Fig. 3

3D PIV analysis on the embryogenesis of two T. castaneum embryos. Each vector field in a. 1–3 and b. 1-3 is plotted on top of the two volumes it was computed from, where the red signal corresponds to the initial time point and blue intensities belong to the consecutive time point. A few spurious vectors obtained on the background due to the fluorescence bleeding from the embryo were manually curated. Embryos are shown from their ventral and lateral sides. a-b.1 At the onset of gastrulation, serosa nuclei at the anterior end of both analyzed embryos collectively spread towards the dorsal side of the embryos. Moreover, the central and posterior regions on the ventral side undergo coordinated condensation movements that will later give rise to the internalizing germband. a-b.2 The wide-spread serosa cells over the anterior pole and the dorsal side engage in a highly coordinated movement of the tissue towards the posterior pole. Time points a-b.3 are characterized by a highly collective flow of serosa cells towards the ventral side, leading to the emergence and closing of the serosa window. Serosa cells at the anterior pole, dorsal side and the posterior pole collectively migrate clock-wise towards the ventral midline, giving rise to a cell migration pattern resembling a vortex. c Exemplary post-processing analyses applied to the vector field shown in a.1. From left to right: velocity map showing higher velocities in red, divergence(purple)/convergence(cyan) map, collectiveness map displaying higher local collectiveness in yellow, and pseudo-trajectories at the anterior pole of the embryo in a.1) over 10 time points (5 h)