Cockroaches that lack Blattabacterium endosymbionts: the phylogenetically divergent genus Nocticola

Dating in the Dark: Elevated Substitution Rates in Cave Cockroaches (Blattodea: Nocticolidae) Have Negative Impacts on Molecular Date Estimates

Rates of nucleotide substitution vary substantially across the Tree of Life, with potentially confounding effects on phylogenetic and evolutionary analyses. A large acceleration in mitochondrial substitution rate occurs in the cockroach family Nocticolidae, which predominantly inhabit subterranean environments. To evaluate the impacts of this among-lineage rate heterogeneity on estimates of phylogenetic relationships and evolutionary timescales, we analyzed nuclear ultraconserved elements (UCEs) and mitochondrial genomes from nocticolids and other cockroaches. Substitution rates were substantially elevated in nocticolid lineages compared with other cockroaches, especially in mitochondrial protein-coding genes. This disparity in evolutionary rates is likely to have led to different evolutionary relationships being supported by phylogenetic analyses of mitochondrial genomes and UCE loci. Furthermore, Bayesian dating analyses using relaxed-clock models inferred much deeper divergence times compared with a flexible local clock. Our phylogenetic analysis of UCEs, which is the first genome-scale study to include all 13 major cockroach families, unites Corydiidae and Nocticolidae and places Anaplectidae as the sister lineage to the rest of Blattoidea. We uncover an extraordinary level of genetic divergence in Nocticolidae, including two highly distinct clades that separated ~115 million years ago despite both containing representatives of the genus Nocticola. The results of our study highlight the potential impacts of high among-lineage rate variation on estimates of phylogenetic relationships and evolutionary timescales.

Comparative Transcriptomics of Fat Bodies between Symbiotic and Quasi-Aposymbiotic Adult Females of Blattella germanica with Emphasis on the Metabolic Integration with Its Endosymbiont Blattabacterium and Its Immune System

We explored the metabolic integration of Blattella germanica and its obligate endosymbiont Blattabacterium cuenoti by the transcriptomic analysis of the fat body of quasi-aposymbiotic cockroaches, where the endosymbionts were almost entirely removed with rifampicin. Fat bodies from quasi-aposymbiotic insects displayed large differences in gene expression compared to controls. In quasi-aposymbionts, the metabolism of phenylalanine and tyrosine involved in cuticle sclerotization and pigmentation increased drastically to compensate for the deficiency in the biosynthesis of these amino acids by the endosymbionts. On the other hand, the uricolytic pathway and the biosynthesis of uric acid were severely decreased, probably because the reduced population of endosymbionts was unable to metabolize urea to ammonia. Metabolite transporters that could be involved in the endosymbiosis process were identified. Immune system and antimicrobial peptide (AMP) gene expression was also reduced in quasi-aposymbionts, genes encoding peptidoglycan-recognition proteins, which may provide clues for the maintenance of the symbiotic relationship, as well as three AMP genes whose involvement in the symbiotic relationship will require additional analysis. Finally, a search for AMP-like factors that could be involved in controlling the endosymbiont identified two orphan genes encoding proteins smaller than 200 amino acids underexpressed in quasi-aposymbionts, suggesting a role in the host-endosymbiont relationship.

Exploring Gut Microbial Dynamics and Symbiotic Interaction in Blattella germanica Using Rifampicin

Blattella germanica harbours two cohabiting symbiotic systems: an obligate endosymbiont, Blattabacterium, located inside bacteriocytes and vertically transmitted, which is key in nitrogen metabolism, and abundant and complex gut microbiota acquired horizontally (mainly by coprophagy) that must play an important role in host physiology. In this work, we use rifampicin treatment to deepen the knowledge on the relationship between the host and the two systems. First, we analysed changes in microbiota composition in response to the presence and removal of the antibiotic with and without faeces in one generation. We found that, independently of faeces supply, rifampicin-sensitive bacteria are strongly affected at four days of treatment, and most taxa recover after treatment, although some did not reach control levels. Second, we tried to generate an aposymbiotic population, but individuals that reached the second generation were severely affected and no third generation was possible. Finally, we established a mixed population with quasi-aposymbiotic and control nymphs sharing an environment in a blind experiment. The analysis of the two symbiotic systems in each individual after reaching the adult stage revealed that endosymbiont's load does not affect the composition of the hindgut microbiota, suggesting that there is no interaction between the two symbiotic systems in Blattella germanica.

Symbioses shape feeding niches and diversification across insects

For over 300 million years, insects have relied on symbiotic microbes for nutrition and defence. However, it is unclear whether specific ecological conditions have repeatedly favoured the evolution of symbioses, and how this has influenced insect diversification. Here, using data on 1,850 microbe-insect symbioses across 402 insect families, we found that symbionts have allowed insects to specialize on a range of nutrient-imbalanced diets, including phloem, blood and wood. Across diets, the only limiting nutrient consistently associated with the evolution of obligate symbiosis was B vitamins. The shift to new diets, facilitated by symbionts, had mixed consequences for insect diversification. In some cases, such as herbivory, it resulted in spectacular species proliferation. In other niches, such as strict blood feeding, diversification has been severely constrained. Symbioses therefore appear to solve widespread nutrient deficiencies for insects, but the consequences for insect diversification depend on the feeding niche that is invaded.

