Meeting Abstract

P2.102  Sunday, Jan. 5 15:30  Salinity variation and the mechanics of echinoderm gastrulation WONG, J. *; VON DASSOW, M.; Willamette University; Duke University Marine Lab jwong@willamette.edu

We seek to understand how the physics of morphogenesis modulates environmental effects on development. Here we ask how salinity affects the sensitivity of sand dollar (Dendraster excentricus) embryos to inducers of exogastrulation, a defect in which the archenteron evaginates rather than invaginates. Salinity variation is common in near-shore marine environments and has a clear physical effect: swelling or shrinking cells. We hypothesized that if the apical extracellular matrix resists cell swelling, the pressure inside the embryo will rise, promoting archenteron evagination. However, if the blastocoel matrix resists embryo expansion, the pressure will drop, promoting invagination. If neither the blastocoel nor apical matrix resists embryo expansion, the internal pressure will not change, so salinity should not affect sensitivity to exogastrulation. Exogastrulation can be induced by many treatments. We used low calcium (10% of normal) artificial seawater as an inducer because it is non-toxic. We compared its effects in normal (32 ppt) and low (25 ppt) salinity, a range that Dendraster embryos can experience in nature. Preliminary observations indicate that low salinity alone did not cause exogastrulation, but low salinity made embryos more sensitive to exogastrulation induced by low calcium treatment. The similarity of blastocoel to cell volume ratio among treatments, combined with gross similarity in blastula shapes, suggests that the internal pressure did not change greatly. While further quantitative analysis is necessary, this appears inconsistent with our predictions, tentatively suggesting that effects of salinity on exogastrulation are not due primarily to internal pressure changes.