（要旨）． アカボウクジラ科鯨類 3 種における陰茎および関係する生殖器構造の形態学的研究． アカボウクジラ科鯨類は，種間および雌雄間で高い形態的多様性を有しており，性選択が種分化を促進する重要な要因である可能性が示唆されている．しかしながら，アカボウクジラ科鯨類の生殖器に関する知見は限られている．本研究では，漁業および死亡漂着によって得られたアカボウクジラ科鯨類に属する，ツチクジラ，アカボウクジラ，タイヘイヨウアカボウモドキの 3 種の雄性生殖器構造を解剖学的および組織学的に調べた．基本的な生殖器の構造は 3 種間で共通しており，これらは他のハクジラ類と同様の形態学的特徴を有していた．3 種とも陰茎は円錐形で，共通の内部構造を有していたが，一部のハクジラ類で報告されている尿道突起に類似した陰茎伸長部といった特徴的な構造は認められなかった．アカボウクジラの前立腺および前立腺圧迫筋は極めて小さく，ツチクジラにおいても同様の筋構造と痕跡的な前立腺様組織が認められた．タイヘイヨウアカボウモドキでは組織の劣化のため前立腺は特定できなかったが，他のハクジラ類で認められるような発達した前立腺圧迫筋は認められなかった．本研究で得られた知見は，知見が少ないアカボウクジラ科鯨類の繁殖生態の理解に貢献する貴重な知見を提供するものである．
The waters around the Chichijima Islands of the Ogasawara Islands, approximately 1000 km south of mainland Japan, are known breeding areas for humpback whales Megaptera novaeangliae, although their suitable habitat in this area has not been assessed in a spatially explicit manner. This study examined the relationship between the spatial distribution of humpback whales and topographic factors, using boat-based sighting survey data from 2013 and 2015–2018. A generalized additive model (GAM) and a maximum entropy model (Maxent) were used to estimate the suitable habitat of humpback whales. Both models demonstrated that the whale distribution was related to water depth and seabed slope, with water depth having a particularly strong influence. High suitability was observed at shallow water depths and gentle slopes, reaching a maximum at depths of 50–60 m and slopes of 0.5–0.8°. Additionally, suitable habitats were more extensive off the west coast than off the east coast, suggesting that the western area was more suitable for whales. The resulting habitat suitability map provides valuable information about their key habitats and can be utilized for their appropriate conservation in this area. Published online 18 May, 2026; Print publication 31 July, 2026
Understanding the food habits of Asiatic black bear (Ursus thibetanus) in the Satoyama landscape is crucial for developing effective management strategies. To understand that, in the warm temperate zone of Western Japan, we analyzed 288 fecal samples from the western part of Northern Kinki. The results indicated a strong dependence on anthropogenic foods such as Diospyros kaki from summer to autumn and Phyllostachys edulis in spring. Notably, hard mast of Quercus species, which are dominant in the study area, were less preferred than soft mast. Dietary composition fluctuated annually. From 2021 to 2023, the consumption of D. kaki fluctuated annually depending on the availability of soft mast in the forest. Consequently, bear captures in and around villages also fluctuated. Autumn 2024 was a poor mast year for many tree species, including soft mast and D. kaki, resulting in a mass bear occurrence. In this autumn, Castanea crenata (hard mast) served as the most consumed item. This suggests that soft mast functions as regular “main food item” for bears during autumn in the study area. Conversely, D. kaki serves as an “alternative food item” during years of poor soft mast availability, while C. crenata may serves as further “alternative food item”. Published online 4 May, 2026; Print publication 31 July, 2026
This study presents the first estimate of body length in free-ranging narrow-ridged finless porpoises (Neophocaena asiaeorientalis), based on footage obtained using an unmanned aerial vehicle (UAV). UAV-captured videos were used to identify porpoise surfacing events, with the moment of breathing selected as optimal for morphometric analysis. Still images were extracted from these events, and body length (BL) was measured. To improve measurement accuracy, a linear regression model was developed to convert pixel lengths into real-world dimensions as a function of flight altitude, calibrated using reference objects placed both on land and at sea. Across 67 measured events, the estimation errors ranged from 1.6 to 3.0%. Repeated measurements from the same individuals yielded a mean standard deviation of 0.9 cm, and a coefficient of variation (CV) of 0.7%, indicating high precision. Estimated body lengths ranged from 93.8 to 168.0 cm. To the best of our knowledge, this study presents the first length distribution data for free-ranging finless porpoises. Furthermore, this study proposes a standardized and replicable approach for selecting frames in UAV-based morphometric analysis in small cetaceans. These results offer a valuable baseline for future assessments of health and reproductive status and may contribute to conservation strategies for this endangered species.
