Meeting Abstract

P1.88  Saturday, Jan. 4 15:30  A generalized mechanical model of effects of salinity on blastula expansion VON DASSOW, M; Duke University Marine Laboratory mvondass@gmail.com

The physical mechanisms that drive morphogenetic shape changes could influence how organisms respond to environmental variation. The formation of the blastocoel (a cavity inside the embryo) in echinoderm embryos provides a good test case both because of its simple geometry and direct relation to dispersal ability. Planktotrophic echinoderm embryos form hollow spherical blastulae which swim in the plankton. The size of the blastula and the blastocoel-to-cell-layer volume ratio might influence swimming ability after hatching. Different mechanisms could drive expansion of the blastocoel in different taxa. Here I use a generalized mathematical model to investigate how combinations of expansion mechanisms would interact with salinity variation (which alters cell size) to alter embryo proportions. The model is based balancing forces after a differential change in cell size. It allows one to investigate responses to cell swelling given differing mechanical contributions of the cell layer, the apical extracellular matrix, and the blastocoel. This model predicts that if cell packing geometry determines blastula size, the blastocoel will expand with the cells as salinity drops. However, the model predicts that if the balance between internal pressure and elastic resistance to expansion determines blastocoel size, the blastocoel will shrink as cells swell. How these relations are altered depending on the nature of the resistance to blastula expansion (whether elastic, viscous, or plastic) will be discussed. This model indicates that mechanisms that drive expansion and mechanisms that resist expansion should be equally important in determining sensitivity to salinity.