Density-dependent emergent dynamics of sea urchin embryos

Living systems serve as a robust platform for probing the complexities of nonequilibrium self-organization. Here, we report on the dynamics and emergent phases of sea urchin embryo assemblies. Sea urchin embryos undergo significant morphological transformations over their developmental time, breaking shape symmetry in addition to violating time-reversal and rotational invariance. These broken symmetries, coupled with nonreciprocal interactions, give rise to distinct, emergent states that depend on embryo density. Specifically, we observe global vortex formation at higher densities and more fluid-like behavior at lower densities. We use a combination of experiments, data analysis, and theory to reveal the underlying mechanisms driving these nonequilibrium phases and phase transitions. Our research holds promising implications for the engineering of bio-inspired metamaterials.