Evidence for cocladogenesis between diverse dictyopteran lineages and their intracellular endosymbionts

The fine structure of colleterial glands in two cockroaches and three termites, including a detailed study of Cryptocercus punctulatus (Blattaria, Cryptocercidae) and Mastotermes darwiniensis (Isoptera, Mastotermitidae)

The colleterial glands of insects are organs associated with the female genital apparatus. In cockroaches, these glands produce secretions that cover two parallel rows of eggs during oviposition, and in oviparous species, these secretions become the tanned, sculpted, rigid outer casing of the ootheca. The goal of this study was to compare the gross anatomy of the colleterial glands and the ultrastructure of their component tubules in the phylogenetically significant genera Cryptocercus (Blattaria) and Mastotermes (Isoptera). Recent studies indicate that cockroaches in the genus Cryptocercus are the sister group of termites, and Mastotermes is the only termite known to produce a cockroach-like ootheca. One additional oviparous cockroach, Therea, and two additional termites, Zootermopsis and Pseudacanthotermes, were also examined. As in other cockroaches, the colleterial glands of Cryptocercus and Therea are asymmetrical, with a well developed bipartite left gland and a smaller right gland. In the termites Mastotermes, Zootermopsis, and Pseudacanthotermes, the colleterial glands are composed of a well-developed, paired, anterior gland and a small posterior gland; histological staining and cytological evidence suggest that these are homologues of the left and the right colleterial glands of cockroaches, respectively. At the ultrastructural level, colleterial gland tubules are made of cells belonging to a modified class 1 type cell in the cockroaches, in Mastotermes, and in Zootermopsis; the latter lays its eggs singly, without a surrounding ootheca-like structure. In the advanced termite Pseudacanthotermes, the tubules are made of secretory units belonging to the class 3 cell type. This study demonstrates that the cytological characteristics of colleterial glands in basal termites are similar to those of cockroaches, whether the termite secretes an oothecal casing that covers two parallel rows of eggs, as in Mastotermes, or lays its eggs singly, as in Zootermopsis. The function of colleterial glands in non-mastotermitid termites is unknown.

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.

Molecular phylogeny of Cryptocercus wood-roaches based on mitochondrial COII and 16S sequences, and chromosome numbers in Palearctic representatives

Woodroaches of the genus Cryptocercus are subsocial and xylophagous cockroaches, distributed in North America and Asia. Studies on male chromosome number in Nearctic species have shown that diploid numbers vary from 2n=37 to 2n=47; numbers from Palearctic species were heretofore unknown. Two hypotheses have been proposed to explain the varying number of chromosomes among Nearctic species: the serial reduction hypothesis, and the parallel scenario. We performed phylogenetic analyses of the COII gene in these species and found evidence for the topology (47(45(43(39,37), which is congruent with the serial reduction hypothesis. We also determined chromosome numbers for the first time in Palearctic species, and found Cryptocercus primarius and Cryptocercus relictus to have relatively low chromosome numbers (2n=17-21) compared to their Nearctic relatives. Finally, our study determined the phylogenetic position of Cryptocercus primarius among other Asian taxa.

Dissociation and horizontal transmission of codispersing lichen symbionts in the genus Lepraria (Lecanorales: Stereocaulaceae)

Lichenized fungi of the genus Lepraria lack ascomata and conidiomata, and symbionts codisperse by soredia. Here, it is determined whether algal symbionts associated with Lepraria are monophyletic, and whether fungal and algal phylogenies are congruent, both of which are indicative of a long-term, continuous association between symbionts. The internal transcribed spacer (ITS) and part of the actin type I locus were sequenced from algae associated with Lepraria, and the fungal ITS and mitochondrial small subunit (mtSSU) were sequenced from fungal symbionts. Phylogenetic analyses tested for monophyly of algal symbionts and congruence between algal and fungal phylogenies. Algae associated with Lepraria were not monophyletic, and identical algae associated with different Lepraria individuals and species. Algal and fungal phylogenies were not congruent, suggesting a lack of strict codiversification. This study suggests that associations between symbionts are not strictly maintained over evolutionary time. The ability to switch partners may provide benefits similar to genetic recombination, which may have helped this lineage persist.

