キタオットセイにおけるテストステロンの非侵襲的な測定手法の開発

• 資料種別: 博士論文
• タイトル: キタオットセイにおけるテストステロンの非侵襲的な測定手法の開発
• 著者・編者: 大槻, 真友子
• 著者標目: 大槻, 真友子
• 出版事項: Hokkaido University
• 出版年月日等: 2019-09-25
• 出版年（W3CDTF）: 2019-09-25
• 並列タイトル等: Development of non-invasive techniques to measure testosterone in the northern fur seal (Callorhinus ursinus)
• 寄与者: 三谷, 曜子; 宮下, 和士; 山羽, 悦郎; 井尻, 成保
• 授与機関名: 北海道大学; Hokkaido University
• 授与年月日: 2019-09-25
• 授与年月日（W3CDTF）: 2019-09-25
• 報告番号: 甲第13744号
• 学位: 博士(環境科学)
• 本文の言語コード: eng
• NDC: 468
• 対象利用者: 一般
• 一般注記: 出版タイプ： VoR; (主査) 准教授 三谷 曜子, 教授 宮下 和士, 教授 山羽 悦郎, 准教授 井尻 成保（大学院水産科学研究院）; 環境科学院（生物圏科学専攻）
• DOI: 10.14943/doctoral.k13744; https://doi.org/10.14943/doctoral.k13744
• 国立国会図書館永続的識別子: info:ndljp/pid/14550342; https://dl.ndl.go.jp/pid/14550342
• コレクション（個別）: 国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文; https://dl.ndl.go.jp/collections/A00014
• 収集根拠: 博士論文（自動収集）
• 受理日（W3CDTF）: 2025-11-07T22:06:00+09:00
• 記録形式（IMT）: application/pdf
• オンライン閲覧公開範囲: 国立国会図書館内限定公開
• デジタル化資料送信: 図書館・個人送信対象外
• 遠隔複写可否（NDL）: 可
• 掲載誌（URI）: https://doi.org/10.14943/doctoral.k13744; http://hdl.handle.net/2115/93134
• 参照（URI）: http://hdl.handle.net/2115/76075
• 連携機関・データベース: 国立国会図書館 : 国立国会図書館デジタルコレクション; https://dl.ndl.go.jp

• 要約等: The reproductive physiology of wildlife can provide useful insights into population dynamics. Information about the physiological state of animals is generally collected through blood sampling, which involves capture and anaesthesia of animals. In the past few decades, however, non-invasive techniques of endocrine monitoring have been developed to study the reproductive status of animals using indicators such as faeces and hair. The least invasive method examines faeces, since faecal collection does not require physical contact with animals. As a result, faecal hormones are now commonly studied in captive animals. An advantage of hair sampling is that hair can be biopsied in the wild. In the present study, I used faeces and hair in place of blood to study the reproductive status of the northern fur seal (Callorhinus ursinus) males.The sexually dimorphic northern fur seal congregates in rookeries during the breeding season in summer, and occurs in offshore waters without hauling out during the non-breeding season in winter. Males become sexually mature at age 4, but usually become capable of establishing breeding territories (i.e., socially mature) at age 8. Socially mature males return to their rookeries to establish territories before the breeding season, while juvenilesremain offshore during the breeding season. Spatial segregation of males occurs during the non-breeding season off southern Hokkaido in the Sea of Japan where they have been increasingly plundering fish from fishing gear. Since demographic information about males can help evaluate the impact of this plundering, development of a maturity-assessment method for free-ranging seals using non-invasive techniques could enhance our understanding of males in this community. The objective of this study was to measure testosterone in male northern fur seals using non-invasive techniques and to determine the sexual maturityof free-ranging seals during the non-breeding season.In Chapter 2, I examined the relationships between serum testosterone and faecal testosterone metabolites in a captive seal to develop non-invasive monitoring of faecal testosterone metabolite levels. I found a significant relationship between the faecal testosterone metabolites and serum testosterone levels when the faeces were collected approximately one day after blood withdrawal. In addition, the seasonal changes in faecal testosterone metabolites showed similar trends with serum testosterone levels, showing higher testosterone levels during the breeding season. These results indicate that serum testosterone levels can be estimated using faecal testosterone metabolites. This method will be a useful tool to non-invasively monitor the reproductive cycles of male northern fur seals. iiIn Chapter 3, I compared the concentrations of faecal testosterone metabolites with age, sampling months and testis weight of free-ranging northern fur seals to evaluate their sexual maturity. Forty-five males were collected in 2011–2017 in waters off Hokkaido. The testis weight and age of the fur seals showed a significant positive relationship although no monthly differences were obtained between mature and socially mature seals. Significant differences in monthly faecal testosterone metabolites between mature and socially mature seals were obtained only in April. Furthermore, the individual differences in the faecal testosterone metabolite levels in mature and socially mature animals were large, possibly because environmental cues such as prey availability and energetic demands can differ among individuals and differently affect endocrine systems. My results also indicate that faeces are a more useful tool in captivity since factors in the captive environment such as photoperiod and prey are often controlled so that faecal steroid metabolites likely are comparable in captive conditions.Hair is another endocrine matrix that can assess the reproductive status of animals non-invasively. However, it is unknown if hair samples can assess pinniped reproductive status. In Chapter 4, I examined the sexual maturity of males during the non-breeding season off Hokkaido using hair testosterone levels. A total of 57 hair samples were collected from males during the non-breeding seasons of 2011–2018. The testosterone levels of juveniles were significantly lower than those of mature seals. Elongated spermatids, which occur in the final phase of spermatogenesis, were present in seals collectedbetween April and June. Seals collected in May, during the spermatogenesis progresses, showed the highest testosterone levels. Myresults demonstrate that juvenile males can be distinguished from mature males using hair testosterone levels in May preceding the breeding season. In conclusion, non-invasive techniques to assess the reproductive status of northern fur seal males were developed. In captivity, faecal testosterone metabolites were a useful tool to evaluate the status during the breeding season, whereas hair was an invaluable tool to determine the maturity of free-ranging seals. An advantage of these methodologies is that they do not disturb the animals before sampling. Furthermore, data on male reproductive status can enhance our understanding offur seal ecology, such as the distribution of the seals off Hokkaido during the non-breeding season, and clarify the connection between non-breeding and breeding seasons. This method can be applied in various pinnipeds and will be especially useful for species that spend time offshore, since hair can be biopsied in the wild.
• DOI: 10.14943/doctoral.k13744; https://doi.org/10.14943/doctoral.k13744
• 記録形式（IMT）: application/pdf
• 一次資料へのリンクURL: Mayuko_OTSUKI.pdf （fulltext）; https://eprints.lib.hokudai.ac.jp/repo/huscap/all/93134/Mayuko_OTSUKI.pdf
• オンライン閲覧公開範囲: インターネット公開
• 参照（URI）: HDL; https://hdl.handle.net/2115/76075
• 連携機関・データベース: 国立情報学研究所 : 学術機関リポジトリデータベース（IRDB）（機関リポジトリ）; https://irdb.nii.ac.jp
• 提供元機関・データベース: 北海道大学 : 北海道大学学術成果コレクション