Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2016 Mar 16;283(1826):20152470.
doi: 10.1098/rspb.2015.2470.

Defining Individual Size in the Model Filamentous Fungus Neurospora Crassa

Affiliations
Free PMC article

Defining Individual Size in the Model Filamentous Fungus Neurospora Crassa

Linda Ma et al. Proc Biol Sci. .
Free PMC article

Abstract

It is challenging to apply the tenets of individuality to filamentous fungi: a fungal mycelium can contain millions of genetically diverse but totipotent nuclei, each capable of founding new mycelia. Moreover, a single mycelium can potentially stretch over kilometres, and it is unlikely that its distant parts share resources or have the same fitness. Here, we directly measure how a single mycelium of the model ascomycete Neurospora crassa is patterned into reproductive units (RUs), meaning subpopulations of nuclei that propagate together as spores, and function as reproductive individuals. The density of RUs is sensitive to the geometry of growth; we detected 50-fold smaller RUs when mycelia had expanding frontiers than when they were constrained to grow in one direction only. RUs fragmented further when the mycelial network was perturbed. In mycelia with expanding frontiers, RU composition was strongly influenced by the distribution of genotypes early in development. Our results provide a concept of fungal individuality that is directly connected to reproductive potential, and therefore to theories of how fungal individuals adapt and evolve over time. Our data show that the size of reproductive individuals is a dynamic and environment-dependent property, even within apparently totally connected fungal mycelia.

Keywords: chimaerism; fungal biology; individuality; unit of selection.

Figures

Figure 1.
Figure 1.
(a) Schematic of sampling method, and the biological interpretation of sample and spore heterozygosities for a mycelium containing hH1::DsRed nuclei (red pluses) and hH1::gfp nuclei (green dots). The sample heterozygosity H measures the diversity of nuclear genotypes in the sample, and the spore heterozygosity h the diversity of dikaryotic spores. (b) Classification of real spores by PerkinsCS. Spores are identified by template matching in transmitted light images then classified as either hH1::DsRed homokaryons (white circles), hH1::gfp homokaryons (green squares) or heterokaryons (white squares). In the magnified image, the number of nuclei is also shown. (Online version in colour.)
Figure 2.
Figure 2.
(a) In mycelia grown in plates, sample heterozygosity (H) is systematically larger than spore heterozygosity (h), allowing us to measure the number of RUs present. H and h are indistinguishable in mycelia with one-dimensional growth. (b) Densities of RUs in the plates (no. RUs per cm2) do not depend on sampling location. (Inset) RU density estimates as a function of number of spores counted—convergence occurs before 1000 spores (our experimental sample size). (Online version in colour.)
Figure 3.
Figure 3.
(a) RU formation depends on physical mixing within the mycelium: mycelia with a growing frontier had more RUs than mycelia constrained to grow in one dimension. Perturbing network connectivity using sorbose or dessication stress also increased the number of RUs. (b) Starting mycelia with unmixed spores tests for whether RUs are constituted early in mycelial development. In plates, unmixed spores produce unmixed RUs (green solid line, unmixed spores; red dash-dot line with × symbols, mixed spores) but RUs in race tubes remained uniformly diverse (orange solid line with + symbols, unmixed spores; blue dashed line with O symbols, mixed spores). Here we measure RU diversity by plotting fluctuations in p (fraction of hH1::DsRed nuclei) across RUs. Inset shows the same data over a smaller interval of p fluctuations. (Online version in colour.)

Similar articles

See all similar articles

Cited by 1 article

Publication types

LinkOut - more resources

Feedback