Shear stress experienced by echinoderm eggs in the oviduct during spawning: Potential role in the evolution of egg properties

Shear stresses experienced by eggs in the oviduct of the echinoid Arbacia p unctulata during spawning were calculated using engineering equations that describe laminar how through pipes. Shear stresses in the oviduct ranged fr om 0 to 58.7 Pa. Two properties of eggs were identified that ha have the po tential either to minimize the shear stress in the oviduct or to reduce the damage experienced by eggs exposed to high shear stress. These properties are the viscosity of the eggs and the presence of extracellular layers on e ggs of A. punctulata. The viscosity of eggs decreases with increasing shear rates, which reduces the magnitude of shear stress experienced in the ovid uct, while the extracellular layers mitigate the effect of shear stress on the eggs. Eggs with intact extracellular layers mere damaged less frequentl y than were those with the extracellular layers removed. The results of thi s research indicate that physical stresses may be important selective facto rs in the evolution of gamete properties.