Demonstrating the general structure and cell types of the fat body in Blatta orientalis (Oriental Cockroach)

The fat body is a tissue that originates from mesoderm in insects. It consists of several cell types. The basic cell of the fat body is trophocyte. Glycogen, protein and lipid which are required for energy are stored in these cells. Mycetocyte, urocyte, chromotocyte and haemoglobin cells are the other cell types which originate from differentiated trophocytes. Of the cells found in cockroaches, mycetocytes contain an endosymbiont species of bacteria while urocytes are specialized cells for storing and discharging uric acid. Oenocyte, which is not the fat body cell type but associated with epidermis and the fat body cells, is also found in cockroaches. In this research, the fat body distribution was shown for the first time in three selected sections (thorax, beginning and end of abdomen) in all stages of Blatta orientalis (Linnaeus, 1758). In addition, the fat body cell types and distribution were determined by histological, histochemical and ultrastructural studies. As a result, trophocytes, mycetocytes, urocytes of the fat body and oenocytes which are related to the fat body were determined in B. orientalis. Also, it was revealed that the fat body content increased in the selected regions of the stages depending on the development. We hope that these findings will contribute to data about the fat body and give some directions to insecticide studies.

Enhanced Mutation Rate, Relaxed Selection, and the "Domino Effect" are associated with Gene Loss in Blattabacterium, A Cockroach Endosymbiont

Intracellular endosymbionts have reduced genomes that progressively lose genes at a timescale of tens of million years. We previously reported that gene loss rate is linked to mutation rate in Blattabacterium, however, the mechanisms causing gene loss are not yet fully understood. Here, we carried out comparative genomic analyses on the complete genome sequences of a representative set of 67 Blattabacterium strains, with sizes ranging between 511 and 645 kb. We found that 200 of the 566 analyzed protein-coding genes were lost in at least one lineage of Blattabacterium, with the most extreme case being one gene that was lost independently in 24 lineages. We found evidence for three mechanisms influencing gene loss in Blattabacterium. First, gene loss rates were found to increase exponentially with the accumulation of substitutions. Second, genes involved in vitamin and amino acid metabolism experienced relaxed selection in Cryptocercus and Mastotermes, possibly triggered by their vertically inherited gut symbionts. Third, we found evidence of epistatic interactions among genes leading to a "domino effect" of gene loss within pathways. Our results highlight the complexity of the process of genome erosion in an endosymbiont.

Multifunctional cellulase enzymes are ancestral in Polyneoptera

Many hemimetabolous insects produce their own cellulase enzymes from the glycoside hydrolase family 9, first observed in termites and cockroaches. Phasmatodea have multiple cellulases, some of which are multifunctional and can degrade xylan or xyloglucan. To discover when these abilities evolved, we identified cellulases from the Polyneoptera sampled by the 1000 Insect Transcriptome and Evolution (1KITE) project, including all cockroach and termite transcriptomes. We hoped to identify what role enzyme substrate specificities had in the evolution of dietary specification, such as leaf-feeding or wood-feeding. Putative cellulases were identified from the transcriptomes and analysed phylogenetically. All cellulases were amplified from an exemplar set of Polyneoptera species using rapid amplification of cDNA ends PCR and heterologously expressed in an insect cell line, then tested against different polysaccharides for their digestive abilities. We identified several multifunctional xyloglucanolytic enzymes across Polyneoptera, plus a large group of cellulase-like enzymes found in nearly all insect orders with no discernible digestive ability. Multifunctional xylanolytic cellulases remain unique to Phasmatodea. The presence or absence of multifunctional enzymes does not impact dietary specification, but rather having multiple, multifunctional cellulase genes is an ancestral state for Polyneoptera and possibly Insecta. The prevalence of multifunctional cellulases in other animals demands further investigation.

Parallel and Gradual Genome Erosion in the Blattabacterium Endosymbionts of Mastotermes darwiniensis and Cryptocercus Wood Roaches

