The Maternal Effect Gene Wds Controls Wolbachia Titer in Nasonia

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The endosymbiont Wolbachia in Eurasian populations of Drosophila melanogaster

The endosymbiotic [alpha]-proteobacteria Wolbachia is widely spread among arthropods and Filariidae nematodes. This bacterium is transmitted vertically via a transovarian route. Wolbachia is a cause of several reproductive abnormalities in the host species. We analyzed the isofemale lines created using flies collected from Drosophila melanogaster natural populations for infection with the endosymbiont Wolbachia. Wolbachia were genotyped according to five variable markers: the presence of insertion sequence IS5 in two loci, the copy number of two minisatellite repeats, and an inversion. Overall, 665 isofemale lines isolated from the populations of D. melanogaster from Ukraine, Belarus, Moldova, Caucasus, Central Asia, Ural, Udmurtia, Altai, West and East Siberia, and Far East in 1974 through 2005 were used in the work. The samples from Ukrainian, Altaian, and Middle Asian populations were largest. The infection rate of D. melanogaster populations from Middle Asia, Altaian, and Eastern Europe (Ukraine, Moldavia, and Belarus) with Wolbachia amounted to 64, 56, and 39%, respectively. The D. melanogaster population from the Caucasus displayed heterogeneity in the genotypes of this cytoplasmic infection. The Wolbachia genotype wMel, detected in all the populations studied, was the most abundant. The genotype wMelCS2 was always present in the populations from Middle Asia and Altai and was among the rare variants in the D. melanogaster populations from the Eastern Europe. Single instances of the Wolbachia genotype wMelCS occurred in a few flies from the Central Asian and Altai populations, but was not found this genotype in the other regions.     

Wolbachia Utilize Host Actin for Efficient Maternal Transmission in Drosophila melanogaster

Wolbachia pipientis is a ubiquitous, maternally transmitted bacterium that infects the germline of insect hosts. Estimates are that Wolbachia infect nearly 40% of insect species on the planet, making it the most prevalent infection on Earth. The bacterium, infamous for the reproductive phenotypes it induces in arthropod hosts, has risen to recent prominence due to its use in vector control. Wolbachia infection prevents the colonization of vectors by RNA viruses, including Drosophila C virus and important human pathogens such as Dengue and Chikungunya. Here we present data indicating that Wolbachia utilize the host actin cytoskeleton during oogenesis for persistence within and transmission between Drosophila melanogaster generations. We show that phenotypically wild type flies heterozygous for cytoskeletal mutations in Drosophila profilin (chic²²¹/+ and chic¹³²⁰/+) or villin (qua^6-396/+) either clear a Wolbachia infection, or result in significantly reduced infection levels. This reduction of Wolbachia is supported by PCR evidence, Western blot results and cytological examination. This phenotype is unlikely to be the result of maternal loading defects, defects in oocyte polarization, or germline stem cell proliferation, as the flies are phenotypically wild type in egg size, shape, and number. Importantly, however, heterozygous mutant flies exhibit decreased total G-actin in the ovary, compared to control flies and chic²²¹ heterozygous mutants exhibit decreased expression of profilin. Additionally, RNAi knockdown of profilin during development decreases Wolbachia titers. We analyze evidence in support of alternative theories to explain this Wolbachia phenotype and conclude that our results support the hypothesis that Wolbachia utilize the actin skeleton for efficient transmission and maintenance within Drosophila.     

The endosymbiont Wolbachia increases insulin/IGF-like signalling in Drosophila

Insulin/IGF-like signalling (IIS) is an evolutionarily conserved pathway that has diverse functions in multi-cellular organisms. Mutations that reduce IIS can have pleiotropic effects on growth, development, metabolic homeostasis, fecundity, stress resistance and lifespan. IIS is also modified by extrinsic factors. For instance, in the fruitfly Drosophila melanogaster, both nutrition and stress can alter the activity of the pathway. Here, we test experimentally the hypothesis that a widespread endosymbiont of arthropods, Wolbachia pipientis, can alter the degree to which mutations in genes encoding IIS components affect IIS and its resultant phenotypes. Wolbachia infection, which is widespread in D. melanogaster in nature and has been estimated to infect 30 per cent of strains in the Bloomington stock centre, can affect broad aspects of insect physiology, particularly traits associated with reproduction. We measured a range of IIS-related phenotypes in flies ubiquitously mutant for IIS in the presence and absence of Wolbachia. We show that removal of Wolbachia further reduces IIS and hence enhances the mutant phenotypes, suggesting that Wolbachia normally acts to increase insulin signalling. This effect of Wolbachia infection on IIS could have an evolutionary explanation, and has some implications for studies of IIS in Drosophila and other organisms that harbour endosymbionts.     

