Allopatric instead of parapatric divergence in an ectomycorrhizal fungus (Laccaria trichodermophora) in tropical sky-islands

In tropical sky-islands, cold-affinity populations tend to become isolated at highlands during the interglacial periods, and to expand into the lowlands where they become more connected during the glacial periods. Although this has been widely studied in trees, it is poorly understood how fungal symbionts can differentiate among mountains (allopatrically), or within a single mountain (parapatrically) due to climate fluctuations. Here, we conducted population genomic analyses on the ectomycorrhizal fungus Laccaria trichodermophora in three tropical sky-islands using Genotyping by Sequencing (GBS) at low DNA concentrations. There were no significant differences between altitudes within a single mountain, but we observed significant genetic differentiation among populations from different mountains, supporting the allopatric differentiation hypothesis. Our results indicate that L. trichodermophora populations are under a sky-island population dynamics that started during the Pleistocene climate fluctuations. (C) 2020 Elsevier Ltd and British Mycological Society. All rights reserved.