Evidence from multiple gene sequences indicates that termites evolved from wood-feeding cockroaches

Major changes in microbial diversity and community composition across gut sections of a juvenile Panchlora cockroach

Investigations of gut microbiomes have shed light on the diversity and genetic content of these communities, and helped shape our understanding of how host-associated microorganisms influence host physiology, behavior, and health. Despite the importance of gut microbes to metazoans, our understanding of the changes in diversity and composition across the alimentary tract, and the source of the resident community are limited. Here, using community metagenomics and 16S rRNA gene sequencing, we assess microbial community diversity and coding potential in the foregut, midgut, and hindgut of a juvenile Panchlora cockroach, which resides in the refuse piles of the leaf-cutter ant species Atta colombica. We found a significant shift in the microbial community structure and coding potential throughout the three gut sections of Panchlora sp., and through comparison with previously generated metagenomes of the cockroach's food source and niche, we reveal that this shift in microbial community composition is influenced by the ecosystems in which Panchlora sp. occurs. While the foregut is composed of microbes that likely originate from the symbiotic fungus gardens of the ants, the midgut and hindgut are composed of a microbial community that is likely cockroach-specific. Analogous to mammalian systems, the midgut and hindgut appear to be dominated by Firmicutes and Bacteroidetes with the capacity for polysaccharide degradation, suggesting they may assist in the degradation of dietary plant material. Our work underscores the prominence of community changes throughout gut microbiomes and highlights ecological factors that underpin the structure and function of the symbiotic microbial communities of metazoans.

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.

Genetic insights into family group co-occurrence in Cryptocercus punctulatus, a sub-social woodroach from the southern Appalachian Mountains

The wood-feeding cockroach Cryptocercus punctulatus Scudder (Blattodea: Cryptocercidae) is an important member of the dead wood (saproxylic) community in montane forests of the southeastern United States. However, its population biology remains poorly understood. Here, aspects of family group co-occurrence were characterized to provide basic information that can be extended by studies on the evolution and maintenance of sub-sociality. Broad sampling across the species’ range was coupled with molecular data (mitochondrial DNA (mtDNA) sequences). The primary questions were: (1) what proportion of rotting logs contain two or more different mtDNA haplotypes and how often can this be attributed to multiple families inhabiting the same log, (2) are multi-family logs spatially clustered, and (3) what levels of genetic differentiation among haplotypes exist within a log, and how genetically similar are matrilines of co-occurring family groups? Multi-family logs were identified on the premise that three different mtDNA haplotypes, or two different haplotypes among adult females, is inconsistent with a single family group founded by one male–female pair. Results showed that of the 88 rotting logs from which multiple adult C. punctulatus were sampled, 41 logs (47%) contained two or more mtDNA haplotypes, and at least 19 of these logs (22% overall) were inferred to be inhabited by multiple families. There was no strong evidence for spatial clustering of the latter class of logs. The frequency distribution of nucleotide differences between co-occurring haplotypes was strongly right-skewed, such that most haplotypes were only one or two mutations apart, but more substantial divergences (up to 18 mutations, or 1.6% uncorrected sequence divergence) do occasionally occur within logs. This work represents the first explicit investigation of family group co-occurrence in C. punctulatus, providing a valuable baseline for follow-up studies.

Progress, pitfalls and parallel universes: a history of insect phylogenetics

The phylogeny of insects has been both extensively studied and vigorously debated for over a century. A relatively accurate deep phylogeny had been produced by 1904. It was not substantially improved in topology until recently when phylogenomics settled many long-standing controversies. Intervening advances came instead through methodological improvement. Early molecular phylogenetic studies (1985-2005), dominated by a few genes, provided datasets that were too small to resolve controversial phylogenetic problems. Adding to the lack of consensus, this period was characterized by a polarization of philosophies, with individuals belonging to either parsimony or maximum-likelihood camps; each largely ignoring the insights of the other. The result was an unfortunate detour in which the few perceived phylogenetic revolutions published by both sides of the philosophical divide were probably erroneous. The size of datasets has been growing exponentially since the mid-1980s accompanied by a wave of confidence that all relationships will soon be known. However, large datasets create new challenges, and a large number of genes does not guarantee reliable results. If history is a guide, then the quality of conclusions will be determined by an improved understanding of both molecular and morphological evolution, and not simply the number of genes analysed.

IDENTIFICATION OF THE FGL-AMIDE ALLATOSTATIN GENE OF THE PRIMITIVE TERMITE Mastotermes darwiniensis AND THE WOODROACH Cryptocercus darwini

Allatostatins with the C-terminal ending Tyr/Phe-Xaa-Phe-Gly-Leu/Ile-amide (FGLa/ASTs) are widespread neuropeptides with multiple functions. The gene encoding the FGLa/AST polypeptide precursor was first isolated from cockroaches and since then could be identified in many insects and crustaceans. With its strictly conserved regions in combination with variable regions the gene seems to be a good candidate for phylogenetic analyses between closely and distantly related species. Here, the structure of the FGLa/AST gene of the most primitive termite, the giant northern termite Mastotermes darwiniensis Froggatt, was identified. The FGLa/AST gene of the woodroach Cryptocercus darwini was also determined. Precursor sequences of both species possess the general organization of dictyopteran FGLa/AST precursors containing 14 putative FGLa/AST peptides. In M. darwiniensis, only 11 out of the 14 FGLa/AST-like peptides possess the C-terminal conserved region Y/FXFGL/I/V/M and four of the putative peptide structures are not followed by a Gly residue that would lead to nonamidated peptides. Phylogenetic analyses show the high degree of similarity of dictyopteran FGLa/AST sequences. The position of termites, nested within the Blattaria, confirms that termites have evolved from primitive cockroaches.