Trail-Following Pheromones in Basal Termites, with Special Reference to Mastotermes darwiniensis

In the framework of an evolutionary study, trail pheromones have been studied in the most basal extant termite, Mastotermes darwiniensis (Mastotermitidae), and two other basal termites, the Termopsidae Porotermes adamsoni (Porotermitinae) and Stolotermes victoriensis (Stolotermitinae). Although workers of M. darwiniensis do not walk in single file while exploring a new environment under experimental conditions and are unable to follow artificial trails in 'open field' experiments, they do secrete a trail-following pheromone from their sternal glands. This unique behavior might reflect a primitive function of communication of the sternal gland. The major component of the pheromone appears to be the same in the three basal species: the norsesquiterpene alcohol (E)-2,6,10-trimethyl-5,9-undecadien-1-ol. This represents a new chemical category of trail-following pheromones for termites. The quantity of pheromone was estimated as 20 pg/individual in M. darwiniensis, 700 pg/individual in P. adamsoni, and 4 pg/individual in S. victoriensis. The activity threshold was 1 ng/cm in M. darwiniensis and 10 pg/cm in P. adamsoni. In M. darwiniensis, the trail pheromone was secreted by sternal gland 4 and to a lesser degree by sternal gland 3, sternal gland 5 being almost inactive. This study highlighted phylogenetic relationships between the Mastotermitidae and two subfamilies of the Termopsidae, the Porotermitinae and the Stolotermitinae. Furthermore, it indicated a heterogeneity within the Termopsidae, with Porotermitinae and Stolotermitinae on one hand, and Termopsinae on the other. Finally, Mastotermitidae and Termopsidae, with C14 trail pheromones, are clearly separated from the Kalotermitidae, Rhinotermitidae, and Termitidae that secrete C12 or C20 trail pheromones.

Cospeciation in the triplex symbiosis of termite gut protists (Pseudotrichonympha spp.), their hosts, and their bacterial endosymbionts

A number of cophylogenetic relationships between two organisms namely a host and a symbiont or parasite have been studied to date; however, organismal interactions in nature usually involve multiple members. Here, we investigated the cospeciation of a triplex symbiotic system comprising a hierarchy of three organisms -- termites of the family Rhinotermitidae, cellulolytic protists of the genus Pseudotrichonympha in the guts of these termites, and intracellular bacterial symbionts of the protists. The molecular phylogeny was inferred based on two mitochondrial genes for the termites and nuclear small-subunit rRNA genes for the protists and their endosymbionts, and these were compared. Although intestinal microorganisms are generally considered to have looser associations with the host than intracellular symbionts, the Pseudotrichonympha protists showed almost complete codivergence with the host termites, probably due to strict transmissions by proctodeal trophallaxis or coprophagy based on the social behaviour of the termites. Except for one case, the endosymbiotic bacteria of the protists formed a monophyletic lineage in the order Bacteroidales, and the branching pattern was almost identical to those of the protists and the termites. However, some non-codivergent evolutionary events were evident. The members of this triplex symbiotic system appear to have cospeciated during their evolution with minor exceptions; the evolutionary relationships were probably established by termite sociality and the complex microbial community in the gut.

Karyology, mitochondrial DNA and the phylogeny of Australian termites

A comprehensive karyological characterization of 20 Australian and three European species of Isoptera, together with a mitochondrial gene analysis is presented. Higher termites appear karyotypically very uniform, while lower termites are highly variable. The differences in chromosome number are explained through Robertsonian changes or multiple translocation events. An ancestral acrocentric karyotype can be suggested as the most primitive one. In Kalotermitidae chromosomal repatterning has repeatedly arisen with the X0-male type possibly representing a XY-derived condition. This argues against a simple origin of termites from cockroaches. The fixed chromosome number of Rhinotermitidae and Termitidae (2n=42, XY/XX) may be explained with the non-random nature of chromosomal evolution. A sex-linked multivalent, either with a ring or a chain structure, is found in the majority of species. Phylogenetic analyses on COII sequences recognize Mastotermitidae as the basal lineage and define the Rhinotermitidae+Termitidae cluster with a good bootstrap support. Kalotermitidae fail to be joined in a single cluster in agreement with the detected chromosomal variability. On the other hand, the karyotypic conservation of the Termitidae family contrasts with the polytomy evidenced at the subfamily level.