The pelvis plays a vital role for locomotion, posture, and reproduction in mammals. Consequently, it displays species-specific morphological characteristics that are valuable for taxonomic identification, particularly when investigating skeletal remains and fossil records. In the case of bats, isolated pelvic bones are abundantly found from cave sediments. Nevertheless, the scarcity of systematic research on the bat pelvis often hinders taxonomic identifications of such isolated bones. Therefore, this study aims to describe the pelvic morphology of bat species distributed in Japan and identify potential diagnostic characters based on these morphological traits using landmark-based measurements. Results showed that five bat families living in Japan exhibited remarkable differences in pelvic morphology, thus facilitating family-level identification. Principal component analysis of the first and second components revealed two primary morphological clusters, (1) Pteropodidae, Vespertilionidae, and Miniopteridae and (2) Rhinolophidae and Hipposideridae. These findings suggested that the morphology of the acetabulum and iliopubic eminence closely reflected interfamily or interspecific variations and thus serves as a reliable diagnostic character. Although differentiating among closely related taxa based on pelvic morphology alone is difficult, the pelvic size relative to body size provides effective species identification.
Miniopterus fuliginosus is a widely distributed vespertilionid bat in East Asia. Due to its strong long-distance flight capability and the inherent challenges of morphological classification, systematic studies on the population genetics and morphological variation remain limited. In this study, we conducted a comprehensive comparative analysis of M. fuliginosus populations from China and Japan, integrating molecular phylogenetics, traditional morphometrics, and skull-based geometric morphometrics. Our results reveal pronounced morphological divergence between the Chinese and Japanese populations, despite genetic admixture. Chinese individuals exhibit larger body and skull dimensions, while geometric morphometrics highlight distinct skull shape differences, particularly in molar row, rostral configuration, braincase shape, orientation of the auditory meatus, and mandible morphology. Those variations are closely associated with diet, ecological niches, and flight behaviors of bats' ecology, suggesting the island-mainland environmental contrasts, as well as climatic zonation differences between China and Japan may play an important role in shaping the morphological divergence of M. fuliginosus. The observed genetic admixture likely results from the species' inherent long-distance dispersal and/or seasonal migratory behavior, which facilitates frequent gene flow among populations. Additionally, our study reviewed the Japanese endemic species M. fuscus and reports a potential new distribution in Taiwan, China.
Human-bear conflict is a significant issue in Japan. Understanding genetic diversity, population structure, and local population size of the Asian black bear is essential for improving ecological knowledge and developing conservation and management measures of this species. We examined sex, mitochondrial (mt) DNA variations, and 12 nuclear microsatellite genotypes from hair-derived DNA collected in the Kiso region, Nagano Prefecture. After verifying microsatellite genotypes, we identified 30 distinct individuals (six males, 18 females) within an approximately 48 km2 area. MtDNA analysis revealed that all males shared haplotype E01, while females possessed three haplotypes, including E07, detected in Nagano for the first time but previously reported in Tohoku region and Toyama Prefecture. STRUCTURE analysis did not reveal any genetic cluster in nuclear DNA, but significant spatial genetic structures were identified in both mtDNA and nuclear DNA. No evidence of a recent bottleneck was detected. This study is the first to examine the local genetic structure of the black bear in Nagano. Although no genetic clusters were detected, the estimated effective population size was not large, underscoring the importance of continued genetic monitoring. These findings provide insights into anticipating potential conflict zones and guiding conservation and management measures in the Kiso region.
A stomach content analysis of 80 stranded and bycatch narrow-ridged finless porpoises in Ise and Mikawa Bays, central Japan, was conducted between 1992 and 2020. Prey items were identified in 76 samples. We combined three types of analyses to comprehensively explain their feeding habits: 1) numerical abundance and frequency of occurrence were used to analyze prey type utilization, 2) a combined rank index was used to search for important prey taxa, and 3) cluster analysis of flexible mixture modeling was used to detect the characteristics of feeding. Our results showed that the food habits of this population were characterized by frequent cephalopod and nektonic fish feeding and infrequent but large amount of benthic fish feeding. They changed their prey seasonally, where cephalopods were dominant during the spring-summer season. Cephalopods belonging to Teuthida and Octopoda, and fish belonging to Clupeiformes, Sillagidae, Gobiidae, and Callionymiae were suggested as important prey. We showed that in Ise and Mikawa Bays, porpoises likely feed opportunistically on various fish species and cephalopods.
