A comparative analysis of Wolbachia-induced host reproductive phenotypes reveals transition rate heterogeneity.
ABSTRACT: The endosymbiotic bacterium Wolbachia infects a wide range of arthropods and their relatives. It is an intracellular parasite transmitted through the egg from mother to offspring. Wolbachia can spread and persist through various means of host reproductive manipulation. How these different mechanisms of host manipulation evolved in Wolbachia is unclear. Which host reproductive phenotype is most likely to be ancestral and whether evolutionary transitions between some host phenotypes are more common than others remain unanswered questions. Recent studies have revealed multiple cases where the same Wolbachia strain can induce different reproductive phenotypes in different hosts, raising the question to what degree the induced host phenotype should be regarded as a trait of Wolbachia. In this study, we constructed a phylogenetic tree of Wolbachia and analyzed the patterns of host phenotypes along that tree. We were able to detect a phylogenetic signal of host phenotypes on the Wolbachia tree, indicating that the induced host phenotype can be regarded as a Wolbachia trait. However, we found no clear support for the previously stated hypothesis that cytoplasmic incompatibility is ancestral to Wolbachia in arthropods. Our analysis provides evidence for heterogeneous transition rates between host phenotypes.
Project description:Maternally-transmitted endosymbiotic bacteria are ubiquitous in insects. Among other influential phenotypes, many heritable symbionts of arthropods are notorious for manipulating host reproduction through one of four reproductive syndromes, which are generally exerted during early developmental stages of the host: male feminization; parthenogenesis induction; male killing; and cytoplasmic incompatibility (CI). Major advances have been achieved in understanding mechanisms and identifying symbiont factors involved in reproductive manipulation, particularly male killing and cytoplasmic incompatibility. Nonetheless, whether cytoplasmically-transmitted bacteria influence the maternally-loaded components of the egg or early embryo has not been examined. In the present study, we investigated whether heritable endosymbionts that cause different reproductive phenotypes in Drosophila melanogaster influence the mRNA transcriptome of early embryos. We used mRNA-seq to evaluate differential expression in Drosophila embryos lacking endosymbionts (control) to those harbouring the male-killing Spiroplasma poulsonii strain MSRO-Br, the CI-inducing Wolbachia strain wMel, or Spiroplasma poulsonii strain Hyd1; a strain that lacks a reproductive phenotype and is naturally associated with Drosophila hydei. We found no consistent evidence of influence of symbiont on mRNA composition of early embryos, suggesting that the reproductive manipulation mechanism does not involve alteration of maternally-loaded transcripts. In addition, we capitalized on several available mRNA-seq datasets derived from Spiroplasma-infected Drosophila melanogaster embryos, to search for signals of depurination of rRNA, consistent with the activity of Ribosome Inactivating Proteins (RIPs) encoded by Spiroplasma poulsonii. We found small but statistically significant signals of depurination of Drosophila rRNA in the Spiroplasma treatments (both strains), but not in the symbiont-free control or Wolbachia treatment, consistent with the action of RIPs. The depurination signal was slightly stronger in the treatment with the male-killing strain. This result supports a recent report that RIP-induced damage contributes to male embryo death.
Project description:Wolbachia are rickettsial intracellular symbionts of arthropods and nematodes. In arthropods, they act as selfish genetic elements and manipulate host reproduction, including sex-ratio distortion and cytoplasmic incompatibility (CI). Previous studies showed that infection of feminizing Wolbachia and CI Wolbachia sympatrically occurred in the butterfly Eurema hecabe. We demonstrate that feminization-infecting individuals can rescue sperm modified by CI-infecting males. Phylogenetic analysis revealed that feminized individuals are infected with two distinct Wolbachia strains: one is shared with CI-inducing matrilines, and the other is only found in feminized matrilines. Therefore, the simultaneous double manipulation, CI rescue and feminization, is caused by different Wolbachia strains in feminized individuals, not by a single Wolbachia with two functions. This is the first finding of double infection of Wolbachia with different reproductive manipulations.
