Geometry Shapes Evolution of Early Multicellularity
A) The probability of death that yields the most group offspring is shown for each threshold of group size for different rounds of cell reproduction (blue for 21, red for 19). The degree caps follow the same organization broken down by probability of death. In general the probability of death for a degree cap of 4 and no cap is the best strategy for most group sizes. Once the group size gets large () lower probabilities of death begin to win as it is advantageous not to divide large groups. B) The best strategies from A for group size thresholds ¡ are distinguished by death delay (number of rounds without reproduction before a cell is susceptible to death). The optimal strategy of for no cap has no death delay, i.e. all cells are susceptible to death. For group size thresholds around where degree cap of 4 with probability of death does better, the death delay increases with group size threshold. This increased death delay effectively lowers the probability of death. C) The average size of group offspring as a percent of parent size is shown for each optimal strategy from A (death delays included). The values are all under and are much smaller than those experimentally observed. There was, however, only one strategy which left more symmetrical groups (a degree cap of 3 with the highest probability of death).