Cell condition, competition, and chimerism in the social amoeba Dictyostelium discoideum

When multicellularity originates through the aggregation of genetically variable cells, the interests of the component cells may conflict with each other. A prediction of conflict is that stronger cells will force weaker cells into non-reproductive tissues. However, if stronger cells are better in the reproductive tissues than in the somatic ones, then the same result may be expected in clonal organisms that optimize their development. We explored these issues in the social amoeba Dictyostelium discoideum by forming chimeras between weakened cells and normal cells that were genetically identical. We reduced the condition of amoebae (measured as increased doubling time) by growing them in media lacking glucose, or more acid than normal. Weakened cells were less competitive compared to healthy cells in becoming spore, supporting our prediction of evolutionary conflict. However, spores from weakened cells also proliferated slightly less rapidly than normal spores, indicating that there may also be an advantage in clonal groups to put strong cells in spores.