The Termite Worker Phenotype Evolved as a Dispersal Strategy for Fertile Wingless Individuals before Eusociality

Termites are eusocial insects that evolved from solitary cockroaches. It is not known precisely what factors drove the evolution of termite eusociality, that is, skewed reproduction with distinct winged reproductive and wingless worker phenotypes. In other eusocial insects (bees and wasps), reproductive skew evolved first and phenotype differences evolved second. We propose that the reverse pattern occurred in termites, that is, that the winged-wingless diphenism evolved before eusociality. We discuss existing phylogenetic and pheromonal evidence supporting our hypothesis. We provide new experimental evidence from the most basal termite species (Mastotermes darwiniensis), suggesting that the ancestral state was indeed diphenic but presocial. We propose that the mechanism promoting a winged-wingless diphenism-in the absence of eusociality-was greater predation of aerial than terrestrial dispersers, and we support this with a game theoretic model. We augment our hypothesis with a novel explanation for the evolution of the developmental pathways leading to winged and wingless phenotypes in termites. An added benefit of our hypothesis is that it neatly explains the origin of termite eusociality itself: in the pre-eusocial ancestral species, the poor dispersal ability of the wingless phenotype would have led to clustering of relatives around shared resources-a prerequisite for nonparental care of close relatives.

Structure and Evolution of Insect Sperm: New Interpretations in the Age of Phylogenomics

This comprehensive review of the structure of sperm in all orders of insects evaluates phylogenetic implications, with the background of a phylogeny based on transcriptomes. Sperm characters strongly support several major branches of the phylogeny of insects-for instance, Cercophora, Dicondylia, and Psocodea-and also different infraordinal groups. Some closely related taxa, such as Trichoptera and Lepidoptera (Amphiesmenoptera), differ greatly in sperm structure. Sperm characters are very conservative in some groups (Heteroptera, Odonata) but highly variable in others, including Zoraptera, a small and morphologically uniform group with a tremendously accelerated rate of sperm evolution. Unusual patterns such as sperm dimorphism, the formation of bundles, or aflagellate and immotile sperm have evolved independently in several groups.

The nature of alarm communication in Constrictotermes cyphergaster (Blattodea: Termitoidea: Termitidae): the integration of chemical and vibroacoustic signals

Alarm signalling is of paramount importance to communication in all social insects. In termites, vibroacoustic and chemical alarm signalling are bound to operate synergistically but have never been studied simultaneously in a single species. Here, we inspected the functional significance of both communication channels in Constrictotermes cyphergaster (Termitidae: Nasutitermitinae), confirming the hypothesis that these are not exclusive, but rather complementary processes. In natural situations, the alarm predominantly attracts soldiers, which actively search for the source of a disturbance. Laboratory testing revealed that the frontal gland of soldiers produces a rich mixture of terpenoid compounds including an alarm pheromone. Extensive testing led to identification of the alarm pheromone being composed of abundant monoterpene hydrocarbons (1S)-α-pinene and myrcene, along with a minor component, (E)-β-ocimene. The vibratory alarm signalling consists of vibratory movements evidenced as bursts; a series of beats produced predominantly by soldiers. Exposing termite groups to various mixtures containing the alarm pheromone (crushed soldier heads, frontal gland extracts, mixture of all monoterpenes, and the alarm pheromone mixture made of standards) resulted in significantly higher activity in the tested groups and also increased intensity of the vibratory alarm communication, with the responses clearly dose-dependent. Lower doses of the pheromone provoked higher numbers of vibratory signals compared to higher doses. Higher doses induced long-term running of all termites without stops necessary to perform vibratory behaviour. Surprisingly, even crushed worker heads led to low (but significant) increases in the alarm responses, suggesting that other unknown compound in the worker's head is perceived and answered by termites. Our results demonstrate the existence of different alarm levels in termites, with lower levels being communicated through vibratory signals, and higher levels causing general alarm or retreat being communicated through the alarm pheromone.

Summary: We inspected the functional significance of both vibroacoustic and chemical communication channels in Constrictotermes cyphergaster (Termitidae: Nasutitermitinae), confirming the hypothesis that these are not exclusive but rather complementary processes.

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.

