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

Abstract

When a parasite attacks an insect, the outcome is commonly modulated by the presence of defensive heritable symbionts residing within the insect host. Previous studies noted markedly different strengths of Spiroplasma‐mediated fly survival following attack by the same strain of wasp. One difference between the two studies was the strain of Spiroplasma used. We therefore performed a laboratory experiment to assess whether Spiroplasma‐mediated protection depends upon the strain of Spiroplasma. We perform this analysis using the two strains of male‐killing Spiroplasma used previously, and examined response to challenge by two strains of Leptopilina boulardi and two strains of Leptopilina heterotoma wasp. We found no evidence Spiroplasma strain affected fly survival following wasp attack. In contrast, analysis of the overall level of protection, including the fecundity of survivors of wasp attack, did indicate the two Spiroplasma strains tested varied in protective efficiency against three of the four wasp strains tested. These data highlight the sensitivity of symbiont‐mediated protection phenotypes to laboratory conditions, and the importance of common garden comparison. Our results also indicate that Spiroplasma strains can vary in protective capacity in Drosophila, but these differences may exist in the relative performance of survivors of wasp attack, rather than in survival of attack per se.

Preliminary Characterization of Phage-like Particles from the Male-Killing MollicuteSpiroplasma poulsonii(an Endosymbiont ofDrosophila)

“…Could having unpackaged extra-chromosomal copies (Scenario 2) or multiple chromosomal copies (Scenario 3) enable higher RIP2 protein synthesis? Could the different RIP2 gene copy numbers detected in published datasets (not from particle-enriched extractions) of MSRO-Br vs. MSRO-Ug be related to the higher degree of overall protection against certain wasps reported for MSRO-Br [115]?…”

“…Thus, the higher RIP2 copy numbers detected in MSRO-Br could reflect a higher number of chromosomal copies, or a higher abundance of extrachromosomal copies, which could be condition-dependent. If RIP2 gene copy numbers differ between MSRO-Br and MSRO-Ug, they could be related to the higher degree of overall protection against certain wasps reported for MSRO-Br (Jones and Hurst 2020).…”

Differential gene expression in a tripartite interaction:Drosophila,Spiroplasmaand parasitic wasps

“…On the other hand, it may reflect energy investment for a fly function such as immune response, which is energetically expensive (Schlenke et al, 2007;Dolezal et al, 2019). If it indeed reflects investment in immune functions, these have not been detected (this study; Schlenke et al, 2007) and are unsuccessful, as the fly generally does not survive attacks by this strain of L. heterotoma (Xie et al, 2014;Jones & Hurst, 2020b). The L. heterotoma-induced downregulation of genes related to spermatogenesis; a phenomenon not induced by Ganaspis sp., is an interesting contrast between the two wasps.…”

“…Parasitism by L. heterotoma in the presence of Spiroplasma results in no wasp survival, and in variable survival of D. melanogaster (range: <1 to 40%). Other factors that affect fly survival are species and strain of Drosophila, wasp, and Spiroplasma, as well as experimental conditions, including temperature (Mateos et al, 2016;Jones & Hurst, 2020a, 2020bCorbin et al, 2021). Wasp species that are negatively affected by Spiroplasma are referred as "Spiroplasma-susceptible".…”

“…Herein, we used an RNA-seq approach to evaluate the transcriptomic response of D. melanogaster during interactions involving Spiroplasma and two wasps that are generalists of the genus Drosophila: the Spiroplasma-susceptible L. heterotoma and the Spiroplasma-resistant Ganaspis sp. In addition, we evaluated the effect of wasp parasitism on the expression of Spiroplasma RIP genes in two closely related substrains of sMel, which have similar genomes (Gerth et al, 2021), but confer different levels of overall protection against L. boulardi (two strains tested) and one of two strains of L. heterotoma (Jones & Hurst, 2020b).…”