Group-selection via aggregative propagule-formation enables cooperative multicellularity in an individual based, spatial model
Fig 4
Terminal cooperator ratio depending on association propbability AC (x axis), dissociation probability (DC, y axis), propagation mechanism (rows) and size-dependent selection (s, columns; e.g. predation).
Each pixel on the heatmap represents the mean of terminal cooperator ratio of 7 independent simulations. The white asterisk denotes the parameters of the first experiment (Fig 3). When size-dependent selection was not in effect (A, left column), only defectors survive in case of no colonization, and the introduction of selection (e.g. predation stress) clearly benefits cooperators with reasonable association rates (A, right column). Random dispersal (B left) shows a slight benefit for cooperators due to decreased competition at the new habitat, but only for high association rate and even higher dissociation rates. In case of random refuge and fragmentation (C, D), size-dependent selection barely has any effect. Aggregation-based dispersion (E) always benefits cooperators, regardless of predation stress or even association/dissociation rates. Aggregation-based propagation is beneficial when there is no predation stress (F left) but is even more advantageous when predation is introduced (F right). For more details and explanation, see text; for the time-evolution of independent simulations for selected (AC, D) pairs, see Fig I in S1 Text; for a detailed examination of differences in division at certain (AC, D) pairs, see Fig J in S1 Text. Parameters are as in Table 1, except for aggregation-based fragmentation, where T = 150 000 000.