ZIVKOVIC, B.D.*; STEELE, C.T.; UNDERWOOD, H.; SIOPES, T.: Critical photoperiod and reproduction in female Japanese quail: Role of the eyes and pineal
A previous study showed that removal of the eyes did not alter the stimulatory effect of a long (e.g., LD 14:10) photoperiod on the reproductive response of female Japanese quail. The reproductive response to long photoperiods in the blind quail was mediated by extraretinal photoreceptors. The current study was designed to test the role of the eyes and pineal in the reproductive response to photoperiods near the "critical" photoperiod; that is, the minimum photoperiod required to drive the reproductive response. In the first experiment, birds blinded by eye removal (EX) held in LD 12:12 had a rapid onset of egg-laying while the intact controls did not exhibit egg-laying for up to 110 days. However, EX birds responded to a shortening of the photoperiod by ceasing to lay indicating that they remained photoperiodic. In the second experiment, groups of birds (intact, EX, pinealectomized, EX+pinealectomized, and optic-nerve-sectioned) were exposed to incremental increases of photoperiod by 15 minutes every 10 days, beginning with LD 10:14. Various criteria were assessed to measure the reproductive response including rate of response time to: onset of lay, 50% lay and maximum lay. Optic-nerve-sectioned birds consistently required the shortest photoperiods, while pinealectomized birds consistently required the longest photoperiods, for all criteria. For some of the criteria EX birds required shorter photoperiods than intact quail. The data indicated that the eyes are involved in measurement of critical photoperiod and that interrupting the neural output (optic-nerve-section birds) had a different effect than removal of both hormonal (melatonin?) and neural outputs (EX birds).