Fungal sporocarps house diverse and host-specific communities of fungicolous fungi

Abstract

Sporocarps (fruit bodies) are the sexual reproductive stage in the life cycle of many fungi. They are highly nutritious and consequently vulnerable to grazing by birds and small mammals, and invertebrates, and can be infected by microbial and fungal parasites and pathogens. The complexity of communities thriving inside sporocarps is largely unknown. In this study, we revealed the diversity, taxonomic composition and host preference of fungicolous fungi (i.e., fungi that feed on other fungi) in sporocarps. We carried out DNA metabarcoding of the ITS2 region from 176 sporocarps of 11 wood-decay fungal host species, all collected within a forest in northeast Finland. We assessed the influence of sporocarp traits, such as lifespan, morphology and size, on the fungicolous fungal community. The level of colonisation by fungicolous fungi, measured as the proportion of non-host ITS2 reads, varied between 2.8-39.8% across the 11 host species and was largely dominated by Ascomycota. Host species was the major determinant of the community composition and diversity of fungicolous fungi, suggesting that host adaptation is important for many fungicolous fungi. Furthermore, the alpha diversity was consistently higher in short-lived and resupinate sporocarps compared to long-lived and pileate ones, perhaps due to a more hostile environment for fungal growth in the latter too. The fungicolous fungi represented numerous lineages in the fungal tree of life, among which a significant portion was poorly represented with reference sequences in databases.

Fig. 1. Proportion and taxonomic composition of the fungicolous fungi.

A Bar plot representing the proportion of ITS2 sequences corresponding to non-host fungicolous fungi relative to all fungal sequences including the hosts. For each species, an average was calculated from 16 individual sporocarps and error bars represent 95% confidence intervals, indicating systematic differences across species. B Average proportion of 15 main orders (alphabetical listing) of fungicolous fungi, where blue colours represent Basidiomycota, red Ascomycota and green Mucoromycota.

Fig. 2. Alpha diversity of fungicolous fungal communities.

Box plots illustrating variation in OTU richness (A, B) and Shannon diversity (C, D) of fungicolous fungi across 11 wood-decay fungal species. For each fungal host species, 16 sporocarps were analysed (excluding two fompin samples). The black dots represent data falling outside the interquartile range while the median is indicated by the dark line. The smaller frames (down left corner) compare long- and short-lived sporocarps (A, C) and pileate and resupinate sporocarps (B, D), respectively. Statistical differences between the different categories were evaluated using a Wilcoxon test with p value < 0.05.

Fig. 3. Non-metric multidimensional scaling (NMDS) plot based on Bray–Curtis dissimilarity matrix of fungicolous fungal community composition in 11 polypore species (in different colours) sampled within a forest.

The ellipses reflect the standard error of the sample means and the bars represent the standard deviation. The explanatory variables with significant contribution to the constrained ordination are listed in Table 1. An NMDS plot displaying individual samples is included as Fig. S5.

Fig. 4. Network displaying 454 significant co-occurrences between 11 wood-decay fungal hosts and fungicolous fungi.

Fungal hosts are represented by filled-square symbols while circles represent fungicolous fungal OTUs coloured according to phyla. The 236 OTUs of fungicolous fungi that are specific to a single host are located on the outer edge while 218 OTUs shared between two hosts or more are indicated on the inner edge. All edges represent a significant link (999 permutations test, p value < 0.05) between a host species and a fungicolous fungal OTU.