Expression and evolution of hexamerins from the tobacco hornworm, Manduca sexta, and other Lepidoptera

Hexamerins are large hemolymph-proteins that accumulate during the late larval stages of insects. Hexamerins have emerged from hemocyanin, but have lost the ability to bind oxygen. Hexamerins are mainly considered as storage proteins for non-feeding stages, but may also have other functions, e.g. in cuticle formation, transport and immune response. The genome of the hornworm Manduca sexta harbors six hexamerin genes. Two of them code for arylphorins (Msex2.01690, Msex2.15504) and two genes correspond to a methionine-rich hexamerin (Msex2.10735) and a moderately methionine-rich hexamerin (Msex2.01694), respectively. Two other genes do not correspond to any known hexamerin and distantly resemble the arylphorins (Msex2.01691, Msex2.01693). Five of the six hexamerin genes are clustered within ∼45 kb on scaffold 00023, which shows conserved synteny in various lepidopteran genomes. The methionine-rich hexamerin gene is located at a distinct site. M. sexta and other Lepidoptera have lost the riboflavin-binding hexamerin. With the exception of Msex2.01691, which displays low mRNA levels throughout the life cycle, all hexamerins are most highly expressed during pre-wandering phase of the 5th larval instar of M. sexta, supporting their role as storage proteins. Notably, Msex2.01691 is most highly expressed in the brain, suggesting a divergent function. Phylogenetic analyses showed that hexamerin evolution basically follows insect systematics. Lepidoptera display an unparalleled diversity of hexamerins, which exceeds that of other hexapod orders. In contrast to previous analyses, the lepidopteran hexamerins were found monophyletic. Five distinct types of hexamerins have been identified in this order, which differ in terms of amino acid composition and evolutionary history: i. the arylphorins, which are rich in aromatic amino acids (∼20% phenylalanine and tyrosine), ii. the distantly related arylphorin-like hexamerins, iii. the methionine-rich hexamerins, iv. the moderately methionine rich hexamerins, and v. the riboflavin-binding hexamerins.

Diet shapes the gut microbiota of the omnivorous cockroach Blattella germanica

The gut microbiota of insects contributes positively to the physiology of its host mainly by participating in food digestion, protecting against pathogens, or provisioning vitamins or amino acids, but the dynamics of this complex ecosystem is not well understood so far. In this study, we have characterized the gut microbiota of the omnivorous cockroach Blattella germanica by pyrosequencing the hypervariable regions V1-V3 of the 16S rRNA gene of the whole bacterial community. Three diets differing in the protein content (0, 24 and 50%) were tested at two time points in lab-reared individuals. In addition, the gut microbiota of wild adult cockroaches was also analyzed. In contrast to the high microbial richness described on the studied samples, only few species are shared by wild and lab-reared cockroaches, constituting the bacterial core in the gut of B. germanica. Overall, we found that the gut microbiota of B. germanica is highly dynamic as the bacterial composition was reassembled in a diet-specific manner over a short time span, with no-protein diet promoting high diversity, although the highest diversity was found in the wild cockroaches analyzed. We discuss how the flexibility of the gut microbiota is probably due to its omnivorous life style and varied diets.

Polyploidy versus endosymbionts in obligately thelytokous thrips

Background

Thelytoky, the parthenogenetic development of females, has independently evolved in several insect orders yet the study of its mechanisms has so far mostly focussed on haplodiploid Hymenoptera, while alternative mechanisms of thelytoky such as polyploidy are far less understood. In haplodiploid insects, thelytoky can be encoded in their genomes, or induced by maternally inherited bacteria such as Wolbachia or Cardinium. Microbially facilitated thelytoky usually results in complete homozygosity due to gamete duplication and can be reverted into arrhenotoky, the parthenogenetic development of males, through treatment with antibiotics. In contrast, genetically encoded thelytoky cannot be removed and may result in conservation of heterozygosity due to gamete fusion. We have probed the obligate thelytoky of the greenhouse thrips, Heliothrips haemorrhoidalis (Bouché), a significant cosmopolitan pest and a model species of thelytoky in the haplodiploid insect order Thysanoptera. Earlier studies suggested terminal fusion as a mechanism for thelytoky in this species, while another study reported presence of Wolbachia; later it was speculated that Wolbachia plays a role in this thrips’ thelytokous reproduction.

Results

By using PCR and sequence analysis, we demonstrated that global population samples of H. haemorrhoidalis were not infected with Wolbachia, Cardinium or any other known bacterial reproductive manipulators. Antibiotic treatment of this thrips did also not result in male production. Some individuals carried two different alleles in two nuclear loci, histone 3 and elongation factor 1 alpha, suggesting heterozygosity. However, the majority of individuals had three different alleles suggesting that they were polyploid. Genetic diversity across both nuclear loci was low in all populations, and absent from mitochondrial cytochrome oxidase I, indicating that this species had experienced genetic bottlenecks, perhaps due to its invasion biology or a switch to thelytoky.

Conclusions

Geographically broad sampling and experimental manipulation revealed low genetic diversity, absence of Wolbachia but presence of three different alleles of nuclear loci in most analysed individuals of obligately thelytokous H. haemorrhoidalis. This suggests that polyploidy may be involved in the thelytokous reproduction of this thrips species, and polyploidy may be a contributing factor in the reproduction of Thysanoptera and other haplodiploid insect orders.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0304-6) contains supplementary material, which is available to authorized users.

