CUNNINGHAM, Adele*; WATTS, Stephen A.; University of Alabama at Birmingham: Do oocytes of the sea urchin Lytechinus variegatus compete for nutrients?

Adult Lytechinus variegatus were collected over a period of 28 months (three reproductive seasons; n= ~ 16 urchins per month) and H&E slides were made from gonad sections. Histology indicates that oocytes develop asynchronously over a period of months before major spring and minor summer spawns. However, some oocytes are apparently reabsorbed by somatic cells of the gonad, the nutritive phagocytes. Failure to discriminate different stages for phagocytosis would result in a sterile gonad; therefore, some system by which nutritive phagocytes recognize different stages of oocyte development has been hypothesized. Recent work on endocytosis by oocytes indicates that endocytosis increases greatly at about 50 mu:μm. Other studies on acid phosphatase activity of oocytes indicate oocytes sometimes become autocatalytic. Which oocytes will mature and which will be reabsorbed? Do oocytes compete for nutrients? Competition may explain how nutritive phagocytes selectively reabsorb some oocytes. Histology of L. variegatus further indicates that some spawning events, especially summer spawns, are relatively minor and occur with many immature oocytes present in the gonad. Inadequate nutrient allocation to the gonad at high summer temperatures may limit the number of oocytes that can reach maturity synchronously. Supported by the Mississippi Alabama Sea Grant Consortium.