Cyanobacteria blooms pose a substantial threat to freshwater systems globally. While zooplankton grazers such as Daphnia can have an important role in suppressing cyanobacteria blooms, cyanobacteria can adversely impact Daphnia fitness and even kill them. Earlier work has shown an evolutionary increase in tolerance to cyanobacteria across years and strong genotype × genotype interactions determining the interaction between Daphnia and the cyanobacterium Microcystis. Here, we test the hypothesis that Daphnia magna can adapt during 1 growing season to changes in dominant strains of Microcystis. Over 2 consecutive years, we collected D. magna clonal lineages and Microcystis strains from a single pond early and late in the growing season and we assessed whether Daphnia survival differed when exposed to Microcystis strains from either the same or a different time point within the growth season. Our findings reveal important Daphnia genotype × Microcystis genotype interactions, with Daphnia survival being higher when exposed to Microcystis from the same time point than when exposed to Microcystis of a different time point. Our results extend earlier findings to variation within 1 single natural system and growth season, and suggest an important impact of rapid (co)evolutionary dynamics shaping the tolerance of zooplankton grazers to cyanobacteria.