The evolutionary history of termites as inferred from 66 mitochondrial genomes

Termites have colonized many habitats and are among the most abundant animals in tropical ecosystems, which they modify considerably through their actions. The timing of their rise in abundance and of the dispersal events that gave rise to modern termite lineages is not well understood. To shed light on termite origins and diversification, we sequenced the mitochondrial genome of 48 termite species and combined them with 18 previously sequenced termite mitochondrial genomes for phylogenetic and molecular clock analyses using multiple fossil calibrations. The 66 genomes represent most major clades of termites. Unlike previous phylogenetic studies based on fewer molecular data, our phylogenetic tree is fully resolved for the lower termites. The phylogenetic positions of Macrotermitinae and Apicotermitinae are also resolved as the basal groups in the higher termites, but in the crown termitid groups, including Termitinae + Syntermitinae + Nasutitermitinae + Cubitermitinae, the position of some nodes remains uncertain. Our molecular clock tree indicates that the lineages leading to termites and Cryptocercus roaches diverged 170 Ma (153-196 Ma 95% confidence interval [CI]), that modern Termitidae arose 54 Ma (46-66 Ma 95% CI), and that the crown termitid group arose 40 Ma (35-49 Ma 95% CI). This indicates that the distribution of basal termite clades was influenced by the final stages of the breakup of Pangaea. Our inference of ancestral geographic ranges shows that the Termitidae, which includes more than 75% of extant termite species, most likely originated in Africa or Asia, and acquired their pantropical distribution after a series of dispersal and subsequent diversification events.

The clypeal gland: a new exocrine gland in termite imagoes (Isoptera: Serritermitidae, Rhinotermitidae, Termitidae)

Social insects possess a rich set of exocrine organs producing diverse pheromones and defensive compounds. This is especially true for termite imagoes, which are equipped with several glands producing, among others, sex pheromones and defensive compounds protecting imagoes during the dispersal flight and colony foundation. Here, we describe the clypeal gland, a new termite exocrine organ occurring in the labro-clypeal region of imagoes of most Rhinotermitidae, Serritermitidae and Termitidae species. The clypeal gland of Coptotermes testaceus consists of class 1 (modified epidermal cell) and class 3 (bicellular gland unit) secretory cells. Ultrastructural features suggest that the gland secretes volatile compounds and proteins, probably after starting the reproduction. One peculiar feature of the gland is the presence of multiple secretory canals in a single canal cell, a feature never observed before in other insect glands. Although the function of the gland remains unknown, we hypothesize that it could produce secretion signalling the presence of functional reproductives or their need to be fed.

Physiology of digestion and the molecular characterization of the major digestive enzymes from Periplaneta americana

Cockroaches are among the first insects to appear in the fossil record. This work is part of ongoing research on insects at critical points in the evolutionary tree to disclose evolutionary trends in the digestive characteristics of insects. A transcriptome (454 Roche platform) of the midgut of Periplanetaamericana was searched for sequences of digestive enzymes. The selected sequences were manually curated. The complete or nearly complete sequences showing all characteristic motifs and highly expressed (reads counting) had their predicted sequences checked by cloning and Sanger sequencing. There are two chitinases (lacking mucin and chitin-binding domains), one amylase, two α- and three β-glucosidases, one β-galactosidase, two aminopeptidases (none of the N-group), one chymotrypsin, 5 trypsins, and none β-glucanase. Electrophoretic and enzymological data agreed with transcriptome data in showing that there is a single β-galactosidase, two α-glucosidases, one preferring as substrate maltase and the other aryl α-glucoside, and two β-glucosidases. Chromatographic and enzymological data identified 4 trypsins, one chymotrypsin (also found in the transcriptome), and one non-identified proteinase. The major digestive trypsin is identifiable to a major P. americana allergen (Per a 10). The lack of β-glucanase expression in midguts was confirmed, thus lending support to claims that those enzymes are salivary. A salivary amylase was molecularly cloned and shown to be different from the one from the midgut. Enzyme distribution showed that most digestion occurs under the action of salivary and midgut enzymes in the foregut and anterior midgut, except the posterior terminal digestion of proteins. A counter-flux of fluid may be functional in the midgut of the cockroach to explain the low excretory rate of digestive enzymes. Ultrastructural and immunocytochemical localization data showed that amylase and trypsin are released by both merocrine and apocrine secretion mainly from gastric caeca. Finally, a discussion on Polyneoptera digestive physiology is provided.

Gene expression and molecular phylogenetic analyses of beta-glucosidase in the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

Beta-glucosidase (BG) is known as a multifunctional enzyme for social maintenance in terms of both cellulose digestion and social communication in termites. However, the expression profiles of each BG gene and their evolutionary history are not well understood. First, we cloned two types of BG homologs (RsBGI and RsBGII) from the termite Reticulitermes speratus (Kolbe). Gene expression analyses showed that RsBGI expression levels of primary queens and kings from 30 to 100 days after colony foundation were high, but those of reproductives dropped after day 400. Extremely low gene expression levels of RsBGI were observed in eggs, whereas workers had significantly higher expression levels than those of soldiers and other colony members. Consequently, RsBGI gene expression levels changed among each developmental stage, and RsBGI was shown to be involved in cellulose digestion. On the other hand, the RsBGII gene was consistently expressed in all castes and developmental stages examined, and notable expression changes were not observed among them, including in eggs. It was indicated that RsBGII is a main component involved in social communication, for example, the egg-recognition pheromone shown in this species previously. Finally, we obtained partial gene homologs from other termite and cockroach species, including the woodroach (genus Cryptocercus), which is the sister group to termites, and performed molecular phylogenetic analyses. The results showed that the origin of the BG gene homologs preceded the divergence of termites and cockroaches, suggesting that the acquisition of multifunctionality of the BG gene also occurred in cockroach lineages.

