Quourm sensing allows bacterial populations to coordinate the expression of traits by responding to signaling molecules.  This project investigates how adaptations to the mechaniams that promote intercellular communication contribute to genetic diversity within bacterial species.  To determine whether signaling molecules are a selective pressure in vitro, Vibrio fischeri populations were propagated in the presence and absence of signaling molecules.  Those grown with signaling molecules acquired mutations resulting in the inability to express quourm sensing-regulated traits.