| Abstract #452, Date 2/16/99, Session N, Podium , 8:45a |
| Increased production of statoconia in the statocyst of pond snails reared in microgravity |
| *M.L. Wiederhold, J.L. Harrison, C.A. Ortiz (Univ. Texas Hlth. Sci. Ctr. San Antonio) |
Previous studies in the marine mollusk, Aplysia californica, demonstrated that statoconia production was reduced, in a graded manner, with increasing g in embryos and larvae reared on a centrifuge. Here we have tested the hypothesis that a larger mass of statoconia would be produced in the statocysts of mollusks reared in microgravity. Adult pond snails (Biomphalaria glabrata) were maintained in the Closed Equilibrated Biological Aquatic System (CEBAS) on Space Shuttle flights STS-89 (9-day flight) and STS-90 (16-day flight, Neurolab). These snails are hermaphroditic, so each animal will lay a spawn pack, containing 20 - 30 eggs, almost every day. Statoconia are first formed 4 days after spawning and the young hatch at about one week. Thus, functional statocysts can be formed in snails conceived and developed during either the 9- or 16-day flight. Several hundred young snails were retrieved from both the flight and ground-control units in both flights. The average total volume of statoconia in 1-mm snails retrieved from the flight unit on STS-89 was 30% larger than in animals of the same size reared in the ground-control unit. For 2-mm snails, the total volume was 50% larger in the flight-reared animals. In STS-90, for 1.5-mm snails retrieved on landing day, total statoconial volume was 23% larger than ground controls, while for 1.5-mm snails 5 days post landing, the difference was 34%. For 2-mm snails from STS-90 on landing day, the total volume for flight-reared snails was 5% less, whereas 5 days post landing, the flight-reared animals had statoconial volume 38% larger than ground-control specimens. The volumes of individual statoconia were estimated from their profile when collected on a filter, after digesting the soft tissue with bleach. The distribution of statoconia sizes was indistinguishable between flight- and ground-reared snails of 1, 1.5 and 2.0 mm diameters, with the total number of statoconia being approximately 50% greater in the flight-reared animals. Thus, the increase in total volume of statoconia produced in microgravity is due to an increased production of statoconia of the same size as in ground controls, without an increase in the size of individual stones. |