Area In Central Japan Research Articles

Active use of local exercise facilities can improve physical performance of community-dwelling older adults.

[Purpose] In this study, we investigated the effects of local exercise facility use on physical function of Japanese community-dwelling older adults. [Participants and Methods] We analyzed data obtained from a cohort project initiated in 1991. The study included approximately 4,800 individuals from suburban areas of central Japan; we investigated 322 older individuals residing in Municipality A, who underwent physical fitness assessments in 2018 and 2019. We recorded participants' exercise facility use frequency and physical performance, based on handgrip strength, open-eye single-leg standing, timed up-and-go, and walking speed tests. [Results] Baseline values in the open-eye single-leg standing test were significantly higher in the no-use than in the low- and high-use groups. Follow-up assessments revealed that grip strength was significantly higher in the high-use than in the no- and low-use groups. [Conclusion] Active use of exercise facilities was positively correlated with maintenance and improvement in physical fitness among participants, which highlights the benefits of easily accessible exercise facilities in maintaining long-term physical function. Future studies should focus on functions that extend beyond physical fitness to develop effective support programs that address the evolving health needs of the aging population.

Social Frailty and Functional Status in Japanese Older Adults: The Mediating Role of Subjective Cognitive Function

ObjectiveThis study aimed to explore the direct and indirect effects of social frailty on functional state trajectories mediated by subjective cognitive function in older adults. DesignLongitudinal study. Setting and ParticipantsOverall, 514 adults aged ≥65 years living in a suburban area of central Japan were included in this study. MethodsFive-item social frailty index (going out, visiting, feeling helpful, living alone, and talking to others), subjective cognitive function from the Kihon Checklist, and instrumental activities of daily living disability. Latent growth curve models were applied to examine the longitudinal relations among the variables. ResultsDuring the 6-year follow-up in latent growth curve models, the initial level of social frailty in older adults was negatively associated with that of functional status (β = −0.53, P < .001), and the rate of change in social frailty was negatively associated with that in functional status (β = −0.78, P < .001). In the mediation model, the indirect effect from the social frailty level to functional status level through subjective cognitive function level was significant (β = −0.14, 95% CI −0.29, −0.09); the rates of change in subjective cognitive function mediated the relationship between those in social frailty and functional status (β = −0.35, 95% CI –0.46, −0.25). Conclusions and ImplicationsThis study found that there is an association between social frailty and functional status in Japanese older adults. Subjective cognitive function mediated this relationship. Hence, additional research is required to investigate additional potential factors linking social frailty and functional status in order to gain a better understanding of the underlying mechanisms.

Semiempirical modeling of the transient response of pore pressure to rainfall and snowmelt in a dormant landslide

This study proposes a simplified, semiempirical hydrological model of the pressure response in a landslide. Various hydrometeorological variables were measured in a dormant landslide underlain by soft sedimentary rocks in a high snowfall area in central Japan. We assessed whether the short-term response of the pore pressure to water inputs by rainfall and/or snowmelt can be predicted using a modified linear diffusion model that describes the seasonal trends of the pore pressure. We applied field observations and regression analysis to characterize the buffering function of the vadose zone. The apparent hydraulic conductivity and hydraulic diffusivity in the vadose zone were low during summer and high during winter and can be described by an empirical function of the pore pressure prior to an event. The pattern of pressure waveforms was accurately reproduced for various water inputs via empirical parameter functions. The model can also reproduce the pore-pressure peaks at different depths and locations within the same landslide with practical certainty. This modeling demonstrated a method that has the potential to predict future landslide instability as long as data from pore-pressure monitoring and water input forecasting are available.

Intrinsic Factors Associated with Dietary Toxin Quantity and Concentration in the Nuchal Glands of a Natricine Snake Rhabdophis Tigrinus.

