A dinoflagellate adaptive behavior model: response to internal biochemicalcues

In this study we built two models to simulate vertical movements of an indi vidual dinoflagellate. In the models, we laid out the flows of the chemical substances inside the cell and their changes in response to such environme ntal changes as nitrate concentration and light intensity. One of the model s 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 i nside the phytoplankter and its environment. In this model, the decision em erges from the results of a cell's internal biochemical fluxes controlled b y the threshold setting. The simulation results of both models with differe nt nutrient conditions were compared in terms of the cell's behavioral patt erns and the amount of protein produced by the cell. The results indicated that balances among the biochemicals and their fluxes can play a significan t role in the directional decisions made by dinoflagellates under some envi ronmental nitrate conditions, and that irregularity in a cell's movements m ay be affected by nitrate availability. Also, the simulation results sugges t that irregular migration produced to meet the predefined criteria for bio chemical fluxes inside the cell can benefit the cell in terms of protein ac cumulation. We propose that the essence of a cell's adaptivity to the envir onment resides in the internal cellular condition represented here by thres hold values associated with biochemical fluxes and their balances, and that it is important to consider an organism's internal condition when construc ting an adaptive behavior model. (C) 2000 Elsevier Science B.V. All rights reserved.