Over the hills, but how far away? Estimates of mushroom geographic range extents

Aim Geographic distributions of mushroom species remain poorly understood despite their importance for advancing our understanding of the habitat requirements, species interactions and ecosystem functions of this key group of organisms. Here, we estimate geographic range extents (maximum within-species geographic distance) of genetically defined operational taxonomic units (OTUs). Location World-wide, with emphasis on the American Pacific Northwest. Taxa Amanita, Agaricus, Cortinarius, Galerina, Hebeloma, Hydnum, Hygrocybe, Hygrophorus, Inocybe, Lepiota, Pholiota, and Russula + Lactarius; other genera in Agaricomycotina. Method We used publicly available OTUs from ribosomal internal transcribed spacer (ITS) sequences (n = 15,373) from 12 mushroom genera with worldwide distributions. For each of 2,324 species-level OTUs, we estimated the maximum within-species range extent based on sample locality records. In parallel, we estimated range extents for species in four tree genera. Contrasting estimates from well-studied trees allowed us to test for potential biases in our range estimates of less well inventoried mushrooms. Results The median range extents across the 2,324 mushroom OTUs varied from 1,200 to 4,039 km, depending on assumptions. These extents were significantly lower than estimates from permuted or randomized data. Mushroom ranges were comparable to the median natural range extent of tree species (1,613 km). In contrast, the tree median species range increased to 16,581 km when anthropogenic range extensions were included. At least 10 mushroom species were similarly broadly distributed, eight of which have been associated with human activity. Main conclusions Overall, like tree species, mycorrhizal and saprotrophic fungi show evidence of biogeographic structure rather than global distributions. This reconstruction of geographic range extents drew upon investments into ITS barcoding of extensive herbarium collections. Large scale analyses such as ours can yield estimates of fungal geographic range extents that are a prerequisite to a deeper understanding of the diverse roles of fungi in ecosystems.