研究者詳細 - 梶村　恒

Fusarium kuroshium is the primary fungal symbiont of an ambrosia beetle, Euwallacea fornicatus, and can kill mango tree in Japan 査読有り国際共著国際誌

Jiang, ZR; Tanoue, M; Masuya, H; Smith, SM; Cognato, AI; Kameyama, N; Kuroda, K; Kajimura, H

SCIENTIFIC REPORTS 13 巻 ( 1 ) 頁： 21634 2023年12月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

This study identifies fungi associated with Euwallacea fornicatus and determines whether these fungal species play the role of primary symbiont. E. fornicatus adults that emerged from the branches of infested trees in Okinawa main island, Japan, were collected and used to isolate fungi. Fusarium kuroshium and Penicillium citrinum were the most dominant fungal associates of females and males, respectively. F. kuroshium was much more frequently isolated from the head, including mycangia (fungus-carrying organs), of females than any other body parts. We inoculated healthy mango saplings with F. kuroshium or F. decemcellulare, both of which were symbionts of E. fornicatus females infesting mango trees. F. kuroshium decreased leaf stomatal conductance and rate of xylem sap-conduction area and increased length and area of xylem discoloration of the saplings, thereby weakening and killing some. These results suggest that F. kuroshium, a mycangial fungus of E. fornicatus, inhibits water flow in mango trees. This study is the first to report that F. kuroshium causes wilt disease in mango trees and that it is a primary fungal symbiont of E. fornicatus.

DOI： 10.1038/s41598-023-48809-8

How much do field mice prefer dwarf bamboo seeds? Two-choice experiments between seeds of Sasa borealis and several tree species on the forest floor 査読有り国際誌

Suzuki, H; Kajimura, H

ECOLOGY AND EVOLUTION 13 巻 ( 10 ) 頁： e10636 2023年10月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ecology and Evolution

Bambusoideae is a taxon of mass-flowering monocarpic perennials with a long life cycle. Forest ecosystems are affected by Bambusoideae seeding and death events in various ways, including an increased abundance of Apodemus spp. The utilization and preference of dwarf bamboo seeds over tree seeds by field mice remain elusive. Therefore, we aimed to determine whether field mice prefer dwarf bamboo to tree seeds. We examined one dwarf bamboo species (Sasa borealis) against four tree species with varying acorn/fruit traits (Castanea crenata, Quercus crispula, Fagus crenata, and Lindera triloba). The seeds were placed in a container in a forest among dead S. borealis culms, with an automatic camera monitoring the setup. The examined seeds were mainly foraged by two field mouse species, Apodemus speciosus and Apodemus argenteus, with preference in the following order: C. crenata, L. triloba, S. borealis, F. crenata, and Q. crispula. Our findings indicated that during S. borealis mast seeding years, predation pressure on F. crenata and Q. crispula seeds could be considerably reduced. This suggests that mast seeding might disrupt the normal pattern of survival, and seed dispersal patterns, potentially altering the forest vegetation composition.

DOI： 10.1002/ece3.10636

Utilization of Sasa borealis seeds by Japanese field mouse: discovery of small-seed caching 査読有り国際誌

Suzuki, H; Kajimura, H

FRONTIERS IN ECOLOGY AND EVOLUTION 11 巻 2023年8月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Frontiers in Ecology and Evolution

Bambusoideae are well-known for their large-scale flowering, seeding, and death events that occur after a vegetative phase that can often last for decades. These events are a valuable resource for many animals. Their mast seeding, in particular, affects rodent populations although the causal relationship between them is speculative. Moreover, the species of animals that utilize this resource also remains unclear. Therefore, this study aimed to examine the interaction between mast seeding plants and animals by conducting a feeding test using the seeds of a dwarf bamboo species (Sasa borealis) at different seasons and in different forest types. The results revealed that two mouse species, Apodemus speciosus and A. argenteus, utilized the seeds. They both predated as well as removed and sometimes buried the seeds, exhibiting small-seed caching behavior. Furthermore, A. speciosus was found to exhibit higher seed predation at covered sites and switching to removal behavior at the more exposed, open sites, while A. argenteus showed no distinguishable trends. Additionally, A. speciosus utilized the seeds less frequently in fall than in summer, suggesting a shift in diet towards acorns when available. Collectively, the results of this study provide novel insights into the interaction between mast seeding plants and the animals that utilize them.

DOI： 10.3389/fevo.2023.1124393

The worldwide invasion history of a pest ambrosia beetle inferred using population genomics 査読有り国際共著国際誌

Urvois, T; Perrier, C; Roques, A; Sauné, L; Courtin, C; Kajimura, H; Hulcr, J; Cognato, AI; Auger-Rozenberg, MA; Kerdelhué, C

MOLECULAR ECOLOGY 32 巻 ( 15 ) 頁： 4381 - 4400 2023年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Molecular Ecology

Xylosandrus crassiusculus, a fungus-farming wood borer native to Southeastern Asia, is the most rapidly spreading invasive ambrosia species worldwide. Previous studies focusing on its genetic structure suggested the existence of cryptic genetic variation in this species. Yet, these studies used different genetic markers, focused on different geographical areas and did not include Europe. Our first goal was to determine the worldwide genetic structure of this species based on both mitochondrial and genomic markers. Our second goal was to study X. crassiusculus' invasion history on a global level and identify the origins of the invasion in Europe. We used a COI and RAD sequencing design to characterize 188 and 206 specimens worldwide, building the most comprehensive genetic data set for any ambrosia beetle to date. The results were largely consistent between markers. Two differentiated genetic clusters were invasive, albeit in different regions of the world. The markers were inconsistent only for a few specimens found exclusively in Japan. Mainland USA could have acted as a source for further expansion to Canada and Argentina through stepping stone expansion and bridgehead events. We showed that Europe was only colonized by Cluster II through a complex invasion history including several arrivals from multiple origins in the native area, and possibly including bridgehead from the United States. Our results also suggested that Spain was colonized directly from Italy through intracontinental dispersion. It is unclear whether the mutually exclusive allopatric distribution of the two clusters is due to neutral effects or due to different ecological requirements.

DOI： 10.1111/mec.16993