Almost all examined cockroaches harbor an obligate intracellular endosymbiont, Blattabacterium cuenoti. On the basis of genome content, Blattabacterium has been inferred to recycle nitrogen wastes and provide amino acids and cofactors for its hosts. Most Blattabacterium strains sequenced to date harbor a genome of ∼630 kbp, with the exception of the termite Mastotermes darwiniensis (∼590 kbp) and Cryptocercus punctulatus (∼614 kbp), a representative of the sister group of termites. Such genome reduction may have led to the ultimate loss of Blattabacterium in all termites other than Mastotermes. In this study, we sequenced 11 new Blattabacterium genomes from three species of Cryptocercus in order to shed light on the genomic evolution of Blattabacterium in termites and Cryptocercus. All genomes of Cryptocercus-derived Blattabacterium genomes were reduced (∼614 kbp), except for that associated with Cryptocercus kyebangensis, which comprised 637 kbp. Phylogenetic analysis of these genomes and their content indicates that Blattabacterium experienced parallel genome reduction in Mastotermes and Cryptocercus, possibly due to similar selective forces. We found evidence of ongoing genome reduction in Blattabacterium from three lineages of the C. punctulatus species complex, which independently lost one cysteine biosynthetic gene. We also sequenced the genome of the Blattabacterium associated with Salganea taiwanensis, a subsocial xylophagous cockroach that does not vertically transmit gut symbionts via proctodeal trophallaxis. This genome was 632 kbp, typical of that of nonsubsocial cockroaches. Overall, our results show that genome reduction occurred on multiple occasions in Blattabacterium, and is still ongoing, possibly because of new associations with gut symbionts in some lineages.

Exploring the diversity of Asian Cryptocercus (Blattodea : Cryptocercidae): species delimitation based on chromosome numbers, morphology and molecular analysis

Woodroaches from the genus Cryptocercus Scudder, 1862 are known to display low levels of morphological divergence, yet significant genetic divergence and variability in chromosome number. Compared with Cryptocercus taxa from North America, the diversity of the genus in Asia has received relatively little attention. We performed morphological and karyotypic examinations of multiple taxa from several previously unsampled mountainous areas of central and south-western China, and identified nine candidate species primarily on the basis of chromosome number. We then investigated diversity across all Asian Cryptocercus, through phylogenetic analyses of 135 COI sequences and 74 28S rRNA sequences from individuals of 28 localities, including species delimitation analysis in General Mixed Yule Coalescent (GMYC) and Automatic Barcode Gap Discovery (ABGD). Phylogenetic results indicated that individuals from the same locality constituted well supported clades. The congruence of GMYC and ABGD results were in almost perfect accord, with 28 candidate species described on the basis of karyotypes (including the nine identified in this study). We provide evidence that each valley population in the Hengduan Mountains contains a separate evolving lineage. We conclude that the principal cause of the rich Cryptocercus diversity in China has been the uplift of the Qinghai-Tibet Plateau.

The Complete Mitogenome of the Wood-Feeding Cockroach Cryptocercus meridianus (Blattodea: Cryptocercidae) and Its Phylogenetic Relationship among Cockroach Families

In this study, the complete mitochondrial genome of Cryptocercus meridianus was sequenced. The circular mitochondrial genome is 15,322 bp in size and contains 13 protein-coding genes, two ribosomal RNA genes (12S rRNA and 16S rRNA), 22 transfer RNA genes, and one D-loop region. We compare the mitogenome of C. meridianus with that of C. relictus and C. kyebangensis. The base composition of the whole genome was 45.20%, 9.74%, 16.06%, and 29.00% for A, G, C, and T, respectively; it shows a high AT content (74.2%), similar to the mitogenomes of C. relictus and C. kyebangensis. The protein-coding genes are initiated with typical mitochondrial start codons except for cox1 with TTG. The gene order of the C. meridianus mitogenome differs from the typical insect pattern for the translocation of tRNA-Ser^AGN, while the mitogenomes of the other two Cryptocercus species, C. relictus and C. kyebangensis, are consistent with the typical insect pattern. There are two very long non-coding intergenic regions lying on both sides of the rearranged gene tRNA-Ser^AGN. The phylogenetic relationships were constructed based on the nucleotide sequence of 13 protein-coding genes and two ribosomal RNA genes. The mitogenome of C. meridianus is the first representative of the order Blattodea that demonstrates rearrangement, and it will contribute to the further study of the phylogeny and evolution of the genus Cryptocercus and related taxa.

Compositional differences among female-associated and embryo-associated microbiota of the viviparous Pacific Beetle cockroach, Diploptera punctata

All cockroach species, except one, harbor the endosymbiont Blattabacterium, transmitted from females to embryos. Adult cockroaches acquire non-Blattabacterium bacteria as part of their gut microbiota over time, but our knowledge of the possible transmission of these non-Blattabacterium bacteria from females to embryos is rudimentary. We characterized the gut microbiota of gravid viviparous Diploptera punctata females and the non-Blattabacterium microbiota of associated developing embryos, as well as the gut microbiota of non-gravid females, and the microbiota of orphan embryos (females not included), following high-throughput sequencing of the 16S rRNA gene to assess bacterial transference. We determined significant differences in community composition between gravid females and associated embryos and overall greater similarity in community composition among embryos than adult females. Results suggest various routes of transference of bacteria from females or the environment to embryos. The bacterial families Halomonadaceae and Shewanellaceae were more abundant in embryos than in gravid females. The functional relevance of these families remains to be elucidated, but provisioning of amino acids deficient in the brood sac secretion is a possibility. Overall, our results highlight the need for further studies investigating the uptake and selective screening of microbes by D. punctata embryos, as well as their functions.

