Maternally transmitted non-bacterial male killer in Drosophila biauraria.
ABSTRACT: A maternally inherited, all-female trait is widely found among arthropods, which is caused by bacterial endosymbionts such as Wolbachia, Rickettsia, Spiroplasma and Cardinium We discovered a single female of Drosophila biauraria, collected from Tomakomai, Hokkaido, Japan, that produced all-female offspring. This all-female trait was maternally inherited in the iso-female line (SP12F) by backcrossing with males of a normal line (SP11-20) with a 1 : 1 sex ratio derived from the same population. The all-female trait was not affected by tetracycline treatment performed for two consecutive generations. However, the microinjection of filter-sterilized homogenate of SP12F females into SP11-20 females established all-female matrilines. Our data suggest the role of transmissible agents, most likely viruses, but not bacteria or protists, as the possible cause of the all-female phenotype, which is likely to be achieved by killing of male embryos because egg hatch rates of SP12F were nearly half those of SP11-20. This is the first report in Diptera to demonstrate a maternally inherited virus-like element as the cause of the male-killing phenotype in D. biauraria.
Project description:BACKGROUND: Maternally inherited bacteria that reside obligatorily or facultatively in arthropods can increase their prevalence in the population by altering their hosts' reproduction. Such reproductive manipulations have been reported from the major arthropod groups such as insects (in particular hymenopterans, butterflies, dipterans and beetles), crustaceans (isopods) and mites. Despite the observation that endosymbiont bacteria are frequently encountered in spiders and that the sex ratio of particular spider species is strongly female biased, a direct relationship between bacterial infection and sex ratio variation has not yet been demonstrated for this arthropod order. RESULTS: Females of the dwarf spider Oedothorax gibbosus exhibit considerable variation in the sex ratio of their clutches and were infected with at least three different endosymbiont bacteria capable of altering host reproduction i.e. Wolbachia, Rickettsia and Cardinium. Breeding experiments show that sex ratio variation in this species is primarily maternally inherited and that removal of the bacteria by antibiotics restores an unbiased sex ratio. Moreover, clutches of females infected with Wolbachia were significantly female biased while uninfected females showed an even sex ratio. As female biased clutches were of significantly smaller size compared to non-distorted clutches, killing of male embryos appears to be the most likely manipulative effect. CONCLUSIONS: This represents to our knowledge the first direct evidence that endosymbiont bacteria, and in particular Wolbachia, might induce sex ratio variation in spiders. These findings are pivotal to further understand the diversity of reproductive phenotypes observed in this arthropod order.
Project description:Many species of arthropod are infected by deleterious inherited micro-organisms. Typically these micro-organisms are inherited maternally. Consequently, some, particularly bacteria of the genus Wolbachia, employ a variety of strategies that favour female over male hosts. These strategies include feminisation, induction of parthenogenesis and male-killing. These strategies result in female biased sex ratios in host populations, which lead to selection for host factors that promote male production. In addition, the intra-genomic conflict produced by the difference in transmission of these cytoplasmic endosymbionts and nuclear factors will impose a pressure favouring nuclear factors that suppress the effects of the symbiont. During investigations of the diversity of male-killing bacteria in ladybirds (Coccinellidae), unexpected patterns of vertical transmission of a newly discovered male-killing taxon were observed in the ladybird Cheilomenes sexmaculata. Initial analysis suggested that the expression of the bacterial male-killing trait varies according to the male(s) a female has mated with. By swapping males between females, a male influence on the expression of the male-killing trait was confirmed. Experiments were then performed to determine the nature of the interaction. These studies showed that a single dominant allele, which rescues male progeny of infected females from the pathological effect of the male-killer, exists in this species. The gene shows typical Mendelian autosomal inheritance and is expressed irrespective of the parent from which it is inherited. Presence of the rescue gene in either parent does not significantly affect the inheritance of the symbiont. We conclude that C. sexmaculata is host to a male-killing gamma-proteobacterium. Further, this beetle is polymorphic for a nuclear gene, the dominant allele of which rescues infected males from the pathogenic effects of the male-killing agent. These findings represent the first reported case of a nuclear suppressor of male-killing in a ladybird. They are considered in regard to sex ratio and intra-genomic conflict theories, and models of the evolutionary dynamics and distribution of inherited symbionts.
