A parasite-mediated life-history shift in Daphnia magna.

The impact of parasitism on host populations will be modulated by both genetic variation for susceptibility, and phenotypically plastic-life-history traits that are altered to lessen the fitness consequences of infection. In this study we tested for life-history shifts in the crustacean Daphnia magna following exposure to the horizontally transmitted microsporidian, Glugoides intestinalis. In two separate experiments, we exposed hosts to parasite spores and measured their fecundity relative to controls. We show that host exposed G. intestinalis show fecundity compensation, i.e. hosts shift their life-history strategy towards early production. Our experiments included multiple host genotypes, and subtle differences among them indicated that fecundity compensation could be subject to parasite-mediated natural selection.