An exceptionally preserved 110 million years old praying mantis provides new insights into the predatory behaviour of early mantodeans

Mantodeans or praying mantises are flying insects and well known for their raptorial behaviour, mainly performed by their first pair of thoracic appendages. We describe here a new, exceptionally preserved specimen of the early mantodean Santanmantis axelrodi Grimaldi, 2003 from the famous 110 million years old Crato Formation, Brazil. The incomplete specimen preserves important morphological details, which were not known in this specific form before for this species or any other representative of Mantodea. Unlike in modern representatives or other fossil forms of Mantodea not only the first pair of thoracic appendages shows adaptations for predation. The femora of the second pair of thoracic appendages bear numerous strong, erect spines which appear to have a sharp tip, with this strongly resembling the spines of the first pair of thoracic appendages. This indicates that individuals of S. axelrodi likely used at least two pairs of thoracic appendages to catch prey. This demonstrates that the prey-catching behaviour was more diverse in early forms of praying mantises than anticipated.

Embryonic development of Eucorydia yasumatsui Asahina, with special reference to external morphology (Insecta: Blattodea, Corydiidae)

As the first step in the comparative embryological study of Blattodea, with the aim of reconstructing the groundplan and phylogeny of Dictyoptera and Polyneoptera, the embryonic development of a corydiid was examined and described in detail using Eucorydia yasumatsui. Ten to fifteen micropyles are localized on the ventral side of the egg, and aggregated symbiont bacterial "mycetomes" are found in the egg. The embryo is formed by the fusion of paired blastodermal regions, with higher cellular density on the ventral side of the egg. This type of embryo formation, regarded as one of the embryological autapomorphies of Polyneoptera, was first demonstrated for "Blattaria" in the present study. The embryo undergoes embryogenesis of the short germ band type, and elongates to its full length on the ventral side of the egg. The embryo undergoes katatrepsis and dorsal closure, and then finally, it acquires its definitive form, keeping its original position on the ventral side of the egg, with its anteroposterior axis never reversed throughout development. The information obtained was compared with that of previous studies on other insects. "Micropyles grouped on the ventral side of the egg" is thought to be a part of the groundplan of Dictyoptera, and "possession of bacteria in the form of mycetomes" to be an apomorphic groundplan of Blattodea. Corydiid embryos were revealed to perform blastokinesis of the "non-reversion type (N)", as reported in blaberoid cockroaches other than Corydiidae ("Ectobiidae," Blaberidae, etc.) and in Mantodea; the embryos of blattoid cockroaches (Blattidae and Cryptocercidae) and Isoptera undergo blastokinesis of the "reversion type (R)," in which the anteroposterior axis of the embryo is reversed during blastokinesis. Dictyopteran blastokinesis types can be summarized as "Mantodea (N) + Blattodea [= Blaberoidea (N) + Blattoidea (R) + Isoptera (R)]".

Reconstructing the phylogeny of Blattodea: robust support for interfamilial relationships and major clades

Cockroaches are among the most recognizable of all insects. In addition to their role as pests, they play a key ecological role as decomposers. Despite numerous studies of cockroach phylogeny in recent decades, relationships among most major lineages are yet to be resolved. Here we examine phylogenetic relationships among cockroaches based on five genes (mitochondrial 12S rRNA, 16S rRNA, COII; nuclear 28S rRNA and histone H3), and infer divergence times on the basis of 8 fossils. We included in our analyses sequences from 52 new species collected in China, representing 7 families. These were combined with data from a recent study that examined these same genes from 49 species, resulting in a significant increase in taxa analysed. Three major lineages, Corydioidea, Blaberoidea, and Blattoidea were recovered, the latter comprising Blattidae, Tryonicidae, Lamproblattidae, Anaplectidae, Cryptocercidae and Isoptera. The estimated age of the split between Mantodea and Blattodea ranged from 204.3 Ma to 289.1 Ma. Corydioidea was estimated to have diverged 209.7 Ma (180.5-244.3 Ma 95% confidence interval [CI]) from the remaining Blattodea. The clade Blattoidea diverged from their sister group, Blaberoidea, around 198.3 Ma (173.1-229.1 Ma). The addition of the extra taxa in this study has resulted in significantly higher levels of support for a number of previously recognized groupings.

Utility of mtDNA-COI Barcode Region for Phylogenetic Relationship and Diagnosis of Five Common Pest Cockroaches

BACKGROUND

Cockroaches are of vital importance medically and hygienically as they can disperse human pathogenic agents and are especially responsible for food contamination and spreading of food borne pathogens. In this study, part of mtDNA-COI gene of five common pest cockroaches was tested for diagnostic and phylogenetic purposes.

METHODS

We have described barcode region of mtDNA-COI gene of five cockroach species: Blattella germanica, Blatta orientalis, Periplaneta americana, Shelfordella lateralis, and Supella longipalpa, along with the development of a PCR-RFLP method for rapid detection and differentiation of these health pest species.