Project description:The maternally inherited endosymbiont Wolbachia is widespread in arthropods and nematodes and can play an important role in the ecology and evolution of its host through reproductive manipulation. Here, we survey Wolbachia in Belonocnema treatae, a widely distributed North American cynipid gall forming wasp that exhibits regional host specialization on three species of oaks and alternation of sexually and asexually reproducing generations. We investigated whether patterns of Wolbachia infection and diversity in B. treatae are associated with the insect's geographic distribution, host plant association, life cycle, and mitochondrial evolutionary history.Screening of 463 individuals from 23 populations including sexual and asexual generations from all three host plants across the southern U.S. showed an average infection rate of 56% with three common Wolbachia strains: wTre1-3 and an additional rare variant wTre4. Phylogenetic analysis based on wsp showed that these strains are unrelated and likely independently inherited. We found no difference in Wolbachia infection frequency among host plant associated populations or between the asexual and sexual generations, or between males and females of the sexual generation. Partially incomplete Wolbachia transmission rates might explain the occurrence of uninfected individuals. A parallel analysis of the mitochondrial cytochrome oxidase I gene in B. treatae showed high mtDNA haplotype diversity in both infected and uninfected populations suggesting an ancestral infection by Wolbachia as well as a clear split between eastern and western B. treatae mtDNA clades with a sequence divergence of >?6%. The strain wTre1 was present almost exclusively in the western clade while wTre2 and wTre3 occur almost exclusively in eastern populations. In contrast, the same strains co-occur as double-infections in Georgia and triple-infections in two populations in central Florida.The diversity of Wolbachia across geographically and genetically distinct populations of B. treatae and the co-occurrence of the same strains within three populations highlights the complex infection dynamics in this system. Moreover, the association of distinct Wolbachia strains with mitochondrial haplotypes of its host in populations infected by different Wolbachia strains suggests a potential role of the endosymbiont in reproductive isolation in B. treatae.
Project description:Wolbachia are maternally transmitted endosymbionts that often alter their arthropod hosts' biology to favor the success of infected females, and they may also serve as a speciation microbe driving reproductive isolation. Two of these host manipulations include killing males outright and reducing offspring survival when infected males mate with uninfected females, a phenomenon known as cytoplasmic incompatibility. Little is known about the mechanisms behind these phenotypes, but interestingly either effect can be caused by the same Wolbachia strain when infecting different hosts. For instance, wRec causes cytoplasmic incompatibility in its native host Drosophila recens and male killing in D. subquinaria. The discovery of prophage WO elements in most arthropod Wolbachia has generated the hypothesis that WO may encode genes involved in these reproductive manipulations. However, PCR screens for the WO minor capsid gene indicated that wRec lacks phage WO. Thus, wRec seemed to provide an example where phage WO is not needed for Wolbachia-induced reproductive manipulation. To enable investigation of the mechanism of phenotype switching in different host backgrounds, and to examine the unexpected absence of phage WO, we sequenced the genome of wRec. Analyses reveal that wRec diverged from wMel approximately 350,000 years ago, mainly by genome reduction in the phage regions. While it lost the minor capsid gene used in standard PCR screens for phage WO, it retained two regions encompassing 33 genes, several of which have previously been associated with reproductive parasitism. Thus, WO gene involvement in reproductive manipulation cannot be excluded and reliance on single gene PCR should not be used to rule out the presence of phage WO in Wolbachia. Additionally, the genome sequence for wRec will enable transcriptomic and proteomic studies that may help elucidate the Wolbachia mechanisms of altered reproductive manipulations associated with host switching, perhaps among the 33 remaining phage genes.