The snake Rhabdophis tigrinus sequesters cardiotonic steroids, bufadienolides (BDs), from ingested toads and stores them in the nuchal glands as defensive toxins. It has previously been shown that there are individual differences in the total quantity of BDs stored in the nuchal glands of adult R. tigrinus and that BD quantities and profiles of R. tigrinus exhibit geographic variation. However, no previous study has examined the total quantity of BDs as a percentage of body mass (relative BD quantity) and the concentration of BDs in the nuchal gland fluid (BD gland concentration). In addition, intrinsic factors that are associated with relative BD quantity and BD concentration have not been examined within a single population. We collected 158 adult snakes from an area of central Japan from May to October and analyzed their BD quantities by UV analysis. We assessed individual differences in BD quantity, relative BD quantity and BD gland concentration. We found that 1) in approximately 60% of the 158 individuals, the BD gland concentration was greater than 50%; 2) body length and body condition are positively correlated with relative BD quantity and BD gland concentration; 3) even in a single population, individual differences of BD quantity are large, and are greater in females than in males; and 4) relative BD quantity and BD gland concentration of females during the gestation season are lower than those during the non-gestation season.

Complex host/symbiont integration of a multi-partner symbiotic system in the eusocial aphid Ceratovacuna japonica.

Some hemipteran insects rely on multiple endosymbionts for essential nutrients. However, the evolution of multi-partner symbiotic systems is not well-established. Here, we report a co-obligate symbiosis in the eusocial aphid, Ceratovacuna japonica. 16S rRNA amplicon sequencing unveiled co-infection with a novel Arsenophonus sp. symbiont and Buchnera aphidicola, a common obligate endosymbiont in aphids. Both symbionts were housed within distinct bacteriocytes and were maternally transmitted. The Buchnera and Arsenophonus symbionts had streamlined genomes of 432,286bp and 853,149bp, respectively, and exhibited metabolic complementarity in riboflavin and peptidoglycan synthesis pathways. These anatomical and genomic properties were similar to those of independently evolved multi-partner symbiotic systems, such as Buchnera-Serratia in Lachninae and Periphyllus aphids, representing remarkable parallelism. Furthermore, symbiont populations and bacteriome morphology differed between reproductive and soldier castes. Our study provides the first example of co-obligate symbiosis in Hormaphidinae and gives insight into the evolutionary genetics of this complex system.

Changes in Social Relationships and Physical Functions in Community-Dwelling Older Adults.

Social relationships are associated with physical function. However, little scholarly attention has been focused on the effect of changing social factors on physical function. This study was designed to examine the effects on physical function of changes in social relationships in adults aged 65 years and older. This study is part of a longitudinal, prospective cohort study that was conducted on community-dwelling older adults in a suburban area of central Japan. Baseline self-report data were collected in 2011, and a follow-up survey was conducted in 2017. Social relationships were assessed using the Index of Social Interaction, and physical function was evaluated using a subscale of the Kihon Checklist. Chi-square tests, Mann-Whitney U tests, and multiple logistic regression analysis were used to analyze data from 442 older adults who were functionally independent at baseline. After controlling for covariates in 2011, negative changes in social relationships (odds ratio [ OR ] = 3.20, 95% CI [1.18, 8.69]) were found to be associated with physical function decline. Moreover, 1-point increases in the different social-relationship values between baseline and follow-up were associated with protective effects against functional decline ( OR = 0.71, 95% CI [0.63, 0.80]). Furthermore, median trends between baseline and follow-up revealed associations between decreasing ( OR = 4.18, 95% CI [1.53, 11.39]) and continuously low ( OR = 2.98, 95% CI [1.42, 6.28]) social relationships and physical function decline. The findings support a strong association between negative changes in social relationships and physical function decline and highlight the importance of promoting social relationships to delay physical function decline in older adults.