Project description:Maternally inherited Wolbachia endosymbionts manipulate arthropod reproduction in various ways. In the butterfly Eurema mandarina, a cytoplasmic incompatibility-inducing Wolbachia strain wCI and the associated mtDNA haplotypes are known to originate from the sister species Eurema hecabe, which offered a good case study for microbe-mediated hybrid introgression. Besides wCI, some females with the Z0 karyotype harbour a distinct Wolbachia strain wFem, which causes all-female production by meiotic drive and feminization. We report that a considerable proportion of E. mandarina females (65.7%) were infected with both wCI and wFem (CF) on Tanegashima Island. While females singly infected with wCI (C) produced offspring at a 1 : 1 sex ratio, CF females produced only females. Although Z-linked sequence polymorphism showed no signs of divergence between C and CF females, mtDNA split into two discrete clades; one consisted of C females and the other CF females, both of which formed a clade with E. hecabe but not with uninfected E. mandarina This suggests that CF matrilines also, but independently, experienced a selective sweep after hybrid introgression from E. hecabe Distinct evolutionary forces were suggested to have caused C and CF matrilines to diverge, which would be irreversible because of the particular phenotype of wFem.
Project description:Cytoplasmic incompatibility (CI) is an intriguing, widespread, symbiont-induced reproductive failure that decreases offspring production of arthropods through crossing incompatibility of infected males with uninfected females or with females infected with a distinct symbiont genotype. For years, the molecular mechanism of CI remained unknown. Recent genomic, proteomic, biochemical, and cell biological studies have contributed to understanding of CI in the alphaproteobacterium Wolbachia and implicate genes associated with the WO prophage. Besides a recently discovered additional lineage of alphaproteobacterial symbionts only moderately related to Wolbachia, Cardinium (Bacteroidetes) is the only other symbiont known to cause CI, and genomic evidence suggests that it has very little homology with Wolbachia and evolved this phenotype independently. Here, we present the first transcriptomic study of the CI Cardinium strain cEper1, in its natural host, Encarsia suzannae, to detect important CI candidates and genes involved in the insect-Cardinium symbiosis. Highly expressed transcripts included genes involved in manipulating ubiquitination, apoptosis, and host DNA. Female-biased genes encoding ribosomal proteins suggest an increase in general translational activity of Cardinium in female wasps. The results confirm previous genomic analyses that indicated that Wolbachia and Cardinium utilize different genes to induce CI, and transcriptome patterns further highlight expression of some common pathways that these bacteria use to interact with the host and potentially cause this enigmatic and fundamental manipulation of host reproduction. IMPORTANCE The majority of insects carry maternally inherited intracellular bacteria that are important in their hosts' biology, ecology, and evolution. Some of these bacterial symbionts cause a reproductive failure known as cytoplasmic incompatibility (CI). In CI, the mating of symbiont-infected males and uninfected females produces few or no daughters. The CI symbiont then spreads and can have a significant impact on the insect host population. Cardinium, a bacterial endosymbiont of the parasitoid wasp Encarsia in the Bacteroidetes, is the only bacterial lineage known to cause CI outside the Alphaproteobacteria, where Wolbachia and another recently discovered CI symbiont reside. Here, we sought insight into the gene expression of a CI-inducing Cardinium strain in its natural host, Encarsia suzannae. Our study provides the first insights into the Cardinium transcriptome and provides support for the hypothesis that Wolbachia and Cardinium target similar host pathways with distinct and largely unrelated sets of genes.
