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Habitat fragmentation strongly restricts gene flow in endangered ectomycorrhizal fungal populations: evidence from Rhizopogon togasawarius, specific to Pseudotsuga japonica, across the entire distribution range
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  • Hiroshi Abe,
  • Lu Gan,
  • Masao Murata,
  • Kazuhide Nara
Hiroshi Abe
The University of Tokyo

Corresponding Author:h_abe@s.nenv.k.u-tokyo.ac.jp

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Lu Gan
The University of Tokyo Graduate School of Frontier Sciences Environmental Studies
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Masao Murata
Akita Forestry Research and Training Center
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Kazuhide Nara
The University of Tokyo
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Abstract

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 pair separated by a distance of only 8 km (FST = 0.075), indicating extremely limited gene flow between populations. DIYABC-RF analyses implied that population divergence occurred approximately 6000 generations ago between the two regions, and nearly 1500 generations ago between the nearest populations within Shikoku Island, related to past climate events. Because of prolonged genetic isolation, significant inbreeding was confirmed in four of five populations, where effective population sizes became very small (Ne = 9.0–58.0). Although evaluation of extinction risks for microorganisms is challenging, our conservation genetic results indicated that habitat fragmentation increases extinction risk through population genetic mechanisms, and therefore should not be overlooked in biodiversity conservation efforts.
Submitted to Molecular Ecology
Submission Checks Completed
Assigned to Editor
Reviewer(s) Assigned
05 Jul 2024Reviewer(s) Assigned
25 Jul 2024Review(s) Completed, Editorial Evaluation Pending
26 Jul 2024Editorial Decision: Revise Minor
16 Aug 20241st Revision Received
19 Aug 2024Submission Checks Completed
19 Aug 2024Assigned to Editor
19 Aug 2024Review(s) Completed, Editorial Evaluation Pending
27 Aug 2024Editorial Decision: Revise Minor
29 Aug 20242nd Revision Received
29 Aug 2024Submission Checks Completed
29 Aug 2024Assigned to Editor
29 Aug 2024Review(s) Completed, Editorial Evaluation Pending
03 Sep 2024Editorial Decision: Accept