RESUMEN
Heritable symbionts display a wide variety of transmission strategies to travel from one insect generation to the next. Parasitoid wasps, one of the most diverse insect groups, maintain several heritable associations with viruses that are beneficial for wasp survival during their development as parasites of other insects. Most of these beneficial viral entities are strictly transmitted through the wasp germline as endogenous viral elements within wasp genomes. However, a beneficial poxvirus inherited by Diachasmimorpha longicaudata wasps, known as Diachasmimorpha longicaudata entomopoxvirus (DlEPV), is not integrated into the wasp genome and therefore may employ different tactics to infect future wasp generations. Here, we demonstrated that transmission of DlEPV is primarily dependent on parasitoid wasps, since viral transmission within fruit fly hosts of the wasps was limited to injection of the virus directly into the larval fly body cavity. Additionally, we uncovered a previously undocumented form of posthatch transmission for a mutualistic virus that entails external acquisition and localization of the virus within the adult wasp venom gland. We showed that this route is extremely effective for vertical and horizontal transmission of the virus within D. longicaudata wasps. Furthermore, the beneficial phenotype provided by DlEPV during parasitism was also transmitted with perfect efficiency, indicating an effective mode of symbiont spread to the advantage of infected wasps. These results provide insight into the transmission of beneficial viruses among insects and indicate that viruses can share features with cellular microbes during their evolutionary transitions into symbionts.
Asunto(s)
Entomopoxvirinae , Interacciones Microbiota-Huesped , Simbiosis , Tephritidae , Avispas , Animales , Evolución Biológica , Entomopoxvirinae/fisiología , Tephritidae/virología , Avispas/genética , Avispas/virologíaRESUMEN
Insects are known to host a wide variety of beneficial microbes that are fundamental to many aspects of their biology and have substantially shaped their evolution. Notably, parasitoid wasps have repeatedly evolved beneficial associations with viruses that enable developing wasps to survive as parasites that feed from other insects. Ongoing genomic sequencing efforts have revealed that most of these virus-derived entities are fully integrated into the genomes of parasitoid wasp lineages, representing endogenous viral elements (EVEs) that retain the ability to produce virus or virus-like particles within wasp reproductive tissues. All documented parasitoid EVEs have undergone similar genomic rearrangements compared to their viral ancestors characterized by viral genes scattered across wasp genomes and specific viral gene losses. The recurrent presence of viral endogenization and genomic reorganization in beneficial virus systems identified to date suggest that these features are crucial to forming heritable alliances between parasitoid wasps and viruses. Here, our genomic characterization of a mutualistic poxvirus associated with the wasp Diachasmimorpha longicaudata, known as Diachasmimorpha longicaudata entomopoxvirus (DlEPV), has uncovered the first instance of beneficial virus evolution that does not conform to the genomic architecture shared by parasitoid EVEs with which it displays evolutionary convergence. Rather, DlEPV retains the exogenous viral genome of its poxvirus ancestor and the majority of conserved poxvirus core genes. Additional comparative analyses indicate that DlEPV is related to a fly pathogen and contains a novel gene expansion that may be adaptive to its symbiotic role. Finally, differential expression analysis during virus replication in wasps and fly hosts demonstrates a unique mechanism of functional partitioning that allows DlEPV to persist within and provide benefit to its parasitoid wasp host.