Project description:BACKGROUND: Endosymbionts that manipulate the reproduction of their hosts have been reported widely in invertebrates. One such group of endosymbionts is the male-killers. To date all male-killers reported are bacterial in nature, but comprise a diverse group. Ladybirds have been described as a model system for the study of male-killing, which has been reported in multiple species from widespread geographic locations. Whilst criteria of low egg hatch-rate and female-biased progenic sex ratio have been used to identify female hosts of male-killers, variation in vertical transmission efficiency and host genetic factors may result in variation in these phenotypic indicators of male-killer presence. Molecular identification of bacteria and screening for bacterial presence provide us with a more accurate method than breeding data alone to link the presence of the bacteria to the male-killing phenotype. In addition, by identifying the bacteria responsible we may find evidence for horizontal transfer between endosymbiont hosts and can gain insight into the evolutionary origins of male-killing. Phylogenetic placement of male-killing bacteria will allow us to address the question of whether male-killing is a potential strategy for only some, or all, maternally inherited bacteria. Together, phenotypic and molecular characterisation of male-killers will allow a deeper insight into the interactions between host and endosymbiont, which ultimately may lead to an understanding of how male-killers identify and kill male-hosts. RESULTS: A male-killer was detected in the Japanese coccinellid, Propylea japonica (Thunberg) a species not previously known to harbour male-killers. Families produced by female P. japonica showed significantly female-biased sex ratios. One female produced only daughters. This male-killer trait was maternally inherited and antibiotic treatment produced a full, heritable cure. Molecular analysis identified Rickettsia to be associated with the trait in this species of ladybird. CONCLUSION: We conclude that P. japonica is host to a bacterial male-killer that is vertically inherited with variable transmission efficiency. Rickettsia presence correlates with the male-killing trait, but there is some variation in the phenotypic expression of the trait due to interaction with host factors. Phylogenetic analysis using the 16S rRNA and 17 kDa antigen genes suggests there may have been horizontal transfer of Rickettsial male-killers between different ladybird hosts.
Project description:Ladybirds are a hot-spot for the invasion of male-killing bacteria. These maternally inherited endosymbionts cause the death of male host embryos, to the benefit of female sibling hosts and the bacteria that they contain. Previous studies have shown that high temperatures can eradicate male-killers from ladybirds, leaving the host free from infection. Here we report the discovery of two maternally inherited sex ratio distorters in populations of a coccinellid, Coccinella undecimpunctata, from a hot lowland region of the Middle East. DNA sequence analysis indicates that the male killing is the result of infection by Wolbachia, that the trait is tetracycline sensitive, and that two distinct strains of Wolbachia co-occur within one beetle population. We discuss the implications of these findings for theories of male-killing and suggest avenues for future field-work on this system.
Project description:Many arthropod hosts are infected with bacterial endosymbionts that manipulate host reproduction, but few bacterial taxa have been shown to cause such manipulations. Here, we show that a bacterial strain in the genus Rickettsiella causes cytoplasmic incompatibility (CI) between infected and uninfected hosts. We first surveyed the bacterial community of the agricultural spider Mermessus fradeorum (Linyphiidae) using high throughput sequencing and found that individual spiders can be infected with up to five different strains of maternally inherited symbiont from the genera Wolbachia, Rickettsia, and Rickettsiella. The Rickettsiella strain was pervasive, found in all 23 tested spider matrilines. We used antibiotic curing to generate uninfected matrilines that we reciprocally crossed with individuals infected only with Rickettsiella. We found that only 13% of eggs hatched when uninfected females were mated with Rickettsiella-infected males; in contrast, at least 83% of eggs hatched in the other cross types. This is the first documentation of Rickettsiella, or any Gammaproteobacteria, causing CI. We speculate that induction of CI may be much more widespread among maternally inherited bacteria than previously appreciated. Further, our results reinforce the importance of thoroughly characterizing and assessing the inherited microbiome before attributing observed host phenotypes to well-characterized symbionts such as Wolbachia.
