FIG. 34.12

What determines the shape of fungal spores that are ejected into the air?

BACKGROUND Many fungi disperse their spores by ejecting them forcibly into the air. For spores to be picked up by the wind, however, they must escape a layer of still air called the boundary layer that lies close to the ground. Escape from the boundary layer is easier if spores have a size and shape that minimize drag, the resistance of air to the movement of an object.

HYPOTHESIS In fungi that eject their spores into the atmosphere, natural selection favors spore shapes that minimize drag.

EXPERIMENT Working from computer models for minimizing drag on airplane wings, scientists modeled spore shapes that minimize drag. These models took into account spore size as well as the physical characteristics of the air through which spores travel. The scientists then measured spore shape for more than 100 species of spore-ejecting fungi.

RESULTS Nearly three-quarters of the examined spores had shapes that came within 1% of the shape calculated to minimize drag (shown in the figure as blue outlines). Related species that do not eject spores forcibly were less likely to have drag-minimizing shapes.

CONCLUSION Natural selection has acted on fungi to facilitate spore dispersal by wind.

SOURCE Roper, M., et al. 2008. “Explosively Launched Spores of Ascomycete Fungi Have Drag-Minimizing Shapes.” Proceedings of the National Academy of Sciences, USA 105:20583–20588.