Long-chain alkenones in the Shimosa Group reveal palaeotemperatures of the Pleistocene interglacial Palaeo-Tokyo Bays

The Shimosa Group, a Middle- to Late-Pleistocene sedimentary succession, has been the focus of stratigraphic attention because it lies beneath the Tokyo metropolitan area of central Japan. It is also of palaeoclimatic significance because it contains important interglacial marine strata of the past 450,000 years. Because the marine strata of the Shimosa Group were formed in the shallow inner bay known as the Palaeo-Tokyo Bay, rare occurrences of planktonic foraminifera make it difficult to quantitatively reconstruct the palaeo-sea surface temperatures (SSTs). Here, we extracted long-chain alkenones (LCAs) from the core GS-UR-1 penetrating the Shimosa Group to Marine Isotope Stage (MIS) 11. We found that the alkenone unsaturation ratio appears to reflect the SST of the Palaeo-Tokyo Bay formed during the peaks of MISs 5e, 7e, 9, and 11, which was consistent with the inflowing water mass changes inferred from the benthic foraminiferal assemblages. The palaeo-SSTs during each interglacial period were 2–3 °C higher than the pre-industrial levels of Tokyo Bay and seemed to reach a level similar to that of the Holocene thermal maximum. The findings of this study demonstrate that the LCA-based proxy, which has not before been utilised in studies on the Shimosa Group, has strong potential to provide palaeoceanic and stratigraphic information.

Impact of environmental factors on energy balance of greenhouse for strawberry cultivation

This study elucidated the effects of passive solar greenhouses on strawberry cultivation in temperate areas. The energy required to heat the greenhouse was calculated. Furthermore, the results of a field test performed in a temperate area in central Japan were presented. Environmental conditions such as the ambient temperature, solar radiation, and relative humidity were experimentally investigated. The results of this study indicate that the maximum temperature difference between the inside and ambient air temperatures was 16.4 °C during the evaluation period. The maximum reduction in solar radiation through a transparent vinyl sheet in the greenhouse was approximately 30% when compared with the ambient solar radiation. Additionally, heating requirements were estimated to achieve optimal cultivation conditions in the future. The monthly heating requirement of the greenhouse was between 60.0 and 327.6 MJ/(m 2 ･month), and the energy requirement for heating was found to be maximum in the extremely cold month of January. The energy required for controlling the optimum environment for sensitive plant cultivation was proposed. The proposed evaluation methods can also be applied to other regions for cooling. • Effect of passive solar greenhouse on strawberry cultivation is investigated. • Field test is performed in a temperate area in central Japan. • Greenhouse provides thermal comfort for strawberry crop during winter. • Heat energy required for optimum cultivation in an area is estimated. • Validity of energy analysis proposed in this study is demonstrated.

Seasonal Diel Activity Patterns of Three Sympatric Ungulates in Forested Area in Central Japan

The diel activity pattern is a key factor in the coexistence mechanism of sympatric wild animals, enabling temporal niche partitioning. Although previous studies on sympatric ungulates (sika deer, Japanese serow, and wild boar) have reported dietary and spatial niche partitioning, temporal niche partitioning in these sympatric ungulates is not well understood. In this study, we aimed to elucidate the seasonal diel activity patterns of three sympatric ungulates in Gifu Prefecture, Japan, where they have been sympatrically distributed since 1978. We placed 21 camera traps from August 2017 to November 2019, and investigated diel activity patterns and photographic frequencies over three time periods (daytime, night-time, and twilight). Although we found no seasonal changes in diel activity patterns of three ungulates, but patterns showed differences among species. While sika deer showed crepuscular activity, wild boars and Japanese serows showed nocturnal activity. In addition, Japanese serows showed temporal niche partitioning against sika deer. Consequently, we suggest that the relationship between sika deer and Japanese serow is competitive in terms of diel activity patterns.

Changes in the birth prevalence of orofacial clefts in Japan: Has the birth prevalence of orofacial clefts been affected by improved accuracy of prenatal diagnosis?