Project description:Terrestrial arthropods are commonly infected with maternally inherited bacterial symbionts that cause cytoplasmic incompatibility (CI). In CI, the outcome of crosses between symbiont-infected males and uninfected females is reproductive failure, increasing the relative fitness of infected females and leading to spread of the symbiont in the host population. CI symbionts have profound impacts on host genetic structure and ecology and may lead to speciation and the rapid evolution of sex determination systems. Cardinium hertigii, a member of the Bacteroidetes and symbiont of the parasitic wasp Encarsia pergandiella, is the only known bacterium other than the Alphaproteobacteria Wolbachia to cause CI. Here we report the genome sequence of Cardinium hertigii cEper1. Comparison with the genomes of CI-inducing Wolbachia pipientis strains wMel, wRi, and wPip provides a unique opportunity to pinpoint shared proteins mediating host cell interaction, including some candidate proteins for CI that have not previously been investigated. The genome of Cardinium lacks all major biosynthetic pathways but harbors a complete biotin biosynthesis pathway, suggesting a potential role for Cardinium in host nutrition. Cardinium lacks known protein secretion systems but encodes a putative phage-derived secretion system distantly related to the antifeeding prophage of the entomopathogen Serratia entomophila. Lastly, while Cardinium and Wolbachia genomes show only a functional overlap of proteins, they show no evidence of laterally transferred elements that would suggest common ancestry of CI in both lineages. Instead, comparative genomics suggests an independent evolution of CI in Cardinium and Wolbachia and provides a novel context for understanding the mechanistic basis of CI.
Project description:Insects commonly harbor maternally inherited intracellular symbionts in nature, and the microbial partners often exert influence on host reproduction and fitness to promote their prevalence. Here, we investigated composition of symbionts and their biological effects in the invasive Bemisia tabaci MED species of a whitefly complex. Our field surveys revealed that populations of the MED whitefly, in addition to the primary symbiont Portiera, mainly contain two secondary symbionts Hamiltonella, which is nearly fixed in the host populations, and Cardinium with infection frequencies ranging from 0 to 86%. We isolated and established Cardinium-positive and Cardinium-free whitefly lines with a similar nuclear genetic background from a field population, and compared performance of the two whitefly lines. The infection of Cardinium incurred significant fitness costs on the MED whitefly, including reduction of fecundity and egg viability as well as delay in development. We then selectively removed Hamiltonella from the Cardinium-free whitefly line and compared performance of two whitefly lines, one harboring both Portiera and Hamiltonella and the other harboring only Portiera. While depletion of Hamiltonella had little or only marginal effects on the fecundity, developmental rate, and offspring survival, the Hamiltonella-free whitefly line produced very few female offspring, often reducing the progeny female ratio from about 50% to less than 1%. Our findings indicate that the varying costs and benefits of the association between these two symbionts and the MED whitefly may play an important role in shaping their differential prevalence in the field.
Project description:Terrestrial arthropods, including insects, commonly harbor maternally inherited intracellular symbionts that confer benefits to the host or manipulate host reproduction to favor infected female progeny. These symbionts may be especially vulnerable to thermal stress, potentially leading to destabilization of the symbiosis and imposing costs to the host. For example, increased temperatures can reduce the density of a common reproductive manipulator, Wolbachia, and the strength of its crossing incompatibility (cytoplasmic incompatibility, or CI) phenotype. Another manipulative symbiont, Cardinium hertigii, infects ~ 6-10% of Arthropods, and also can induce CI, but there is little homology between the molecular mechanisms of CI induced by Cardinium and Wolbachia. Here we investigated whether temperature disrupts the CI phenotype of Cardinium in a parasitic wasp host, Encarsia suzannae. We examined the effects of both warm (32°C day/ 29°C night) and cool (20°C day/ 17°C night) temperatures on Cardinium CI and found that both types of temperature stress modified aspects of this symbiosis. Warm temperatures reduced symbiont density, pupal developmental time, vertical transmission rate, and the strength of both CI modification and rescue. Cool temperatures also reduced symbiont density, however this resulted in stronger CI, likely due to cool temperatures prolonging the host pupal stage. The opposing effects of cool and warm-mediated reductions in symbiont density on the resulting CI phenotype indicates that CI strength may be independent of density in this system. Temperature stress also modified the CI phenotype only if it occurred during the pupal stage, highlighting the likely importance of this stage for CI induction in this symbiosis.