Coevolutionary Arms Races Driven by Conflict: a Test in Social Amoeba

University Of Houston, Houston TX

Investigators

Abstract

Cooperation is observed across all levels of biological organization: genomes cooperate within cells, cells cooperate within multicellular organisms, and individuals cooperate to form societies. However, at each of these levels, there are some individuals who cheat and others who do not, and biologists still do not fully understand how populations evolve stable systems with both types of individuals or how this coevolution is distributed across populations of the same species in nature. This is because individuals who cheat gain the benefits of cooperation without paying their fair share of the cost, and thus this should spread rapidly through populations. Studying the natural distributions of cheating and cooperation in populations is important because cheating is prevalent in the natural world and occurs across all levels of biological organization, from genes that enhance their own transmission to the detriment of the individual that harbors them, to brood parasites that trick others into raising their young. More importantly, the evolution of mechanisms to prevent cheating was likely critical to the emergence of biological complexity. Moreover, cheating can influence everything from the success of symbioses to the emergence of cancer, and thus has important applications to both medicine and agriculture. The novelty of this project is that the researchers will document natural populations of a slime mold in the wild to determine if there is variation (and coevolution) in the degree of cheating and in resistance to cheating across space and through time. The research also takes a population genomic approach to determine the genes involved in cheating and resistance. Overall the goal is to understand the ecological and evolutionary processes influencing the dynamics of cheating in nature. One prominent hypothesis is that cheating selects for mechanisms to resist or suppress it, which in turn selects for mechanisms to overcome that resistance. Cheating might thus give rise to an arms race of adaptations and counter-adaptations. If so, then social conflict, just like other forms of selective conflict, may cause rapid, divergent, and never-ending change, driving evolutionary divergence and diversification. To date, this arms race hypothesis has garnered support from laboratory experiments and molecular evolution analyses, but there is no work examining how cheating impacts the evolutionary trajectories of social traits in nature. The goal of this research is to test several predictions of this hypothesis in natural populations of the social amoeba (or cellular slime mold) Dictyostelium discoideum. This organism has an unusual form of multicellularity that renders it particularly vulnerable to cheating. The research will quantify phenotypic patterns of adaptation and counter-adaptation in nature, inspired by approaches used to elucidate other forms of selective conflict, such as host-pathogen or genetic conflict. Longitudinal sampling across space and time, combined with the ability to save and revive past and future social partners, offers a unique opportunity to observe coevolution in situ and constitutes a major advantage over other model systems.