The cooperation of the haves and the have-nots

Upon starvation, Dictyostelium discoideum (D.d.) exhibit social behavior mediated by the chemical messenger cyclic adenosine monophosphate (cAMP). Large scale cAMP waves synchronize the population of starving cells and enable them to aggregate and form a multi-cellular organism. Here, we explore the effect of cell-to-cell variability in the production of cAMP on aggregation. We create a mixture of extreme cell-to-cell variability by mixing a few cells that produce cAMP ( haves ) with a majority of mutants that cannot produce cAMP ( have-nots ). Surprisingly, such mixtures aggregate, although each population on its own cannot aggregate. We show that (1) a lack of divalent ions kills the haves at low densities and (2) the have-nots supply the cAMP degrading enzyme, phosphodiesterase, which, in the presence of divalent ions, enables the mixture to aggregate. Our results suggest that a range of degradation rates induces optimal aggregation. The haves and the have-nots cooperate by sharing complementary resources.