Advection of PAR-3 is independent of cluster size. (A and B) Cluster size only modestly affects diffusivity. (A) Distribution of diffusivities for 400 random clusters selected from all particles (16 embryos) for each of the indicated intensity bins (τ = 2 s). Mean values indicated. (B) Plot of mean cluster diffusivity per embryo across cluster size bins reveals a general trend of decreasing diffusivity with cluster size but note that clusters are generally very slowly diffusing in all bins. Mean values across all embryos indicated by bars. (C) The distribution of PAR-3 cluster displacements is shifted along the flow-parallel axis. Data shown for all clusters from a single embryo, τ = 5 s, n (steps) = 542, 1,033, 1,196, 844. (D) Fit values for advection velocity parallel (υ_x, red) and perpendicular (υ_y, blue) relative to the flow axis are similar for differently sized clusters. Lines connect paired values from single embryos. (E and F) Coupling coefficients are independent of cluster intensity, diffusivity. Coupling coefficients were fit from particles binned by indicated intensity bands (E) or diffusivity (F) on a per-embryo basis. Mean indicated. (G) Measured parallel (υ_x, red) and perpendicular (υ_y, blue) advection velocities (τ = 0.5 s) for single Halo-tagged molecules binned by diffusivity (τ = 0.2 s). (H) Coupling coefficients derived from Halo::PAR-3 single-molecule tracking are independent of diffusivity. Coupling coefficients were fit from molecules binned by indicated diffusivity on a per embryo basis. Mean indicated. (I) Distribution of effective diffusivities for PAR-3 clusters (green, n = 5,644, 16 embryos) and single JF-549 labeled molecules (yellow, n = 4,500, 12 embryos). For the purposes of this comparison, diffusivity was calculated using τ = 1 s in both cases. (Kolmogorov–Smirnov given non-normal distributions). (J) Coupling coefficients between clusters and Halo particles were not significantly different (unpaired t-test, two-tailed).