Wolbachia transfer from Drosophila melanogaster into D. simulans: Host effect and cytoplasmic incompatibility relationships.

Wolbachia are maternally transmitted endocellular bacteria causing a reproductive incompatibility called cytoplasmic incompatibility (CI) in several arthropod species, including Drosophila. CI results in embryonic mortality in incompatible crosses. The only bacterial strain known to infect Drosophila melanogaster (wDm) was transferred from a D. melanogaster isofemale line into uninfected D. simulans isofemale lines by embryo microinjections. Males from the resulting transinfected lines induce >98% embryonic mortality when crossed with uninfected D. simulans females. In contrast, males from the donor D. melanogaster line induce only 18-32% CI on average when crossed with uninfected D. melanogaster females. Transinfected D. simulans lines do not differ from the D. melanogaster donor line in the Wolbachia load found in the embryo or in the total bacterial load of young males. However, >80% of cysts are infected by Wolbachia in the testes of young transinfected males, whereas only 8% of cysts are infected in young males from the D. melanogaster donor isofemale line. This difference might be caused by physiological differences between hosts, but it might also involve tissue-specific control of Wolbachia density by D. melanogaster. The wDm-transinfected D. simulans lines are unidirectionally incompatible with strains infected by the non-CI expressor Wolbachia strains wKi, wMau, or wAu, and they are bidirectionally incompatible with strains infected by the CI-expressor Wolbachia strains wHa or wNo. However, wDm-infected males do not induce CI toward females infected by the CI-expressor strain wRi, which is found in D. simulans continental populations, while wRi-infected males induce partial CI toward wDm-infected females. This peculiar asymmetrical pattern could reflect an ongoing divergence between the CI mechanisms of wRi and wDm. It would also confirm other results indicating that the factor responsible for CI induction in males is distinct from the factor responsible for CI rescue in females.     

Asymmetrical reinforcement and Wolbachia infection in Drosophila

Reinforcement refers to the evolution of increased mating discrimination against heterospecific individuals in zones of geographic overlap and can be considered a final stage in the speciation process. One the factors that may affect reinforcement is the degree to which hybrid matings result in the permanent loss of genes from a species' gene pool. Matings between females of Drosophila subquinaria and males of D. recens result in high levels of offspring mortality, due to interspecific cytoplasmic incompatibility caused by Wolbachia infection of D. recens. Such hybrid inviability is not manifested in matings between D. recens females and D. subquinaria males. Here we ask whether the asymmetrical hybrid inviability is associated with a corresponding asymmetry in the level of reinforcement. The geographic ranges of D. recens and D. subquinaria were found to overlap across a broad belt of boreal forest in central Canada. Females of D. subquinaria from the zone of sympatry exhibit much stronger levels of discrimination against males of D. recens than do females from allopatric populations. In contrast, such reproductive character displacement is not evident in D. recens, consistent with the expected effects of unidirectional cytoplasmic incompatibility. Furthermore, there is substantial behavioral isolation within D. subquinaria, because females from populations sympatric with D. recens discriminate against allopatric conspecific males, whereas females from populations allopatric with D. recens show no discrimination against any conspecific males. Patterns of general genetic differentiation among populations are not consistent with patterns of behavioral discrimination, which suggests that the behavioral isolation within D. subquinaria results from selection against mating with Wolbachia-infected D. recens. Interspecific cytoplasmic incompatibility may contribute not only to post-mating isolation, an effect already widely recognized, but also to reinforcement, particularly in the uninfected species. The resulting reproductive character displacement not only increases behavioral isolation from the Wolbachia-infected species, but may also lead to behavioral isolation between populations of the uninfected species. Given the widespread occurrence of Wolbachia among insects, it thus appears that there are multiple ways by which these endosymbionts may directly and indirectly contribute to reproductive isolation and speciation.     

