Project description:Insecta s. str. (=Ectognatha), comprise the largest and most diversified group of living organisms, accounting for roughly half of the biodiversity on Earth. Understanding insect relationships and the specific time intervals for their episodes of radiation and extinction are critical to any comprehensive perspective on evolutionary events. Although some deeper nodes have been resolved congruently, the complete evolution of insects has remained obscure due to the lack of direct fossil evidence. Besides, various evolutionary phases of insects and the corresponding driving forces of diversification remain to be recognized. In this study, a comprehensive sample of all insect orders was used to reconstruct their phylogenetic relationships and estimate deep divergences. The phylogenetic relationships of insect orders were congruently recovered by Bayesian inference and maximum likelihood analyses. A complete timescale of divergences based on an uncorrelated log-normal relaxed clock model was established among all lineages of winged insects. The inferred timescale for various nodes are congruent with major historical events including the increase of atmospheric oxygen in the Late Silurian and earliest Devonian, the radiation of vascular plants in the Devonian, and with the available fossil record of the stem groups to various insect lineages in the Devonian and Carboniferous.
Project description:BACKGROUND: The phylogenetic position of the Protura, traditionally considered the most basal hexapod group, is disputed because it has many unique morphological characters compared with other hexapods. Although mitochondrial genome information has been used extensively in phylogenetic studies, such information is not available for the Protura. This has impeded phylogenetic studies on this taxon, as well as the evolution of the arthropod mitochondrial genome. RESULTS: In this study, the mitochondrial genome of Sinentomon erythranum was sequenced, as the first proturan species to be reported. The genome contains a number of special features that differ from those of other hexapods and arthropods. As a very small arthropod mitochondrial genome, its 14,491 nucleotides encode 37 typical mitochondrial genes. Compared with other metazoan mtDNA, it has the most biased nucleotide composition with T = 52.4%, an extreme and reversed AT-skew of -0.351 and a GC-skew of 0.350. Two tandemly repeated regions occur in the A+T-rich region, and both could form stable stem-loop structures. Eighteen of the 22 tRNAs are greatly reduced in size with truncated secondary structures. The gene order is novel among available arthropod mitochondrial genomes. Rearrangements have involved in not only small tRNA genes, but also PCGs (protein-coding genes) and ribosome RNA genes. A large block of genes has experienced inversion and another nearby block has been reshuffled, which can be explained by the tandem duplication and random loss model. The most remarkable finding is that trnL2(UUR) is not located between cox1 and cox2 as observed in most hexapod and crustacean groups, but is between rrnL and nad1 as in the ancestral arthropod ground pattern. The "cox1-cox2" pattern was further confirmed in three more representative proturan species. The phylogenetic analyses based on the amino acid sequences of 13 mitochondrial PCGs suggest S. erythranum failed to group with other hexapod groups. CONCLUSIONS: The mitochondrial genome of S. erythranum shows many different features from other hexapod and arthropod mitochondrial genomes. It underwent highly divergent evolution. The "cox1-cox2" pattern probably represents the ancestral state for all proturan mitogenomes, and suggests a long evolutionary history for the Protura.
Project description:Two-pronged bristletails (Diplura) are traditionally classified into three major superfamilies: Campodeoidea, Projapygoidea, and Japygoidea. The interrelationships of these three superfamilies and the monophyly of Diplura have been much debated. Few previous studies included Projapygoidea in their phylogenetic considerations, and its position within Diplura still is a puzzle from both morphological and molecular points of view. Until now, no mitochondrial genome has been sequenced for any projapygoid species. To fill in this gap, we determined and annotated the complete mitochondrial genome of Octostigma sinensis (Octostigmatidae, Projapygoidea), and of three more dipluran species, one each from the Campodeidae, Parajapygidae, and Japygidae. All four newly sequenced dipluran mtDNAs encode the same set of genes in the same gene order as shared by most crustaceans and hexapods. Secondary structure truncations have occurred in trnR, trnC, trnS1, and trnS2, and the reduction of transfer RNA D-arms was found to be taxonomically correlated, with Campodeoidea having experienced the most reduction. Partitioned phylogenetic analyses, based on both amino acids and nucleotides of the protein-coding genes plus the ribosomal RNA genes, retrieve significant support for a monophyletic Diplura within Pancrustacea, with Projapygoidea more closely related to Campodeoidea than to Japygoidea. Another key finding is that monophyly of Diplura cannot be recovered unless Projapygoidea is included in the phylogenetic analyses; this explains the dipluran polyphyly found by past mitogenomic studies. Including Projapygoidea increased the sampling density within Diplura and probably helped by breaking up a long-branch-attraction artifact. This finding provides an example of how proper sampling is significant for phylogenetic inference.
Project description:With the great development of sequencing technologies and systematic methods, our understanding of evolutionary relationships at deeper levels within the tree of life has greatly improved over the last decade. However, the current taxonomic methodology is insufficient to describe the growing levels of diversity in both a standardised and general way due to the limitations of using only morphological traits to describe clades. Herein, we propose the idea of a molecular classification based on hierarchical and discrete amino acid characters. Clades are classified based on the results of phylogenetic analyses and described using amino acids with group specificity in phylograms. Practices based on the recently published phylogenomic datasets of insects together with 15 de novo sequenced transcriptomes in this study demonstrate that such a methodology can accommodate various higher ranks of taxonomy. Such an approach has the advantage of describing organisms in a standard and discrete way within a phylogenetic framework, thereby facilitating the recognition of clades from the view of the whole lineage, as indicated by PhyloCode. By combining identification keys and phylogenies, the molecular classification based on hierarchical and discrete characters may greatly boost the progress of integrative taxonomy.
Project description:The aim of this experiment was to compare the transciptome of the fall armyworm (Spodoptera frugiperda) strain SUS (a laboratory insecticide-susceptible standard) with organophosphate (OP) and pyrethroid (PYR) resistant strains were collected in cornfields located in Minas Gerais and Mato Grosso States, Brazil, in 2008 and maintained in the laboratory under selection with chlorpyrifos (at increasing discriminating doses from 100 up to 400 µg of insecticide/g of insect in a topical bioassay) or lambda-cyhalothrin (from 8.4 up to 27 µg of insecticide/g of insect) respectively The custom microarray used in this study was designed using the Agilent eArray platform (Agilent Technologies). A SurePrint HD (8×15k) expression array was designed using the base composition and the best probe methodologies to design sense orientation 60-mer probes with a 3′ bias. The FAW EST database (SPODOBASE) was used as the reference transcriptome (Negre, Hotelier et al. 2006). These sequences are derived from 8 cDNA libraries as follows: Sf1F: Fat body, Sf1H: Hemocyte, Sf1M: Midgut, Sf1P: Pool of various tissues, Sf2H: Immune Challenged hemocytes, Sf2L: Sf21 Cell lines sequences, Sf2M: Xenobiotic Induced Midgut and Sf9L: Sf9 cell lines sequences. All assembled contigs and singlets were kindly sent by the website maintainers. The BLAST2GO software v.2.3.1 (http://www.blast2go.org) was used to annotate the EST database. 60-mer probes were designed for all 7,552 assembled contigs and 5,519 annotated singlets (BlastX), totaling 13,071 sequences. For contigs encoding detoxification enzymes (P450s, GSTs and CEs) three probes were designed. Additional probe groups for 15 control genes were also included. For reference all sequences are included in the zip file with array data. References: Negre, V., T. Hotelier, et al. (2006). "SPODOBASE : an EST database for the lepidopteran crop pest Spodoptera." BMC Bioinformatics 7: 322.