MUSEUM SPECIMENS AND PHYLOGENIES ELUCIDATE ECOLOGY'S ROLE IN COEVOLUTIONARY ASSOCIATIONS BETWEEN MITES AND THEIR BEE HOSTS

Coevolutionary associations between hosts and symbionts (or parasites) are often reflected in correlated patterns of divergence as a consequence of limitations on dispersal and establishment on new hosts. Here we show that a phylogenetic correlation is observed between chaetodactylid mites and their hosts, the long-tongued bees; however, this association manifests itself in an atypical fashion. Recently derived mites tend to be associated with basal bee lineages, and vice versa, ruling out a process of cospeciation, and the existence of mites on multiple hosts also suggests ample opportunity for host shifts. An extensive survey of museum collections reveals a pattern of infrequent host shifts at a higher taxonomic level, and yet, frequent shifts at a lower level, which suggests that ecological constraints structure the coevolutionary history of the mites and bees. Certain bee traits, particularly aspects of their nesting behavior, provide a highly predictive framework for the observed pattern of host use, with 82.1% of taxa correctly classified. Thus, the museum survey and phylogenetic analyses provide a unique window into the central role ecology plays in this coevolutionary association. This role is apparent from two different perspectives--as (a) a constraining force evident in the historical processes underlying the significant correlation between the mite and bee phylogenies, as well as (b) by the highly nonrandom composition of bee taxa that serve as hosts to chaetodactylid mites.

Symbiosis as an adaptive process and source of phenotypic complexity

Genomics has revealed that inheritance systems of separate species are often not well segregated: genes and capabilities that evolve in one lineage are often stably acquired by another lineage. Although direct gene transfer between species has occurred at some level in all major groups, it appears to be far more frequent in prokaryotes than in multicellular eukaryotes. An alternative to incorporating novel genes into a recipient genome is acquiring a stable, possibly heritable, symbiotic association and thus enjoying benefits of complementary metabolic capabilities. These kinds of symbioses have arisen frequently in animals; for example, many insect groups have diversified on the basis of symbiotic associations acquired early in their evolutionary histories. The resulting associations are highly complex, often involving specialized cell types and organs, developmental mechanisms that ensure transfer of symbionts between generations, and mechanisms for controlling symbiont proliferation and location. The genomes of long-term obligate symbionts often undergo irreversible gene loss and deterioration even as hosts evolve dependence on them. In some cases, animal genomes may have acquired genes from symbionts, mirroring the gene uptake from mitochondrial and plastid genomes. Multiple symbionts often coexist in the same host, resulting in coadaptation among several phylogenetically distant genomes.

Co-cladogenesis spanning three phyla: leafhoppers (Insecta: Hemiptera: Cicadellidae) and their dual bacterial symbionts

