Publications
Influences of topography on nitrate export from forested watersheds on Yakushima Island, a Natural World Heritage site
A study on Yakushima Island, a UNESCO Natural World Heritage site, reveals that topography significantly influences nitrate export from forested watersheds. The research demonstrates how atmospheric nitrate deposition and river water chemistry vary across different elevations, providing critical insights into nutrient cycling in pristine forest ecosystems. Long-term monitoring data were analyzed to assess the relationship between topographical features—such as slope and elevation—and nitrate concentrations in river waters. This work highlights the importance of considering geographical factors when studying nutrient dynamics in natural environments, offering implications for conservation efforts in similar protected areas.
Paleo Tsunamis and Storm Surges Recorded by Fossil Coral on Yakushima Island, Japan
A new study reveals that Yakushima Island, Japan, has experienced frequent large wave events throughout the Holocene, with potential tsunamis and storm surges occurring at intervals of approximately 1500 to 2000 years. Researchers dated fossilized coral within beach boulders deposited above sea level, identifying four distinct deposition events between 6187–2692 calibrated years before present (cal yr BP). These findings suggest that the island's proximity to active volcanic and subduction zones poses a significant risk of future geohazards. Additional modeling could further clarify whether these deposits resulted from storm surges or tsunamis, providing critical data for hazard prediction in southeast Japan.
Submarine sediment distribution and its controlling factors around the western areaoff Tokara Islands and southern area off Yakushima Island
A comprehensive analysis of submarine sediment distribution around the western Tokara Islands and southern Yakushima Island reveals strong influences from the Kuroshio Current on both geological and biological processes. The study, conducted through 95 surface sediment sampling points and one core sample, found that sediment types—ranging from coarse sand to mud—are shaped by abundant fine-grained material supplied from surrounding landmasses and localized bottom currents. In Yakushima's southern region, extensive rock exposures along ridge lines and the presence of biogenic debris in sandy sediments suggest intensified erosion and sediment movement linked to Kuroshio Current dynamics. Analysis of foraminifera, coral distributions, and environmental DNA further indicates that biological productivity is closely tied to these oceanographic factors.
Distribution and characterization of nematodes in above-ground microhabitats in a natural pristine cedar forest in Yakushima Island, Japan
Nematode communities in old-growth cedar forests, such as those found on Yakushima Island, exhibit distinct compositions and trophic structures depending on microhabitats like fallen trees with mosses and living barks. A study revealed that bacterivorous nematodes dominate decaying barks (45%), while fungivorous nematodes thrive in living barks (61%). Predatory-omnivorous nematodes were most abundant in mossy environments (51%), particularly those with nitrogen-rich conditions, contrasting with the high carbon-to-nitrogen ratios in cedar trunks. This suggests that old-growth forests provide diverse microhabitats supporting specialized nematode taxa, highlighting their ecological significance in nutrient cycling and biodiversity.
Dynamics of rumen microbiome in sika deer (Cervus nippon yakushimae) from unique subtropical ecosystem in Yakushima Island, Japan
Wild Yaku sika deer (Cervus nippon yakushimae) on Yakushima Island exhibit unique rumen bacterial microbiota (RBM) that enable dietary flexibility under high population density. This study revealed that the RBM of wild Yaku sika has higher species richness and diversity compared to other sika deer populations, likely due to their access to diverse, tannin-rich plants in the island's subtropical ecosystem. High-density populations showed increased Firmicutes abundance and higher tannase gene prevalence, suggesting an adaptive response to unpalatable feed sources. The research combined high-throughput sequencing with targeted cultivation and functional analyses to characterize the RBM, providing insights into how microbial adaptations support nutritional resilience in wild ruminants.
Effects of Sika Deer and the Unique Relationship with Forest Vegetation in Yakushima Island
Sika deer significantly impact evergreen broad-leaved forests on Yakushima Island, Japan, with their effects varying depending on population density. Unlike findings in cooler climates, where deer typically cause severe vegetation degradation, Yakushima's unique ecosystem—characterized by high forest productivity and endemic sika deer morphology—mitigates some of these impacts. The study highlights that while deer influence forest regeneration, the relationship is more nuanced than previously understood, suggesting that deer density alone does not fully predict ecological outcomes. By analyzing spatial and temporal variations in deer populations across undisturbed forests, researchers provide new insights into how sika deer shape forest dynamics, offering a framework for studying similar systems globally.
