Masatsugu Suzuki

Growth-related changes in histology and immunolocalization of steroid hormone receptors in gonads of the immature male green turtle (Chelonia mydas)

Studies on the population dynamics of sea turtles require histological evaluation of the ontogenetic development and the activity of the gonads for reproduction. To investigate the growth-related changes of gonads in the immature male green turtle (Chelonia mydas), the histological changes of testes and epididymides and the localization of the androgen receptor, estrogen receptor alpha, estrogen receptor beta, and progesterone receptor were examined. The testes were categorized histologically into six developmental stages, and a scarce relationship between straight carapace length and gonadal development was confirmed based on the histological analysis. Several kinds of steroid hormone receptors were examined to show distributions in both testes and epididymides, for which their immunoreactivities were enhanced according to the developmental stage of the testes. These results suggest that straight carapace length is not an adequate indicator of maturity determination, whereas histological and immunohistochemical evaluations are useful in identifying the growth stages of green turtles, owing to the higher sensitivity to steroid hormones that appear during growth.

Genetic variation in the harbor seal (Phoca vitulina) and spotted seal (Phoca largha) around Hokkaido, Japan, based on mitochondrial cytochrome b sequences

The harbor seal (Phoca vitulina) and spotted seal (Phoca largha) are the main seal species around Hokkaido, Japan. While some investigations have been conducted on the ecology and morphology of these two species, there is a lack of genetic information. We studied variation in mitochondrial cytochrome b sequences in the two species. Fifteen haplotypes were observed in 39 harbor seals from Erimo, Akkeshi, and Nosappu, and 23 were observed in 31 spotted seals from Erimo, Akkeshi, Nosappu, Rausu, Yagishiri Island, and Hamamasu. Phylogenetic trees showed two harbor seal lineages: Group I contained primarily haplotypes from Erimo, and Group II contained haplotypes from Akkeshi and Nosappu. Because the Erimo population had fewer haplotypes and less nucleotide diversity than the Akkeshi and Nosappu populations, we considered it to be Isolated from the others. In contrast, genetic variance within populations of spotted seals (97.3%) was far higher than that among populations (2.7%), determined by analysis of molecular variance. There were no significant difference among the spotted seal populations, indicating the absence of distinct lineages around Hokkaido. The differences in the genetic population structure between the two species could have been generated by their ecological differences. This study provides basic genetic information on these seal species and will contribute to the conservation and management of fisheries and seals throughout Hokkaido.

Classification of the Seminiferous Epithelial Cycle in the Sika Deer (Cervus nippon)

The sika deer (Cervus nippon) is the only Cervidae inhabiting Japan, except a feral foreign cervid, the Reeves’ muntjac (Muntiacus reevesi). The sika deer is short-day seasonal breeder, and its rut occurs from October to December (Suzuki et al. 1992). When considering the biology of seasonal breeders, it is especially important to elucidate testicular functions during seasonal testicular changes. In the mature testes of the roe deer during the breeding season, the composition of the seminiferous epithelium periodically changes throughout spermatogenesis (Blottner et al. 1996). Many studies on the stages of the epithelial cycle have been reported in experimental and domestic animals (Foote et al. 1972; Swierstra et al. 1974; Berndtson 1977; Ekstedt et al. 1986; Pawar and Wrobel 1991). For example, the seminiferous epithelial cycle is divided into 14 stages in the rat (Leblond and Clermont 1952) and 8 stages in the bull (Wrobel and Schimmel 1989). Information about these stages is essential for morphological and functional researches on the testes and provides the basis of understanding testicular regulatory mechanisms (Toppari et al. 1986; Zhu et al. 1997; Zhou et al. 2002; Schon et al. 2004; Klonisch et al. 2006). In the rat, the morphological changes of the Sertoli cells with each seminiferous epithelial stage are concerned with the control of phosphorylation of the cytoskeletal protein, vimentin (Zhu et al. 1997). In the mouse, androgen receptors in the Sertoli cells show stage-dependent expression with the most intense expression in stages VI–VII (Zhou et al. 2002). Histological studies on postnatal testicular development and seasonal changes of the testes have been reported in the sika deer (Yamauchi et al. 1982). Structural changes of the seminiferous tubules, plasma and fecal testosterone levels and localization of steroidogenic enzymes have already been examined with annual testicular changes of the sika deer (Suzuki et al. 1992; Yamauchi et al. 1997; Kameyama et al. 2002; Hayakawa et al. 2004). However, the stages of the seminiferous epithelial cycle are not yet fully defined in the sika deer, although they have been reported in other cervids, the fallow deer (Wrobel et al. 1993) and roe deer (Schon et al. 2004). In the present study, therefore, we categorized the seminiferous epithelial stages in the sika deer.

