Dynamics of Morphogenesis in a Giant Single-Celled Organism Feeding on Light*

In developmental biology the emergence of macroscopic pattern and morphology is commonly studied as a consequence of cell-to-cell interaction. However, there are macroscopic cells which exhibit organ-like regions, while having a shared cytoplasm throughout, thus presenting a challenge to this paradigm.

Here we study dynamics of morphogenesis in Caulerpa. It is a marine green alga consisting of differentiated organs resembling leaves, stems and roots. While the individual can reach meter-long scales, it is a single multinucleated giant cell.

We track over weeks algal segments regenerating under various illumination protocols.  The main control parameters are the temporal-pattern and -average of the photon flux. Caulerpa is a photo-autotroph, hence light also plays the role of a main energy source. Using Active Contours, we study the time evolution of curves delineating the two-dimensional projection of the samples. 

Studying this seemingly primitive light-fed Homeostatic System offers an opportunity to explore relationships among morphogenesis, time-restricted feeding, and anticipatory behaviour.