Solving the aerodynamics of fungal flight: how air viscosity slows spore motion

• Published in: Fungal biology Vol. 114; no. 11; pp. 943 - 948
• Main Authors: Fischer, Mark W.F., Stolze-Rybczynski, Jessica L., Davis, Diana J., Cui, Yunluan, Money, Nicholas P.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.11.2010
• Subjects: Ballistospore; Biomechanics; Dispersal; Fungi - chemistry; Fungi - cytology; Models, Biological; Reproduction; Spore discharge; Spores; Spores, Fungal - chemistry; Spores, Fungal - cytology; Viscosity; Biomechanics; Reproduction; Ballistospore; Spore discharge; Dispersal; Spores
• ISSN: 1878-6146; 1878-6162
• DOI: 10.1016/j.funbio.2010.09.003

Viscous drag causes the rapid deceleration of fungal spores after high-speed launches and limits discharge distance. Stokes’ law posits a linear relationship between drag force and velocity. It provides an excellent fit to experimental measurements of the terminal velocity of free-falling spores and other instances of low Reynolds number motion (Re < 1). More complex, non-linear drag models have been devised for movements characterized by higher Re, but their effectiveness for modeling the launch of fast-moving fungal spores has not been tested. In this paper, we use data on spore discharge processes obtained from ultra-high-speed video recordings to evaluate the effects of air viscosity predicted by Stokes’ law and a commonly used non-linear drag model. We find that discharge distances predicted from launch speeds by Stokes’ model provide a much better match to measured distances than estimates from the more complex drag model. Stokes’ model works better over a wide range projectile sizes, launch speeds, and discharge distances, from microscopic mushroom ballistospores discharged at <1 m s −1 over a distance of <0.1 mm (Re < 1.0), to macroscopic sporangia of Pilobolus that are launched at >10 m s −1 and travel as far as 2.5 m (Re > 100).