Fig. 4. Ensemble average concentrations are determined by the stoichiometry with slowest dynamics.

a, Phase portrait of condensate dynamics in the $\phi$–$V$ plane. Orange and grey arrows are determined from measured WSP-1 and F-actin amounts and, in contrast to Fig. 2c, using measured condensate volumes based on the assumption that cortical condensates have a spherical shape. Yellow, green and blue arrows are calculated from the empirically determined growth laws expressed in the $\phi$–$V$ plane. Colours denote time rate change vector magnitudes. The thick line denotes the experimentally determined volume nullcline. b, Rate of change of volume as a function of instantaneous volume and effective F-actin volume fraction. Condensates transition from growth to shrinkage at an effective F-actin volume fraction of 0.8 (the orange dashed line), which corresponds to the region of slow kinetics within the transition region (Figs. 2d and c and d). c, Mass flux phase portrait current magnitude. Contour lines (68%, 25%) depict the most commonly occupied total intensity values. The orange dashed line indicates the effective F-actin volume fraction corresponding to the centre of the transition region (Fig. 2d), and coincides with lowest total currents and slowest kinetics. d, Concentration flux phase portrait current magnitude. Contour lines (68%, 25%) depict the most commonly occupied concentration values and reflect the preferential maintenance of a pair of concentrations. This pair of concentrations lies at the intersection of the line of constant total density (yellow) and the line of dominant stoichiometry (orange), which corresponds to the orange lines in a–c and to the transition regions of Fig. 2c,d (see also Extended Data Fig. 5 for moderate arx-2 RNAi conditions).

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