Endosymbioses are a major form of biological complexity affecting the ecological and evolutionary diversification of many eukaryotic groups. These associations are exemplified by nutritional symbioses of insects for which phylogenetic studies have demonstrated numerous cases of long-term codiversification between a bacterial and a host lineage. Some insects, including most leafhoppers (Insecta: Hemiptera: Cicadellidae), have more than one bacterial symbiont within specialized host cells, raising questions regarding the patterns of codiversification of these multiple partners and the evolutionary persistence of complex symbiotic systems. Previous studies reported the presence of two dominant symbiont types in a member of the leafhopper subfamily Cicadellinae (sharpshooters). In this study, 16S rRNA sequences were obtained and used to examine the occurrence and evolutionary relationships of the two dominant symbiont types across 29 leafhopper species. Candidatus Sulcia muelleri (Bacteroidetes) was detected in all leafhopper species examined, a finding that is consistent with a previous report of its ancient association with the Auchenorrhyncha (a grouping that includes leafhoppers, treehoppers, cicadas, planthoppers, and spittlebugs). Baumannia cicadellinicola (Proteobacteria), previously known from only five sharpshooter species, was found only in the sharpshooter tribes Cicadellini and Proconiini, as well as in the subfamily Phereurhininae. Mitochondrial and nuclear gene sequences were obtained and used to reconstruct host phylogenies. Analyses of host and symbiont data sets support a congruent evolutionary history between sharpshooters, Sulcia and Baumannia and thus provide the first strong evidence for long-term co-inheritance of multiple symbionts during the diversification of a eukaryotic host. Sulcia shows a fivefold lower rate of 16S rDNA sequence divergence than does Baumannia for the same host pairs. The term 'coprimary' symbiont is proposed for such cases.

'Candidatus Streptomyces philanthi', an endosymbiotic streptomycete in the antennae of Philanthus digger wasps

Symbiotic interactions with bacteria are essential for the survival and reproduction of many insects. The European beewolf (Philanthus triangulum, Hymenoptera, Crabronidae) engages in a highly specific association with bacteria of the genus Streptomyces that appears to protect beewolf offspring against infection by pathogens. Using transmission and scanning electron microscopy, the bacteria were located in the antennal glands of female wasps, where they form dense cell clusters. Using genetic methods, closely related streptomycetes were found in the antennae of 27 Philanthus species (including two subspecies of P. triangulum from distant localities). In contrast, no endosymbionts could be detected in the antennae of other genera within the subfamily Philanthinae (Aphilanthops, Clypeadon and Cerceris). On the basis of morphological, genetic and ecological data, 'Candidatus Streptomyces philanthi' is proposed. 16S rRNA gene sequence data are provided for 28 ecotypes of 'Candidatus Streptomyces philanthi' that reside in different host species and subspecies of the genus Philanthus. Primers for the selective amplification of 'Candidatus Streptomyces philanthi' and an oligonucleotide probe for specific detection by fluorescence in situ hybridization (FISH) are described.

Molecular Interactions between Bacterial Symbionts and Their Hosts

Symbiotic bacteria are important in animal hosts, but have been largely overlooked as they have proved difficult to culture in the laboratory. Approaches such as comparative genomics and real-time PCR have provided insights into the molecular mechanisms that underpin symbiont-host interactions. Studies on the heritable symbionts of insects have yielded valuable information about how bacteria infect host cells, avoid immune responses, and manipulate host physiology. Furthermore, some symbionts use many of the same mechanisms as pathogens to infect hosts and evade immune responses. Here we discuss what is currently known about the interactions between bacterial symbionts and their hosts.

Cascading host-associated genetic differentiation in parasitoids of phytophagous insects

The extraordinary diversity of phytophagous insects may be attributable to their narrow specialization as parasites of plants, with selective tradeoffs associated with alternate host plants driving genetic divergence of host-associated forms via ecological speciation. Most phytophagous insects in turn are attacked by parasitoid insects, which are similarly specialized and may also undergo host-associated differentiation (HAD). A particularly interesting possibility is that HAD by phytophagous insects might lead to HAD in parasitoids, as parasitoids evolve divergent lineages on the new host plant-specific lineages of their phytophagous hosts. We call this process 'cascading host-associated differentiation' (cascading HAD). We tested for cascading HAD in parasitoids of two phytophagous insects, each of which consists of genetically distinct host-associated lineages on the same pair of goldenrods (Solidago). Each parasitoid exhibited significant host-associated genetic divergence, and the distribution and patterns of divergence are consistent with divergence in sympatry. Although evidence for cascading HAD is currently limited, our results suggest that it could play an important role in the diversification of parasitoids attacking phytophagous insects. The existence of cryptic host-associated lineages also suggests that the diversity of parasitoids may be vastly underestimated.

