Figure 1. An illustration of the proposed cost to cells that carry rare recognition cures in co-development with incompatible strains.

(a) Starvation of vegetative cells. The hexagons represent cells; grey—cells with common recognition cues, green—cells with rare, incompatible recognition cues. (b) Aggregation—the cells stream toward a central source of cAMP but the recognition cues have no effect yet. (c) The onset of multicellularity. Rare incompatible cells are segregated from the majority and excluded to the periphery of the mound. (d) Fruiting body—the dark green ellipses represent spores after development. On the basis of our hypothesis, we proposed that the incompatible cells would be excluded from the fruiting body. (e) Spore germination—the small black ellipses represent bacteria, which are consumed by the amoebae as they hatch from the spores. Cells with uncommon recognition cues have suffered a reproductive cost following segregation and are eliminated from the population.