PHOTOPERIODIC CONTROL OF THE TERMINATION OF REPRODUCTION IN JAPANESE-QUAIL (COTURNIX-COTURNIX-JAPONICA)

Typically, birds come into breeding in the spring as a response to long days, and end reproduction some weeks later by becoming refractory to those long days. The refractory state is subsequently dissipated by the short days of autumn and winter, so producing once again a bird that can respond to long days. Bird species differ in the extent to which refractoriness is developed; the present experiments took advantage of the relative, rather than the absolute, refractoriness in quail to measure quantitatively the dissipation process. Quail were made refractory by exposure to long days, then transferred to short days and at various times thereafter photostimulated with longer daylengths, the degree of photoresponsiveness being assessed by measuring changes in luteinizing hormone (LH) secretion or cloacal gland size or both. The most clearcut results came from using 13L:11D as the test stimulus to measure photoresponsiveness, and this indicated, in both intact and castrated quail, no response to 13L:11D after one week one short days, a minor response after two weeks, a strong response after three weeks and a full response after five weeks. Thus refractoriness appears to be dissipated gradually under short days, and not in an all-or-none fashion. Confirmation of this conclusion came from experiments in which refractory quail were moved to short days and after one or two weeks transferred to a range of long daylengths. After one week of short days no responses were obtained to 13L:11 D or 14L:10D and moderate responses only to 16L:8D, but after two weeks of short days the magnitudes of all the responses were increased. Other experiments showed that the depth of refractoriness (as assessed by transferring to short days and then to 13L:11D) was dependent upon the previous duration of exposure to long days and to length of that long day. Finally, the development of refractoriness over a three month period on long days was also investigated.