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.