Heterologous Overexpression of a Mutant Termite Cellulase Gene inEscherichia coliby DNA Shuffling of Four Orthologous Parental cDNAs

Among cellulase genes, those of animals are known for their difficulty in overexpression. We constructed a chimeric library by family shuffling of endo-beta-1,4-glucanase genes from four different termite species (Reticulitermes speratus, Nasutitermes takasagoensis, Coptotermes formosanus, and Coptotermes acinaciformis) sharing 78.5-96% homology in amino acid sequence. The constructed library was screened by Congo red plate assay combined with 96-well micro-enzyme assay, and clones showing enhanced CMCase activities were obtained. The mutated genes were overexpressed in Escherichia coli intracellularly as an active form. The endo-beta-1,4-glucanase (CMCase) activity in soluble fractions of E. coli harboring the mutant genes was 20-30 fold higher than that of wild-type genes. The mutant enzyme showed high activity against CMC and properties similar to those of the native enzymes.

Cryptotermes brevis (Isoptera: Kalotermitidae) in the Azores: lessons after 2 yr of monitoring in the Archipelago

The dispersal flights of West Indian drywood termite, Cryptotermes brevis (Walker) (Isoptera: Kalotermitidae) were surveyed in the major cities of Azores. The sampling device used to estimate termite density consisted of a yellow adhesive trap (size 45 by 24 cm), placed with an artificial or natural light source in a dark attic environment. In addition, data from two other projects were used to improve the knowledge about the geographical distribution of the species. The level of infestation in the two main Azorean towns differed, with high levels in the houses of Angra do Heroísmo, whereas in Ponta Delgada, there are fewer houses with high levels of infestation. The infestation in Ponta Delgada shows a pattern of spreading from the center outward to the city's periphery, whereas in Angra do Heroísmo, there was a pattern of spreading outward from several foci. The heavy infestation observed in Angra do Heroísmo and the clear increase of infestation levels observed from 2010 to 2011 is a reason for concern and calls for an urgent application of an Integrated Pest Management (IPM) control strategy.

Endogenous cellulase enzymes in the stick insect (Phasmatodea) gut

High cellulase (endo-beta-1,4-glucanase) activity was detected in the anterior midgut of the walking stick (Phasmatodea) Eurycantha calcarata. The enzyme was isolated and analyzed via mass spectrometry. RT-PCR revealed two endoglucanase genes, EcEG1 and EcEG2. Mascot analysis of the purified enzyme confirms it to be the product of gene EcEG1. Homologous cDNAs were also isolated from a distantly related species, Entoria okinawaensis, suggesting a general distribution of cellulase genes in phasmids. Phasmid cellulases showed high homology to endogenously-produced glycoside hydrolase family 9 (GH9) endoglucanases from insects, especially to those of termites, cockroaches, and crickets. The purified E. calcarata enzyme showed clear antigency against an anti-serum for termite GH9 cellulase, which, together with the sequence homology, further suggests an endogenous origin of the enzyme. This discovery suggests a possible nutritive value for cellulose in the leaf-feeding phasmids, unlike in herbivorous Lepidoptera.

Correlated SEM, FIB-SEM, TEM, and NanoSIMS imaging of microbes from the hindgut of a lower termite: methods for in situ functional and ecological studies of uncultivable microbes

The hindguts of lower termites harbor highly diverse, endemic communities of symbiotic protists, bacteria, and archaea essential to the termite's ability to digest wood. Despite over a century of experimental studies, ecological roles of many of these microbes are unknown, partly because almost none can be cultivated. Many of the protists associate with bacterial symbionts, but hypotheses for their respective roles in nutrient exchange are based on genomes of only two such bacteria. To show how the ecological roles of protists and nutrient transfer with symbiotic bacteria can be elucidated by direct imaging, we combined stable isotope labeling (13C-cellulose) of live termites with analysis of fixed hindgut microbes using correlated scanning electron microscopy, focused ion beam-scanning electron microscopy (FIB-SEM), transmission electron microscopy, and high resolution imaging mass spectrometry (NanoSIMS). We developed methods to prepare whole labeled cells on solid substrates, whole labeled cells milled with a FIB-SEM instrument to reveal cell interiors, and ultramicrotome sections of labeled cells for NanoSIMS imaging of 13C enrichment in protists and associated bacteria. Our results show these methods have the potential to provide direct evidence for nutrient flow and suggest the oxymonad protist Oxymonas dimorpha phagocytoses and enzymatically degrades ingested wood fragments, and may transfer carbon derived from this to its surface bacterial symbionts.

