Social interactions in two species of social amoebae Dictyostelium discoideum and Dicyosteliuum purpureum
Jack, Chandra Nicole
Strassmann, Joan E.
Doctor of Philosophy
The core of sociality and one of the key forces behind the transition to multicellularity is cooperation. The study of social behavior in microorganisms has gained considerable attention in the last decade as researchers have discovered that many of the cooperative social interactions found in higher organisms can also be found in microbes. The dictyostelids are particularly amenable to the study of social evolution because of the potential for conflict and cooperation during multicellular formation. The formation of the multicellular fruiting body may lead to conflict because all nearby cells aggregate together, which may be distinct clones, each trying to increase its own fitness. I first explored how D. discoideum and D. purpureum interact and if either species looks to cheat the other when they interact. I found that both species prefer being clonal but cooperate with each other when it seems the benefits outweigh the costs. Cooperating amoebae are able to make larger fruiting bodies, which are advantageous for migration and dispersal, but both species suffer a cost in producing fewer spores per fruiting body. I next examined short-range social dispersal in the social amoebae, D. discoideum and D. purpureum. It appears that the evolutionary loss of stalked migration gives D. discoideum cells the advantage of delaying specialization and the ability to colonize more distant locations, but has significant costs due to migration distance, such as the fraction of cells that become fertile spores. In my final study, we examine the interaction of different clones of D. discoideum before and after migration. We show that chimerism and migration interact to produce fruiting bodies that have a proportionally higher spore allocation compared to clonal fruiting bodies after migration but were unable to determine whether the results that we see are an indication of clones defecting in a tragedy of the commons or more cooperation. With further study will be able to better explain the affects of cooperation on group dispersal and whether it can be used as a mechanism to reduce local competition.