Asunto(s)
Entomopoxvirinae/genética , Genoma Viral/genética , Genómica , Poxviridae/genética , Simbiosis , Avispas/virología , Animales , Entomopoxvirinae/fisiología , Femenino , Masculino , Poxviridae/fisiología , Replicación Viral/genéticaRESUMEN
For insects known as parasitoid wasps, successful development as a parasite results in the death of the host insect. As a result of this lethal interaction, wasps and their hosts have coevolved strategies to gain an advantage in this evolutionary arms race. Although normally considered to be strict pathogens, some viruses have established persistent infections within parasitoid wasp lineages and are beneficial to wasps during parasitism. Heritable associations between viruses and parasitoid wasps have evolved independently multiple times, but most of these systems remain largely understudied with respect to viral origin, transmission and replication strategies of the virus, and interactions between the virus and host insects. Here, we report a detailed characterization of Diachasmimorpha longicaudata entomopoxvirus (DlEPV), a poxvirus found within the venom gland of Diachasmimorpha longicaudata wasps. Our results show that DlEPV exhibits similar but distinct transmission and replication dynamics compared to those of other parasitoid viral elements, including vertical transmission of the virus within wasps, as well as virus replication in both female wasps and fruit fly hosts. Functional assays demonstrate that DlEPV is highly virulent within fly hosts, and wasps without DlEPV have severely reduced parasitism success compared to those with a typical viral load. Taken together, the data presented in this study illustrate a novel case of beneficial virus evolution, in which a virus of unique origin has undergone convergent evolution with other viral elements associated with parasitoid wasps to provide an analogous function throughout parasitism.IMPORTANCE Viruses are generally considered to be disease-causing agents, but several instances of beneficial viral elements have been identified in insects called parasitoid wasps. These virus-derived entities are passed on through wasp generations and enhance the success of the wasps' parasitic life cycle. Many parasitoid-virus partnerships studied to date exhibit common features among independent cases of this phenomenon, including a mother-to-offspring route of virus transmission, a restricted time and location for virus replication, and a positive effect of virus activity on wasp survival. Our characterization of Diachasmimorpha longicaudata entomopoxvirus (DlEPV), a poxvirus found in Diachasmimorpha longicaudata parasitoid wasps, represents a novel example of beneficial virus evolution. Here, we show that DlEPV exhibits functional similarities to known parasitoid viral elements that support its comparable role during parasitism. Our results also demonstrate unique differences that suggest DlEPV is more autonomous than other long-term viral associations described in parasitoid wasps.
Asunto(s)
Interacciones Microbiota-Huesped/fisiología , Poxviridae/fisiología , Simbiosis , Avispas/virología , Animales , Evolución Biológica , Entomopoxvirinae/genética , Entomopoxvirinae/fisiología , Regulación Viral de la Expresión Génica , Genes Virales , Genoma Viral , Poxviridae/genética , Interferencia de ARN , Fenómenos Fisiológicos de los Virus , Replicación Viral , Virus , Venenos de AvispasRESUMEN
Drosophila melanogaster is an important model for antiviral immunity in arthropods, but very few DNA viruses have been described from the family Drosophilidae. This deficiency limits our opportunity to use natural host-pathogen combinations in experimental studies, and may bias our understanding of the Drosophila virome. Here, we report fourteen DNA viruses detected in a metagenomic analysis of 6668 pool-sequenced Drosophila, sampled from forty-seven European locations between 2014 and 2016. These include three new nudiviruses, a new and divergent entomopoxvirus, a virus related to Leptopilina boulardi filamentous virus, and a virus related to Musca domestica salivary gland hypertrophy virus. We also find an endogenous genomic copy of galbut virus, a double-stranded RNA partitivirus, segregating at very low frequency. Remarkably, we find that Drosophila Vesanto virus, a small DNA virus previously described as a bidnavirus, may be composed of up to twelve segments and thus represent a new lineage of segmented DNA viruses. Two of the DNA viruses, Drosophila Kallithea nudivirus and Drosophila Vesanto virus are relatively common, found in 2 per cent or more of wild flies. The others are rare, with many likely to be represented by a single infected fly. We find that virus prevalence in Europe reflects the prevalence seen in publicly available datasets, with Drosophila Kallithea nudivirus and Drosophila Vesanto virus the only ones commonly detectable in public data from wild-caught flies and large population cages, and the other viruses being rare or absent. These analyses suggest that DNA viruses are at lower prevalence than RNA viruses in D.melanogaster, and may be less likely to persist in laboratory cultures. Our findings go some way to redressing an earlier bias toward RNA virus studies in Drosophila, and lay the foundation needed to harness the power of Drosophila as a model system for the study of DNA viruses.