Abstract
Symbionts are widespread and might have a substantial effect on the outcome of interactions between species, such as in host-parasitoid systems. Here, we studied the effects of symbionts on the outcome of host-parasitoid interactions in a four-partner system, consisting of the parasitoid wasp Leptopilina boulardi, its two hosts Drosophila melanogaster and D. simulans, the wasp virus LbFV, and the endosymbiotic bacterium Wolbachia. The virus is known to manipulate the superparasitism behavior of the parasitoid whereas some Wolbachia strains can reproductively manipulate and/or confer pathogen protection to Drosophila hosts. We used two nuclear backgrounds for both Drosophila species, infected with or cured of their respective Wolbachia strains, and offered them to L. boulardi of one nuclear background, either infected or uninfected by the virus. The main defence mechanism against parasitoids, i.e. encapsulation, and other important traits of the interaction were measured. The results showed that virus-infected parasitoids are less frequently encapsulated than uninfected ones. Further experiments showed that this viral effect involved both a direct protective effect against encapsulation and an indirect effect of superparasitism. Additionally, the Wolbachia strain wAu affected the encapsulation ability of its Drosophila host but the direction of this effect was strongly dependent on the presence/absence of LbFV. Our results confirmed the importance of heritable symbionts in the outcome of antagonistic interactions.
Highlights
Endosymbionts are extremely frequent in arthropods, especially in insects
In the global analysis of experiment 1, there was a contribution of the temporal block suggesting that some environmental parameters that were not controlled for in this experiment significantly influenced the outcome of the Drosophila-parasitoid interaction
The Drosophila nuclear background was always significant showing that the outcome of host-parasitoid interaction was highly dependent on the host genotype (Table 2)
Summary
By providing additional heritable genetic material, they may contribute to the adaptation of their insect host [1,2]. Many insect parasitoids harbour viral symbionts allowing them to cope with the host’s immune defenses, increasing the virulence of these parasitoids [13,14,15,16]. These heritable viruses are injected into the parasitoid’s host together with the eggs, suppressing, to varying degrees, the immune reaction of the parasitized host [17]
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