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Kohyama K, Inoshima Y, Kiyota M. Fluctuations in serum steroid hormone concentrations and body mass during growth and sexual maturation in captive northern fur seals (Callorhinus ursinus). J Vet Med Sci 2021; 84:171-180. [PMID: 34866092 PMCID: PMC8810328 DOI: 10.1292/jvms.21-0330] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Northern fur seals (Callorhinus ursinus) have a distinct life history pattern comprising annual terrestrial breeding and oceanic migration, and the physiological changes
associated with these patterns are of particular interest for understanding their environmental adaptations. However, owing to their oceanic distribution, limited information is available on
the reproductive physiology of wild individuals during the immature stage and the winter migration period. This study aimed to determine the relationships among the seasonal hormone
profiles, body growth, age, and pregnancy using monthly serum samples collected over 3–5 years from two male and two female captive individuals during pubescence and sexual maturation. Small
increases in the serum testosterone signaled puberty in males aged 3 and 4 years. Thereafter, males showed considerable increases in testosterone during breeding seasons, indicating sexual
maturity. Immature female serum progesterone was maintained at low levels, but after pubescence, females showed an increase in serum progesterone in August, the month next to the peak of
delivery, followed by a decrease. In non-pregnant females, progesterone did not increase significantly until the next breeding season, but in pregnant females, they increased again from
February to March and then gradually decreased. Immature males increased body mass constantly and reached puberty when their body mass exceeded 20 kg, and they showed seasonal weight
fluctuations after puberty. These results provide fundamental information for determining sexual maturity and pregnancy in this species based on sex steroid hormones and body mass
measurements.
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Affiliation(s)
| | - Yasuo Inoshima
- Cooperative Department of Veterinary Medicine, Gifu University.,The United Graduate School of Veterinary Sciences, Gifu University.,Education and Research Center for Food Animal Health, Gifu University (GeFAH).,Joint Graduate School of Veterinary Sciences, Gifu University
| | - Masashi Kiyota
- Graduate School of Fisheries and Environmental Sciences, Nagasaki University
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Sexual segregation in juvenile Antarctic fur seals. Oecologia 2021; 197:339-352. [PMID: 34309704 DOI: 10.1007/s00442-021-04983-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2021] [Accepted: 06/28/2021] [Indexed: 10/20/2022]
Abstract
Sexual segregation, the differential space, habitat or resource use by males and females, can have profound implications for conservation, as one sex may be more vulnerable to environmental and anthropogenic stressors. The drivers of sexual segregation, such as sex differences in body size, breeding constraints, and social behaviour, have been well studied in adults but are poorly understood in immature animals. To determine whether sexual segregation occurs in juvenile Antarctic fur seals, Arctocephalus gazella, and investigate the underlying drivers, we deployed Global Location Sensors on 26 males and 19 females of 1-3 years of age at Bird Island, South Georgia. Sexual segregation occurred in foraging distribution, primarily in latitude, with females foraging closer to South Georgia and the Polar Front, and males foraging further south near the Antarctic Peninsula. This segregation was particularly evident in Feb-Apr and May-Nov, and males spent more time hauled out than females in May-Nov. Although juveniles have no immediate reproductive commitments, reproductive selection pressures are still likely to operate and drive sex differences in body size, risk-taking, and social roles. These factors, coupled with prey distribution, likely contributed to sexual segregation in juvenile Antarctic fur seals. Consequently, male and female juveniles may compete with different fisheries and respond differently to environmental change, highlighting the importance of considering sex and age groups in species conservation efforts.
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Nagel R, Mews S, Adam T, Stainfield C, Fox-Clarke C, Toscani C, Langrock R, Forcada J, Hoffman JI. Movement patterns and activity levels are shaped by the neonatal environment in Antarctic fur seal pups. Sci Rep 2021; 11:14323. [PMID: 34253749 PMCID: PMC8275608 DOI: 10.1038/s41598-021-93253-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Accepted: 06/04/2021] [Indexed: 02/06/2023] Open
Abstract
Tracking studies of juveniles are rare compared to those of adults, and consequently little is known about the influence of intrinsic and extrinsic factors on activity during this critical life stage. We used hourly GPS data, collected from 66 Antarctic fur seal pups from birth until moulting, to investigate the explanatory power of multiple individual-based and environmental variables on activity levels. Pups were sampled from two nearby breeding colonies of contrasting density during two subsequent years, and a two-state hidden Markov model was used to identify modalities in their movement behaviour, specifically 'active' and 'inactive' states. We found that movement was typified by central place exploration, with active movement away from and subsequent return to a location of inactivity. The probability of such directed exploration was unaffected by several factors known to influence marine mammal movement including sex, body condition, and temperature. Compared to pups born at the high-density colony, pups at low-density were more active, increased their activity with age, and transitioned earlier into the tussock grass, which offers protection from predators and extreme weather. Our study illustrates the importance of extrinsic factors, such as colony of birth, to early-life activity patterns and highlights the adaptive potential of movement.
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Affiliation(s)
- Rebecca Nagel
- grid.7491.b0000 0001 0944 9128Department of Animal Behaviour, Bielefeld University, 33501 Bielefeld, Germany
| | - Sina Mews
- grid.7491.b0000 0001 0944 9128Department of Business Administration and Economics, Bielefeld University, 33501 Bielefeld, Germany
| | - Timo Adam
- grid.7491.b0000 0001 0944 9128Department of Business Administration and Economics, Bielefeld University, 33501 Bielefeld, Germany ,grid.11914.3c0000 0001 0721 1626Centre for Research into Ecological and Environmental Modelling, School of Mathematics and Statistics, The Observatory, Buchanan Gardens, University of St Andrews, St Andrews, KY16 9LZ UK
| | - Claire Stainfield
- grid.478592.50000 0004 0598 3800British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 OET UK
| | - Cameron Fox-Clarke
- grid.478592.50000 0004 0598 3800British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 OET UK
| | - Camille Toscani
- grid.478592.50000 0004 0598 3800British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 OET UK
| | - Roland Langrock
- grid.7491.b0000 0001 0944 9128Department of Business Administration and Economics, Bielefeld University, 33501 Bielefeld, Germany
| | - Jaume Forcada
- grid.478592.50000 0004 0598 3800British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 OET UK
| | - Joseph I. Hoffman
- grid.7491.b0000 0001 0944 9128Department of Animal Behaviour, Bielefeld University, 33501 Bielefeld, Germany ,grid.478592.50000 0004 0598 3800British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 OET UK
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