Fungal spore diversity reflects substrate-specific deposition challenges

Abstract

Sexual spores are important for the dispersal and population dynamics of fungi. They show remarkable morphological diversity, but the underlying forces driving spore evolution are poorly known. We investigated whether trophic status and substrate associations are associated with morphology in 787 macrofungal genera. We show that both spore size and ornamentation are associated with trophic specialization, so that large and ornamented spores are more probable in ectomycorrhizal than in saprotrophic genera. This suggests that spore ornamentation facilitates attachment to arthropod vectors, which ectomycorrhizal species may need to reach lower soil layers. Elongated spore shapes are more common in saprotrophic taxa, and genera associated with above ground substrates are more likely to have allantoid (curved elongated) spores, probably to lower the risk of wash out by precipitation. Overall, our results suggest that safe arrival on specific substrates is a more important driver of evolution in spore morphology than dispersal per se.

Figure 1

Spore trait differences (estimated mean ± s.e.) across trophic status.

Figure 2

A schematic illustration representing different trophic guilds, substrate associations and spore shapes. Values represent the expected probability of the occurrence of a given feature from logistic linear models controlling for phylogeny. Superscripts refer to significance level for pairwise differences (in the log odds ratios) to the reference level (see Tables 1 and 2).

Figure 3

Spore trait differences (estimated mean ± s.e.) across saprotrophic substrates.