Extremely low level of genetic diversity in Gentiana yakushimensis , an endangered species in Yakushima Island, Japan
A rare and endangered plant species, Gentiana yakushimensis, found exclusively on Yakushima Island, Japan, exhibits extremely low genetic diversity and high inbreeding levels compared to its congener. Population genetic analysis using genome-wide single nucleotide polymorphisms (SNPs) revealed that the species likely experienced a population expansion during the Last Glacial Maximum followed by a recent bottleneck event. This demographic history suggests that the current low genetic diversity may not fully reflect recent reductions in population size, necessitating long-term monitoring to understand the time lag between population decline and genetic diversity changes. The study highlights the importance of assessing conservation priorities for endangered species using population genetics.
Geographical and seasonal variation of plant taxa detected in faces of Cervus nippon yakushimae based on plant DNA analysis in Yakushima Island
Yakushima's Yaku-sika deer (Cervus nippon yakushimae) primarily feed on evergreen tall trees, but their consumption of understory herbaceous plants, including ferns, contributes to the degradation of understory vegetation. Plant DNA analysis of deer feces revealed that managed areas with reduced deer density exhibited higher diversity in food plant species compared to unmanaged areas, suggesting that active management can restore understory plant diversity. The study used next-generation sequencing of chloroplast DNA fragments (rbcL region) from feces collected across five areas and four seasons in 2018, providing insights into the dietary habits and ecological impact of this invasive deer population on Yakushima Island's biodiversity.
Molecular phylogeny and taxonomy of the Hydrangea serrata complex (Hydrangeaceae) in western Japan, including a new subspecies of H. acuminata from Yakushima
Scientists have identified a new subspecies of Hydrangea acuminata, Hydrangea acuminata subsp. yakushimensis, endemic to Yakushima Island, Japan. This discovery challenges the current classification of the Hydrangea serrata complex, which was thought to include only six varieties. Through morphological analysis and molecular phylogeny using chloroplast and nuclear genomic regions along with Multiplex ISSR genotyping by sequencing (MIG-seq), researchers also reclassified two previously recognized varieties as distinct taxa: Hydrangea minamitani and Hydrangea acuminata subsp. australis. Yakushima, a biodiversity hotspot with approximately 50 endemic species, emerges as a critical site for further taxonomic exploration.
Seasonal responses and host uniqueness of gut microbiome of Japanese macaques in lowland Yakushima
A study on the gut microbiome of Japanese macaques (Macaca fuscata) in Yakushima revealed that both diet and host individuality significantly shape microbial composition. Over 13 months, dietary shifts—particularly between leaf-dominated, fruit, and invertebrate-based diets—correlated with changes in gut microbiome diversity and function. Leaf-feeding periods enriched the microbiome with Spirochaetes and Tenericutes, while fruit and invertebrate consumption showed opposite trends. The research highlights the dual influence of environmental factors (diet) and host uniqueness on microbial communities, suggesting that macaques rely heavily on microbial fermentation to process otherwise indigestible plant material.
A new subspecies of Stellaria alsine (Caryophyllaceae) from Yakushima, Japan
Researchers have identified a new subspecies of Stellaria alsine (Caryophyllaceae) from Yakushima, Japan. This discovery was made using MIG-seq to construct a detailed phylogenetic tree, which revealed the taxon's close relationship with S. alsine. The newly described subspecies, named Stellaria alsine subsp. nanasubsp. nov., adds to the island's rich biodiversity, further highlighting Yakushima's significance as a hotspot for endemic species. This finding contributes to our understanding of plant diversity and evolution in this unique UNESCO World Heritage Site.
