Bioscientifica Proceedings

Circannual clocks drive rhythms in reproduction and many other seasonal characteristics but the underlying control of these long-term oscillators remains a mystery. Now, we propose that circannual timing involves mechanisms that are integral to the ontogenetic life-history programme where annual transitions are generated by cell birth, death and tissue regeneration throughout the life cycle ߝ the histogenesis hypothesis. The intrinsic cycle is then timed by cues...

Summary. In the ram, changes in daylength influence testicular activity by modifying the release of luteinizing hormone-releasing hormone (LH-RH) and thus the gonadotrophins. To investigate the nature of this response the hourly fluctuations in the circulating levels of prolactin, luteinizing hormone (LH) and melatonin were measured in rams kept under various artificial lighting conditions.In Exp. 1, 8 Soay rams (4 control and 4 from whi...