RESULTS

The PCR generates a single 710 bp-sized amplicon in all cockroach specimens, followed by direct sequencing. AluI predicted from the sequencing data provided different RFLP profiles among five species. There was a significant intra-species variation within the American cockroach populations, but no genetic variation within other species. Accordingly, phylogenetic analysis demonstrates common monophyly for cockroach families in agreement with conventional taxonomy. However S. longipalpa (Ectobiidae) diverged as an early ancestor of other cockroaches and was not associated with other Ectobiidae.

CONCLUSION

The PCR-RFLP protocol might be useful when the conventional taxonomic methods are not able to identify specimens, particularly when only small body parts of specimens are available or they are in a decaying condition. mtDNA-COI gene shows potentially useful for studying phylogenetic relationships of Blattodea order.

Complete mitochondrial genomes of two blattid cockroaches, Periplaneta australasiae and Neostylopyga rhombifolia, and phylogenetic relationships within the Blattaria

Complete mitochondrial genomes (mitogenomes) of two cockroach species, Periplaneta australasiae and Neostylopyga rhombifolia, 15,605 bp and 15,711 bp in length, respectively, were determined. As reported for other cockroach mitogenomes, the two mitogenomes possessed typical ancestral insect mitogenome gene composition and arrangement. Only several small intergenic spacers were found: one, which was common in all sequenced cockroach mitogenomes except for the genus Cryptocercus, was between tRNA-Ser (UCN) and ND1 and contained a 7bp highly conserved motif (WACTTAA). Three different types of short tandem repeats in the N. rhombifolia control region (CR) were observed. The homologous alignments of these tandem repeats with other six cockroach mitogenome CRs revealed a low similarity. Three conserved sequence blocks (CSB) were detected in both cockroach mitochondrial CRs. CSB1 was specific for blattinine mitogenomes and was highly conserved with 95% similarity, speculating that this block was a possible molecular synapomorphy for this subfamily. CSB3 located nearby downstream of CSB1 and has more variations within blattinine mitogenomes compared with CSB1. The CSB3 was capable of forming stable stem-loop structure with a small T-stretch in the loop portion. We assessed the influence of four datasets and two inference methods on topology within Orthopteroidea. All genes excluding the third codon positions of PCGs could generate more stable topology, and higher posterior probabilities than bootstrap values were presented at some branch nodes. The phylogenetic analysis with different datasets and analytical methods supported the monophyly of Dictyoptera and supported strongly the proposal that Isoptera should be classified as a family (Termitidae) of the Blattaria. Specifically, Shelfordella lateralis was inserted in the clade Periplaneta. Considering the K2P genetic distance, morphological characters, and the phylogenetic trees, we suggested that S. lateralis should be placed in the genus Periplaneta.

Species Delimitation and Phylogenetic Relationships in Ectobiid Cockroaches (Dictyoptera, Blattodea) from China

We collected Ectobiidae cockroach specimens from 44 locations in the south of the Yangtze valley. We obtained 297 COI sequences specimens and carried out phylogenetic and divergence dating analyses, as well as species delimitation analysis using a General Mixed Yule Coalescent (GMYC) framework. The intraspecific and interspecific sequence divergence in Ectobiidae cockroaches ranged from 0.0 to 7.0% and 4.6 to 30.8%, respectively. GMYC analysis resulted in 53 (confidence interval: 37-65) entities (likelihood ratio = 103.63) including 14 downloaded species. The COI GMYC groups partly corresponded to the ectobiid species and 52 ectobiid species were delimited successfully based on the combination of GMYC result with morphological information. We used the molecular data and 6 cockroach fossil calibrations to obtain a preliminary estimate of the timescale of ectobiid evolution. The major subfamilies in the group were found to have diverged between ~125-110 Ma, and morphospecies pairs were found to have diverged ~10 or more Ma.

Exact quantification of cellular robustness in genome-scale metabolic networks

Motivation: Robustness, the ability of biological networks to uphold their functionality in spite of perturbations, is a key characteristic of all living systems. Although several theoretical approaches have been developed to formalize robustness, it still eludes an exact quantification. Here, we present a rigorous and quantitative approach for the structural robustness of metabolic networks by measuring their ability to tolerate random reaction (or gene) knockouts.

Results: In analogy to reliability theory, based on an explicit consideration of all possible knockout sets, we exactly quantify the probability of failure for a given network function (e.g. growth). This measure can be computed if the network’s minimal cut sets (MSCs) are known. We show that even in genome-scale metabolic networks the probability of (network) failure can be reliably estimated from MSCs with lowest cardinalities. We demonstrate the applicability of our theory by analyzing the structural robustness of multiple Enterobacteriaceae and Blattibacteriaceae and show a dramatically low structural robustness for the latter. We find that structural robustness develops from the ability to proliferate in multiple growth environments consistent with experimentally found knowledge.

Conclusion: The probability of (network) failure provides thus a reliable and easily computable measure of structural robustness and redundancy in (genome-scale) metabolic networks.

Availability and implementation: Source code is available under the GNU General Public License at https://github.com/mpgerstl/networkRobustnessToolbox.

