Why do some fungi grow fast and others slowly? The fungal growth-rate hypothesis

In general, there is a dichotomy in growth mode between ‘moulds’ (filamentous ascomycetes and mucoromycetes), and ‘mushrooms’ (filamentous basidiomycetes): mould mycelia tend to grow fast, to be short-lived and to produce asexual spores, while mushroom mycelia tend to grow slowly, are among the longest-lived organisms known and generally do not produce asexual spores. I propose that this dichotomy is due to a fundamental difference in growth strategy. On one hand, mould mycelia typically grow like a ‘pyramid-scheme’: an exponentially increasing number of hyphae provides the mycelium with a constant supply of a growth-limiting nutrient such as nitrogen. However, ‘the pyramid scheme crashes’ when space and resources become limiting, necessitating dispersal via sporulation. On the other hand, mushroom mycelia typically grow sustainably with linear expansion of hyphae. However, linear growth provides insufficient influx of the growth-limiting nutrient to supply the entire colony at a constant rate, explaining that generally only the colony edge is active in mushrooms. I discuss evidence for this model and implications for mutation rate and rate of evolution.