Biology bacteriocyte-associated endosymbionts of plant sap-sucking insects

Psyllids, whiteflies, aphids, and mealybugs are members of the suborder Sternorrhyncha and share a common property, namely the utilization of plant sap as their food source. Each of these insect groups has an obligatory association with a different prokaryotic endosymbiont, and the association is the result of a single infection followed by maternal, vertical transmission of the endosymbionts. The result of this association is the domestication of the free-living bacterium to serve the purposes of the host, namely the synthesis of essential amino acids. This domestication is probably in all cases accompanied by a major reduction in genome size. The different properties of the genomes and fragments of the genomes of these endosymbionts suggest that there are different constraints on the permissible evolutionary changes that are probably a function of the gene repertoire of the endosymbiont ancestor and the gene losses that occurred during the reduction of genome size.

Symbiosis and insect diversification: an ancient symbiont of sap-feeding insects from the bacterial phylum Bacteroidetes

Several insect groups have obligate, vertically transmitted bacterial symbionts that provision hosts with nutrients that are limiting in the diet. Some of these bacteria have been shown to descend from ancient infections. Here we show that the large group of related insects including cicadas, leafhoppers, treehoppers, spittlebugs, and planthoppers host a distinct clade of bacterial symbionts. This newly described symbiont lineage belongs to the phylum Bacteroidetes. Analyses of 16S rRNA genes indicate that the symbiont phylogeny is completely congruent with the phylogeny of insect hosts as currently known. These results support the ancient acquisition of a symbiont by a shared ancestor of these insects, dating the original infection to at least 260 million years ago. As visualized in a species of spittlebug (Cercopoidea) and in a species of sharpshooter (Cicadellinae), the symbionts have extraordinarily large cells with an elongate shape, often more than 30 mum in length; in situ hybridizations verify that these correspond to the phylum Bacteroidetes. "Candidatus Sulcia muelleri" is proposed as the name of the new symbiont.

"Endomicrobia": cytoplasmic symbionts of termite gut protozoa form a separate phylum of prokaryotes

Lignocellulose digestion by wood-feeding termites depends on the mutualistic interaction of unusual, flagellate protists located in their hindgut. Most of the flagellates harbor numerous prokaryotic endosymbionts of so-far-unknown identity and function. Using a full-cycle molecular approach, we show here that the endosymbionts of the larger gut flagellates of Reticulitermes santonensis belong to the so-called termite group 1 (TG-1) bacteria, a group of clones previously obtained exclusively from gut homogenates of Reticulitermes speratus that are only distantly related to other bacteria and are considered a novel bacterial phylum based on their 16S rRNA gene sequences. Fluorescence in situ hybridization with specifically designed oligonucleotide probes confirmed that TG-1 bacteria are indeed located within the flagellate cells and demonstrated that Trichonympha agilis (Hypermastigida) and Pyrsonympha vertens (Oxymonadida) harbor phylogenetically distinct populations of symbionts (<95% sequence similarity). Transmission electron microscopy revealed that the symbionts are small, spindle-shaped cells (0.6 microm in length and 0.3 microm in diameter) surrounded by two membranes and located within the cytoplasm of their hosts. The symbionts of the two flagellates are described as candidate species in the candidate genus "Endomicrobium." Moreover, we provide evidence that the members of the TG-1 phylum, for which we propose the candidate name "Endomicrobia," are phylogenetically extremely diverse and are present in and also restricted to the guts of all lower termites and wood-feeding cockroaches of the genus Cryptocercus, the only insects that are in an exclusive, obligately mutualistic association with such unique cellulose-fermenting protists.

Adaptive evolution in GroEL from distantly related endosymbiotic bacteria of insects

Many symbioses between bacteria and insects resulted from ancient infections followed by strict vertical transmission within host lineages. The strong bottlenecks under which this transmission occurs promote the neutral fixation of slightly deleterious mutations by genetic drift. As predicted by Muller's ratchet, this fixation will drive endosymbiotic bacteria through an irreversible dynamics of fitness loss. The chaperonin GroEL has been proposed as a compensatory mechanism whereby endosymbiotic bacteria of aphids persist. Here, we show that endosymbiotic bacteria of insects from two phylogenetically very distant bacterial phyla have fixed amino acid substitutions by positive selection in functionally important GroEL regions involved in either GroES/peptide binding or in the en bloc movement of the GroEL apical domain. These results, together with the high levels of constitutive expression of GroEL in these endosymbionts, provide valuable insights into the evolution of a molecular mechanism responsible for the maintenance of the symbiotic lifestyle.

