Phylogeography of post-Pleistocene population expansion in Dasyscyphella longistipitata (Leotiomycetes, Helotiales), an endemic fungal symbiont of Fagus crenata in Japan

During the Last Glacial Maximum (LGM), drastic environmental changes modified the topology of the Japanese Archipelago, impacting species distributions. An example is Fagus crenata, which has a present continuous distribution throughout Japan. However, by the end of the LGM it was restricted to southern refugia. Similarly, Dasyscyphella longistipitata (Leotiomycetes, Helotiales, Lachnaceae) occurs strictly on cupules of F. crenata, sharing currently an identical distribution. As the effects of the LGM remain poorly understood for saprobiotic microfungal species, herein we identified past structuring forces that shaped the current genetic diversity within D. longistipitata in relation to its host using a phylogeographic approach. We inferred present and past potential distributions through species distribution modeling, identifying environmental suitability areas in mid-southern Japan from which subsequent colonizations occurred. Our findings suggest that current high genetic diversity and lack of genetic structure within D. longistipitata are the result of recent multiple re-colonization events after the LGM.