This thesis studies the connections between two ubiquitous biological phenomenon: cooperation and communication; and one may debate whether the latter is a specific example of the prior.More specifically, the questions examined in this document center on bacteria and their common form of chemical communication known as quorum sensing. My broad interests and opinions regarding quorum sensing are that they play an immense role in providing feedbacks that adjust cellular behavior and gene expression to optimize growth in response to a plethora of environmental cues and signals. The more specific topics examined in this document relate to the tendency of quorum sensing to regulate cooperative behaviors such as public goods production. Such cooperative behaviors are susceptible to cheating by non-participants if they can enjoy a benefit that a given behavior produces without contributing to that behavior. We examined the stability of quorum sensing in a variety of conditions, particularly where public goods positively contribute to fitness, and pursue explanations for how cooperative goods production and the overlaying regulation of quorum sensing can be maintained and stabilized in the presence of potential cheats, and how such behavior holds up over evolutionary time.A few interesting results were revealed from this research. Firstly, it was definitively shown that quorum sensing regulation provides a distinct advantage in the face of cheats compared to unconditional cooperators. Quorum sensers were able to appropriately regulate cell physiology, including public goods production, in such a way that this strategy had equivalent fitness to an obligate defector in the environment tested, whereas unconditional cooperators paid heavy costs in terms of growth rate, and were thus outcompeted by other strains at low cell densities, and also cheated by defectors at high cell densities. Together, this provides the strongest reported experimental evidence to date that quorum sensing regulation itself can stabilize cooperative behaviors, even in the absence of other layered mechanisms such as policing or positive assortment by clustering.Additionally, cooperative strategies were found to be able to invade metapopulations of mostly defectors when sufficient assortment of competing types was achieved. This was found to be true for both Vibrio harveyi and Vibrio cholerae. Maximum evasion of defectors was achieved when cooperator strains were able to both form structures to separate from competitors (by way of dispersal by motility), and the ability to disperse from other cells through motile phenotypes. Again, the most successful strategy in this regard came from the functional wild type quorum senser as compared to an unconditionally cooperating strategy.Lastly, experimental evolution of Vibrio harveyi populations was conducted in minimal media for 2000 generations. These populations underwent a variety of adaptations to the experimental environment, which was examined in detail through high-throughput genomic sequencing. It was discovered that wild type populations sustained higher fractions of bioluminescent cooperators as well as a higher degree of phenotypic diversity in terms of quorum sensing, while nearly all unconditional cooperator populations experienced rapid evolution and sweeps by de novo defectors. Additionally, many of the evolved forms in wild type populations appear to be optimizing and exhibit intermediate bioluminescent and protease production phenotypes.
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