The cellular basis of feeding-dependent body size plasticity in sea anemones

Animals with indeterminate growth can adapt their growth rate and body size to changing food availability throughout their lifetime. As the cellular basis underlying food-dependent growth plasticity is poorly understood, we quantified how the sea anemones Nematostella vectensis and Exaiptasia diaphana (Aiptasia) respond to feeding and starvation on organismal and cellular levels. Using mathematical modelling to analyse growth phases, we found that growth and shrinkage rates in Nematostella are exponential, stereotypic and accompanied by high levels of cell gain or loss, respectively. During starvation and re-feeding, a considerable proportion of juvenile polyp cells (>7%) reversibly shift between S/G ₂ /M and G ₁ /G ₀ cell cycle phases, suggesting a tight nutritional control of quiescence and cell cycle re-entry. In the facultative symbiotic sea anemone Aiptasia, we found that growth and cell proliferation rates are dependent on the symbiotic state and, in comparison to Nematostella , respond less strongly to changes in food supply. Altogether, we provide a benchmark and resource to study the nutritional regulation of body plasticity on molecular, cellular and genomic levels using the rich functional toolkit available for Nematostella .