Schlenke TA, Morales J, Govind S, Clark AG. Contrasting infection strategies in generalist and specialist wasp parasitoids of Drosophila melanogaster.
PLoS Pathog 2008;
3:1486-501. [PMID:
17967061 PMCID:
PMC2042021 DOI:
10.1371/journal.ppat.0030158]
[Citation(s) in RCA: 155] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2006] [Accepted: 09/14/2007] [Indexed: 11/18/2022] Open
Abstract
Although host–parasitoid interactions are becoming well characterized at the organismal and cellular levels, much remains to be understood of the molecular bases for the host immune response and the parasitoids' ability to defeat this immune response. Leptopilina boulardi and L. heterotoma, two closely related, highly infectious natural parasitoids of Drosophila melanogaster, appear to use very different infection strategies at the cellular level. Here, we further characterize cellular level differences in the infection characteristics of these two wasp species using newly derived, virulent inbred strains, and then use whole genome microarrays to compare the transcriptional response of Drosophila to each. While flies attacked by the melanogaster group specialist L. boulardi (strain Lb17) up-regulate numerous genes encoding proteolytic enzymes, components of the Toll and JAK/STAT pathways, and the melanization cascade as part of a combined cellular and humoral innate immune response, flies attacked by the generalist L. heterotoma (strain Lh14) do not appear to initiate an immune transcriptional response at the time points post-infection we assayed, perhaps due to the rapid venom-mediated lysis of host hemocytes (blood cells). Thus, the specialist parasitoid appears to invoke a full-blown immune response in the host, but suppresses and/or evades downstream components of this response. Given that activation of the host immune response likely depletes the energetic resources of the host, the specialist's infection strategy seems relatively disadvantageous. However, we uncover the mechanism for one potentially important fitness tradeoff of the generalist's highly immune suppressive infection strategy.
The fruitfly Drosophila melanogaster has become a model system for the study of innate immunity, and parasitic wasps are one of the most obvious natural pathogens of Drosophila, making this a great system for studying interactions between the host immune system and pathogen virulence proteins. We have focused on two closely related wasp species, Leptopilina boulardi and L. heterotoma, that successfully parasitize D. melanogaster hosts in nature. Both wasps inject venom loaded with virus-like particles into their hosts to prevent host-mediated melanotic encapsulation and killing of their eggs. However, there are substantial differences in the effects of the venom from these two wasp species. L. heterotoma venom causes lysis of host hemocytes (blood cells) and prevents the host from mounting any substantial immune transcriptional response, while L. boulardi venom has a relatively weak and localized effect on host hemocyte survival and does not prevent immune response activation. Thus, these wasps allow us to compare the benefits and drawbacks of relatively immune suppressive versus relatively immune evasive parasite infection strategies in a natural system.
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