PMC

(A) The fraction of composition effect profiles promoting irreversible strategies at various cell differentiation costs () and maturity sizes (). Irreversible strategies were only found for maturity size 2⁶ = 64 cells and larger. (B) The fraction of composition effect profiles promoting irreversible strategies at unequal differentiation costs . A rare occurrences of irreversible strategies (∼1%) was detected at the maturity size cells in a narrow range of cell differentiation costs but not at the smaller sizes. (C) The range of cell differentiation costs allowing evolution of irreversible strategies at at the maturity size () cells. For irreversible strategies to evolve at such a small size, the differentiation from soma-role to germ-role must be much more costly than the opposite transition ().

Panels show composition profiles coloured according to the class of differentiation strategy: irreversible (green), reversible (orange), and no differentiation (black). In the synchronous model (top row), due to very asymmetric costs, irreversible differentiation is capable of evolving at small maturity sizes (eight cells). In the asynchronous model (bottom row), irreversible differentiation is not observed below 32 cells. Even at large sizes, the fraction of profiles promoting irreversible differentiation remains small.

(A-C) The fraction of 200 random composition effect profiles promoting irreversible strategy at various cell differentiation costs (, ) at fixed maturity size (panel A), 10 (B), and 15 (C). Larger maturity sizes promote the evolution of irreversible differentiation across all cell differentiation costs. (D-F) The fraction of composition effect profiles promoting irreversible strategy at unequal cell differentiation costs (panel D), (E), and (F). Even with unequal differentiation costs, the minimal maturity size allowing the evolution of irreversible differentiation stays roughly the same — cells. Dashed lines indicate overlap between panels. The legend is the same as that in .

The green curve shows the dynamics of the expected fraction of soma-role cells in an organism using an irreversible strategy (, , ). The orange curve shows the dynamics of the expected fraction of soma-role cells in an organism using the specific reversible strategy , . In this strategy, the number of offspring produced at the end of the life cycle is the same as in the considered irreversible strategy. At the same time, the fraction of soma-role cells during the life cycle is larger. Therefore, under costless differentiation, the presented reversible strategy is more effective than the considered irreversible strategy.