In the northern part of Okinawa-jima Island, a Natural World Heritage site inhabited by many endangered and endemic species, a non-native sika deer Cervus nippon was sighted on October 21, 2024. Two days later, a sika deer fecal pellet was collected from the forest floor near the first observed location. In this study, DNA metabarcoding analysis was performed on feces to identify the plant species consumed by sighted individuals to consider the potential impacts of sika deer when established in this ecosystem. Analysis of five fecal samples of a single fecal pellet revealed the presence of 24 angiosperm species across 18 families, and four fern species across three families. Among these, two species are endemic to the Ryukyu Archipelago, including one classified as Critically Endangered (CR) on the Red List of Ministry of the Environment, Japan. These results indicate that establishment of sika deer populations in this region may have a significant impact on the survival of endangered species and ecosystems. Therefore, it is desirable to promptly remove sighted individuals and establish a system to prevent further invasions.
Invasive non-native species cause multifaceted and serious problems in the environments into which they are introduced. Sika deer (Cervus nippon) are a well-known invasive species worldwide. Even in Japan, where sika deer is native species, biological invasion issues have arisen due to the introduction of sika deer into areas where they did not originally exist. On 21 October 2024 a male deer with three pointed antlers was sighted in the Yambaru region of Okinawa-jima Island, Japan. Here, we analysed the extracted DNA from deer fecal samples in Yambaru to genetically identify the sex and origin. The results of the sex identification marker showed that the individual was male. Examination of mtDNA haplotypes showed a significant genetic affinity with Kinkazan Island in northern Japan. From Kinkazan Island, deer were actively captured and transported off the island to zoos throughout Japan between the 1920s and the 1970s. The Kinkazan Island lineage has likely been maintained in captivity for at least 40 years without interruption. Following this long period, one or more individuals of the lineage were brought to Okinawa-jima Island and subsequently escaped or were released. To address this issue, institutional measures are required, including systems that enable rapid response to escapes and, more fundamentally, those that prevent escapes.
Animals produce sounds that convey various types of information to conspecifics. Although narrow-ridged finless porpoises (NRFPs) are thought to rely on sounds for their underwater lives, the specific information encoded in these sounds remains unclear. In this study, we examined the effects of body length and sex on the peak frequency of echolocation clicks in 11 captive NRFPs. Presumed on-axis clicks were recorded from six females and five males housed in three aquariums. A generalized linear mixed model was applied with peak frequency as the response variable. Body length and sex were included as fixed effects, and individual identity was included as a random effect. The significance of the fixed effects was assessed using likelihood ratio tests. The results revealed that peak frequency was negatively correlated with body length and significantly lower in males than in females. Specifically, larger individuals produced lower-frequency clicks, and the intercepts of the regression lines differed between sexes. These findings suggest that NRFPs may be capable of recognizing the sex of conspecifics through click frequency, potentially facilitating the identification of reproductive partners within the active range of sounds.
Accurate identification of sympatric mustelid species is essential for understanding their ecological roles, yet traditional identification methods based on scat morphology often lead to misclassification. In this study, we identified mustelid feces collected on Sado Island, Japan, using DNA analysis and evaluated the reliability of fecal size for discrimination. A total of 343 fecal samples were collected, and DNA was successfully amplified in 341 samples using three commercial extraction kits. Species-specific multiplex PCR targeting the mitochondrial control region identified 331 samples as Japanese marten (Martes melampus) and 10 as Japanese weasel (Mustela itatsi). Maximum fecal diameter was measured in 323 marten and 10 weasel samples. The mean diameter was significantly larger in martens (9.8 +/- 2.2 mm) than in weasels (7.3 +/- 1.6 mm), with overlapping prediction intervals at both 95% and 99% confidence levels. Had species identification relied only on fecal diameter, most samples classified as weasels would actually have belonged to martens. These results highlight the limitations of fecal size as a discriminatory marker and emphasize the importance of DNA methods in mustelid research. We also show that dry feces-commonly encountered in field conditions-can be reliably used for DNA analysis, offering advantages for future studies.
Associations and interactions between infants and non-parents, termed allomaternal behavior, have been reported in many odontocete species but are sparsely documented in solitary species. Narrow-ridged finless porpoises (Neophocaena asiaeorientalis) rarely form large groups and are typically considered solitary. In this study, we used a drone to observe newborn porpoises swimming alongside adults at Machiya Beach in Mie, Japan. Newborns estimated to be less than six months old, based on their body length ratio to that of an adult, were selected for the study. In four cases, the adults swimming parallel to the neonates switched. Each of the four newborns swam in parallel to the two adults. Back-rubbing behavior and suckling were observed between adults and neonates in two cases. No agonistic behavior was observed in any of the cases. We discussed the possibility that these social behaviors represented care by the adult, neonatal use of a tolerant or indifferent adult, or abuse (e.g., kidnapping) by the adult. This is the first report of social behavior between neonates and non-maternal adults in wild narrow-ridged finless porpoises. Our findings suggest that this species is more socially active than previously considered.