Fecal metabolite analysis of Japanese macaques in Yakushima by LC-MS/MS and LC-QTOF-MS
A comprehensive fecal metabolite analysis of Japanese macaques on Yakushima Island revealed distinct differences between two monkey groups, primarily driven by variations in nucleic acid metabolites and free amino acids. Using LC-MS/MS, researchers quantified 59 substances, including key components of the citrate cycle, while LC-QTOF-MS detected over 12,000 compounds, highlighting discrepancies in plant secondary metabolites such as cyanogenic glycosides, flavonoids, and phenolics. This study underscores the potential of fecal metabolite profiling to elucidate dietary and ecological differences among primate populations.
Influence of environmental parameters on habitat use by sympatric freshwater eels Anguilla marmorata and Anguilla japonica on Yakushima Island, Japan
Sympatric freshwater eels, Anguilla marmorata and A. japonica, exhibit distinct habitat preferences on Yakushima Island, Japan, with the tropical species favoring clear, fast-flowing mainstems and tributaries characterized by larger substrates, fewer fallen leaves, higher current velocity, and lower turbidity, while the temperate species dominates stagnant, muddy environments like estuaries, backwaters, irrigation channels, and reservoirs. This segregation persists across life stages and body sizes, indicating strong environmental preferences that must be considered for conservation in sympatric zones. The study analyzed habitat use patterns using field observations to elucidate these ecological distinctions.
Spatial Genetic Structure of the Sika Deer (Cervus nippon) Population on Yakushima: Significant Genetic Differentiation on a Small Island
A study on Yakushima Island reveals that the sika deer population, despite its small geographic range, maintains high genetic diversity due to significant genetic differentiation among subpopulations. Using 12 microsatellite loci, researchers identified two primary subpopulations (stN and stS) with STRUCTURE analysis, further refined into four distinct groups by GENELAND (glN, glE, glS, glW). All pairwise comparisons showed statistically significant genetic differentiation, indicating limited gene flow between these groups. While a large river marks the western boundary of one subpopulation, no clear landscape feature explains the eastern divide. The findings suggest that management strategies for this UNESCO World Heritage Site should account for these spatial population structures across multiple time scales to preserve genetic diversity effectively.
Spatiogenetic characterization of S receptor kinase (SRK) alleles in naturalized populations of Raphanus sativus L. var. raphanistroides on Yakushima island
Research on Yakushima Island reveals high diversity of S receptor kinase (SRK) alleles in naturalized radish populations, with four novel alleles potentially unique to the island. The study mapped allele distribution and found evidence of pollen exchange among nearby plants, suggesting gene flow within these populations. While most alleles matched those in cultivated radishes, sequence diversity hindered PCR amplification, mirroring challenges seen in cultivars. This work highlights the dynamic genetic structure of naturalized plant populations and introduces a methodology applicable to other self-incompatible species.
The genus Rhyacophila Stephens (Trichoptera, Rhyacophilidae) in Yakushima Island, northern Ryukyu, southwestern Japan
A taxonomic revision of the caddisfly genus Rhyacophila on Yakushima Island, Japan, reveals four previously undescribed species and two newly recorded species. The new species—R. yakushima, R. arakawa, R. miyanoura, and R. nagata—belong to distinct species groups within the genus, expanding the known biodiversity of the region. Additionally, R. brevicephala and R. shikotsuensis are documented for the first time on Yakushima, contributing to the island's ecological inventory. The study employs morphological analysis of adult specimens to delineate these taxa, providing critical insights into the diversity and distribution of Rhyacophilidae in the northern Ryukyu Archipelago.
Tourism and Counterurbanization in a Low-Amenity Peripheral Island: A Longitudinal Study at Yakushima Island in Kagoshima, Japan
A decade-long study on Yakushima Island, Japan, reveals that the island's population dynamics are intricately linked to tourism development and counterurbanization. The research found that population growth varied significantly among the 24 villages due to factors such as accessibility, proximity to tourism attractions, weather conditions, and housing availability. Nature emerged as a pivotal factor in attracting both Japanese and international in-migrants, with many relocating with aspirations of becoming tour guides or entrepreneurs. While tourism stagnated post-2008, an increase in international tourists created niche markets before the COVID-19 pandemic, drawing foreign in-migrants to the island. The study employed longitudinal data collection over 10 years to investigate population trends, migration motivations, and contributions to tourism, providing insights into the complex interplay between human migration and tourism development in low-amenity peripheral islands.
