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

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 ofSpiroplasma-mediated fly survival following attack by the same strain of wasp. One difference between the two studies was the strain ofSpiroplasmaused. We therefore performed a laboratory experiment to assess whetherSpiroplasma-mediated protection depends upon the strain ofSpiroplasma. We perform this analysis using the two strains of male-killingSpiroplasmaused previously, and examined response to challenge by two strains ofLeptopilina boulardiand two strains ofLeptopilina heterotomawasp. We found no evidenceSpiroplasmastrain 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 twoSpiroplasmastrains 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 thatSpiroplasmastrains can vary in protective capacity inDrosophila, but these differences may exist in the relative performance of survivors of wasp attack, rather than in survival of attack per se.