Mammal Study

We analyzed the stomach contents of wild boars (Sus scrofa) inhabiting evergreen forests in western Japan and found that they were dependent on the masting of acorns of Castanopsis cuspidata. The increased availability of C. cuspidata acorns positively affected their consumption by wild boars. In the good mast years, wild boars consumed C. cuspidata acorns from November to June of the following year. No significant annual variation in body condition was detected, suggesting that alternative food resources (e.g., bamboo shoots) may have maintained the body condition of wild boars, even in poor mast years. A strong negative correlation was found between the consumption of C. cuspidata acorns and the amount of crop damage to vegetables. This study revealed the wild boar as a pulsed food resource feeder, which has not yet been identified in Japan, and emphasized the importance of considering C. cuspidata masting for designing effective strategies for mitigating crop damage.

To estimate the reproductive schedule of the Okinawa spiny rat on the basis of its body size distribution, we developed a nest box with an auto-trigger camera. Three camera-installed nest boxes were used in the field in the northern part of Okinawa Island beginning in September 2015. The distance between eyes, an index of body size, was measured in 850 images of spiny rats. The reproductive schedule was estimated based on the emergence period of subadults. With the emergence of subadults, the distribution of body size index becomes a mixture of two normal distributions consisting of adults and subadults, so a Gaussian mixture model was employed to identify each distribution. The Gaussian mixture model revealed that the distribution of the estimated distance between eyes could be divided into two clusters, with a mixing ratio of 0.11 for Group 1 (subadult) and 0.89 for Group 2 (adult). Most individuals belonging to Group 1 appeared during the winter months of December to March, indicating that subadults were weaned primarily during this season. Consequently, reproduction of the Okinawa spiny rat is thought to be limited in autumn and winter.

Benten-Jima Rock, located off Cape Soya, Hokkaido, has been a Steller sea lion (SSL; Eumetopias jubatus) winter haulout for decades. The animals usually occupy the site from October to May. Observations have been sporadic, although the population count started to increase in 2005. We have monitored SSL numbers since 2012 using several survey methods, such as observation by direct counting and remote archival cameras. Since these data were not sufficient, owing to blind spots, we started using unmanned aerial vehicle (UAV) surveys in 2016 and corrected the previously collected data. Using these methods, a considerable number of SSLs were observed at Benten-Jima Rock during 2016–2017. The maximum number of SSLs was 3158 on land and 3056 in the water near the site, as counted from UAV images on May 2, 2017. Based on hot brand marks, we found that Benten-Jima Rock hosted SSLs from all ten main rookeries along the Asian coast. The majority (∼60%) were from Tuleny Island near the east coast of Sakhalin. The cause of this extraordinary increase in SSL numbers at Benten-Jima Rock remains unclear and requires further monitoring and research.

Cryopreservation of somatic tissues and cells can be applied to biodiversity conservation. Although vitrification is widely used for tissue cryopreservation, it is challenging to obtain viable cells in facilities that lack adequate experimental tools, such as zoos. In this study, we established a simple tissue cryopreservation method for obtaining viable cells. Using mouse tissues of the ears and skin, we explored the conditions suitable for cryopreservation. After freezing, the tissues were thawed, and the cells were isolated. The tissues were then cut into small pieces to obtain viable cells. The use of a cryopreservative solution and freezing at –80°C increased the probability of obtaining viable cells. Viable cells were obtained and cultured even after the ear tissues were stored at room temperature for 24 h. Our method allowed primary cells to be isolated and cultured from ear tissues of dead animal. Further, we examined whether cells isolated from cryopreserved tissues could be studied in vitro. We found that treatment with lipopolysaccharides and Poly I:C increased the mRNA expression of pro-inflammatory cytokines in wild boar cells. These data suggest that the simple cryopreservation method developed here can be applied to biodiversity conservation and basic science studies of wild animal cells.

The purpose of the present study was to determine whether and how the fruit-foraging behaviors of two frugivorous carnivorans, the raccoon dog (Nyctereutes procyonoides) and Japanese badger (Meles anakuma), are influenced by the presence of humans. In the first investigation, we contrasted the frequency and duration of foraging visits to fruit-bearing trees in an urban forest and a mountain forest. In the second investigation, we employed a modeling approach to ascertain whether the degree of shelter affected tree selection in the urban forest by these frugivorous species. The results of the first investigation showed that both species foraged almost solely at night in the urban forest and had significantly shorter visit times in the urban forest than in the mountain forest. The second investigation revealed that both species selected to forage in sheltered places where the forest floor was covered with vegetation. We found that fruit production did not affect tree choice in these places, indicating that the mammals prioritize avoiding humans over effective foraging in places with more plentiful fruits. These tendencies to forage at night and in areas with adequate shelter indicate that these species have adapted their behaviors to avoid humans in urban environments.

In the Japanese field mice, Apodemus argenteus and A. speciosus, loss of a tail part has often been observed under natural conditions. Such loss is considered a way of avoiding damage during physical accidents and attacks. Here, we studied the types of losses, types of caudal breakages, and breakage positions along the tail. The losses mainly consisted of intervertebral breakage (inter-VB) and intravertebral breakage (intra-VB). VB occurred widely along the tail in both Apodemus species and showed no specific tendency for the inter-VB positions. Intra-VB was confirmed at caudal vertebrae of the middle portion of the tail, consisting of vertebrae with lower relative width (minimum width/maximum length in each caudal vertebra) ranges showing a mean of approximately 0.15–0.28 in both Apodemus species. Previous studies in lizards and rodents found autotomic inter-VB and intra-VB to be positioned in a specific small portion of the tail. However, we found that in field mice, inter-VB and intra-VB were widely distributed along the tail without a regular position. Therefore, it is suggested that both inter-VB and intra-VB as self-defense ways in Apodemus appear to be mere torn-off breakages rather than autotomies, due to certain fragilities in intra- and intervertebral structures.

Hybrid cetaceans occur in both captive and natural environments. This study is the first to describe the external morphological and genetic characterizations of natural intrageneric hybridization between the common bottlenose dolphin, Tursiops truncatus, and the Indo-Pacific bottlenose dolphin, T. aduncus, in Japanese waters. In November 2019, a stray dolphin was seen in Moriura Bay, Wakayama, Japan, and was a male that measured 241.5 cm in body length in July 2020, after an incidental catch in February 2020. Moderate speckles in the genital area of the dolphin were observed, which is a characteristic of T. aduncus. The dolphin had 22–23 pairs of teeth in each jaw, a quantity consistent for both species. The length of the rostrum and the size of flippers were within the range of T. aduncus. The mitochondrial DNA D-loop region haplotype was 99% homology with those from T. aduncus found in Chinese and Japanese waters. Microsatellite analysis revealed that the dolphin contained ratios of approximately 50% of both T. truncatus and T. aduncus lineages; the dolphin could therefore be an F1 hybrid between a female T. aduncus and a male T. truncatus. Further genetic studies are required to elucidate the origin of this hybrid dolphin.