Coexistence of two different genotypes of Sarcoptes scabiei derived from companion dogs and wild raccoon dogs in Gifu, Japan: The genetic evidence for transmission between domestic and wild canids

Sarcoptes scabiei is the causal agent of sarcoptic mange in domestic/companion dogs (Canis lupus familiaris) and raccoon dogs (Nyctereutes procyonoides). Although there have been successful cases of experimental transmission of S. scabiei from mangy wild Canidae hosts to healthy dogs, and suspected cases of transmission between raccoon dogs and companion dogs, no clear-cut evidence has been obtained. In the present study, the genetic relationships between Sarcoptes mites from raccoon dogs and companion dogs living in the same region were elucidated.One hundred and thirty Sarcoptes mites from 22 raccoon dogs and 5 companion dogs were collected from the Gifu area in Japan. Using 9 microsatellite markers, the genotypes were compared, and the genetic structure of these mites was analyzed. In 6 pairs of companion dog- and raccoon dog-derived mites, 17 out of the 18 alleles analyzed were identical. Using a Bayesian approach, these 130 mites were separated into at least two groups, and companion dog- and raccoon dog-derived mites were segregated into both groups. In addition, comparatively large numbers of alleles at these loci were revealed by comparison with data from past studies. These results demonstrated that the host specificity at the 9 microsatellite-level could not be confirmed, strongly suggesting the transmission of Sarcoptes mites between raccoon dogs and companion dogs. This is the first report to provide a genetic evidence of Sarcoptes transmission between domestic and wild mammals in the natural environment. The possibility of a prior introduction of mites with novel genotypes (e.g., spillover of sarcoptic mange from domestic/companion dogs to raccoon dogs) could not be eliminated when considering the cause of the large number of alleles, and the coexistence of 2 mite groups in sympatric raccoon dogs and companion dogs in this local area.

Isolation and antimicrobial susceptibility of Plesiomonas shigelloides from great cormorants ( Phalacrocorax carbo hanedae ) in Gifu and Shiga Prefectures, Japan

Plesiomonas shigelloides is a causal agent of gastroenteritis, sepsis and meningitis in humans. We examined the prevalence of P. shigelloides among great cormorants (Phalacrocorax carbo hanedae) in Japan and the antimicrobial susceptibility of isolates. P. shigelloides was isolated from 33 (47.8%) of 69 fecal samples from great cormorants in 2014. All 33 isolates were subjected to antimicrobial susceptibility testing using broth microdilution methods, which showed resistance to ampicillin (31 isolates, 93.9%), tetracycline (two isolates, 6.1%) and trimethoprim (one isolate, 3.0%). The high prevalence of P. shigelloides in the great cormorants implicates the possible microbiological risk to public health.

Accessory corpora lutea formation in pregnant Hokkaido sika deer (Cervus nippon yesoensis) investigated by examination of ovarian dynamics and steroid hormone concentrations

Generally, sika deer conceive a single fetus, but approximately 80% of pregnant females have two corpora lutea (CLs). The function of the accessory CL (ACL) is unknown; moreover, the process of ACL formation is unclear, and understanding this is necessary to know its role. To elucidate the process of ACL formation, the ovarian dynamics of six adult Hokkaido sika deer females were examined ultrasonographically together with peripheral estradiol-17β and progesterone concentrations. ACLs formed in three females that conceived at the first estrus of the breeding season, but not in those females that conceived at the second estrus. After copulation, postconception ovulation of the dominant follicle of the first wave is induced by an increase in estradiol-17β, which leads to formation of an ACL. A relatively low concentration of progesterone after the first estrus of the breeding season is considered to be responsible for the increase in estradiol-17β after copulation.

