The Importance of Being Spiral: Models and Tests of Territory Size in Slime
Mold Communities

Edward Cox

Princeton University

The cellular slime mold Dictyostelium begins life as a population of autonomous free living amoebae. When they exhaust the food supply, they signal to each other, eventually forming a community of amoebae that cooperates as a chemotactic, thermosensitive population of cells that move together as a primitive tissue. The chemotactic signal for cooperation is cyclic AMP. Cells emit and respond to it, and many thousands of cells on a surface behave as an excitable system, relaying the cyclic AMP signal as a complex pattern of wave forms. These waves interact, and from these early interactions, spiral waves quickly evolve. Computational and genetic experiments suggest that the formation of spiral waves is under genetic control, and further suggest that a particular enzyme involved in controlling threshold sensitivity of the chemotactic system breaks the circular symmetry of early waves to form spirals. This expectation has been confirmed with mutant strains. Since spiral wave forms are ubiquitous in
nature, I will discuss how these findings might be related to reentrant waves in heart muscle, Ca waves in the fertilized egg, and emerging evidence of excitable 2D dynamics in populations of animals.