  Plant and animal cells are commonly understood as acquiring specialized
functions through differentiation and asymmetric division. However, unique
capabilities are also acquired when two or more cells fuse together, mixing
cytoplasmic and genetic material. Here, we combine imaging experiments with
biophysical modeling to perform the first risk-benefit analysis of cell-cell
fusion. On one hand, we find fusion introduces an intrinsic instability to the
population dynamics. On the other hand, we measure an unusual physiological
scaling suggesting these cells grow substantially larger at lower energetic
costs. Further analysis of the cytoskeleton finds a size-associated phase
separation of F-actin that self-organizes multinucleated cell phenotypes.
