Photoperiodic regulation of gametogenesis and growth in the sea urchin Strongylocentrotus purpuratus

Abstract

AbstractOur experiments demonstrate that both gametogenesis and growth in the sea urchin Strongylocentrotus purpuratus are under photoperiodic control. Juvenile sea urchins (4–8 mm diameter) were collected in September 1979 and reared for 18 months under two photoperiodic regimes with changing daylengths as in the natural annual cycle. One regime followed inphase (ambient) photoperiods; the other was kept 6 months out of phase with ambient photoperiods. In March of both 1980 and 1981 most of the in‐phase animals (like field animals) contained numerous gametes while the out‐of‐phase animals contained very few gametes. DNA synthesis (estimated by autoradiography with tritiated thymidine) was high in the in‐phase males and low in the out‐of‐phase males. In September of 1980, the situation was reversed. In animals exposed to two successive “winter” photoperiod regimes, gamete production continued for 6 months; in those exposed to two successive “summers,” there was little gamete production. These experiments suggest that either long days inhibit gametogenesis or short days enhance it. The normal peak of body growth in the summer and fall was also shifted 6 months out of phase in animals kept on the out‐of‐phase photoperiod regime; this shift was reflected in size, in weight, and in the growth zones of the skeletal plates. Feeding rates did not differ between animals on the two photoperiod regimes, suggesting that photoperiod does not influence energy intake but rather determines whether energy is allocated to body and gonad growth or to gametogenesis and gamete maintenance.