Nest sanitation through defecation: antifungal properties of wood cockroach feces

The wood cockroach Cryptocercus punctulatus nests as family units inside decayed wood, a substrate known for its high microbial load. We tested the hypothesis that defecation within their nests, a common occurrence in this species, reduces the probability of fungal development. Conidia of the entomopathogenic fungus, Metarhizium anisopliae, were incubated with crushed feces and subsequently plated on potato dextrose agar. Relative to controls, the viability of fungal conidia was significantly reduced following incubation with feces and was negatively correlated with incubation time. Although the cockroach's hindgut contained abundant β-1,3-glucanase activity, its feces had no detectable enzymatic function. Hence, these enzymes are unlikely the source of the fungistasis. Instead, the antifungal compound(s) of the feces involved heat-sensitive factor(s) of potential microbial origin. When feces were boiled or when they were subjected to ultraviolet radiation and subsequently incubated with conidia, viability was "rescued" and germination rates were similar to those of controls. Filtration experiments indicate that the fungistatic activity of feces results from chemical interference. Because Cryptocercidae cockroaches have been considered appropriate models to make inferences about the factors fostering the evolution of termite sociality, we suggest that nesting in microbe-rich environments likely selected for the coupling of intranest defecation and feces fungistasis in the common ancestor of wood cockroaches and termites. This might in turn have served as a preadaptation that prevented mycosis as these phylogenetically related taxa diverged and evolved respectively into subsocial and eusocial organizations.

The cellulolytic system of the termite gut

The demand for the usage of natural renewable polymeric material is increasing in order to satisfy the future needs for energy and chemical precursors. Important steps in the hydrolysis of polymeric material and bioconversion can be performed by microorganisms. Over about 150 million years, termites have optimized their intestinal polysaccharide-degrading symbiosis. In the ecosystem of the "termite gut," polysaccharides are degraded from lignocellulose, such as cellulose and hemicelluloses, in 1 day, while lignin is only weakly attacked. The understanding of the principles of cellulose degradation in this natural polymer-degrading ecosystem could be helpful for the improvement of the biotechnological hydrolysis and conversion of cellulose, e.g., in the case of biogas production from natural renewable plant material in biogas plants. This review focuses on the present knowledge of the cellulose degradation in the termite gut.

Maintenance of essential amino acid synthesis pathways in the Blattabacterium cuenoti symbiont of a wood-feeding cockroach

In addition to harbouring intestinal symbionts, some animal species also possess intracellular symbiotic microbes. The relative contributions of gut-resident and intracellular symbionts to host metabolism, and how they coevolve are not well understood. Cockroaches and the termite Mastotermes darwiniensis present a unique opportunity to examine the evolution of spatially separated symbionts, as they harbour gut symbionts and the intracellular symbiont Blattabacterium cuenoti. The genomes of B. cuenoti from M. darwiniensis and the social wood-feeding cockroach Cryptocercus punctulatus are each missing most of the pathways for the synthesis of essential amino acids found in the genomes of relatives from non-wood-feeding hosts. Hypotheses to explain this pathway degradation include: (i) feeding on microbes present in rotting wood by ancestral hosts; (ii) the evolution of high-fidelity transfer of gut microbes via social behaviour. To test these hypotheses, we sequenced the B. cuenoti genome of a third wood-feeding species, the phylogenetically distant and non-social Panesthia angustipennis. We show that host wood-feeding does not necessarily lead to degradation of essential amino acid synthesis pathways in B. cuenoti, and argue that ancestral high-fidelity transfer of gut microbes best explains their loss in strains from M. darwiniensis and C. punctulatus.

Cellulases from insects

Bioethanol is currently produced by the fermentation of sugary and starchy crops, but waste plant biomass is a more abundant source because sugars can be derived directly from cellulose. One of the limiting steps in the biomass-to-ethanol process is the degradation of cellulose to fermentable sugars (saccharification). This currently relies on the use of bacterial and/or fungal cellulases, which tend to have low activity under biorefinery conditions and are easily inhibited. Some insect species feed on plant biomass and can efficiently degrade cellulose to produce glucose as an energy source. Although insects were initially thought to require symbiotic relationships with bacteria and fungi to break down cellulose, several species in the orders Dictyoptera, Orthoptera, and Coleoptera have now been shown to produce their own cellulases in the midgut or salivary glands, and putative cellulase genes have been identified in other orders. Insect cellulases often work in concert with cellulases provided by symbiotic microbiota in the gut to achieve efficient cellulolysis. We discuss the current status of insect cellulases and potential strategies that could be used to find novel enzymes and improve their efficiency.