We have been conducting a survey on the birth prevalence of orofacial clefts, including cleft lip with or without cleft palate and cleft palate, in the Tokai area in central Japan every year for 37 years. Along with the yearly trends in the birth prevalence of orofacial clefts in that area for the past 37 years, we discuss whether the artificial abortion rate of fetuses with orofacial clefts has increased through the improved performance of ultrasonic imaging equipment. We also compare the yearly trends in the birth prevalence of congenital anomalies, including orofacial clefts, in Japan with those in other countries or areas where artificial abortion due to birth defects is legally permitted, and discuss the impact of improved accuracy of ultrasound imaging on the rate of artificial termination of pregnancy. The fact that the birth prevalence of orofacial clefts has basically remained unchanged for more than 30 years, even with recent more detailed prenatal diagnosis based on the improvement of ultrasonic diagnostic equipment, has allowed us tentatively to conclude that prenatal diagnosis is not currently threatening the right to life of the fetuses with orofacial clefts.

Estimating fractured rock effective permeability using discrete fracture networks constrained by electrical resistivity data

Although the permeability of fractured rock mass is a fundamentally important property for the safe construction of civil and mining engineering structures such as tunnels, in situ characterization of permeability without resorting to hydraulic tests is difficult. For rapid, wide-area estimation, a method that can be conducted at a field-scale using geological and geophysical investigation data is proposed. The method is not based on conventional hydraulic test results. Instead, it combines the stochastic generation of fracture networks with the crack tensor theory. The most important parameter for this method is the fracture length distribution. Although the distribution parameters in the DFN model are assigned through sampling, a bias is generally experienced because of the limited sampling area. To improve the estimation of such parameters, in-situ electrical resistivity data and a symmetric self-consistent method are used to constrain the fracture length distribution. The proposed method is applied to the fractured crystalline rock mass of the Mizunami Underground Research Laboratory (URL) in the Tono area of central Japan. Its effectiveness and correctness are demonstrated through good correspondence of the derived effective permeability with the in-situ measured permeability.

Outbreak of the stick insect, Ramulus mikado (Phasmatodea, Phasmatidae), in the Akashina area of Japan (Azumino City, Nagano Prefecture)

AbstractIn August 2017, an outbreak of the stick insect, Ramulus mikado (Rehn, 1904), was observed in the Akashina area in Central Japan. This stick insect is a wingless, non‐flying species that inhabits East Asia. Although it seems that the occurrence of many individuals emerging together had been observed in the 2 or 3 years prior, the outbreak in 2017 was on a far larger scale, and was therefore not comparable to anything observed previously. Indeed, it was also observed that the stick insects fed on almost all leaves of the large Japanese zelkova trees until the trees were bare. Additionally, mass gatherings of the stick insects on the walls of houses in the area were observed. In Japan, there have been no other reports of outbreaks of R. mikado, thus this represents a unique case. In the Akashina area, the population's sex ratio is heavily biased towards females, as is the case with other populations, indicating that they reproduce parthenogenetically. However, among our observations, one individual of the 724 specimens collected in the present study was in fact a male. As there have only ever been about 10 observed cases of R. mikado males, the male individual collected in our field research constitutes a valuable record.

Case Study for the Predictive Environmental Risk Assessment of Hexamethylenetetramine Release to the Yodo River during a Massive Tsunami Attack

Untreated hexamethylenetetramine (HMT) was discharged into the Tone River in the central area of Japan, and the risk management plan in the watershed area has been strengthened because HMT is the precursor of formaldehyde (FA) regulated by Japanese water supply law. The release of HMT could occur not only in steady but also in unsteady environmental conditions. In this context, no quantitative environmental risk assessments have dealt with the combined events of FA precursor outflow and natural disasters, such as a massive tsunami attack. In this study, we estimated the time course changes of HMT concentrations at the near water treatment plant (WTP) intakes due to tsunami run-up in the river after HMT discharge from facilities along the river during a massive tsunami attack, then potential ecological and health impacts were estimated. This method has a strong analytical ability to reveal the relationship between wave source and inland water run-up in consideration of 3D density flow. For ecological risk, the half maximal effective concentration (EC50) was employed. We found that HMT concentration would not reach a level of concern even after the accident. For potential health risk in terms of the possible maximum inlet concentration of HMT at the WTP, the FA formation amount was 5.3 × 10−2 mg/L, which was below the water quality standard.

