Developmentally driven formation and dissolution of living chiral crystals*

The emergent dynamics exhibited by collections of living organisms often shows signatures of symmetries that are broken at the single-organism level. At the same time, early organism development itself is accompanied by a sequence of symmetry breaking events that eventually establish the body plan. Combining these key aspects of collective phenomena and embryonic development, we describe here the spontaneous formation of hydrodynamically stabilized active crystals made of hundreds of starfish embryos during early development. As development progresses and embryos change morphology, crystals become increasingly disordered and eventually stop forming. We introduce a minimal hydrodynamic model that is fully parameterized by experimental measurements of single embryos and can quantitatively describe the stability, formation and rotation of emerging living crystals. A detailed analysis of developmental changes in the swimming properties of single embryos and associated sources of effective noise in embryo-embryo interactions provides insights into the mechanisms that eventually lead to the dissolution of clusters. Our work thereby quantitatively connects developmental symmetry breaking events on the single-embryo level with the remarkable macroscopic properties of a novel living chiral crystal system.