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Cooperation is ubiquitous in nature. Two (or more) parties working together can generate great benefits for both sides, and numerous examples for complex forms of collaboration exist in humans and other animals. However, cooperative systems can be vulnerable to exploitation by" cheats", which do not contribute, but nevertheless reap the benefits of cooperation. How cooperative behaviors might have evolved in light of this risk of cheating is therefore an important research topic in evolutionary biology.

Historically, social behaviors were mainly investigated in" higher animals" such as vertebrates and insects. However, by now we have realized that even single-celled bacteria socially engage with each other, and can thus be used to study cooperation. A good example for collaboration among bacteria is the production of iron-scavenging siderophores: these molecules are secreted by bacterial cells when iron is scarce, bind to extracellular iron and can then be taken up by any cell in the surrounding environment with a matching receptor. In the bacterial pathogen Pseudomonas aeruginosa, it was shown that siderophore non-producing “cheats”, which do not produce siderophores but can use those made by others, can invade a population of producers and destabilize the cooperative system. Since siderophores and other secreted metabolites are important for virulence in many bacterial pathogens, it was suggested that these social dynamics would also impact the evolution of virulence. In my thesis, I investigated different aspects of cooperative behaviors in bacteria, using siderophore production in P. aeruginosa as a model system. I particularly …