[C virus of Drosophila and dynamics of host population]

Drosophila melanogaster populations are naturally infected by the Drosophila C virus (DCV). Ingestion of this non-hereditary virus early in the life-cycle has a positive effect. Demographic parameters measured on DCV-free and DCV-infected populations of the same genotype enabled us to compute the population growth rates (multiplication rates) by means of matrix models. The DCV-infected sample had a larger growth rate both for low and high larval densities. Since it is not possible to experiment on a mixed population where DCV-free and DCV-infected individuals live together, a model combining competition and contamination was used. Simulations showed that coexistence of free and infected animals can occur. Such a result leads us to question the relation between population growth rate and fitness.