Competition between local and global chemotaxis during Dictyostelium Discoideum aggregation

Chemotaxis, the directed migration of cells in response to chemical gradients, is a common process in biological systems. A frequently studied chemotactic system is Dictyostelium Discoideum, a social amoeba. When deprived of food, a population of Dictyostelium cells aggregate into large mounds using chemotaxis. During this process, a signaling center is formed that emits periodic cAMP pulses of the chemoattractant cAMP, followed by a refractory period. Nearby cells not only respond by moving toward the signaling center but also secrete cAMP. This relay mechanism results in chemoattractant waves that propagate outward from the center. These outward waves, however, must compete with chemoattractant gradients generated by small, local clusters away from the center. To study the interplay between this global and local chemotaxis, we couple a reaction diffusion model for cAMP dynamics with a Langevin description of cell dynamics. Our results reveal three distinct regimes: a dilute regime where local chemotaxis is negligible, a local aggregated regime where local chemotaxis dominates, and an oscillatory regime when both effects compete. Our research suggests that strong local chemotaxis can shape aggregate formation, providing new insights into the aggregation stage of Dictyostelium and similar organisms.