Berlin 2005 – scientific programme

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SYBN: Biological and Social Networks

SYBN 3: Biologische und Soziale Netzwerke, Postersitzung

SYBN 3.17: Poster

Monday, March 7, 2005, 14:00–15:30, Poster TU E

Transition from an excitable to an oscillatory state in Dictyostelium discoideum — •Christiane Hilgardt¹, Andrey A. Polezhaev² und Stefan C. Müller¹ — ¹Otto-von-Guericke University Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany — ²P.N. Lebedev Physical Institute, Leninsky prosp. 53, 119991 Moscow, Russia

Under conditions of starvation populations of the amoebae Dictyostelium discoideum aggregate mediated by chemical excitation waves of cAMP. Two types of waves can be observed, either spiral or circular-shaped ones. We investigate the transition of Dictyostelium patterns from the excitable to the oscillatory behaviour, in particular, the change from spiral waves to target patterns. In experiments a continuous transition from the spiral type pattern to target waves was observed at the later stages of aggregation. On the basis of a model for Dictyostelium aggregation we give a theoretical explanation for such transitions. It is shown that cell density can be an effective bifurcation parameter. Under certain conditions the active medium is shifted from the excitable to the oscillatory state while the frequency of oscillations is proportional to the square root of the cell density. Thus the regions with the highest cell density, during the early stages of the spatial rearrangement of the cells, become pacemakers and produce target patterns. These analytic results were confirmed in numerical simulations of the model. We implement the model results into a biological context and discuss the role of experimental conditions and controlling factors for the type of the observed pattern.