A virus-Drosophila association: the first steps towards co-evolution?

Drosophila melanogaster can be parasitized by a picornavirus, the Drosophila C virus (DCV). The virus is not hereditary, but it is horizontally transmitted (by ingestion or contact). When first larval instars come into contact with DCV unusual interactions are observed between host and microparasite. DCV acts differently depending on the stage in the host's life cycle. It boosts the reproductive capacity of adults, but it diminishes survival during the pre-reproductive period. In infected flies, the DCV target organs are principally the follicular cells and the fat body. The infected cells resemble DCV-free cells. According to the parameters of the Drosophila lifecycle, measured for different Drosophila strains, at different temperatures, and for different viral doses, DCV could be considered either as a parasite, because it increases pre-adult mortality, or as a mutualist, because it increases the reproductive capacity of the host and decreases its developmental time. Like many viruses, DCV is extremely pathogenic when injected into flies, which then die within a few days. Only one strain resists the disease longer. The resistant phenotype is dominant. Genes of chromosome 3 of the host are involved. Interactions are discussed in terms of an ‘arms race’ and ‘peaceful cohabitation’. They are also considered in terms of biodiversity for the host and for the microparasite.