(full paper is archived in the Miller Library)
Title: Adaptive membrane fluidity in the intertidal snail Littorina keenae
Student Author(s): Rais, Amber
Faculty Advisor(s): Somero, George
Location: Final papers Biology 175H
Date: June 2002
Abstract: Many poikilotherms exhibit adaptive changes in cellular membrane fluidity (homeoviscous adaptation) to counter potentially disruptive effects of thermal variation in their environments. The process of homeoviscous adaptation was studied in an intertidal snail, Littorina keenae, which encounters wide variation in body temperature due to differences in microhabitat conditions and the effects of tidal rhythms. This study investigated the effects of thermal variation arising from microhabitat differences between two geographic sites and from tidal cycle effects within a single site on membrane fluidity. L. keenae, a species widespread along the North American Pacific Coast, was studied at two sites on Cabrillo Point at Hopkins Marine Station in Central California, one being wind and wave exposed (exposed site), the other relatively protected by its cove-like orientation (protected site). Protected site individuals exhibited body temperature fluctuations as great as 20°C within a six-hour period (10 to 30°C), whereas the exposed population exhibited only a 10°C range in the most extreme case (10 to 20°C). Fluidities of membranes of gill and mantle tissue were quantified by measuring fluorescence anisotropy using the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Samples from the exposed site population collected prior to and following midday low tide exhibited no differences in membrane viscosity. However, in one instance exposed individuals collected at the same time showed two distinct levels of membrane fluidity, suggesting disparate thermal histories. In addition, comparisons with previously published data on membrane fluidity for other species may indicate that L. keenae is compensating toward its upper thermal range.