Cospeciation analysis of an obligate pollination mutualism: have Glochidion trees (Euphorbiaceae) and pollinating Epicephala moths (Gracillariidae) diversified in parallel?

Species-specific obligate pollination mutualism between Glochidion trees (Euphorbiaceae) and Epicephala moths (Gracillariidae) involves a large number of interacting species and resembles the classically known fig-fig wasp and yucca-yucca moth associations. To assess the extent of parallel cladogenesis in Glochidion-Epicephala association, we reconstruct phylogenetic relationships of 18 species of Glochidion using nuclear ribosomal DNA sequences (internal and external transcribed spacers) and those of the corresponding 18 Epicephala species using mitochondrial (the cytochrome oxidase subunit I gene) and nuclear DNA sequences (the arginine kinase and elongation factor-1alpha genes). Based on the obtained phylogenies, we determine whether Glochidion and Epicephala have undergone parallel diversification using several different methods for investigating the level of cospeciation between phylogenies. These tests indicate that there is generally a greater degree of correlation between Glochidion and Epicephala phylogenies than expected in a random association, but the results are sensitive to selection of different phylogenetic hypotheses and analytical methods for evaluating cospeciation. Perfect congruence between phylogenies is not found in this association, which likely resulted from host shift by the moths. The observed significant discrepancy between Glochidion and Epicephala phylogenies implies that the one-to-one specificity between the plants and moths has been maintained through a complex speciation process or that there is an underestimated diversity of association between Glochidion trees and Epicephala moths.

Wolbachia.Bacterial Endosymbionts of Filarial Nematodes

Filarial nematodes are important helminth parasites of the tropics and a leading cause of global disability. They include species responsible for onchocerciasis, lymphatic filariasis and dirofilariasis. A unique feature of these nematodes is their dependency upon a symbiotic intracellular bacterium, Wolbachia, which is essential for normal development and fertility. Advances in our understanding of the symbiosis of Wolbachia bacteria with filarial nematodes have made rapid progress in recent years. Here we summarise our current understanding of the evolution of the symbiotic association together with insights into the functional basis of the interaction derived from genomic analysis. Also we discuss the contribution of Wolbachia to inflammatory-mediated pathogenesis and adverse reactions to anti-filarial drugs and describe the outcome of recent field trials using antibiotics as a promising new tool for the treatment of filarial infection and disease.

Major alteration of the expression site of endogenous cellulases in members of an apical termite lineage

Termites are among the most important cellulose-digesting animals on earth, and are well-known for the symbiotic relationship they have with cellulolytic trichomonad and oxymonad flagellates (unicellular eukaryotes). Perhaps less well-known is the fact that approximately 75% of the approximately 2600 described termite species -- those belonging to the family Termitidae -- do not harbour such flagellates. Unlike most termites from other families, the majority of termitids do not consume wood, feeding instead on soil, leaf litter, fungi, grass, or lichen. Recent years have seen the characterization of the endogenous cellulase enzymes that help termites digest cellulose, from one flagellate-harbouring species (Reticulitermes speratus), as well as one termitid (Nasutitermes takasagoensis). The genes encoding the enzymes in these two termites are similar. However, their site of expression differs markedly -- the salivary glands in R. speratus and the midgut in N. takasagoensis. To investigate this difference further, we performed a comparative study of cellulase expression in various termitid and flagellate-harbouring species, using enzyme assays and reverse transcription polymerase chain reactions. Taxa from phylogenetically basal lineages were consistently found to express endogenous genes specifically in the salivary glands, whilst those from a relatively apical lineage containing termitids expressed cellulases solely in the midgut. Relatively low levels of cellulase activity were found in nonwood-feeding species, while the wood-feeding Coptotermes formosanus -- arguably the most destructive pest species world-wide -- was found to have high levels of activity in all parts of the gut when compared to all other termites. In the light of these results, as well as recently accumulated phylogenetic data, we discuss scenarios for the evolution of cellulose digestion in termites.