Evaluation of Stored Body Fat in Nuisance-killed Japanese Black Bears (Ursus thibetanus japonicus)

We evaluated the stored body fat of Japanese black bears (Ursus thibetanus japonicus) killed as nuisances in Gifu and Fukushima prefectures, Japan, during 2005–2007. We employed femur marrow fat (FMF), modified kidney fat index (mKFI), and abdominal subcutaneous fat (ASF) as indices for quantitative evaluation. We examined the basic characteristics of these indices, such as seasonality, age and sex dependency, and the quantitative relationship among them. mKFI and ASF increased towards the beginning of the denning period (December), while FMF was relatively stable throughout the sampling period (July–December). In cubs, all indices showed significantly lower values than in the older age classes. There seemed to be a catabolizing order between FMF and mKFI, but not between mKFI and ASF. We also evaluated the yearly change in the indices, and discussed its relevance to the incidence of bear intrusion into human residential areas. Bears nuisance-killed in summer (July–September) 2006 had a significantly larger amount of stored body fat than those killed in summer 2007, although the number of nuisance kills was larger in 2006 than in 2007. This suggests that poor nutritional condition is not a direct cause of bear intrusion.

Community-Based Wildlife Management: A Case Study of Sika Deer in Japan

The Japanese hunter population is declining, while human–wildlife conflicts (e.g., damage by overabundant sika deer) have become an issue in suburban and rural areas. Beginning in 2004, a community-based deer management program was initiated by a local nongovernmental organization in collaboration with stakeholders in Nishiokoppe Village, Hokkaido, Japan. The goal was to integrate deer management with a contribution to the local economy by attracting visitor hunters and to develop a hunter education program. For the first 3 years, 60 hunters made 136 visits, hunted 337 days, and harvested 280 deer, while 173 persons attended the hands-on hunter education programs that can help recruit younger hunters. The programs generated 191,000 USD during the years, providing employment for several local residents. We suggest that a combination of recreational hunting and hunter education in rural areas can promote community-based wildlife management in a highly developed and high density society where hunting participation is declining.

Molecular identification of the Cryptosporidium deer genotype in the Hokkaido sika deer (Cervus nippon yesoensis) in Hokkaido, Japan

The protozoan Cryptosporidium occurs in a wide range of animal species including many Cervidae species. Fecal samples collected from the Hokkaido sika deer (Cervus nippon yesoensis), a native deer of Hokkaido, in the central, western, and eastern areas of Hokkaido were examined by polymerase chain reaction (PCR) to detect infections with Cryptosporidium and for sequence analyses to reveal the molecular characteristics of the amplified DNA. DNA was extracted from 319 fecal samples and examined with PCR using primers for small-subunit ribosomal RNA (SSU-rRNA), actin, and 70-kDa heat shock protein (HSP70) gene loci. PCR-amplified fragments were sequenced and phylogenetic trees were created. In 319 fecal samples, 25 samples (7.8xa0%) were positive with SSU-rRNA PCR that were identified as the Cryptosporidium deer genotype. Among Cryptosporidium-positive samples, fawns showed higher prevalence (16.1xa0%) than yearlings (6.4xa0%) and adults (4.7xa0%). The result of Fisher’s exact test showed a statistical significance in the prevalence of the Cryptosporidium deer genotype between fawn and other age groups. Sequence analyses with actin and HSP70 gene fragments confirmed the SSU-rRNA result, and there were no sequence diversities observed. The Cryptosporidium deer genotype appears to be the prevalent Cryptosporidium species in the wild sika deer in Hokkaido, Japan.

Estimation of the fertility rates of Japanese wild boars (Sus scrofa leucomystax) using fetuses and corpora albicans

Effective population control of Japanese wild boar (Sus scrofa leucomystax) requires reliable information about population dynamics. Fertility rate is the fundamental component of reproduction to evaluate population dynamics. However, little is known regarding the fertility rate of Japanese wild boar. The traditional hunting practices make it difficult to obtain pregnant females and calculate the fertility rate by checking fetuses as is performed in other countries. Therefore, we focused on the corpora albicans (CA) as the CA remains in the ovaries of postpartum females after pregnancy. This study aimed to evaluate the utility of CA and estimate the fertility rate of Japanese wild boars using CA. Histological analysis of ovaries enabled us to discriminate type 1 CA, which remains for 1xa0year after breeding. Type 1 CA is a superior indicator compared with lactation in the non-pregnancy season because it allows verification of postpartum females over a long period. The fertility rate was calculated by the combination of pregnant and postpartum females using fetuses and type 1 CA from April to November. The fertility rate of the females captured after the second pregnancy season was 90.3xa0% during the pregnancy period and 100xa0% during the non-pregnancy period. The high fertility rate of adult females suggests that intensive adult female harvesting is needed. Our new method to determine fertility rates contributes to developing a monitoring system to adequately control Japanese wild boar population.