Annual variations and sex-related differences of estradiol-17beta levels in the anthozoan Renilla koellikeri.

In the sea pansy Renilla koellikeri, estradiol-17beta (E(2)) levels exhibited an annual pattern of secretion that correlated with the reproductive cycle, and displayed sex-specific and tissue-specific differences. The E(2) levels were low during the non-reproductive period extending from autumn to winter. A first rise of E(2) concentrations occurred in March when gonad maturation resumed, as indicated by an increase in lipid storage. This suggests that E(2) may influence the beginning of gonad maturation in the sea pansy. Estradiol-17beta returned to basal levels in April and May when lipids rose sharply. A second, more significant surge of E(2) levels occurred in June when spawning was initiated and it was more marked in female than in male colonies. This suggests that E(2) may participate in synchronising of oocyte maturation around spawning time to optimise the probability of fertilisation. The higher E(2) levels in somatic tissues (peduncle and polyps) than in eggs during the March peak revealed a non-reproductive origin for E(2) and the need for transport of E(2) through the gastrovascular cavity to reach reproductive tissues. Further analyses are required to determine the relative contribution of E(2) to reproductive events and its pathway of synthesis in this colonial anthozoan.