Evolutionary relationships of primary prokaryotic endosymbionts of whiteflies and their hosts

Whiteflies (Hemiptera: Sternorrhyncha: Aleyrodidae) are plant sap-sucking insects that harbor prokaryotic primary endosymbionts (P-endosymbionts) within specialized cells located in their body cavity. Four-kilobase DNA fragments containing 16S-23S ribosomal DNA (rDNA) were amplified from the P-endosymbiont of 24 whiteflies from 22 different species of 2 whitefly subfamilies. In addition, 3-kb DNA fragments containing mitochondrial cytB, nd1, and large-subunit rDNA (LrDNA) were amplified from 17 whitefly species. Comparisons of the P-endosymbiont (16S-23S rDNA) and host (cytB-nd1-LrDNA) phylogenetic trees indicated overall congruence consistent with a single infection of a whitefly ancestor with a bacterium and subsequent cospeciation (cocladogenesis) of the host and the P-endosymbiont. On the basis of both the P-endosymbiont and host trees, the whiteflies could be subdivided into at least five clusters. The major subdivision was between the subfamilies Aleyrodinae and Aleurodicinae. Unlike the P-endosymbionts of may other insects, the P-endosymbionts of whiteflies were related to Pseudomonas and possibly to the P-endosymbionts of psyllids. The lineage consisting of the P-endosymbionts of whiteflies is given the designation "Candidatus Portiera" gen. nov., with a single species, "Candidatus Portiera aleyrodidarum" sp. nov.

Host-symbiont stability and fast evolutionary rates in an ant-bacterium association: cospeciation of camponotus species and their endosymbionts, candidatus blochmannia

Bacterial endosymbionts are widespread across several insect orders and are involved in interactions ranging from obligate mutualism to reproductive parasitism. Candidatus Blochmannia gen. nov. (Blochmannia) is an obligate bacterial associate of Camponotus and related ant genera (Hymenoptera: Formicidae). The occurrence of Blochmannia in all Camponotus species sampled from field populations and its maternal transmission to host offspring suggest that this bacterium is engaged in a long-term, stable association with its ant hosts. However, evidence for cospeciation in this system is equivocal because previous phylogenetic studies were based on limited gene sampling, lacked statistical analysis of congruence, and have even suggested host switching. We compared phylogenies of host genes (the nuclear EF-1alphaF2 and mitochondrial COI/II) and Blochmannia genes (16S ribosomal DNA [rDNA], groEL, gidA, and rpsB), totaling more than 7 kilobases for each of 16 Camponotus species. Each data set was analyzed using maximum likelihood and Bayesian phylogenetic reconstruction methods. We found minimal conflict among host and symbiont phylogenies, and the few areas of discordance occurred at deep nodes that were poorly supported by individual data sets. Concatenated protein-coding genes produced a very well-resolved tree that, based on the Shimodaira-Hasegawa test, did not conflict with any host or symbiont data set. Correlated rates of synonymous substitution (d(S)) along corresponding branches of host and symbiont phylogenies further supported the hypothesis of cospeciation. These findings indicate that Blochmannia-Camponotus symbiosis has been evolutionarily stable throughout tens of millions of years. Based on inferred divergence times among the ant hosts, we estimated rates of sequence evolution of Blochmannia to be approximately 0.0024 substitutions per site per million years (s/s/MY) for the 16S rDNA gene and approximately 0.1094 s/s/MY at synonymous positions of the genes sampled. These rates are several-fold higher than those for related bacteria Buchnera aphidicola and Escherichia coli. Phylogenetic congruence among Blochmannia genes indicates genome stability that typifies primary endosymbionts of insects.