Effect of Fixed Daylengths on the Photoperiodic Regulation of Gametogenesis in the Sea UrchinStrongylocentrotus purpuratus

Abstract

The gametogenic response of the sea urchin Strongylocentrotus purpuratus was compared under treatments of different photoperiod regimes of fixed and seasonal changing daylength. Quantification of gametogenic activity in en- zymatically dissagregated ovaries and in histological sections of testes have shown that the sea urchin is sensitive to both fixed and variable daylengths. After one year at fixed short day (8L:16D) or fixed neutral day (12L:12D) the gonads were ripe and in active gametogenesis, the same as were gonads of animals reared at changing photoperiod and sampled during the short-day phase of the cycle. Under fixed long day (16L:8D) the gonads lacked significant amount of gametes and had the cell constitution found in gonads of animals reared at changing photoperiod and sampled during the long-day phase of the cycle. Measurement of a critical daylength related to the autumnal equinox seems to be part of the mechanism in the photoperiodic regulation of vitellogenic oocyte growth and spermatogenesis in these animals.