Project description:BACKGROUND: The maternally inherited ?-Proteobacteria Wolbachia pipientis is an obligate endosymbiont of nematodes and arthropods, in which they induce a variety of reproductive alterations, including Cytoplasmic Incompatibility (CI) and feminization. The genome of the feminizing wVulC Wolbachia strain harboured by the isopod Armadillidium vulgare has been sequenced and is now at the final assembly step. It contains an unusually high number of ankyrin motif-containing genes, two of which are homologous to the phage-related pk1 and pk2 genes thought to contribute to the CI phenotype in Culex pipiens. These genes encode putative bacterial effectors mediating Wolbachia-host protein-protein interactions via their ankyrin motifs. RESULTS: To test whether these Wolbachia homologs are potentially involved in altering terrestrial isopod reproduction, we determined the distribution and expression of both pk1 and pk2 genes in the 3 Wolbachia strains that induce CI and in 5 inducing feminization of their isopod hosts. Aside from the genes being highly conserved, we found a substantial copy number variation among strains, and that is linked to prophage diversity. Transcriptional analyses revealed expression of one pk2 allele (pk2b2) only in the feminizing Wolbachia strains of isopods. CONCLUSIONS: These results reveal the need to investigate the functions of Wolbachia ankyrin gene products, in particular those of Pk2, and their host targets with respect to host sex manipulation.
Project description:Wolbachia (Alphaproteobacteria) is an inherited endosymbiont of arthropods and filarial nematodes and was reported to be widespread across insect taxa. While Wolbachia's effects on host biology are not understood from most of these hosts, known Wolbachia-induced phenotypes cover a spectrum from obligate beneficial mutualism to reproductive manipulations and pathogenicity. Interestingly, data on Wolbachia within the most species-rich order of arthropods, the Coleoptera (beetles), are scarce. Therefore, we screened 128 species from seven beetle families (Buprestidae, Hydraenidae, Dytiscidae, Hydrophilidae, Gyrinidae, Haliplidae, and Noteridae) for the presence of Wolbachia. Our data show that, contrary to previous estimations, Wolbachia frequencies in beetles (31% overall) are comparable to the ones in other insects. In addition, we used Wolbachia MLST data and host phylogeny to explore the evolutionary history of Wolbachia strains from Hydraenidae, an aquatic lineage of beetles. Our data suggest that Wolbachia from Hydraenidae might be largely host genus specific and that Wolbachia strain phylogeny is not independent to that of its hosts. As this contrasts with most terrestrial Wolbachia-arthropod systems, one potential conclusion is that aquatic lifestyle of hosts may result in Wolbachia distribution patterns distinct from those of terrestrial hosts. Our data thus provide both insights into Wolbachia distribution among beetles in general and a first glimpse of Wolbachia distribution patterns among aquatic host lineages.
Project description:In many arthropods, maternally inherited endosymbiotic bacteria can increase infection frequency by manipulating host reproduction. Multiple infections of different bacteria in a single host population are common, yet few studies have documented concurrent endosymbiont phenotypes or explored their potential interactions. We hypothesized that spiders might be a particularly useful taxon for investigating endosymbiont interactions, because they are host to a plethora of endosymbiotic bacteria and frequently exhibit multiple infections. We established two matrilines from the same population of the linyphiid spider Mermessus fradeorum and then used antibiotic curing and controlled mating assays to demonstrate that each matriline was subject to a distinct endosymbiotic reproductive manipulation. One matriline was co-infected with Rickettsia and Wolbachia and produced offspring with a radical female bias. Antibiotic treatment eliminated both endosymbionts and restored an even sex ratio to subsequent generations. Chromosomal and fecundity observations suggest a feminization mechanism. In the other matriline, a separate factorial mating assay of cured and infected spiders demonstrated strong cytoplasmic incompatibility (CI) induced by a different strain of Wolbachia. However, males with this Wolbachia induced only mild CI when mated with the Rickettsia-Wolbachia females. In a subsequent survey of a field population of M. fradeorum, we detected these same three endosymbionts infecting 55% of the spiders in almost all possible combinations, with nearly half of the infected spiders exhibiting multiple infection. Our results suggest that a dynamic network of endosymbionts may interact both within multiply infected hosts and within a population subject to multiple strong reproductive manipulations.
