Effect of extended photoperiod on the spermatogenic activity of chicken-pheasant hybrids.

1. Males of chicken-pheasant hybrids and non-breeding pheasants were exposed to photoperiods of 10 or 20 h/d to test the effect of light on spermatogenic activity. 2. Testicular weights of hybrids and pheasants exposed to 10 h/d were similar and extending the photoperiod did not increase this in hybrids, although it caused a 48-fold increase, and complete recovery of spermatogenic activity, in pheasant. 3. Extending the photoperiod caused an increase in the number of primary spermatocytes and a corresponding decrease in the number of spermatogonia in hybrids, however, stages beyond primary spermatocytes were not present. This suggests that the stimulus of extending the photoperiod, while sufficient to induce meiosis in existing germ cells, is not enough to effect proliferative bursts or to overcome the meiotic arrest in the hybrids.