Intrinsic Rhythms in a Giant Single-Celled Organism and the Interplay with Time-Dependent Drive, Explored via Self-Organized Macroscopic Waves

Living Systems often seem to follow, in addition to external constraints and interactions, an intrinsic predictive model of the world — a defining trait of Anticipatory Systems.

Caulerpa is a marine green alga with differentiated organs resembling leaves, stems and roots; while an individual can exceed a meter in size, it is a single multinucleated giant cell. Active transport has been hypothesized to play a key role in development. Yet, the most recent reports studying organelle transport in Caulerpa are over three decades old.

Using Raspberry-Pi cameras, we track over weeks the morphogenesis of tens of samples concurrently, while tracing at minute resolution the variation of green coverage; the latter is attributed to chloroplasts redistribution at whole-organism scale, and reveals a pulse-like behavior. Our observations indicate that the initiation of these waves, in regenerating algal segments cultured under periodic illumination, precedes the external light change. The temporal spectrum shows a circadian period, which persists over days even under constant illumination.

We explore the system under non-circadian periods, its relaxation times — analogous to jet lag recovery, and the limits at which the system no longer follows the period of the external drive.