Contact:juergen.zanghellini@boku.ac.at

Supplementary information:Supplementary data are available at Bioinformatics online.

Phylogeny of Dictyoptera: Dating the Origin of Cockroaches, Praying Mantises and Termites with Molecular Data and Controlled Fossil Evidence

Understanding the origin and diversification of organisms requires a good phylogenetic estimate of their age and diversification rates. This estimate can be difficult to obtain when samples are limited and fossil records are disputed, as in Dictyoptera. To choose among competing hypotheses of origin for dictyopteran suborders, we root a phylogenetic analysis (~800 taxa, 10 kbp) within a large selection of outgroups and calibrate datings with fossils attributed to lineages with clear synapomorphies. We find the following topology: (mantises, (other cockroaches, (Cryptocercidae, termites)). Our datings suggest that crown-Dictyoptera-and stem-mantises-would date back to the Late Carboniferous (~ 300 Mya), a result compatible with the oldest putative fossil of stem-dictyoptera. Crown-mantises, however, would be much more recent (~ 200 Mya; Triassic/Jurassic boundary). This pattern (i.e., old origin and more recent diversification) suggests a scenario of replacement in carnivory among polyneopterous insects. The most recent common ancestor of (cockroaches + termites) would date back to the Permian (~275 Mya), which contradicts the hypothesis of a Devonian origin of cockroaches. Stem-termites would date back to the Triassic/Jurassic boundary, which refutes a Triassic origin. We suggest directions in extant and extinct species sampling to sharpen this chronological framework and dictyopteran evolutionary studies.

Physiology of environmental adaptations and resource acquisition in cockroaches

Cockroaches are a group of insects that evolved early in geological time. Because of their antiquity, they for the most part display generalized behavior and physiology and accordingly have frequently been used as model insects to examine physiological and biochemical mechanisms involved with water balance, nutrition, reproduction, genetics, and insecticide resistance. As a result, a considerable amount of information on these topics is available. However, there is much more to be learned by employing new protocols, microchemical analytical techniques, and molecular biology tools to explore many unanswered questions.

Roles of fat body trophocytes, mycetocytes and urocytes in the American cockroach, Periplaneta americana under starvation conditions: an ultrastructural study

In insects, trophocytes (adipocytes) are major cells of a storage organ, the fat body, from which stored glycogen and lipids are mobilized under starvation. However, cockroaches have 2 additional types of cell in the fat body: mycetocytes harboring an endosymbiont, Blattabacterium cuenoti, and urocytes depositing uric acid in urate vacuoles. These cells have not been investigated in terms of their roles under starvation conditions. To gain insight into the roles of trophocytes, mycetocytes and urocytes in cockroaches, structural changes were first investigated in the cells associated with starvation in the American cockroach, Periplaneta americana, by light and electron microscopy. The area of lipid droplets in trophocytes, the endosymbiont population and mitotic activity in mycetocytes, and the area of urate vacuoles in urocytes were analyzed in association with survival rates of the starved cockroaches. After 2 weeks of starvation, trophocytes lost glycogen rosettes and their area of lipid droplets decreased, but almost all cockroaches survived this period. However, further starvation did not reduce the area, but the survival rates dropped rapidly and all cockroaches died in 7 weeks. Endosymbionts were not affected in terms of population size and mitotic activity, even if the cockroaches were dying. The area of urate vacuoles rapidly decreased in a week of starvation and did not recover upon further starvation. These results indicate that starved cockroaches mobilize glycogen and lipids stored in trophocytes to survive for 2 weeks and then die after the exhaustion of nutrients in these cells. Endosymbionts are not digested for the recycling of nutrients, but uric acid is reused under starvation.

Comparative genomics of Blattabacterium cuenoti: the frozen legacy of an ancient endosymbiont genome

Many insect species have established long-term symbiotic relationships with intracellular bacteria. Symbiosis with bacteria has provided insects with novel ecological capabilities, which have allowed them colonize previously unexplored niches. Despite its importance to the understanding of the emergence of biological complexity, the evolution of symbiotic relationships remains hitherto a mystery in evolutionary biology. In this study, we contribute to the investigation of the evolutionary leaps enabled by mutualistic symbioses by sequencing the genome of Blattabacterium cuenoti, primary endosymbiont of the omnivorous cockroach Blatta orientalis, and one of the most ancient symbiotic associations. We perform comparative analyses between the Blattabacterium cuenoti genome and that of previously sequenced endosymbionts, namely those from the omnivorous hosts the Blattella germanica (Blattelidae) and Periplaneta americana (Blattidae), and the endosymbionts harbored by two wood-feeding hosts, the subsocial cockroach Cryptocercus punctulatus (Cryptocercidae) and the termite Mastotermes darwiniensis (Termitidae). Our study shows a remarkable evolutionary stasis of this symbiotic system throughout the evolutionary history of cockroaches and the deepest branching termite M. darwiniensis, in terms of not only chromosome architecture but also gene content, as revealed by the striking conservation of the Blattabacterium core genome. Importantly, the architecture of central metabolic network inferred from the endosymbiont genomes was established very early in Blattabacterium evolutionary history and could be an outcome of the essential role played by this endosymbiont in the host's nitrogen economy.

