Response of life history traits to artificial and natural selection for virulence and non-virulence in a Drosophila parastitoid, Asobara tabida

Co-evolution of host-parasitoid interactions is determined by the costs of host resistance, which received empirical evidence, and the costs of parasitoid virulence, which have been mostly hypothesized. Asobara tabida is a parasitoid which mainly parasitizes Drosophila melanogaster and D. subobscura, the first species being able to resist to the parasitoid development while the second species is not. To parasitize resistant hosts, including D. melanogaster, A. tabida develops sticky eggs which prevent encapsulation, but this virulence mechanism may be costly. Inter-individual and inter-population variation in the proportion of sticky eggs respectively allowed us to (i) artificially select and compare life history traits of a virulent and a non-virulent laboratory strain, and (ii) compare a virulent and a non-virulent field strain, to investigate the hypothetical costs of virulence. We observed strong differences between the two laboratory strains. The non-virulent strain invested fewer resources in reproduction and walked less than the virulent one but lived longer. Concerning the field strains, we observed that the non-virulent strain had larger wings while the virulent one walked more and faster. All together, our results suggest that virulence may not always be costly, but rather that different life histories associated with different levels of virulence may coexist at both intra- and inter-population levels. This article is protected by copyright. All rights reserved