Abstract
A broad class of soil fungi form the annular patterns known as ‘fairy rings’ and provide one of the only means to observe spatio-temporal dynamics of otherwise cryptic fungal growth processes in natural environments. We present observations of novel spiral and rotor patterns produced by fairy ring fungi and explain these behaviors mathematically by first showing that a well known model of fairy ring fungal growth and the Gray-Scott reaction-diffusion model are mathematically equivalent. We then use bifurcation analysis and numerical simulations to identify the conditions under which spiral waves and rotors can arise. We demonstrate that the region of dimensionless parameter space supporting these more complex dynamics is adjacent to that which produces the more familiar fairy rings, and identify experimental manipulations to test the transitions between these spatial modes. These same manipulations could also feasibly induce fungal colonies to transition from rotor/spiral formation to a set of richer, as yet unobserved, spatial patterns.
Highlights
Over 50 species of soil growing fungi, largely within phylum Basidiomycota, form colonies with an annular structure, known as a ‘fairy ring’, that propagates out from an initial point of innoculation [1,2,3,4,5]
The isomorphism between the fairy ring dynamical model and the Gray Scott equations suggests the potential for fungal biomass-resource dynamics to generate richer behavior than annular fairy rings
Our results suggest that fairy rings can adopt more complex spatial forms than simple annuli, and that they appear to do so in a manner that is consistent with the predictions of the simple
Summary
Over 50 species of soil growing fungi, largely within phylum Basidiomycota, form colonies with an annular structure, known as a ‘fairy ring’, that propagates out from an initial point of innoculation [1,2,3,4,5]. The below-ground colony structure is revealed at the soil surface either directly by the presence of fruiting bodies, or indirectly through the effects of the fungal mycelia on surrounding vegetation—typically grasses. A range of negative effects (such as cyanide production, nutrient depletion, water repellency and pathogenic action of the fungi) lead to grass death within the fairy ring [6,7,8,9], while positive or hormonal effects (such as nutrient release, or the hormone-mimicking effects of fungal metabolites) promote leaf growth and local formation of a ring of luxuriant foliage in proximity to actively growing mycelia [10,11,12]. Fairy rings afford a valuable opportunity to observe the macroscopic spatio-temporal dynamics of soil fungi, because the association between vegetation condition and the presence of fungal mycelia is strong and simple (when compared, for instance, to the more complex task of inferring fungal pathogen dynamics from observations of plant disease [13]). PLOS ONE | DOI:10.1371/journal.pone.0149254 March 2, 2016
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