Dynamical States of Self-Organised Waves in a Giant Single-Celled Organism

Living systems often seem to follow an intrinsic predictive model of the world — a defining trait of anticipatory systems. Here we study self-organized waves in Caulerpa, a marine green alga which appears to predict the day/night light cycle. 

Caulerpa consists of differentiated organs resembling leaves, stems and roots. While an individual can exceed a meter in size, it is a single multinucleated giant cell. I will present experimental results, tracking over weeks the morphogenesis of tens of samples concurrently, while tracing at resolution of tens of seconds the variation of the green coverage. The latter reveals waves propagating over centimetres within a few hours, and is attributed to chloroplast redistribution at whole-organism scale. By coarse-graining in space we achieve a reduced description to a dynamic macroscopic observable. We find that the waves are coupled to an effective self-sustained oscillator, and respond to time-dependent illumination.

Time-keeping and synchronization are recurring themes in the research of living systems as contributors to homeostasis. Studying this seemingly primitive light-fed system offers opportunities to explore relations among biological oscillators, morphogenesis, and metabolism — a model to understand self-stabilization far-from-thermal-equilibrium, and emergence of anticipatory behaviour in a natural system.