Wolbachia Infection and Cytoplasmic Incompatibility in Drosophila Species

Forty-one stocks from 30 Drosophila species were surveyed for Wolbachia infection using PCR technology. D. sechellia and two strains of D. auraria were found to be infected and were tested for the expression of cytoplasmic incompatibility, along with D. ananassae and D. melanogaster strains, which are already known to be infected. D. ananassae and D. melanogaster show levels of incompatibility up to 25%, while D. auraria and D. sechellia exhibit levels of egg mortality ~60%. A dot-blot assay using the dnaA sequence as probe was developed to assess the infection levels in individual males that were used in incompatibility crosses. A positive correlation between bacterial density and cytoplasmic incompatibility was observed. The stocks examined can be clustered into at least two groups, depending on the levels of infection relative to the degree of cytoplasmic incompatibility exhibited. One group, containing D. simulans Hawaii, D. sechellia, and D. auraria, exhibits high levels of cytoplasmic incompatibility relative to levels of infection; all the other species and D. simulans Riverside exhibit significantly lower levels of cytoplasmic incompatibility relative to levels of infection. These data show that, in addition to bacterial density, bacterial and/or host factors also affect the expression of cytoplasmic incompatibility.     

Wolbachia infection alters olfactory-cued locomotion in Drosophila spp

Wolbachia pipientis is an endosymbiotic bacterium present in diverse insect species. Although it is well studied for its dramatic effects on host reproductive biology, little is known about its effects on other aspects of host biology, despite its presence in a wide array of host tissues. This study examined the effects of three Wolbachia strains on two different Drosophila species, using a laboratory performance assay for insect locomotion in response to olfactory cues. The results demonstrate that Wolbachia infection can have significant effects on host responsiveness that vary with respect to the Wolbachia strain-host species combination. The wRi strain, native to Drosophila simulans, increases the basal activity level of the host insect as well as its responsiveness to food cues. In contrast, the wMel strain and the virulent wMelPop strain, native to Drosophila melanogaster, cause slight decreases in responsiveness to food cues but do not alter basal activity levels in the host. Surprisingly, the virulent wMelPop strain has very little impact on host responsiveness in D. simulans. This novel strain-host relationship was artificially created previously by transinfection. These findings have implications for understanding the evolution and spread of Wolbachia infections in wild populations and for Wolbachia-based vector-borne disease control strategies currently being developed.     

Inactivation of Wolbachia Reveals Its Biological Roles in Whitefly Host

Background

The whitefly Bemisia tabaci is cryptic species complex composed of numerous species. Individual species from the complex harbor a diversity of bacterial endosymbionts including Wolbachia. However, while Wolbachia is known to have a number of different roles, its role in B. tabaci is unclear. Here, the antibiotic rifampicin is used to selectively eliminate Wolbachia from B. tabaci so as to enable its roles in whitefly development and reproduction to be explored. The indirect effects of Wolbachia elimination on the biology of Encarsia bimaculata, a dominant parasitoid of B. tabaci in South China, were also investigated.

Methodology/Principal Finding

qRT-PCR and FISH were used to show that after 48 h exposure to 1.0 mg/ml rifampicin, Wolbachia was completely inactivated from B. tabaci Mediterranean (MED) without any significant impact on either the primary symbiont, Portiera aleyrodidarum or any of the other secondary endosymbionts present. For B. tabaci MED, Wolbachia was shown to be associated with decreased juvenile development time, increased likelihood that nymphs completed development, increased adult life span and increased percentage of female progeny. Inactivation was associated with a significant decrease in the body size of the 4^th instar which leads us to speculate as to whether Wolbachia may have a nutrient supplementation role. The reduction in nymph body size has consequences for its parasitoid, E. bimaculata. The elimination of Wolbachia lead to a marked increase in the proportion of parasitoid eggs that completed their development, but the reduced size of the whitefly host was also associated with a significant reduction in the size of the emerging parasitoid adult and this was in turn associated with a marked reduction in adult parasitoid longevity.

Conclusions/Significance

Wolbachia increases the fitness of the whitefly host and provides some protection against parasitization. These observations add to our understanding of the roles played by bacterial endosymbionts.     

Variable fitness effects of Wolbachia infection in Drosophila melanogaster

Maternally inherited Wolbachia bacteria are extremely widespread among insects and their presence is usually associated with parasitic modifications of host fitness. Wolbachia pipientis infects Drosophila melanogaster populations from all continents, but their persistence in this species occurs despite any strong parasitic effects. Here, we have investigated the symbiosis between Wolbachia and D. melanogaster and found that Wolbachia infection can have significant survival and fecundity effects. Relative to uninfected flies, infected females from three fly strains showed enhanced survival or fecundity associated with Wolbachia infection, one strain showed both and one strain responded positively to Wolbachia removal. We found no difference in egg hatch rates (cytoplasmic incompatibility) for crosses between infected males and uninfected females, although there were fecundity differences. Females from this cross consistently produced fewer eggs than infected females and these fecundity differences could promote the spread of infection just like cytoplasmic incompatibility. More surprising, we found that infected females often had the greatest fecundity when mated to uninfected males. This could also promote the spread of Wolbachia infection, though here the fitness benefits would also help to spread infection when Wolbachia are rare. We suggest that variable fitness effects, in both sexes, and which interact strongly with the genetic background of the host, could increase cytoplasmic drive rates in some genotypes and help explain the widespread persistence of Wolbachia bacteria in D. melanogaster populations. These interactions may further explain why many D. melanogaster populations are polymorphic for Wolbachia infection. We discuss our results in the context of host-symbiont co-evolution.     

