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Testosterone levels in hair of free-ranging male northern fur seals (Callorhinus ursinus) in relation to sampling month, age class and spermatogenesis

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Title: Testosterone levels in hair of free-ranging male northern fur seals (Callorhinus ursinus) in relation to sampling month, age class and spermatogenesis
Authors: Otsuki, Mayuko Browse this author
Horimoto, Takanori Browse this author
Kobayashi, Motoki Browse this author
Morita, Yuka Browse this author
Ijiri, Shigeho Browse this author →KAKEN DB
Mitani, Yoko Browse this author →KAKEN DB
Keywords: Gas chromatography-flame ionization detection
northern fur seal
reproductive status
steroid hormones
time-resolved fluoroimmunoassay
Issue Date: 17-May-2021
Publisher: Oxford University Press
Journal Title: Conservation Physiology
Volume: 9
Start Page: 1
End Page: 11
Publisher DOI: 10.1093/conphys/coab031
Abstract: Information about the reproductive status of free-ranging pinnipeds provides useful insight into their population dynamics, which is essential to their management and conservation. To determine the reproductive status of individual animals, blood sampling is often required despite being impractical to collect in open water. Hair as an endocrine marker has been used to less invasively assess the reproductive status of terrestrial animals. However, it is unknown whether pinniped reproductive status can be assessed from hair samples. Here, we examine testosterone levels in hair obtained from 57 male northern fur seals and used it to compare their age class and spermatogenesis during the non-breeding season off Hokkaido. We isolated testosterone from the samples using gas chromatography and measured testosterone levels using time-resolved fluoroimmunoassay. Testosterone levels in hair increased towards the breeding season. In May, testosterone levels were the highest in seals aged between 4 and 7 years, followed by those over the age of 8 years and under the age of 4 years. Spermatids, the final phase of spermatogenesis, werepresent inthe seals sampled between April and June, eventhough testosterone levels were lowin April. The seals with spermatids in May showed the highest testosterone levels. Our results demonstrate that seals with higher testosterone levels in May are likely to be mature males (>= 4 years). Since hair can be collected using biopsy darts in the field, it will be possible to less invasively determine testosterone levels of male seals in the future.
Type: article
Appears in Collections:北方生物圏フィールド科学センター (Field Science Center for Northern Biosphere) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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