Browsing by Author "Cairns, Johannes"

The thesis begins with an introduction to the characteristics of experimental organisms, cyanobacteria and cyanophages, and their role in the marine biogeochemical cycles and food-webs. Subsequently, the methodology of experimental evolution and models of host-parasite dynamics are presented. The aim of the experimental part is to test predictions concerning the effects of host-parasite interactions on the marine nitrogen cycle, food-webs, and host properties. Methods include batch culture growth experiments, liquid chromatography–mass spectrometry, an optical density based phage resistance assay, plaque assay, and microscopy. To the author’s knowledge, this is the first controlled study that demonstrates that viral lysis of a diazotrophic cyanobacterium results in the release of cellular nitrogen to the environment in a form that fuels phytoplankton growth. However, evolution with the phage alters the effect. These observations highlight the importance of host-parasite interactions in biogeochemical cycles and food-webs. Further, a novel phage resistant host genotype with short filaments compared to other sensitive and resistant genotypes was detected, with increased growth ability but decreased buoyancy. Reduced buoyancy is proposed as a novel fitness cost of resistance. Phage-mediated evolution resulted in increased diversity in host filament length, growth ability, and buoyancy, supporting the hypothesis that parasites act as drivers of host diversity.