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Slime mold behavior

General

One very famous focus for models of selforganization is the group behavior of slime mold cells. Normally they move around as individual amoebas throughout their substrate, performing a simple random walk. But when the environmental situation worsens, they suddenly change their behavior and aggregate to a single multi-cellular body. During this aggregation process, a chemical signal is emmited by cells to guide the collective movements. The signal is identified as beeing cAMP.

During aggregation, the cells move uphill to the cAMP gradient in the environment, therefore acummulating in the most densely inhabited zones. When the environmental cAMP-concentration rises over a certain threshold, the moving cells release cAMP by themselves. After such a cAMP release, the cells cannot release additional cAMP, therfore being called “refractory cells”.

The whole process is a self-organizational one, as there cells are all acting without any guidance, neither from special guiding cells that coordinate the aggregations, nor by special pre-existing glues from the environment.

The sporadic release of cAMP leads to waves of cAMP, which are very simular to the waves found in the B-Z-reaction, in the defense behavior of apis dorsata colonies, in the excitational waves on haerts or in the Laola-waves that can be seen on the tribunes of sport stadiums.

Despite the beautiful waves, this system of aggregation leads to very beautiful  “colonies”.

The 3 models

We here present 3 models that model the aggregational behavior of slime molds, from avery basic aproach that was first developed by M. Resnick up to quite elaborate versions, as they have been suggested by S. Camazine.

All models have been ported to NetLogo and have been extended by T. Schmickl.

Pictures:

This picture shows you the life cycle of slime mold:

 

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