Horizontal transfer of Wolbachia between phylogenetically distant insect species by a naturally occurring mechanism.
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Wolbachia is a genus of alpha-proteobacteria found in obligate intracellular association with a wide variety of arthropods, including an estimated 10-20% of all insect species [1]. Wolbachia represents one of a number of recently identified 'reproductive parasites' [2] which manipulate the reproduction of their hosts in ways that enhance their own transmission [3] [4] [5] [6] [7] [8] [9]. The influence of Wolbachia infection on the dynamics of host populations has focused considerable interest on its possible role in speciation through reproductive isolation [3] [10] [11] and as an agent of biological control [2] [12] [13]. Although Wolbachia normally undergoes vertical transmission through the maternal line of its host population [14], there is compelling evidence from molecular phylogenies that extensive horizontal (intertaxon) transmission must have occurred [1] [9] [15] [16] [17]. Some of the best candidate vectors for the horizontal transmission of Wolbachia are insect parasitoids [15], which comprise around 25% of all insect species and attack arthropods from an enormous range of taxa [18]. In this study, we used both fluorescence microscopy and PCR amplification with Wolbachia-specific primers to show that Wolbachia can be transmitted to a parasitic wasp (Leptopilina boulardi) from its infected host (Drosophila simulans) and subsequently undergo diminishing vertical transmission in this novel host species. These results are, to our knowledge, the first to reveal a natural horizontal transfer route for Wolbachia between phylogenetically distant insect species. (+info)
Genetic localization of a Drosophila melanogaster resistance gene to a parasitoid wasp and physical mapping of the region.
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Drosophila melanogaster larvae usually react against eggs of the parasitoid wasp Leptopilina boulardi by surrounding them with a multicellular melanotic capsule. The genetic determinism of this response has been studied previously using susceptible (non-capsule-forming) and resistant (capsule-forming) strains. The results suggest that differences in their encapsulation response involve a single gene, resistance to Leptopilina boulardi (Rlb), with two alleles, the resistant one being dominant. Rlb confers specific protection against Leptopilina boulardi and is thus probably involved in parasitoid recognition. Recent studies have localized this gene on the right arm of the second chromosome and our aim was to precisely determine its genetic and molecular location. Using strains bearing deletions, we demonstrated that resistance to Leptopilina boulardi is conferred by the 55C; 55F3 region and that the 55E2-E6; F3 region is particularly involved. A physical map of the 55C; 56A region was then constructed, based on a set of overlapping cosmid and P1 phage clones. Using single and double digests, cross hybridization of restriction fragments, and location of genetically mapped genes and STSs, a complete, five-enzyme restriction map of this 830-kb region was obtained. (+info)
Developmental analysis of Ganaspis xanthopoda, a larval parasitoid of Drosophila melanogaster.
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Ganaspis xanthopoda is a solitary larval parasitoid wasp of the fruit fly Drosophila melanogaster. The life cycle of Ganaspis xanthopoda in the wild-type and developmental mutant ecdysoneless strains of Drosophila melanogaster is described. The female infects a second-instar host larva. The parasitoid embryo hatches into a mobile first-instar (L1) larva. The L1 parasitoid has fleshy appendages and, while mobile, it remains confined within the wandering larval host. The second-instar larva (L2) is an endoparasite within the host prepupa and lacks appendages. The L2-to-L3 molt is dependent on pupation and marks the transition of the endoparasite into an ectoparasite. The third-instar larva (L3) is a sessile ectoparasite, develops an extensive tracheal system and consumes the host as it progresses through its prepupal and pupal stages. A single adult male or female emerges from the host puparium. The developmental analysis of Ganaspis xanthopoda reveals a tight synchrony between host and parasitoid development which is, at least in part, dependent on the ecdysone levels of the host. (+info)
Mapping of hybrid incompatibility loci in Nasonia.
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According to theory, F(2) hybrid breakdown (lethality or sterility) is due to incompatibilities between interacting genes of the different species (i.e., the breaking up of coadapted gene complexes). Detection of such incompatibilities is particularly straightforward in haplodiploid species, because virgin F(1) hybrid females will produce haploid recombinant F(2) males. This feature allows for screening of the complete genome for recessive genetic incompatibilities. Crosses were performed between Nasonia vitripennis (v) and its sibling species N. giraulti (g). First, a linkage map was produced using RAPD markers. RAPD markers showed an overall bias toward vitripennis alleles, a pattern not predicted by the basic two-interactor Dobzhansky-Muller model. Recovery patterns of visible markers were consistent with those of linked RAPD markers. If particular genetic interactions between two loci are causing hybrid lethality, then those genotypes should be underrepresented or absent among adult F(2) males. Four sets of significant incompatibilities were detected by performing pairwise comparisons of markers on different chromosomes. Likely explanations for the observed patterns are maternal effect-zygotic gene incompatibilities or clustering of incompatibility loci. Due to the short generation time, advantages of haplodiploidy, and availability of markers, Nasonia promises to be a productive system for investigating the genetics of hybrid inviability. (+info)
Genetic support for the evolutionary theory of reproductive transactions in social wasps.
