Heritable variation in an extended phenotype: the case of a parasitoid manipulated by a virus

In host-symbiont interactions, the genes of both host and symbiont can influence phenotypic traits. In the context of a conflict of interest, fitness-related traits are subjected to opposing selective pressures in the genomes of the partners. In the Drosophila parasitoid Leptopilina boulardi, females usually avoid laying eggs into already parasitized larvae. However, when infected by the virus LbFV, they readily lay additional eggs into parasitized larvae. Inducing superparasitism allows the virus to colonize uninfected parasitoid lineages but is usually maladaptive for the parasitoid. We tested for the presence of resistance genes to this behavioural manipulation in the parasitoid genotype by sampling 30 lines from five populations with contrasting viral prevalence, after infecting them with a reference viral isolate. No geographical differentiation was observed although some genotypes underwent less manipulation than others, and these differences were heritable across generations. The viral titre was not correlated with these differences although fecundity differed between extreme lines.