Human societies around the world are regulated by sets of over-lapping rules: fiscal, judicial, etc. Practices, such as coercing, regulating, and policing, prevent cheating and exploitation, and allow for large-scale cooperation that drives modern societies. Such control is necessary because cooperation is fragile: an association that starts out being mutually beneficial can evolve into one that is parasitic. This is especially true in symbiotic relationships in nature, in which different species form intimate partnerships that allow them to trade services and resources. How do hosts maintain cooperation with the most beneficial microbes over the course of evolution? Adaptations that allow individuals to discriminate among partners based on actual symbiotic performance help promote the persistence of cooperation, and allow organisms to negotiate conditions of trade. My lab develops tools to visualize, track and quantify symbiotic trade over space and time. Ultimately, we are interested in predicting how and when cooperation is favored to evolve.