The gonangulum: a reassessment of its morphology, homology, and phylogenetic significance

The gonangulum is a sclerite in the female genitalic region of insects. Its presence or full development has long been considered an apomorphy supporting Zygentoma + Pterygota. Recent studies of female genitalia in several insect orders (K.-D. Klass and co-workers) revealed many new data on the gonangulum and homologous sclerotisations (laterocoxa LC9). Herein the gonangulum area is described (including articulations, muscle attachments, sulci) and compared among Archaeognatha, Zygentoma, Odonata, Dermaptera, Dictyoptera, and Notoptera. A wider perspective is provided to the topic by addressing some novel issues: identification of LC9 sclerotisations in non-insect taxa and in insects that secondarily lack an ovipositor; occurrence of homonomous sclerotisations in other abdominal segments of both sexes; morphological interpretation of LC9; and the role of paedomorphosis in LC9 evolution. As a result, there is currently no support for any insect lineage from this character system. For gonangulum-related characters both a significant intra-ordinal variation and frequent homoplasy are demonstrated using various Odonata, Dermaptera, and Dictyoptera as examples. Divergent fates of LC9 in simplified genitalia are shown using a dermapteran and an odonatan. We view all this as a showcase of how a renewed and more detailed examination of a character system can dramatically change the phylogenetic evidence drawn from it.

Complete mitochondrial genomes of two cockroaches, Blattella germanica and Periplaneta americana, and the phylogenetic position of termites

The mitochondrial genomes are one of the most information-rich markers in phylogenetics. The relationships within superorder Dictyoptera have been debated in the literature. However, the closely related termites (Isoptera) are retained as unranked taxon within the order Blattaria (cockroaches). In this work, we sequenced the complete mitogenomes of two cockroaches, reconstructed the molecular phylogeny and attempted to infer the phylogenetic position of termites in Blattaria more reliably. The complete mtDNA nucleotide sequences of the peridomestic American cockroach (Periplaneta americana L.) and the domestic German cockroach (Blattella germanica L.) are 15,025 and 15,584 bp in size, respectively. The genome shares the gene order and orientation with previously known Blattaria mitogenomes. Most tRNAs could be folded into the typical cloverleaf secondary structure, but the tRNA-Ser (AGN) of P. americana appears to be missing the dihydrouridine arm. Using nucleotide and amino acid sequences as phylogenetic markers, we proposed that termites should be treated as a superfamily (Termitoidea) of cockroaches. We suggested that Polyphagoidea was the sister group of Termitoidea in Blattaria and supported that the suborder Caelifera is more closely related to the Phasmatodea than to the suborder Ensifera of Orthoptera.

Midgut and fat body bacteriocytes in neotropical cerambycid beetles (Coleoptera: Cerambycidae)

Xylophagous insects derive nutrients from intractable substrates by producing or ingesting cellulolytic enzymes, or by maintaining associations with symbiotic microbes. Wood-boring cerambycid beetle larvae sometimes house maternally-transmitted endosymbiotic yeasts that are presumed to provide their hosts with nutritional benefits. These are thought to be absent from species in the large subfamily Lamiinae; nevertheless yeasts have been repeatedly isolated from the guts of neotropical lamiines. The objective of this study was to conduct transmission electron microscopy (TEM) studies of cerambycid larval midgut tissues to determine if gut yeasts were intracellular, or simply present in the gut lumen. Nine cerambycid larvae were harvested from two trees in the Brazil nut family (Lecythidaceae) in the rain forest of SE Peru; seven were identified using mtDNA sequence data and processed for TEM. Yeasts cultured from larval frass or exuvia, and identified with rDNA sequence data, were identical or similar to yeasts previously isolated from beetles. In TEM analyses yeast cells were found only in the gut lumens, sometimes associated with fragments of thick-walled xylem cells. Apparent bacteriocytes were found in either midgut or fat body tissue of three larval specimens, including two lamiines. This is the first report of a potential fat body symbiosis in a cerambycid beetle. Future studies of cerambycid symbiosis should distinguish the identities and potential roles of free-living organisms in the gut lumen from those of organisms harbored within gut epithelial or fat body tissue.

Cephalic morphology of Hymenopus coronatus (Insecta: Mantodea) and its phylogenetic implications

External and internal head structures of the mantodean Hymenopus coronatus are examined and described in detail. The results are elaborately compared with the literature. Strong crests on the anterior tentorial arms that articulate with the subantennal suture, a parietal suture and glossae and paraglossae with anteriorly bent tips are proposed as new potential apomorphies for Mantodea while a head capsule being wider than long, enlarged compound eyes, the presence of a frontal shield or scutellum, lateral lobes in the anterior tentorial arms, the presence of a transverse and an interantennal suture and the reduction of the mentum are confirmed as apomorphies, As potential apomorphies for Dictyoptera the reduction of Musculus tentoriobuccalis lateralis (M. 49) is newly presented and a "perforate" tentorium, lacinial incisivi that are located in a galeal pouch and the presence of a postmola are confirmed. The present study shows the value of cephalic morphology for phylogenetic analysis but also points out that further studies including evolutionary key taxa are essential for resolving the evolutionary adaptations among dictyopterans.

