Universal calcium fluctuations inHydramorphogenesis.

Understanding the collective physical processes that drive robust morphological transitions in animal development necessitates the characterization of the relevant fields involved in morphogenesis. Calcium (Ca²⁺) is recognized as one such field. In this study, we demonstrate that the spatial fluctuations of Ca²⁺duringHydraregeneration exhibit universal characteristics. To investigate this phenomenon, we employ two distinct controls, an external electric field andheptanol, a gap junction-blocking drug. Both lead to the modulation of the Ca²⁺activity and a reversible halting of the regeneration process. The application of an electric field enhances Ca²⁺activity in theHydra's tissue and increases its spatial correlations, while the administration ofheptanolinhibits its activity and diminishes the spatial correlations. Remarkably, the statistical characteristics of Ca²⁺spatial fluctuations, including the coefficient of variation and skewness, manifest universal shape distributions across tissue samples and conditions. We introduce a field-theoretic model, describing fluctuations in a tilted double-well potential, which successfully captures these universal properties. Moreover, our analysis reveals that the Ca²⁺activity is spatially localized, and theHydra's tissue operates near the onset of bistability, where the local Ca²⁺activity fluctuates between low and high excited states in distinct regions. These findings highlight the prominent role of the Ca²⁺field inHydramorphogenesis and provide insights into the underlying mechanisms governing robust morphological transitions.