Fitness effects of Wolbachia and Spiroplasma in Drosophila melanogaster

Maternally inherited endosymbionts that manipulate the reproduction of their insect host are very common. Aside from the reproductive manipulation they produce, the fitness of these symbionts depends in part on the direct impact they have on the female host. Although this parameter has commonly been investigated for single infections, it has much more rarely been established in dual infections. We here establish the direct effect of infection with two different symbionts exhibiting different reproductive manipulation phenotypes, both alone and in combination, in the fruit fly Drosophila melanogaster. This species carries a cytoplasmic incompatibility inducing Wolbachia and a male-killing Spiroplasma, occurring as single or double (co-) infections in natural populations. We assessed direct fitness effects of these bacteria on their host, by comparing larval competitiveness and adult fecundity of uninfected, Wolbachia, Spiroplasma and Wolbachia–Spiroplasma co-infected females. We found no effect of infection status on the fitness of females for both estimates, that is, no evidence of any benefits or costs to either single or co-infection. This leads to the conclusion that both bacteria probably have other sources of benefits to persist in D. melanogaster populations, either by means of their reproductive manipulations (fitness compensation from male death in Spiroplasma infection and cytoplasmic incompatibility in Wolbachia infection) or by positive fitness interactions on other fitness components.     

Wolbachia pipientis: intracellular infection and pathogenesis in Drosophila

Wolbachia pipientis is a vertically transmitted, obligate intracellular symbiont of arthropods. The bacterium is best known for its ability to manipulate host reproductive biology where it can induce cytoplasmic incompatibility, parthenogenesis, feminization and male-killing. In addition to the various reproductive phenotypes it generates through interaction with host reproductive tissue it is also known to infect somatic tissues. However, relatively little is known about the consequences of infection of these tissues with the exception that in some hosts Wolbachia acts as a classical mutualist and in others a pathogen, dramatically shortening adult insect lifespan. Manipulation experiments have demonstrated that the severity of Wolbachia-induced effects on the host is determined by a combination of host genotype, Wolbachia strain, host tissue localization, and interaction with the environment. The recent completion of the whole genome sequence of Wolbachia pipientis wMel strain indicates that it is likely to use a type IV secretion system to establish and maintain infection in its host. Moreover, an unusual abundance of genes encoding proteins with eukaryotic-like ankyrin repeat domains suggest a function in the various described phenotypic effects in hosts.     

Wolbachia感染导致果蝇dHira基因表达下调

Wolbachia是广泛存在于节肢动物体内的一类共生微生物,可通过宿主卵的细胞质传递给子代.     

Toward a Wolbachia Multilocus Sequence Typing System: Discrimination of Wolbachia Strains Present in Drosophila Species

Among the diverse maternally inherited symbionts in arthropods, Wolbachia are the most common and infect over 20% of all species. In a departure from traditional genotyping or phylogenetic methods relying on single Wolbachia genes, the present study represents an initial Multilocus Sequence Typing (MLST) analysis to discriminate closely related Wolbachia pipientis strains, and additional data on sequence diversity in Wolbachia. We report a new phylogenetic characterization of four genes (aspC, atpD, sucB, and pdhB), and provide an expanded analysis of markers described in previous studies (16S rDNA, ftsZ, groEL, dnaA, and gltA). MLST analysis of the bacterial strains present in 16 different Drosophila–Wolbachia associations detected four distinct clonal complexes that also corresponded to maximum-likelihood identified phylogenetic clades. Among the 16 associations analyzed, six could not be assigned to MLST clonal complexes and were also shown to be in conflict with relationships predicted by maximum-likelihood phylogenetic inferences. The results demonstrate the discriminatory power of MLST for identifying strains and clonal lineages of Wolbachia and provide a robust foundation for studying the ecology and evolution of this widespread endosymbiont.     

