the diversity of RNA viruses in basal hexapods and demonstrated that the basal hexapods possess quite high diversity of RNA viral clades.

The mitochondrial genome of the springtail Bourletiella arvalis (Symphypleona, Collembola).

The complete mitochondrial genome of the springtail Bourletiella arvalis (Fitch, 1863) is herein described and applied to a Bayesian phylogenetic analysis, inclusive of all the Collembola mitochondrial DNAs sequenced so far. The gene content and order, as well as the nucleotide composition, conform with the well-known features of hexapods' mitochondrial genomes. The phylogenetic analysis supports the monophyly of Collembola, Poduromorpha, Entomobryomorpha and Symphypleona. However, no mtDNA from Neelipleona is available to date, therefore limiting the application of mitochondrial genomes to further investigate springtail systematics.

Going Deeper into High and Low Phylogenetic Relationships of Protura.

Proturans are small, wingless, soil-dwelling arthropods, generally associated with the early diversification of Hexapoda. Their bizarre morphology, together with conflicting results of molecular studies, has nevertheless made their classification ambiguous. Furthermore, their limited dispersal capability (due to the primarily absence of wings) and their euedaphic lifestyle have greatly complicated species-level identification. Mitochondrial and nuclear markers have been applied herein to investigate and summarize proturan systematics at different hierarchical levels. Two new mitochondrial genomes are described and included in a phylum-level phylogenetic analysis, but the position of Protura could not be resolved with confidence due to an accelerated rate of substitution and extensive gene rearrangements. Mitochondrial and nuclear loci were also applied in order to revise the intra-class systematics, recovering three proturan orders and most of the families/subfamilies included as monophyletic, with the exception of the subfamily Acerentominae. At the species level, most morphologically described species were confirmed using molecular markers, with some exceptions, and the advantages of including nuclear, as well as mitochondrial, markers and morphology are discussed. At all levels, an enlarged taxon sampling and the integration of data from different sources may be of significant help in solving open questions that still persist on the evolutionary history of Protura.

The mitogenome of the jumping bristletail Trigoniophthalmus alternatus (Insecta, Microcoryphia) and the phylogeny of insect early-divergent lineages.

The complete mitochondrial genome of the machilid Trigoniophthalmus alternatus (Silvestri 1904) is herein described and applied to phylogenetic analyses, inclusive of the most early-divergent lineages of hexapods. Both gene content and order generally conform with the organization of the arthropods' mitochondrial genome. One gene translocation involving trnA is the autapomorphic character observed in this species. Another peculiar molecular feature is the long size of the A + T-rich region, due to the occurrence of repeat units. The phylogenetic analyses support the typical placement, along the hexapods' tree, of Ectognatha, Monocondylia and Dicondylia, with Diplura as the adelphotaxon of all true insects.

Soluble proteins of chemical communication: an overview across arthropods.

Detection of chemical signals both in insects and in vertebrates is mediated by soluble proteins, highly concentrated in olfactory organs, which bind semiochemicals and activate, with still largely unknown mechanisms, specific chemoreceptors. The same proteins are often found in structures where pheromones are synthesized and released, where they likely perform a second role in solubilizing and delivering chemical messengers in the environment. A single class of soluble polypeptides, called Odorant-Binding Proteins (OBPs) is known in vertebrates, while two have been identified in insects, OBPs and CSPs (Chemosensory Proteins). Despite their common name, OBPs of vertebrates bear no structural similarity with those of insects. We observed that in arthropods OBPs are strictly limited to insects, while a few members of the CSP family have been found in crustacean and other arthropods, where however, based on their very limited numbers, a function in chemical communication seems unlikely. The question we address in this review is whether another class of soluble proteins may have been adopted by other arthropods to perform the role of OBPs and CSPs in insects. We propose that lipid-transporter proteins of the Niemann-Pick type C2 family could represent likely candidates and report the results of an analysis of their sequences in representative species of different arthropods.