Endogenous Plant Cell Wall Digestion: A Key Mechanism in Insect Evolution

The prevailing view that insects lack endogenous enzymes for plant cell wall (PCW) digestion had led to the hypothesis that PCW digestion evolved independently in different insect taxa through the establishment of symbiotic relationships with microorganisms. However, recent studies reporting endogenous PCW-degrading genes and enzymes for several insects, including phylogenetically basal insects and closely related arthropod groups, challenge this hypothesis. Here, we summarize the molecular and biochemical evidence on the mechanisms of PCW digestion in insects to analyze its evolutionary pathways. The evidence reveals that the symbiotic-independent mechanism may be the ancestral mechanism for PCW digestion. We discuss the implications of this alternative hypothesis in the evolution of plant-insect interactions and suggest that changes in the composition of lignocellulolytic complexes were involved in the evolution of feeding habits and diet specializations in insects, playing important roles in the evolution of plant-insect interactions and in the diversification of insects.

Molecular cloning and functional characterization of an endogenous endoglucanase belonging to GHF45 from the western corn rootworm, Diabrotica virgifera virgifera

A novel insect β-1,4-endoglucanase (DvvENGaseI) gene belonging to the glycoside hydrolase family (GHF) 45 was identified from the western corn rootworm, Diabrotica virgifera virgifera. The cDNA of the DvvENGaseI consisted of a 720 bp open reading frame encoding a 239 amino-acid protein. Analysis of the amino acid sequence revealed that DvvENGaseI exhibits 60% protein sequence identity when compared with an endoglucanase belonging to GHF45 from another beetle, Leptinotarsa decemlineata. Western blot analyses using a polyclonal antiserum developed from a partial peptide sequence revealed that DvvENGaseI expression coincided with body regions corresponding to the fore-, mid- and hindgut, although regions corresponding to the midgut and hindgut were the primary sites for DvvENGaseI expression. Functional analysis of the DvvENGaseI by RNA interference (RNAi) indicated that nearly complete knock-down of gene expression could be obtained by injection of dsRNA based on qRT-PCR and western blot analysis. However, suppression only resulted in slight developmental delays suggesting that this gene may be part of a larger system of cellulose degrading enzymes.

Analysis of extensive [FeFe] hydrogenase gene diversity within the gut microbiota of insects representing five families of Dictyoptera

We have designed and utilized degenerate primers in the phylogenetic analysis of [FeFe] hydrogenase gene diversity in the gut ecosystems of roaches and lower termites. H(2) is an important free intermediate in the breakdown of wood by termite gut microbial communities, reaching concentrations in some species exceeding those measured for any other biological system. The primers designed target with specificity the largest group of enzymatic H domain proteins previously identified in a termite gut metagenome. "Family 3" hydrogenase sequences were amplified from the guts of lower termites, Incisitermes minor, Zootermopsis nevadensis, and Reticulitermes hesperus, and two roaches, Cryptocercus punctulatus and Periplaneta americana. Subsequent analyses revealed that all termite and Cryptocercus sequences were phylogenetically distinct from non-termite-associated hydrogenases available from public databases. The abundance of unique sequence operational taxonomic units (as many as 21 from each species) underscores the previously demonstrated physiological importance of H(2) to the gut ecosystems of these wood-feeding insects. The diversity of sequences observed might be reflective of multiple niches that the enzymes have been evolved to accommodate. Sequences cloned from Cryptocercus and the lower termite samples, all of which are wood feeding insects, clustered closely with one another in phylogenetic analyses to the exclusion of alleles from P. americana, an omnivorous cockroach, also cloned during this study. We present primers targeting a family of termite gut [FeFe] hydrogenases and provide results that are consistent with a pivotal role for hydrogen in the termite gut ecosystem and point toward unique evolutionary adaptations to the gut ecosystem.

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.

Advances in insect phylogeny at the dawn of the postgenomic era

Most species on Earth are insects and thus, understanding their evolutionary relationships is key to understanding the evolution of life. Insect relationships are increasingly well supported, due largely to technological advances in molecular sequencing and phylogenetic computational analysis. In this postgenomic era, insect systematics will be furthered best by integrative methods aimed at hypothesis corroboration from molecular, morphological, and paleontological evidence. This review of the current consensus of insect relationships provides a foundation for comparative study and offers a framework to evaluate incoming genomic evidence. Notable recent phylogenetic successes include the resolution of Holometabola, including the identification of the enigmatic Strepsiptera as a beetle relative and the early divergence of Hymenoptera; the recognition of hexapods as a crustacean lineage within Pancrustacea; and the elucidation of Dictyoptera orders, with termites placed as social cockroaches. Regions of the tree that require further investigation include the earliest winged insects (Palaeoptera) and Polyneoptera (orthopteroid lineages).

Cellulolytic environment in the midgut of the wood-feeding higher termite Nasutitermes takasagoensis

Unlike lower termites, xylophagous higher termites thrive on wood without the aid of symbiotic protists. In the higher termite Nasutitermes takasagoensis, both endogenous endo-β-1,4-glucanase and β-glucosidase genes are expressed in the midgut, which is believed to be the main site of cellulose digestion. To further explore the detailed cellulolytic system in the midgut of N. takasagoensis, we performed immunohistochemistry and digital light microscopy to determine distributions of cellulolytic enzymes in the salivary glands and the midgut as well as the total cellulolytic activity in the midgut. Although cellulolytic enzymes were uniformly produced in the midgut epithelium, the concentration of endo-β-1,4-glucanase activity and luminal volume in the midgut were comparable to those of the wood-feeding lower termite Coptotermes formosanus, which digests cellulose with the aid of hindgut protists. However, the size of ingested wood particles was considerably larger in N. takasagoensis than that in C. formosanus. Nevertheless, it is possible that the cellulolytic system in the midgut of N. takasagoensis hydrolyzes highly crystalline cellulose to a certain extent. The glucose produced did not accumulate in the midgut lumen. Therefore, the present study suggests that the midgut of the higher termite provides the necessary conditions for cellulolysis.