Project description:Wolbachia are maternally inherited bacterial endosymbionts that naturally infect a diverse array of arthropods. They are primarily known for their manipulation of host reproductive biology, and recently, infections with Wolbachia have been proposed as a new strategy for controlling insect vectors and subsequent human-transmissible diseases. Yet, Wolbachia abundance has been shown to vary greatly between individuals and the magnitude of the effects of infection on host life-history traits and protection against infection is correlated to within-host Wolbachia abundance. It is therefore essential to better understand the factors that modulate Wolbachia abundance and effects on host fitness. Nutrition is known to be one of the most important mediators of host-symbiont interactions. Here, we used nutritional geometry to quantify the role of macronutrients on insect-Wolbachia relationships in Drosophila melanogaster. Our results show fundamental interactions between diet composition, host diet selection, Wolbachia abundance and effects on host lifespan and fecundity. The results and methods described here open a new avenue in the study of insect-Wolbachia relationships and are of general interest to numerous research disciplines, ranging from nutrition and life-history theory to public health.
Project description:Wolbachia is a maternally inherited ubiquitous endosymbiotic bacterium of arthropods that displays a diverse repertoire of host reproductive manipulations. For the first time, we demonstrate that Wolbachia manipulates sex chromosome inheritance in a sexually reproducing insect. Eurema mandarina butterfly females on Tanegashima Island, Japan, are infected with the wFem Wolbachia strain and produce all-female offspring, while antibiotic treatment results in male offspring. Fluorescence in situ hybridization (FISH) revealed that wFem-positive and wFem-negative females have Z0 and WZ sex chromosome sets, respectively, demonstrating the predicted absence of the W chromosome in wFem-infected lineages. Genomic quantitative polymerase chain reaction (qPCR) analysis showed that wFem-positive females lay only Z0 eggs that carry a paternal Z, whereas females from lineages that are naturally wFem-negative lay both WZ and ZZ eggs. In contrast, antibiotic treatment of adult wFem females resulted in the production of Z0 and ZZ eggs, suggesting that this Wolbachia strain can disrupt the maternal inheritance of Z chromosomes. Moreover, most male offspring produced by antibiotic-treated wFem females had a ZZ karyotype, implying reduced survival of Z0 individuals in the absence of feminizing effects of Wolbachia. Antibiotic treatment of wFem-infected larvae induced male-specific splicing of the doublesex (dsx) gene transcript, causing an intersex phenotype. Thus, the absence of the female-determining W chromosome in Z0 individuals is functionally compensated by Wolbachia-mediated conversion of sex determination. We discuss how Wolbachia may manipulate the host chromosome inheritance and that Wolbachia may have acquired this coordinated dual mode of reproductive manipulation first by the evolution of female-determining function and then cytoplasmically induced disruption of sex chromosome inheritance.
Project description:Wolbachia are maternally inherited, intracellular, alpha proteobacteria that infect a wide range of arthropods. They cause three kinds of reproductive alterations in their hosts: cytoplasmic incompatibility, parthenogenesis and feminization. There have been many studies of the distribution of Wolbachia in arthropods, but very few crustacean species are known to be infected. We investigated the prevalence of Wolbachia in 85 species from five crustacean orders. Twenty-two isopod species were found to carry these bacteria. The bacteria were found mainly in terrestrial species, suggesting that Wolbachia came from a continental environment. The evolutionary relationships between these Wolbachia strains were determined by sequencing bacterial genes and by interspecific transfers. All the bacteria associated with isopods belonged to the Wolbachia B group, based on 16S rDNA sequence data. All the terrestrial isopod symbionts in this group except one formed an independent clade. The results of interspecific transfers show evidence of specialization of Wolbachia symbionts to their isopod hosts. They also suggest that host species plays a more important role than bacterial phylogeny in determining the phenotype induced by Wolbachia infection.