Effects of Wolbachia on sperm maturation and architecture in Drosophila simulans Riverside

Wolbachia is an intracellular obligate symbiont, that is relatively common in insects and also found in some nematodes. Cytoplasmic incompatibility (CI) is the most commonly expressed form, of several sex altering phenotypes caused by this rickettsial-like bacterium. CI is induced when infected males mate with uninfected females, and is likely the result of bacterial-induced modification of sperm grown in a Wolbachia-infected environment. Several studies have explored the dynamics of Wolbachia bacteria during sperm development in Drosophila. This study confirms and extends these earlier investigations of Wolbachia's distribution and proliferation in male germ cell lines. We examined Wolbachia population dynamics during testis development of Drosophila simulans (Riverside) by studying their distribution during the early mitotic divisions of secondary spermatogonial and subsequent meiotic cyst cells. Wolbachia are found in lower concentration in spermatogonial than in spermatocyte cells. Cytoplasmically incompatible crosses result in low levels of viable embryos despite the occurrence of fairly high levels of uninfected cysts. During meiotic divisions Wolbachia organize themselves at the poles during prophase and telophase but arrange themselves in equatorial bands during metaphase and anaphase. Moreover, during meiosis Wolbachia are asymmetrically divided between some daughter cells. There is no strong relationship between the fusome and Wolbachia and we have not found evidence that bacteria cross the ring canals. Wolbachia were observed at the distal and proximal sides of individualization complexes. Multiple altered sperm structures were observed during the process of individualization of infected sperm.     

Distribution and Evolutionary Impact of Wolbachia on Butterfly Hosts

Wolbachia are maternally inherited endosymbiotic alpha-proteobacteria found in terrestrial arthropods and filarial nematodes. They are transmitted vertically through host cytoplasm and alter host biology by inducing various reproductive alterations, like feminization, parthenogenesis, male killing (MK) and cytoplasmic incompatibility. In butterflies, some effects especially MK and sperm-egg incompatibility are well established. All these effects skew the sex ratio towards female and subsequently favor the vertical transmission of Wolbachia. Some of the insects are also infected with multiple Wolbachia strains which may results in some complex phenomenon. In the present review the potential of Wolbachia for promoting evolutionary changes in its hosts with emphasis on recent advances in interactions of butterfly–Wolbachia is discussed. In addition to this, strain diversity of Wolbachia and its effects on various butterfly hosts are also highlighted.     

Evidence for a global Wolbachia replacement in Drosophila melanogaster

Wolbachia are maternally inherited intracellular alpha-Proteobacteria found in numerous arthropod and filarial nematode species. They influence the biology of their hosts in many ways. In some cases, they act as obligate mutualists and are required for the normal development and reproduction of the host. They are best known, however, for the various reproductive parasitism traits that they can generate in infected hosts. These include cytoplasmic incompatibility (CI) between individuals of different infection status, the parthenogenetic production of females, the selective killing of male embryos, and the feminization of genetic males. Wolbachia infections of Drosophila melanogaster are extremely common in both wild populations and long-term laboratory stocks. Utilizing the newly completed genome sequence of Wolbachia pipientis wMel, we have identified a number of polymorphic markers that can be used to discriminate among five different Wolbachia variants within what was previously thought to be the single clonal infection of D. melanogaster. Analysis of long-term lab stocks together with wild-caught flies indicates that one of these variants has replaced the others globally within the last century. This is the first report of a global replacement of a Wolbachia strain in an insect host species. The sweep is at odds with current theory that cannot explain how Wolbachia can invade this host species given the observed cytoplasmic incompatibility characteristics of Wolbachia infections in D. melanogaster in the field.     

Behavior of Wolbachia endosymbionts from Drosophila simulans in Drosophila serrata, a novel host

Many species harbor the incompatibility-inducing microbe Wolbachia, a maternally inherited endoparasite that causes reduced egg hatch in crosses between infected males and uninfected females. Infected females are immune to this effect, which gives them a relative fitness advantage that results in the spread of the infection. The strength of incompatibility, fitness deficits associated with the infection, and transmission rate from mother to offspring largely determine the rate and extent of spread of Wolbachia in a population. We transferred Wolbachia from Drosophila simulans to Drosophila serrata, a novel host, and compared parameter estimates with those from three naturally occurring Drosophila-Wolbachia associations believed to be of different ages. Transfected D. serrata showed strong incompatibility, low transmission efficiency, and an associated fitness deficit, and they would probably be unable to spread in nature. The comparisons generally supported the predicted evolution of a host-Wolbachia association. The parameters peculiar to any given host-Wolbachia association may determine whether the microbial strain can spread in that host.