A dinoflagellate adaptive behavior model: response to internal biochemical cues

In this study we built two models to simulate vertical movements of an individual dinoflagellate. In the models, we laid out the flows of the chemical substances inside the cell and their changes in response to such environmental changes as nitrate concentration and light intensity. One of the models is called the Clock-Driven Model, in which the cell moves only according to the clock time and exhibits a regular vertical diel movement. The other model, which we call the Decision-Making Model, contains a network to make decisions for the next move, based on the interactions among biochemicals inside the phytoplankter and its environment. In this model, the decision emerges from the results of a cellʹs internal biochemical fluxes controlled by the threshold setting. The simulation results of both models with different nutrient conditions were compared in terms of the cellʹs behavioral patterns and the amount of protein produced by the cell. The results indicated that balances among the biochemicals and their fluxes can play a significant role in the directional decisions made by dinoflagellates under some environmental nitrate conditions, and that irregularity in a cellʹs movements may be affected by nitrate availability. Also, the simulation results suggest that irregular migration produced to meet the predefined criteria for biochemical fluxes inside the cell can benefit the cell in terms of protein accumulation. We propose that the essence of a cellʹs adaptivity to the environment resides in the internal cellular condition represented here by threshold values associated with biochemical fluxes and their balances, and that it is important to consider an organismʹs internal condition when constructing an adaptive behavior model.