No evidence for homeoviscous adaptation in intertidal snails: analysis of membrane fluidity during thermal acclimation, thermal acclimatization, and across thermal microhabitats |
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Authors: | Amber Rais Nathan Miller Jonathon H Stillman |
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Institution: | (1) Hopkins Marine Station, Stanford University, Oceanview Blvd., Pacific Grove, CA 93950, USA;(2) Romberg Tiburon Center, San Francisco State University, 3150 Paradise Dr, Tiburon, CA 94920, USA;(3) Department of Integrative Biology, University of California Berkeley, 3060 Valley Life Sciences, Bldg #3140, Berkeley, CA 94720-2140, USA; |
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Abstract: | Many eurythermal organisms alter composition of their membranes to counter perturbing effects of environmental temperature
variation on membrane fluidity, a process known as homeoviscous adaptation. Marine intertidal gastropods experience uniquely
large thermal excursions that challenge the functional integrity of their membranes on tidal and seasonal timescales. This
study measured and compared membrane fluidity in marine intertidal snail species under three scenarios: (1) laboratory thermal
acclimation, (2) thermal acclimatization during a hot midday low tide, and (3) thermal acclimatization across the vertical
intertidal zone gradient in temperature. For each scenario, we used fluorescence polarization of the membrane probe DPH to
measure membrane fluidity in individual samples of gill and mantle tissue. A four-week thermal acclimation of Tegula funebralis to 5, 15, and 25°C did not induce differences in membrane fluidity. Littorina keenae sampled from two thermal microhabitats at the beginning and end of a hot midday low tide exhibited no significant differences
in membrane fluidity, either as a function of time of day or as a function of thermal microhabitat, despite changes in body
temperature up to 24°C within 8 h. Membrane fluidities of a diverse group of snails collected from high, middle, and low vertical
regions of the intertidal zone varied among species but did not correlate with thermal microhabitat. Our data suggest intertidal
gastropod snails do not exhibit homeoviscous adaptation of gill and mantle membranes. We discuss possible alternatives for
how these organisms counter thermal excursions characteristic of the marine intertidal zone. |
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