Circadian rhythms of oviposition and feeding activity in Japanese quail: effects of cyclic administration of melatonin.

The aim of these experiments was to test the effect of a cyclic administration of melatonin, by mimicking the daily rhythm of hormone levels, on the circadian organization of two distinct functions in quail: oviposition and feeding activity. Laying and feeding rhythms under photoperiodic conditions and constant darkness (DD) were investigated. Under DD, where the two rhythms were free running, a daily rhythm of melatonin was administered. In LD 14 h:10 h, two different individual profiles of laying were established, with stable females laying at the same time each day and delayed females laying progressively later each day. For feeding activity, all birds were clearly synchronized to the photoperiodic cycle. In DD, the laying birds showed a free-running rhythm of oviposition with a period longer than 24 h for both profiles but the delayed profile females had a longer period than stable profile females. In comparison, the free-running period of feeding rhythm of the same birds was shorter than 24 h. A cyclic administration of melatonin had no effect on laying rhythm, which continued to free-run in DD, whereas feeding activity was synchronized as soon as the first cycle of melatonin was administered. From these results, it seems that two different circadian systems drive each of the two types of behavior separately. Melatonin could be the main synchronizer for the temporal control of feeding behavior, but it does not play a part in the control of oviposition in Japanese quail.