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Recent evolutionary models of reproductive partitioning within animal societies (known as 'optimal skew', 'concessions' or 'transactional' models) predict that a dominant individual will often yield some fraction of the group's reproduction to a subordinate as an incentive to stay in the group and help rear the dominant's offspring. These models quantitatively predict how the magnitude of the subordinate's 'staying incentive' will vary with the genetic relatedness between dominant and subordinate, the overall expected group output and the subordinate's expected output if it breeds solitarily. We report that these predictions accord remarkably well with the observed reproductive partitioning between conesting dominant and subordinate queens in the social paper wasp Polistes fuscatus. In particular, the theory correctly predicts that (i) the dominant's share of reproduction, i.e. the skew, increases as the colony cycle progresses and (ii) the skew is positively associated both with the colony's productivity and with the relatedness between dominant and subordinate. Moreover, aggression between foundresses positively correlated with the skew, as predicted by transactional but not alternative tug-of-war models of societal evolution. Thus, our results provide the strongest (quantitative support yet for a unifying model of social evolution. (+info)
Glucosinolate genetics and the attraction of the aphid parasitoid Diaeretiella rapae to Brassica.
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The control of insect pests using parasitoids and carnivores has been successfully applied in protected cropping systems, orchards and forestry. Their success in annual field crops has been more limited due largely to the difficulties of attracting and maintaining a sufficient density of parasitoids in the crop before the levls of the insect herbivores become economically damaging. Parasitoids are known to be attracted to host-plant volatiles; thus, manipulating the host-plant chemistry may provide a means of enhancing the attraction of parasitoids to their prey. In this study we describe the differential attraction of the braconid wasp Diaeretiella rapae to two near-isogenic lines of Brassica oleracea which differ in a gene which alters the chemical structure of the isothiocyanates which are emitted following tissue damage. We demonstrate that, by enhancing the production of but-3-enyl isothiocyanate in B. oleracea and Brassica napus (oilseed rape), we can increase the attraction of D. rapae to these plants under standard field conditions. (+info)
Estimating ancestral geographical distributions: a Gondwanan origin for aphid parasitoids?
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We tested the published hypothesis of a Gondwanan origin for the overwhelmingly northern hemisphere aphid parasitoids (Aphidiinae) as follows: (i) finding their sister group by a phylogenetic analysis of the entire Braconidae (Insecta: Hymenopterai using sequence data from approximately 500 bp fragments of both the nuclear 28S (D2 region) and mitochondrial 16S rDNA genes, (ii) using this sister-group relationship and the more informative 28S D2 gene to estimate the phylogeny of the Aphidiinae and (iii) estimating the ancestral distribution for the Aphidiinae using maximum-likelihood and maximum-parsimony methods. Both methods indicated a Gondwanan origin. (+info)
A gene encoding a polydnavirus structural polypeptide is not encapsidated.
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Polydnaviruses are symbiotic viruses associated with some parasitic Hymenoptera that are vertically transmitted as proviruses within wasp genomes. To study this symbiotic association a gene encoding an abundant Campoletis sonorensis polydnavirus virion protein was characterized. This gene is not encapsidated but resides in the wasp genome where it is expressed only during virus replication. Immunolocalization studies detected the encoded 44-kDa protein only in oviduct tissue with ultrastructural studies detecting epitopes between or on virion envelopes. Expression and localization of the 44-kDa protein are consistent with its being a viral structural protein but localization of the gene only within the wasp genome is atypical, raising the possibility that this protein is adventitiously packaged during virion assembly. To address this possibility, quantitative dot blot and genomic Southern blot hybridizations were performed to determine whether the copy number of the p44 gene increased disproportionately during replication, as would be expected for a gene encoding a virion protein. The copy number of the p44 gene increases in tissues supporting virus replication but is unchanged in other tissues, suggesting that this gene is amplified in replicative cells. The data indicate that genes encoding polydnavirus virion proteins may be distributed between wasp and encapsidated viral genomes. (+info)