9306123 Wallace Fundulus heteroclitus females ovulate and spawn in their natural habitat with a semilunar periodicity coincident with spring tides for up to eight months of the year; they also spawn with a semilunar periodicity under constant, controlled laboratory conditions at any time during the year. Highly elevated levels of circulating estradiol-17 Beta (E2)are associated with each spawning episode. A biological clock for reproductive activity, and involving cyclic E2-release by the ovary, thus appears to exist in this abundant and experimentally convenient teleost. In order to appreciate the operant factors in the reproductive cycling of F. heteroclitus, various aspects of reproductive activity will be monitored by Dr. Wallace over several spawning episodes. These include vitellogenin and gonadotropin levels in the bloodstream and biogenic amine levels in the hypothalamus. If vitellogenin and gonadotropin levels are found to fluctuate, corresponding mRNA levels will be measured in the liver and pituitary, respectively. The manner by which gonadotropins regulate aromatase activity in prematurational follicles (the source of elevated E2 levels) will also be addressed together with the competence of follicles to respond to relevant hormones at various times during the cycle. The effect of E2 on cyclic spawning will be experimentally investigated by administering E2 at various times during the spawning cycle. Other drugs will also be provided in order to explore cause and effect relationships in the hypothalamic- pituitary-gonadal axis. Finally, a series of observations will be made on egg hatching patterns and locomotor activity. Semilunar patterns in such processes, if convincingly demonstrated, would indicate that F. heteroclitus has a genetically determined, biological clock that regulates its overall physiology. ***
