Symbiont-mediated protection varies with wasp genotype in the Drosophila melanogaster–Spiroplasma interaction

Abstract

The ability of an insect to survive attack by natural enemies can be modulated by the presence of defensive symbionts. Study of aphid-symbiont-enemy interactions has indicated that protection may depend on the interplay of symbiont, host and attacking parasite genotypes. However, the importance of these interactions is poorly understood outside of this model system. Here, we study interactions within a Drosophila model system, in which Spiroplasma protect their host against parasitoid wasps and nematodes. We examine whether the strength of protection conferred by Spiroplasma to its host, Drosophila melanogaster varies with strain of attacking Leptopilina heterotoma wasp. We perform this analysis in the presence and absence of ethanol, an environmental factor that also impacts the outcome of parasitism. We observed that Spiroplasma killed all strains of wasp. However, the protection produced by Spiroplasma following wasp attack depended on wasp strain. A composite measure of protection, including both the chance of the fly surviving attack and the relative fecundity/fertility of the survivors, varied from a <4% positive effect of the symbiont following attack of the fly host by the Lh14 strain of wasp to 21% for the Lh-Fr strain in the absence of ethanol. We also observed that environmental ethanol altered the pattern of protection against wasp strains. These data indicate that the dynamics of the Spiroplasma-Drosophila-wasp tripartite interaction depend upon the genetic diversity within the attacking wasp population, and that prediction of symbiont dynamics in natural systems will thus require analysis across natural enemy genotypes and levels of environmental ethanol.

Symbiont-mediated fly survival is independent of defensive symbiont genotype in the Drosophila melanogaster-Spiroplasma-wasp interaction

“…heterotoma, despite survival of <8% observed in previous studies (Xie et al 2014, Jones & Hurst 2020.…”

“…The L. boulardi strains used were the NSRef strain, established from an initial female collected in Gotheron, near Valence, France (Varaldi et al 2003), and the Lb17 strain, initially collected in Winters, California in 2002(Schlenke et al 2007. The L. heterotoma strains used were the inbred Lh14 strain also collected in Winters, California in 2002 (Schlenke et al 2007) and the Lh-Mad strain established from a single female collected in Madeira, Portugal in March 2017 (Jones & Hurst 2020). The wasp stocks were all maintained on second instar Oregon-R larvae at 25°C on a 12:12 light:dark cycle.…”

“…Spiroplasma infected flies that survive wasp attack generally have a lower fecundity than Spiroplasma infected flies which were not exposed to wasps (Xie et al 2011;Jones & Hurst, 2020). To determine whether the wasp attacked survivors were differentially impacted by Spiroplasma strain the average daily emerged offspring of Spiroplasma infected survivors ("Exposed") and Spiroplasma infected flies which did not undergo wasp attack ("Unexposed") was measured for the MSRO-Br and MSRO-Ug strains.…”

“…Despite finding no difference between the survival of flies infected with MSRO-Br and MSRO-Ug against each of the four wasp strains tested, previous work has shown that it is also important to consider, in combination with survival, the fertility of wasp-attacked flies compared to nonattacked controls to produce a complete model of protection (Xie et al, 2011;Jones & Hurst 2020). Taking into account the survival, proportion of adults fertile, and the fecundity of wasp attack survivors, compared to unexposed Spiroplasma-infected controls, a protection index (PI) was calculated as the product of fly survival x p(fertile) x fecundity of exposed vs unexposed Spiroplasma-infected flies (Table 1).…”

“…Recent work has revealed that the genotype of attacking parasitoid wasp is important for the degree of protection conferred by Spiroplasma (Jones & Hurst 2020). It was observed that Spiroplasma (MSRO-Br strain) conferred protection of 40% against the Lh-Fr and Lh-Mad L.…”