Source apportionment in PM2.5 in central Japan using positive matrix factorization focusing on small-scale local biomass burning

Here, we discuss the influences of small-scale biomass burning (BB) originating from local/regional emissions, such as agricultural waste burning, which are difficult to detect via remote sensing. To evaluate the BB contribution, we used a positive matrix factorization (PMF) model with chemical component data including levoglucosan, a useful BB indicator, at multiple urban, suburban, and background sites in central Japan during two weeks in October and November of 2014 and January and February of 2015. High levoglucosan concentrations were observed not only at the suburban sites but also at the urban sites. At the background site located downwind of Northeast China, the levoglucosan concentrations were elevated when air masses were transported from Northeast China, where fire spots were detected. Meanwhile, at the other sites, small-scale local or regional BB emissions prevailed, and fire spots were rarely detected. At these sites, the levoglucosan levels were high although the relevant air masses did not originate in Northeast China. The source apportionment results demonstrated that in fall, BB was a significant source of particulate matter with diameters of less than 2.5 μm (PM2.5), organic carbon, and elemental carbon at all sites. Notably, the BB contributions to PM2.5 were higher at an urban site located near farmland than at other urban sites in fall and winter. Our results indicate that specific BB emission sources, such as local, small, and irregular open field burning, impact the air quality not only at suburban areas but also at urban areas in central Japan.

A comparison of hydrological characteristics between a cypress and mixed-broadleaf forest: Implication on water resource and floods

Broadleaf or conifer forest? – an ongoing dilemma as regards water resource and flood prevention. Although conifer trees use less water and are hydrophobic, existing studies at the watershed scale have shown varying results due to variability in meteorological conditions and forestry practices. In this study, two adjacent headwater catchments [2.42 ha cypress (CF); 2.08 ha mixed-broadleaf (MB)] were gauged. The study area in central Japan has a warm temperate climate with high annual rainfall and typhoons. Daily discharge (n = 1398) and storm event hydrographs (n = 242) were compared between CF and MB and discussed in light of water availability and storm event runoff characteristics. Overall water yield in CF was 6.4% lower than in MB but this was caused by lower streamflow on high discharge periods (30% frequency); thus, may not adversely affect municipal/agricultural water supply. For 70% of the time including during dry periods, water yield was higher in CF. This agrees with the principle that conifers use less water than broadleaf trees – even at the forested catchment scale. Discharge in the CF stream is also less variable than that in the MB stream. During storm events, the CF stream has higher flashiness (shorter response time to rainfall and higher peak discharge) than the MB stream; but in larger storms (≳70 mm), the MB stream may have higher peak discharge. Our data demonstrates that a well-managed plantation forest does not necessarily have inferior hydrological function compared to a natural broadleaf forest, which differs from the stereotype. Frequencies of high and low flows as well as runoff characteristics were also presented in hopes of promoting better forestry decisions when considering water demand and existing stormwater drainage infrastructures.

