Abstract

The forcibly launched spores of ascomycete fungi must eject through a boundary layer of nearly still air in order to be transported by dispersive air flows. Because of their microscopic size spores are quickly brought to rest by fluid drag. However, by coordinating the ejection of thousands or hundreds of thousands of spores, some fungi, such as the crop pathogen Sclerotinia sclerotiorum, are able to sculpt a flow of air that carries spores across the boundary layer and around any intervening obstacles. High speed imaging of the spore launch shows that this synchronization is self-organized, and likely triggered by mechanical stresses within the fruiting body. Many spores are sacrificed in order to create this flow of air—since spores are not genetically identical this cooperative behavior creates the potential for conflict and cheating among spores and between spores and the parent fungus. Surprisingly our calculations show that in order to maximize the benefit that it derives, a spore must synchronize with its neighbors and maximize its cooperative contribution so that cooperative benefits are hydrodynamically targeted to cooperating spores.