Entrainment of cell division in phytoplankton with dynamic energy budgets

We explore the entrainment behavior of cell division in phytoplankton in the context of Dynamic 25 Energy Budget (DEB) theory. In particular, we explore the range of DEB and environmental 26 parameter values within which a cell divides at regular intervals in a periodic light environment 27 with abundant nutrients and investigate the impact of parameter values on the phase of cell 28 division. We consider three types of cells that differ in the evolution of surface area to volume 29 ratio during the cell cycle: cells with a constant shape (isomorphs), cells with a constant surface 30 area (V0-morphs) and cells with a constant surface area to volume ratio (V1-morphs), the latter 31 being the default choice in studies on the population dynamics of unicellular organisms because 32 of its desirable mathematical implications. Only in isomorphs and V0-morphs, however, cell 33 division can be entrained to a periodic light. Regular cell division in V1 is purely coincidental, as 34 it depends on exact choices for parameter values. We attribute this to the fact that V1-morphs 35 lack the negative feedback of size on the dynamics of reserves in V0-morphs and isomorphs. 36 Because entrained isomorphs and V0-morphs divide during the dark hours in our simulations, 37 these two shapes can represent the division behavior of phytoplankton species that complete the 38 cell cycle during the night, such as dinoflagellates and coccolithophores. A description of the 39 division behavior of species completing the cell cycle during the day, such as silicon dependent 40 diatoms and cyanobacteria, requires a more complex model than used in this paper. 41 Furthermore, we explore the robustness of our findings by randomizing model parameters and 42 introducing unevenness in biomass separation between daughter cells during cell division. We 43 conclude that especially the entrainment in V0-morphs is relative insensitive to perturbations