Short day induced gonadal regression in ring doves (Streptopelia risoria): a case for seasonal variation

Changes in follicular size (in diameter) were studied by laparotomy under various photoperiodic regimes in the domesticated ring doves that have been kept under standard laboratory conditions for generations. Follicular response shows two distinct patterns: 1. a shift from standard laboratory photoperiodic regime (LD 14:10) to extra long day (LD 20:4) accelerated the follicular development in the spring as well as in the autumn; 2. a shift from the standard laboratory photoperiodic regime (LD 14:10) to short day (LD 8:16 or LD 1/2:23 1/2) induced follicular regressions in the autumn but not in the spring. We propose that there is a responsive phase (spring) and nonresponsive phase (autumn) of hypothalamo-hypophyseal-ovarian system in the ring doves. Comparison of radioimmunoassay of pituitary and plasma LH value suggests that the responsive and non-responsive phase involves mainly release mechanisms. In the autumn, the release mechanism becomes insensitive to stimuli below certain thresholds. Our ring doves are kept in responsive phase throughout the year under the long photoperiodicity (LD 14:10). However, the effect of long day does not appear to override completely the seasonal effect.