Interactions among fungi and insects involve hundreds of thousands of species. While insect communities on plants have formed some of the classic model systems in ecology, fungus-based communities and the forces structuring them remain poorly studied by comparison. We characterize the arthropod communities associated with fruiting bodies of eight mycorrhizal basidiomycete fungus species from three different orders along a 1200-km latitudinal gradient in northern Europe. We hypothesized that—matching the pattern seen for most insect taxa on plants—we would observe a general decrease of fungal-associated species with latitude. Against this backdrop, we expected local communities to be structured by host identity and phylogeny, with more closely related fungal species sharing more similar communities of associated organisms. As a more unique dimension added by the ephemeral nature of fungal fruiting bodies, we expected further imprints generated by successional change, with younger fruiting bodies harboring communities different from older ones. Using DNA metabarcoding to identify arthropod communities from fungal fruiting bodies, we find that latitude leaves a clear imprint on fungus-associated arthropod community composition, with host phylogeny and decay stage of fruiting bodies leaving lesser but still-detectable effects. The main latitudinal imprint is on a high arthropod species turnover, with no detectable pattern in overall species richness. Overall, these findings paint a new picture of the drivers of fungus-associated arthropod communities, suggesting that latitude will not affect how many arthropod species inhabits a fruiting body, but rather what species occur in it and at what relative abundances (as measured by sequence read counts). These patterns upset simplistic predictions regarding latitudinal gradients in species richness and in the strength of biotic interactions.

Fungal samples were collected from Finland and Estonia by volunteers. Samples were frozen in -21C and homogenized at Helsinki University. DNA was extracted from complete fruiting bodies using salt-isopropanol extraction, and purified using a double step SPRI purification. COI primers (Leray) with heterogeneity spacers were used in PCR, samples were indexed, and equivalent libariers were pooled. Indexed using MiSeq. Data was trimmed, and resulting FASTAs were assigned to ZOTUs and compared against a BOLD reference list. Finally, ZOTUs were hand-filtered to provide a list of arthropod taxa present in individual fruiting bodies.

The purification of the samples is done to get rid of contaminants that disrupt PCR process.