Cytoplasmic feminizing elements in a two-population model: infection dynamics, gene flow modification, and the spread of autosomal suppressors

We investigate the dynamics of a cytoplasmic parasitic element with feminizing effect in a two-population model. We assume that the host species has a ZZ/ZW sex determination system. Our analysis reveals that the feminizer and the W chromosome can stably coexist by dominating different populations if the transmission rate differs significantly between the populations and migration is sufficiently weak. In the equilibrium of coexistence, genetic influx at any host autosomal locus is strongly enhanced in the population where infection is prevalent but not modified in the other population. We further explore conditions for the spread of autosomal suppressor genes that reduce transmission of feminizing elements to the cost of host viability, and compute their equilibrium frequencies. Our results confirm the hypothesis that selfish genetic elements convert infected host populations into genetic sinks, thereby restricting the spread of transmission suppressors.     

Costs and benefits of Wolbachia infection in immature Aedes albopictus depend upon sex and competition level

Bacterial endosymbionts induce various effects on hosts and can dramatically impact host fitness and development. An example is provided by obligate, maternally-inherited Wolbachia, which infect a broad range of invertebrates. Wolbachia are capable of altering host reproduction, thereby promoting infection spread. Wolbachia also pose direct physiological costs and benefits to hosts, complicating their categorization as parasites or mutualists. This study examines for an effect of Wolbachia infection in intra-specific larval competition by Aedes albopictus mosquitoes, with the goal of examining for an impact of Wolbachia infection in mixed populations. Similar to prior work examining for an influence of Wolbachia infection on the fitness of A. albopictus in adults, the results presented here support the hypothesized impact of Wolbachia across all life stages, including immatures. The differential competitiveness of infected larvae detected in our experiments indicates that Wolbachia infected A. albopictus females are less competitive relative to uninfected females when competing under highly competitive conditions. In contrast, under low competitive pressures, infected females experience higher survivorship. Thus, Wolbachia infection shifts from parasitism to mutualism as a function of developmental conditions. Results are discussed in relation to the invasion and persistence of Wolbachia in A. albopictus populations.The results are important to the evolution of stable Wolbachia symbioses, including Wolbachia invasion of an uninfected population. The resulting infection dynamics that occur in an infected population are discussed.     

Chikungunya virus impacts the diversity of symbiotic bacteria in mosquito vector

Mosquitoes transmit numerous arboviruses including dengue and chikungunya virus (CHIKV). In recent years, mosquito species Aedes albopictus has expanded in the Indian Ocean region and was the principal vector of chikungunya outbreaks in La Reunion and neighbouring islands in 2005 and 2006. Vector‐associated bacteria have recently been found to interact with transmitted pathogens. For instance, Wolbachia modulates the replication of viruses or parasites. However, there has been no systematic evaluation of the diversity of the entire bacterial populations within mosquito individuals particularly in relation to virus invasion. Here, we investigated the effect of CHIKV infection on the whole bacterial community of Ae. albopictus. Taxonomic microarrays and quantitative PCR showed that members of Alpha‐ and Gammaproteobacteria phyla, as well as Bacteroidetes, responded to CHIKV infection. The abundance of bacteria from the Enterobacteriaceae family increased with CHIKV infection, whereas the abundance of known insect endosymbionts like Wolbachia and Blattabacterium decreased. Our results clearly link the pathogen propagation with changes in the dynamics of the bacterial community, suggesting that cooperation or competition occurs within the host, which may in turn affect the mosquito traits like vector competence.     

Genetic distinctness of parthenogenetic forms of European Polydrusus weevils of the subgenus Scythodrusus

Abstract Among eight species of Polydrusus weevils which belong to subgenus Scythodrusus, at least two possess parthenogenetic forms: P. (S.) inustus and P. (S.) pilifer. Both of these species consist of dioecious populations in the Caspian area and of parthenogenetic populations in Eastern Europe (P. (S.) inustus), the Caucasus region (both species) and Middle Asia (P. (S.) pilifer). The origin of parthenogenesis in this subgenus is unresolved; however some data suggest that the parthenogenetic forms are of hybrid ancestry. The genetic distinctness of parthenogenetic Scythodrusus was assessed on the basis of COII, ITS2, EF1‐α and Wolbachiawsp, 16S ribosomal DNA, ftsZ and hcpA sequence comparisons. Both taxa turned out to be monophyletic for all markers, which is an evidence against hybridization of their dioecious ancestors. On the other hand, a high frequency of heterozygous P. (S.) inustus females suggests an origin resulting from hybridization between genetically distinct dioecious representatives of this species. Very similar strains of Wolbachia supergroup A were found in both species, indicating that they have been either inherited from a common ancestor or were transmitted between parthenogenetic Scythodrusus weevils and probably spread randomly across their ranges.     

Diversity and phylogenetic relationships of Wolbachia in Drosophila and other native Hawaiian insects

Wolbachia is a genus of parasitic alphaproteobacteria found in arthropods and nematodes, and represents on of the most common, widespread endosymbionts known. Wolbachia affects a variety of reproductive functions in its host (e.g., male killing, cytoplasmic incompatibility, parthenogenesis), which have the potential to dramatically impact host evolution and species formation. Here, we present the first broad-scale study to screen natural populations of native Hawaiian insects for Wolbachia, focusing on the endemic Diptera. Results indicate that Wolbachia infects native Hawaiian taxa, with alleles spanning phylogenetic supergroups, A and B. The overall frequency of Wolbachia incidene in Hawaiian insects was 14%. The incidence of infection in native Hawaiian Diptera was 11% for individuals and 12% for all species screened. Wolbachia was not detected in two large, widespread Hawaiian dipteran families—Dolichopodidae (44 spp screened) and Limoniidae (12 spp screened). Incidence of infection within endemic Hawaiian lineages that carry Wolbachia was 18% in Drosophilidae species, 25% in Caliphoridae species, > 90% in Nesophrosyne species, 20% in Drosophila dasycnemia and 100% in Nesophrosyne craterigena. Twenty unique alleles were recovered in this study, of which 18 are newly recorded. Screening of endemic populations of D. dasycnemia across Hawaii Island revealed 4 unique alleles. Phylogenetic relationships and allele diversity provide evidence for horizontal transfer of Wolbachia among Hawaiian arthropod lineages.     