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.

Development of a PCR-restriction fragment length polymorphism protocol for rapid detection and differentiation of four cockroach vectors (group I "Dirty 22" species) responsible for food contamination and spreading of foodborne pathogens: public health importance

Assessing the adulteration of food products and the presence of filth and extraneous materials is one of the measures that the U.S. Food and Drug Administration (FDA) utilizes in implementing regulatory actions of public health importance. To date, 22 common pest species (also known as the "Dirty 22" species) have been regarded by this agency as the spreaders of foodborne diseases. We have further categorized the Dirty 22 species into four groups: I has four cockroach species, II has two ant species, III has 12 fly species, and IV has four rodent species. The presence of any Dirty 22 species is also considered an indicator of unsanitary conditions in food processing and storage facilities. In this study, we describe the development of a two-step nested PCR protocol to amplify the small subunit ribosomal gene of group I Dirty 22 species that include four cockroach species: Blattella germanica, Blatta orientalis, Periplaneta americana, and Supella longipalpa, along with the development of a PCR-restriction fragment length polymorphism method for rapid detection and differentiation of these violative species. This method will be utilized when the specimen cannot be identified with conventional microscopic taxonomic methods, especially when only small body parts are separated and recovered from food samples for analysis or when these body parts are in a decomposed state. This new PCR-restriction fragment length polymorphism will provide correct identification of group I Dirty 22 species; this information can then be used in regulation and prevention of foodborne pathogens.

Genome shrinkage and loss of nutrient-providing potential in the obligate symbiont of the primitive termite Mastotermes darwiniensis

Beneficial microbial associations with insects are common and are classified as either one or a few intracellular species that are vertically transmitted and reside intracellularly within specialized organs or as microbial assemblages in the gut. Cockroaches and termites maintain at least one if not both beneficial associations. Blattabacterium is a flavobacterial endosymbiont of nearly all cockroaches and the termite Mastotermes darwiniensis and can use nitrogenous wastes in essential amino acid and vitamin biosynthesis. Key changes during the evolutionary divergence of termites from cockroaches are loss of Blattabacterium, diet shift to wood, acquisition of a specialized hindgut microbiota, and establishment of advanced social behavior. Termite gut microbes collaborate to fix nitrogen, degrade lignocellulose, and produce nutrients, and the absence of Blattabacterium in nearly all termites suggests that its nutrient-provisioning role has been replaced by gut microbes. M. darwiniensis is a basal, extant termite that solely retains Blattabacterium, which would show evidence of relaxed selection if it is being supplanted by the gut microbiome. This termite-associated Blattabacterium genome is ∼8% smaller than cockroach-associated Blattabacterium genomes and lacks genes underlying vitamin and essential amino acid biosynthesis. Furthermore, the M. darwiniensis gut microbiome membership is more consistent between individuals and includes specialized termite gut-associated bacteria, unlike the more variable membership of cockroach gut microbiomes. The M. darwiniensis Blattabacterium genome may reflect relaxed selection for some of its encoded functions, and the loss of this endosymbiont in all remaining termite genera may result from its replacement by a functionally complementary gut microbiota.

Transcriptome profiling of female alates and egg-laying queens of the Formosan subterranean termite

Termites are known to have an extraordinary reproductive plasticity and capacity, but the underlying genetic patterns of termite reproductive biology are relatively understudied. The goal of this study was to identify genes for which expression levels differ between dealated precopulatory females (virgins) and egg-laying queens of the Formosan subterranean termite, Coptotermes formosanus Shiraki. We constructed a normalized polyphenic expressed sequence tag (EST) library that represents genomic material from most of the castes and life stages of the Formosan subterranean termite. Microarrays were designed using probes from this EST library and public genomic resources. Virgin females and queens were competitively hybridized to these microarrays and differentially expressed candidate genes were identified. Differential expression of eight genes was subsequently confirmed via reverse transcriptase quantitative PCR (RT-QPCR). When compared to virgins, queens had higher expression of genes coding for proteins related to immunity (gram negative binding protein), nutrition (e.g., termite-derived endo-beta-1,4-glucanase), protein storage, regulation of caste differentiation and reproduction (hexamerin, juvenile hormone binding protein). Queens also had higher transcript levels for genes involved in metabolism of xenobiotics, fat, and juvenile hormone (glutathione-S-transferase-like proteins, and cytochrome P450), among others. In particular, hexamerin, juvenile hormone binding protein, and a cytochrome P450 from the 4C subfamily are likely to be involved in initiating the inactive period during the reproductive cycle of the queen. Vice versa, virgins had higher expression than queens of genes related to respiration, probably due to recent flight activity, and several genes of unknown function.