Genome economization in the endosymbiont of the wood roach Cryptocercus punctulatus due to drastic loss of amino acid synthesis capabilities

Cockroaches (Blattaria: Dictyoptera) harbor the endosymbiont Blattabacterium sp. in their abdominal fat body. This endosymbiont is involved in nitrogen recycling and amino acid provision to its host. In this study, the genome of Blattabacterium sp. of Cryptocercus punctulatus (BCpu) was sequenced and compared with those of the symbionts of Blattella germanica and Periplaneta americana, BBge and BPam, respectively. The BCpu genome consists of a chromosome of 605.7 kb and a plasmid of 3.8 kb and is therefore approximately 31 kb smaller than the other two aforementioned genomes. The size reduction is due to the loss of 55 genes, 23 of which belong to biosynthetic pathways for amino acids. The pathways for the production of tryptophan, leucine, isoleucine/threonine/valine, methionine, and cysteine have been completely lost. Additionally, the genes for the enzymes catalyzing the last steps of arginine and lysine biosynthesis, argH and lysA, were found to be missing and pseudogenized, respectively. These gene losses render BCpu auxotrophic for nine amino acids more than those corresponding to BBge and BPam. BCpu has also lost capacities for sulfate reduction, production of heme groups, as well as genes for several other unlinked metabolic processes, and genes present in BBge and BPam in duplicates. Amino acids and cofactors that are not synthesized by BCpu are either produced in abundance by hindgut microbiota or are provisioned via a copious diet of dampwood colonized by putrefying microbiota, supplying host and Blattabacterium symbiont with the necessary nutrients and thus permitting genome economization of BCpu.

Diversity of insect intestinal microflora

The influence of geographic location, season, age, and part of the digestive tract on bacterial diversity was evaluated on intestinal microflora of honeybees, wasps, and cockroaches using DGGE analysis. PCR-DGGE analyses with universal bacterial primers targeting 200-bp region of the 16S rDNA gene afforded the profile of complex bacterial DNA; specific primers were used to determine the profile of bifidobacteria whose concentration in digestive tract was determined by real-time PCR. Selected PCR products were identified by sequencing. The microflora of the bees exhibited little variations among the hives from distant locations. Their bifidobacterial population formed 2.8-8.4 % of total bacteria and was very homogeneous. The total gut microflora of wasps was also homogeneous, only two samples being affected by the season or the location; on the other hand, wasp bifidobacterial population was very heterogeneous. Cockroaches showed the highest variations in microflora composition, the age and diet being the ultimate factors; bifidobacteria counts also varied among tested individuals (0.1-34.1 % of total bacteria). Our results suggest that nutrition habits are the strongest factor affecting the insect microflora, giving higher variations to omnivorous species.

Wood-feeding cockroaches as models for termite evolution (Insecta: Dictyoptera): Cryptocercus vs. Parasphaeria boleiriana

Isoptera are highly specialized cockroaches and are one of the few eusocial insect lineages. Cryptocercus cockroaches have appeared to many as ideal models for inference on the early evolution of termites, due to their possible phylogenetic relationship and several shared key attributes in life history. Recently, Pellens, Grandcolas, and colleagues have proposed the blaberid cockroach Parasphaeria boleiriana to be an alternative model for the early evolution in termites. We compare the usefulness of Cryptocercus and P. boleiriana as models for termite evolution. Cryptocercus and lower Isoptera (1) can both feed on comparatively recalcitrant wood, (2) have an obligate, rich and unique hypermastigid and oxymonadid fauna in the hindgut, (3) transfer these flagellates to the next generation by anal trophallaxis, (4) have social systems that involve long-lasting biparental care, and, finally, (5) are strongly suggested to be sister groups, so that the key attributes (1)-(4) appear to be homologous between the two taxa. On the other hand, P. boleiriana (1) feeds on soft, ephemeral wood sources, (2) shows no trace of the oxymonadid and hypermastigid hindgut fauna unique to Cryptocercus and lower Isoptera, nor does it have any other demonstrated obligate relationship with hindgut flagellates, (3) is likely to lack anal trophallaxis, (4) has only a short period of uniparental brood care, and (5) is phylogenetically remote from the Cryptocercus+Isoptera clade. These facts would argue against any reasonable usage of P. boleiriana as a model for the early evolution of Isoptera or even of the clade Cryptocercus+Isoptera. Cryptocercus thus remains an appropriate model-taxon-by-homology for early termite evolution. As compared to P. boleiriana, some other Blaberidae (such as the Panesthiinae Salganea) appear more useful as model-taxa-by-homoplasy for the early evolution of the Cryptocercus+Isoptera clade, as their brooding behavior is more elaborate than in P. boleiriana.