Adaptation to experimental alterations of the operational sex ratio in populations of Drosophila melanogaster

Theory predicts that males adapt to sperm competition by increasing their investment in testis mass to transfer larger ejaculates. Experimental and comparative data support this prediction. Nevertheless, the relative importance of sperm competition in testis size evolution remains elusive, because experiments vary only sperm competition whereas comparative approaches confound it with other variables, in particular male mating rate. We addressed the relative importance of sperm competition and male mating rate by taking an experimental evolution approach. We subjected populations of Drosophila melanogaster to sex ratios of 1:1, 4:1, and 10:1 (female:male). Female bias decreased sperm competition but increased male mating rate and sperm depletion. After 28 generations of evolution, males from the 10:1 treatment had larger testes than males from other treatments. Thus, testis size evolved in response to mating rate and sperm depletion, not sperm competition. Furthermore, our experiment demonstrated that drift associated with sex ratio distortion limits adaptation; testis size only evolved in populations in which the effect of sex ratio bias on the effective population size had been compensated by increasing the numerical size. We discuss these results with respect to reproductive evolution, genetic drift in natural and experimental populations, and consequences of natural sex ratio distortion.     

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.     

Wolbachia infection in crustaceans: novel hosts and potential routes for horizontal transmission

Thirty‐five percent of isopods are estimated to be infected by Wolbachia, an intracellular maternally inherited α‐Proteobacterium. Previous studies have indicated that horizontal transfer of Wolbachia strains may occur, although the mechanisms are unclear. The wsp gene was sequenced from 17 Wolbachia strains harboured by crustacean host species and three from their associated predators and parasites. Two major clades of Wolbachia were found in crustacean, with relatives also found in insects, the other restricted to crustaceans. Highly divergent Wolbachia strains were found in a woodlouse‐eating spider and its prey, suggesting no intertaxon bacterial exchange via the predator–prey route. The phylogenetic proximity of Wolbachia from parasitoid flies or phoretic mites to those from isopods suggests that horizontal symbiont transmission may have occurred between those taxa. Two distant Wolbachia strains were detected in two intertidal amphipods; these strains were closely related to different coastal isopod symbionts, suggesting Wolbachia transmission may occur between distantly related crustacean hosts living under the same ecological conditions.     

Evidence of natural Wolbachia infections and molecular identification of field populations of Culex pipiens complex (Diptera: Culicidae) mosquitoes in western Turkey

Establishing reliable risk projection information about the distribution pattern of members of the Culex pipiens complex is of particular interest, as these mosquitoes are competent vectors for certain disease‐causing pathogens. Wolbachia, a maternally inherited bacterial symbiont, are distributed in various arthropod species and can induce cytoplasmic incompatibility, i.e., reduced egg hatch, in certain crosses. It is being considered as a tool for population control of mosquito disease vectors. The Aegean region is characterized by highly populated, rural, and agricultural areas and is also on the route of the migratory birds. In this study, a fragment of the 658 bp of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene, which includes the barcode region, was employed to differentiate Cx. pipiens complex species found in this region. Moreover, for the first time, the prevalence of Wolbachia endobacteria in these natural populations was examined using PCR amplification of a specific wsp gene. Our results revealed a widespread (more than 90%, n=121) presence of the highly efficient West Nile virus vector Cx. quinquefasciatus in the region. We also found that Wolbachia infection is widespread; the average prevalence was 62% in populations throughout the region. This study provided valuable information about the composition of Cx. pipiens complex mosquitoes and the prevalence of Wolbachia infection in these populations in the Aegean region. This information will be helpful in tracking mosquito‐borne diseases and designing and implementing Wolbachia‐based control strategies in the region.     

The Wolbachia protein TomO interacts with a host RNA to induce polarization defects in Drosophila oocytes

Wolbachia is an endosymbiont prevalent in arthropods. To maximize its transmission thorough the female germline, Wolbachia induces in infected hosts male‐to‐female transformation, male killing, parthenogenesis, and cytoplasmic incompatibility, depending on the host species and Wolbachia strain involved. However, the molecular mechanisms underlying these host manipulations by Wolbachia remain largely unknown. The Wolbachia strain wMel, an inhabitant of Drosophila melanogaster, impairs host oogenesis only when transplanted into a heterologous host, for example, Drosophila simulans. We found that egg polarity defects induced by wMel infection in D. simulans can be recapitulated in the natural host D. melanogaster by transgenic overexpression of a variant of the Wolbachia protein Toxic manipulator of oogenesis (TomO), TomO_wMel^?HS, in the female germline. RNA immunoprecipitation assays demonstrated that TomO physically associates with orb mRNA, which, as a result, fails to interact with the translation repressor Cup. This leads to precocious translation of Orb, a posterior determinant, and thereby to the misspecification of oocytes and accompanying polarity defects. We propose that the ability of TomO to bind to orb mRNA might provide a means for Wolbachia to enter the oocyte located at the posterior end of the egg chamber, thereby accomplishing secure maternal transmission thorough the female germline.