Ponds support higher bird diversity than rice paddies in a hilly agricultural area in Japan

The aim of the present study was to evaluate bird diversity (richness, abundance, and community composition) in three types of artificial wetlands (rice paddies, carp aquaculture ponds, and farm ponds for irrigation) while considering bird habitat groups and seasons and to reveal the environmental characteristics of wetlands (e.g. wetland type, water depth, and vegetation cover) associated with bird richness and abundance. Bird and environmental characteristics were surveyed in 30 sites (10 sites per wetland type) in the hilly agricultural area of central Japan, considering four bird groups (open-land, wetland, bush, and woodland) and three seasons (breeding, migrating, and wintering). Bird richness of each group was the highest in farm ponds, followed by carp ponds and then rice paddies, throughout the year, except for bush and woodland species. Abundance levels of open-land, woodland, and total species were significantly higher in farm ponds than in rice paddies and carp ponds in the wintering season (and also in migrating season for open-land species). Effects of wetland type, wetland area, vegetation cover on water surface, and slope of bank to bird species and abundance differed among bird groups. There were no differences in community compositions among wetland types, although significant differences were apparent among seasons. Therefore, for bird diversity conservation in hilly agricultural areas, (1) various wetland types creating a spatial–temporal heterogeneity of environments is important, (2) preserving ponds rather than rice paddies would be effective, and (3) steeper slopes and richer vegetation cover on water surfaces should be considered for waterbirds.

Changes in extremely heavy and light snow-cover winters due to global warming over high mountainous areas in central Japan

To investigate future changes in snow cover and snowfall over mountainous areas in central Japan, we conducted regional climate projections using a high-resolution non-hydrostatic regional climate model (NHRCM) with 5 km and 1 km grid spacings. Boundary conditions are derived from the database for Policy Decision making for Future climate change (d4PDF) 20 km regional climate projections (d4PDF20). The d4PDF20 assumes two future climates when global mean surface air temperatures are approximately 2 K and 4 K warmer than in the preindustrial period. Experiments with 5 km grid spacing are conducted by NHRCM for 372 years in d4PDF20 in each climate. Experiments with 1 km grid spacing are performed focusing on 5 years with heavy, median, and light snow cover of mountainous areas in each climate. In the years with heavy snow cover in 2 K and 4 K warming climates, snowfall is enhanced from late December to February at more than 2000 m above sea level (mASL) in the northern parts of Japan’s Northern Alps, resulting in heavy snow cover comparable to that in the present climate. Heavy daily snowfall remarkably increases due to global warming in the years with heavy snow cover. At low elevations below 500 mASL, snowfall decreases in all ranges of snowfall intensity in the 4 K warming climate, while the frequency of heavy daily snowfall increases in the 2 K warming climate. Precipitation is enhanced around the Japan-Sea Polar-airmass Convergence Zone and the mountainous area facing the Sea of Japan, resulting in strengthened heavy snowfall at high elevations where the winter mean temperature is approximately − 10 °C in the present climate. On the other hand, remarkable reductions in snow cover and snowfall are projected in years with light snow cover. Our results indicate that global warming causes heavy and light mid-winter snowfalls at high elevations of Japan’s Northern Alps that are more extreme than those in the present climate.Graphical abstract

Refinement of a gravimetric geoid model for Japan using GOCE and an updated regional gravity field model

We developed a refined gravimetric geoid model for Japan on a 1 × 1.5 arc-minute (2 km) grid from a GOCE-based satellite-only global geopotential model and a regional gravity field model updated in this study. First, we have constructed a regional gravity field model for Japan using updated gravity datasets together with a residual terrain model: 323,431 land gravity data, 77,389 shipborne marine gravity data, and Sandwell’s v28.1 altimetry-derived global marine gravity model. Then, the geoid was determined with the gravity field model. The methodology for gravimetric geoid determination was based on the remove–compute–restore technique with Helmert’s second method of condensation of topography (Stokes–Helmert scheme). Here, the hybrid Meissl–Molodensky modified spheroidal Stokes kernel was employed to minimize the truncation error under an appropriate combination of different kinds of gravity data. In addition, a high-resolution GSI-DEM on a 0.4 × 0.4 arc-second (10 m) grid, together with the SRTM-DEM on a 7.5 × 11.25 arc-second (250 m) grid, was utilized for precisely applying terrain correction to the regional gravity field model. Consequently, we created a gravimetric geoid model for Japan, consistent with 971 GNSS/leveling geoid heights distributed over the four main islands of Japan with a standard deviation of 5.7 cm, showing a considerable improvement by 2.3 cm over the previous model (JGEOID2008). However, there remain some areas with large discrepancies between the computed and GNSS/leveling geoid heights in northern Japan (Hokkaido), mountainous areas in central Japan, and some coastal regions. Since terrestrial gravity data are especially sparse in these areas, we speculated that the largeness of the geoid discrepancies there could be partly attributed to the insufficient coverage and accuracy of gravity data. The Geospatial Information Authority of Japan has started airborne gravity surveys to be covered over the Japanese Islands, and in future, we plan to develop a geoid model for Japan further accurately by incorporating airborne gravity data to come.

