The genotype specific competitive ability does not correlate with infection in natural Daphnia magna populations

Background.; Different evolutionary hypotheses predict a correlation between the fitness of a genotype in the absence of; infection and the likelihood to become infected. The cost of resistance hypothesis predicts that resistant genotypes pay a cost; of being resistant and are less fit in the absence of parasites. The inbreeding-infection hypothesis predicts that the susceptible; individuals are less fit due to inbreeding depression.; Methods and Results.; Here we tested if a host?s natural infection status; was associated with its fitness. First, we experimentally confirmed that cured but formerly infected; Daphnia magna; are; genetically more susceptible to reinfections with; Octosporeabayeri; than naturally uninfected; D.magna. We then collected; from each of 22 populations both uninfected and infected; D.magnagenotypes. All were treated against parasites and kept in; their asexual phase. We estimated their relative fitness in an experiment against a tester genotype and in another experiment; in direct competition. Consistently, we found no difference in competitive abilities between uninfected and cured but formerly; infected genotypes. This was the case both in the presence as well as in the absence of sympatric parasites during the; competition trials.; Conclusions.; Our data do not support the inbreeding-infection hypothesis. They also do not support a cost; of resistance, however ignoring other parasite strains or parasite species. We suggest as a possible explanation for our results; that resistance genes might segregate largely independently of other fitness associated genes in this system.