(a) Life cycle of multicellular C. reinhardtii. Shortly after settling selection and transfer to fresh medium, motile unicells disperse away from the parent cluster. These cells lose motility and develop into clusters prior to the next round of settling. (b) Our model predicts that smaller clusters should experience reduced survival, up to a cluster size of ~70 cells (survival is assured for larger clusters). (c) Shown are the number of surviving offspring a single 64-cell cluster is calculated to produce as a function of propagule size and the number of doublings propagules undergo prior to settling selection (dark blue: 1, red: 2, green: 3, purple: 4, light blue: 5, orange: 6). Despite the reduced survival of smaller clusters during settling selection, unicellular propagules maximize the number of surviving offspring a cluster can produce.