Summer and winter cycles in plasma melatonin levels in the elephant seal (Mirounga Leonina)

• Published in: Australian Journal of Biological Sciences
• Main Authors: Griffiths, D., Bryden, M. M., Seamark, R. F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: CSIRO Publishing 1979
• Subjects: Biotechnology; Developmental Biology; Animal Science and Zoology; General Materials Science; Genetics; Molecular Biology; Endocrinology; Reproductive Medicine; General Medicine; 2700 Medicine; Midwinter; Elephant Seal; Elephant Seals; Mirounga leonina
• Online Access: https://espace.library.uq.edu.au/view/UQ:ba241f9

Plasma melatonin concentration of immature male elephant seals was determined by radioimmunoassay. Comparison of concentrations during two 24-h periods, one in midsummer and one in midwinter, showed that there was a marked circadian cycle in winter which was greatly modified during the long day length of summer. It is suggested that in summer there was sufficient ambient lighting during the night hours to depress the nocturnal rise in plasma melatonin. The complexity of pineal cycles in the natural environment is stressed, and in this regard the polar regions are of particular interest due to the extreme seasonal changes in day length there.