EFFECTS OF COLOURED PLASTIC MULCH ON SOIL HYDROTHERMAL CHARACTERISTICS, GROWTH AND WATER PRODUCTIVITY OF RAINFED SOYBEAN

AbstractSoil thermal regime, a crucial factor in plant growth and development, is influenced by the colour of plastic mulch. The effects of black plastic mulch (BPM), silver plastic mulch (SPM), transparent plastic mulch (TPM) and bare soil on the soil temperature regime as well as on the growth and yield of rainfed soybean were evaluated in a field experiment. The results revealed a strong correlation (r2 = 0.85) between air and soil‐surface temperatures in the case of bare soil, but no correlation (r2 = 0.03) in the case of TPM. The coloured plastic mulching raised soil temperature by 3–7 °C compared to bare soil, with a daily fluctuation of 6–17 °C at the early growth stage, while the soil temperature increased by 1–2 °C, with a daily fluctuation of 4–8 °C in later growth stages. BPM provided 1–4 °C more temperature than SPM and TPM at 5, 15 and 25 cm depths that augmented heat accumulation by 23% and 6% compared to bare soil and TPM, respectively. The coloured mulching significantly (p &lt; 0.05) increased soybean growth attributes and thus augmented seed yield by 31–34% compared to bare soil. However, BPM, by maintaining the highest soil temperature, provided the highest seed yield of soybean. Therefore, BPM is recommended as a suitable mulch in the central Japan area. © 2020 John Wiley &amp; Sons, Ltd.

New Species of Turbo (Marmarostoma) (Gastropoda, Turbinidae) from the Miocene Limestone in Central Japan: A Window into the Miocene Marine Biodiversity in the Northeastern Philippine Sea

The late early to middle Miocene limestone bodies in the Sagara and Izu Peninsula areas of central Japan are reefal deposits that were deposited under a tropical climate and provide a window into the paleodiversity of tropical volcanic islands in the northeastern Philippine Sea Plate. Specimens from the early middle Miocene Megami Limestone in the Sagara area and from the middle Miocene limestone blocks within the Yugashima Group on the Izu Peninsula are described as Turbo (Marmarostoma) histrioides sp. nov. and Turbo (Marmarostoma) izuensis sp. nov., respectively. Discovery of these two new species raises the number of Marmarostoma species from four to six in the Sagara and Izu Peninsula areas, demonstrating that the subgenus was more diverse in the northeastern Philippines Sea Plate during the middle Miocene than it is today. In particular, there are double the number of Marmarostoma species (four species) from the middle Miocene in the Izu Peninsula compared with the modern fauna on the tropical islands of the Izu-Ogasawara Arc. The highest richness of modern species of Marmarostoma is found in the central Indo-West Pacific, where molecular phylogenetic studies have suggested that the subgenus rapidly diversified in the late Oligocene or early Miocene. Nevertheless, Miocene species of this subgenus are sparse in the central IWP, being incongruent to the diversity pattern expected from the molecular studies. The findings reported herein provide an insight into the origin of the central IPW biodiversity hotspot.