Euglena Simulation Experiment Purpose There are two purposes for conducting this simulation. The primary aim is to simulate a population of flagellated1 Euglenoid organisms evolving the ability to navigate toward a light source in order to facilitate photosynthesis. Of utmost importance in this experiment is modeling the environment, various parameters, and organisms after actual biology as much as possible. The secondary aim of this experiment is to gain experience in environment simulation. The simulator software will be designed to be as modular as possible, so that at a later time any parts that are not performing realistically enough can be easily swapped for new modules written using the experience gleaned from the simulation of one-dimensional evolution in Euglena. Procedure The basic procedure for this simulation is probably very similar, if not identical, to those of other evolution simulations. The starting point is an initial population of Euglenoids with various fitnesses (for this experiment, fitness is entirely defined by the quality of “communication” between the photoreceptor and the flagellum; more on this will follow). This initial population will be placed in an aqueous environment containing various chemical substances in and out of solution. The environment’s light source will be dynamic, so that at different times the light intensity map of the environment will be different. The change will be cyclic so that if they are capable, the population can learn the pattern. The Euglenoids will obtain nutrients from the environment and through photosynthesis. Upon reaching a certain size they will reproduce via binary fission and mitosis. Finally, using configurable parameters, mutation will be introduced into the system to allow evolution. The main focus is on the flagellum and the photoreceptor. At the base of the flagellum is a protein crystal that reacts to light as well as a stigma, which acts a shade. As Euglena swim they rotate longitudinally, which causes the stigma to sometimes shade the photoreceptor and sometimes leave it exposed to light. A modular signal is created, which allows the determination of the direction of greatest light intensity. In response to this the dynine in the flagellum must be triggered with ATP to cause the proper whiplash motion to pull the Euglenoid toward the light source. In simulating this locomotion, the following assumptions will be made: first, Euglena are always in some form of motion. Thus, no decision to stay still can be made, but rather the cells will oscillate in areas of highest light intensity. Second, all flagella work perfectly. This simplifies 1 Note that Euglena, as Eukaryotes, possess cilia rather than flagella. However since their cilium is very long, it is generally referred to as a flagellum. All following references to flagellum, flagella, flagellated, etc truly refer to cilia. the evolutionary process. Similarly, it is assumed that all photoreceptors work perfectly. Therefore the only variable in this experiment is the “communication” between the photoreceptor and the flagellum. Three variables will be used to simulate the communication: , i, and a, representing respectively the percentage of time that communication is successful, the smallest amount by which navigation can be off (in percentage of 360 degrees), and the maximum amount by which navigation can be off (in percentage of 360 degrees). It is these variables that will be replicated and, occasionally, mutated in the reproduction process. Another very important part of this experiment is each organism’s metabolism. Metabolic rates will be held constant between individuals to reduce complexity, however metabolism must still be simulated in detail, as it provides the energy needed for locomotion and reproduction. Because Euglena are primarily autotrophic, the following equations are the main concern in modeling their metabolic behavior. 6CO 2 6 H 2 O 2872 kJ C 6 H 12 O6 6O 2 (1) C 6 H 12 O6 6O2 6CO2 6 H 2 O 2872 kJ (2) (1) describes the total of the light and dark reactions involved in photosynthesis. The glucose synthesized is stored as paramylum, which can then be hydrolyzed to obtain glucose again. The paramylum storage is what causes growth to be observed. (2) describes the consumption of synthesized glucose to release energy to form ATP from ADP and inorganic phosphate. Reproduction of each organism’s DNA has been discussed previously. However this is only one step in the reproduction process. In Euglena, reproduction is determined by size and maturity. For the purposes of this experiment, only size will matter. Once an organism reaches a predetermined maximum size, it must wait until nightfall to begin binary fission and mitosis, which take 2-5 hours (this experiment will use the average, 3.5 hours). During this time no purposed motion will occur. Expected Outcomes The expected overall result of this experiment is the evolution of a population of Euglenoids wherein a large majority of them possess the ability to follow a light source in order to maintain a high glucose synthesis rate. As navigation responds solely to light intensities, there is no chance of also evolving a group of organisms that can follow the gradient of increasing acetate concentration. This would, however, be an interesting simulation to investigate later.