Host preference explains the high endemism of ectomycorrhizal fungi in a dipterocarp rainforest.

Ectomycorrhizal (ECM) fungi are important tree symbionts within forests. The biogeography of ECM fungi remains to be investigated because it is challenging to observe and identify species. Because most ECM plant taxa have a Holarctic distribution, it is difficult to evaluate the extent to which host preference restricts the global distribution of ECM fungi. To address this issue, we aimed to assess whether host preference enhances the endemism of ECM fungi that inhabit dipterocarp rainforests. Highly similar sequences of 175 operational taxonomic units (OTUs) for ECM fungi that were obtained from Lambir Hill's National Park, Sarawak, Malaysia, were searched for in a nucleotide sequence database. Using a two-step binomial model, the probability of presence for the query OTUs and the registration rate of barcode sequences in each country were simultaneously estimated. The results revealed that the probability of presence in the respective countries increased with increasing species richness of Dipterocarpaceae and decreasing geographical distance from the study site (i.e. Lambir). Furthermore, most of the ECM fungi were shown to be endemic to Malaysia and neighbouring countries. These findings suggest that not only dispersal limitation but also host preference are responsible for the high endemism of ECM fungi in dipterocarp rainforests. Moreover, host preference likely determines the areas where ECM fungi potentially expand and dispersal limitation creates distance-decay patterns within suitable habitats. Although host preference has received less attention than dispersal limitation, our findings support that host preference has a profound influence on the global distribution of ECM fungi.