There is increasing evidence that rapid phenotypic evolution can strongly influence population dynamics, but how are such eco-evolutionary dynamics influenced by the source of trait variation (i.e., genetic variation or phenotypic plasticity)? To investigate this, we used rotifer-algae microcosm experiments to test how the phenotypic and genetic composition of prey populations affect predator-prey population dynamics. We chose four genetically distinct strains of the green alga Chlamydomonas reinhardtii that varied in their growth rate, standing levels of defense, and inducible defense. To additionally test for strain specificity of plasticity responses, we quantified protein expression of each strain in the presence and absence of rotifer predators (Brachionus calyciflorus). We then tested how different strain combinations influenced the outcome of pairwise competition trials with and without rotifer predation. We tracked individual strain frequencies using quantitative polymerase chain reaction (qPCR), and compared the observed dynamics to a suite of ecoevolutionary models of varying complexity. We found that variation in trade-offs between growth and defense between algal strains strongly influenced the outcome of competition and the overall predator-prey dynamics. Our purely ecological model of the observed dynamics, which allowed for the presence of phenotypic plasticity but no trait variation between strains, never outperformed any of our eco-evolutionary models in which strains could have different trait values. Our best fitting eco-evolutionary model allowed strains to differ in an inducible defense trait. Overall, our results provide some of the first experimental evidence that variation in phenotypically plastic responses among prey genotypes can be an important component of eco-evolutionary dynamics in a predator-prey system.

Environmental factors can interact with the effects of chemical pollutants on natural systems by inducing multiple stressor effects in individual organisms as well as by altering selection pressure on tolerant strains in heterogeneous populations. Predation is a stressful environmental factor relevant for many species. Therefore, the impact of predation by the rotifer Brachionus calyciflorus on tolerance of eight genetically different strains of the green alga Chlamydomonas reinhardtii to simultaneous exposure to each of the three herbicides (diuron, paraquat, and S-metolachlor) was tested. Interactions of combined stressors were analyzed based on the independent action model; additive, synergistic, and antagonistic effects of the combined exposure could be detected depending on the herbicide and strain tested. If cultures were acclimated (pre-exposed) to one stressor, tolerance to the second stressor could be increased. This indicates that physiological changes can induce cotolerance of predation-exposed algae to herbicides and of herbicide-treated algae to predation depending on the combination of stressors. The strain-specific differences in multiple stressor effects also changed the correlation of strains' tolerances to individual stressors determined during combined and single-stressor exposure. Changes in cotolerance to stressors affect selection pressure and population dynamics during long-term exposure. This shows that predation stress can have adverse effects on the toxicity of chemical pollutants to microalgae on the organism and population levels.

Fusarium poae is a pathogen of increasing importance within the disease complex Fusarium head blight (FHB). Eleven microsatellite markers were developed, and 72 F. poae strains from Switzerland and other countries were used to assess the level of marker polymorphism. The number of alleles for each of the markers ranged from 4 to 15, and the average gene diversity was 0.62, ranging from 0.25 to 0.84. Using these novel markers, 44 genotypes could be differentiated among all F. poae strains. Two genotypes were represented by nine and ten strains, respectively, deriving from distinct geographic areas within Switzerland and indicating a potential selection advantage. Four markers were F. poae-specific, whereas seven markers also yielded amplification products in one to four strains of five other Fusarium species. Of the latter, five markers revealed F. poae-specific allele size ranges. Hence, these microsatellite markers could be used both for FHB species differentiation and for intra-specific distinction of F. poae strains.