Effects of volcanic parent materials on the acid buffering capacity of forest soils on Yakushima Island, Japan
A study on Yakushima Island reveals that both granite-derived and volcanic soils exhibit reduced acid-neutralizing capacity (ANC) over time, challenging the assumption that volcanic soils are more resistant to acidification. Despite containing weatherable minerals, volcanic soils showed no significant difference in ANC compared to granite-derived soils after 7300 years of development following a volcanic eruption. The research used titanium mass balance to estimate ANC changes, finding that Al loss primarily drives acidification in granite soils, while base cation leaching and organic acid sorption neutralize acidity in volcanic soils. However, erosion and the mixing of materials from other sources can reduce ANC in surface layers, highlighting complex soil acidification dynamics on Yakushima.
First Record on “Rump-rump Contact” Behavior between Males in wild Japanese Macaques (Macaca fuscata) on Yakushima Island
A novel social behavior, 'rump-rump contact,' has been observed for the first time in wild Japanese macaques (Macaca fuscata) on Yakushima Island. This behavior involves two types: symmetric rump contact (RR type) and rump-to-torso contact (RT type), often accompanied by tail wagging and body clasping, suggesting a role in regulating social tension. Unlike similar behaviors in bonobos, no genital thrusting was observed. The behavior may have evolved from 'presenting' and represents a unique form of tactile communication in nonhuman primates. This discovery highlights potential affinitive relationships beyond strict dominance hierarchies among male macaques, with broader implications for understanding primate social dynamics.
Island-wide Distribution of Japanese Macaques in Yakushima Revealed by Census Targeting Feces on Roads in 2017-2018
A comprehensive island-wide census of Japanese macaques (Macaca fuscata yakui) on Yakushima, conducted in 2017-2018, reveals significant population changes and spatial distribution patterns. The study found that macaques have largely disappeared around northern and eastern villages where hunting for pest control is practiced, despite no change in population trends in the south (also hunted) or west (hunting absent). Roadside feces surveys across 3308 segments identified negative impacts of farms, villages, and hunting on macaque presence. Spatial modeling showed that while farms and villages universally reduced macaque detection, hunting effects were localized to northern and eastern areas, and conifer plantations influenced the western region. The research suggests a shift in macaque behavior or population decline due to hunting pressure, with recommendations for alternative pest control measures like electric fences to mitigate crop damage.
Nitrogen mineralization rates of the soils incubated under different temperatures from different elevations along an environmental gradient on Yakushima Island
Research on Yakushima Island reveals that soil nitrogen (N) mineralization rates, which decrease with elevation, are primarily regulated by the quality of organic matter rather than temperature. Using a 'common-site' approach, scientists incubated soils from seven elevations (170–1550 m a.s.l.) at four temperatures (15, 20, 25, and 30°C) for 10 days. They found that net N mineralization rates declined linearly with elevation at consistent intercepts across temperatures, indicating that inherent soil properties—such as organic matter quality and microbial profiles—drive this pattern. Soil phenolics/N ratios increased with elevation, correlating negatively with N mineralization, further supporting the influence of vegetation shifts on soil biochemistry.
Ranging patterns of Japanese macaques in the coniferous forest of Yakushima: Home range shift and travel rate
Japanese macaques on Yakushima exhibit strategic home range shifts and travel rate adjustments to optimize foraging efficiency amid seasonal fluctuations. The study, conducted over 17 months with supplementary data from a five-year census, revealed that the macaques shift their home range seasonally—occupying higher-altitude primary forest in eastern Yakushima during warmer months (May–September) and logged western areas rich in herbs and small trees during cooler periods. This shift, observed consistently across multiple years, allows them to capitalize on food availability while conserving energy during colder temperatures. Additionally, travel rates increased when foraging for fungi or flowers, which are less densely distributed than fruits, suggesting a fine-tuned response to habitat heterogeneity. The findings underscore the macaques' adaptive behavior in navigating seasonally variable environments.
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