Habitat fragmentation strongly restricts gene flow in endangered ectomycorrhizal fungal populations: Evidence from Rhizopogon togasawarius, specific to Pseudotsuga japonica, across the entire distribution range

Habitat fragmentation reduces gene flow, causing genetic differentiation and diversity loss in endangered species through genetic drift and inbreeding. However, the impact of habitat fragmentation on ectomycorrhizal (ECM) fungi remains unexplored, despite their critical roles in forest ecosystems. Here, we investigated the population genetic structure and the demographic history of Rhizopogon togasawarius, the ECM fungus specifically colonizing the host tree Pseudotsuga japonica, across its entire distribution range (>200 km). These two species are designated as endangered species on the IUCN Red List since they are found only in small, fragmented forests in Japan. We analyzed 236 R. togasawarius individuals from five remaining populations across the Kii Peninsula and the Shikoku Island, separated by a sea channel. Simple sequence repeat (SSR) analyses using 20 loci revealed strong genetic differentiation among populations (FST = 0.255), even significant in the nearest population pai..., , , # Habitat fragmentation strongly restricts gene flow in endangered ectomycorrhizal fungal populations: evidence from Rhizopogon togasawarius, specific to Pseudotsuga japonica, across the entire distribution range

[https://doi.org/10.5061/dryad.p2ngf1vzq](https://doi.org/10.5061/dryad.p2ngf1vzq)

-Table.genotype_microsatellite_236_Rhizopogon_togasawarius.xlsx

Diploid genotypes of 236 *Rhizopogon togasawarius* individuals (rows) for 20 microsatellite markers (columns). First column: sample ID. Second column: Population ID. Third column onward: microsatellite alleles.

-Table.genotype_microsatellite_94_Pseudotsuga_japonica.xlsx

Diploid genotypes of 94 *Pseudotsuga japonica* individuals (rows) for six microsatellite markers (columns). First column: sample ID. Second column: Population ID. Third column onward: microsatellite alleles.