A natural O-ring optimizes the dispersal of fungal spores

Abstract

The forcibly ejected spores of ascomycete fungi must penetrate several millimetres of nearly still air surrounding sporocarps to reach dispersive airflows, and escape is facilitated when a spore is launched with large velocity. To launch, the spores of thousands of species are ejected through an apical ring, a small elastic pore. The startling diversity of apical ring and spore shapes and dimensions make them favoured characters for both species descriptions and the subsequent inference of relationships among species. However, the physical constraints shaping this diversity and the adaptive benefits of specific morphologies are not understood. Here, we develop an elastohydrodynamic theory of the spore's ejection through the apical ring and demonstrate that to avoid enormous energy losses during spore ejection, the four principal morphological dimensions of spore and apical ring must cluster within a nonlinear one-dimensional subspace. We test this prediction using morphological data for 45 fungal species from two different classes and 18 families. Our sampling encompasses multiple loss and gain events and potentially independent origins of this spore ejection mechanism. Although the individual dimensions of the spore and apical ring are only weakly correlated with each other, they collapse into the predicted subspace with high accuracy. The launch velocity appears to be within 2 per cent of the optimum for over 90 per cent of all forcibly ejected species. Although the morphological diversity of apical rings and spores appears startlingly diverse, a simple principle can be used to organize it.

Mushrooms use convectively created airflows to disperse their spores

“…Our analysis of convective dispersal adds to an increasing body of work revealing that fungal sporocarps are exquisitely engineered to maximize spore dispersal potential (5,6,24). Although evaporative cooling is an essential ingredient for spore dispersal and has been observed in many species (20), our analysis reveals the previously unreported role played by the asymmetric thickness of the pileus or of the gap beneath it in shaping and amplifying the dispersive airflow created by the mushroom.…”

Timing of fungal spore release dictates survival during atmospheric transport

“…Atmospheric transport is assumed to be unpredictable, and fungi are assumed to have little control over dispersal, but spore discharge itself appears finely tuned to maximize individual fitness (43)(44)(45)(46)(47)(48). Our results demonstrate that although after leaving a sporocarp individual spores follow unpredictable trajectories, a fungus may still maximize survival of its progeny in the atmosphere by strategizing the timing of spore release.…”

“…48). The ascomycetes, an enormously large and diverse phylum, fire sexual spores from a pressurized cell finely tuned to minimize dissipation (43)(44)(45)(46)(47). The basidiomycetes, a similarly diverse phylum, eject spores using a surface tension catapult and achieve precise control of spore range immediately after discharge (71)(72)(73)(74)(75)(76)(77).…”

An agent-based model of the Foraging Ascomycete Hypothesis

“…There are numerous possible adaptations for directly increasing spore dispersal, such as by increasing spore quantities, optimizing spore or spore-bearing structure morphology, synchronizing spore releases, etc. (Fritz Joerg A. et al, 2013;Galante et al, 2011;Pringle et al, 2015;Roper et al, 2010). Most of these rely directly on spores as the main vector for dispersal, and they also come with energetic costs.…”