Evolutionary adaptation of membranes to temperature.

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Abstract
The fluidity of brain synaptosomal membrane preparations of arctic and hot-springs fish species, 2 temperate water fish species acclimated to different seasonal temperatures, and 2 mammals was estimated using the fluorescence polarization technique. At all measurement temperatures, the fluidity decreased in the order: arctic sculpin [Myoxocephalus verrucosus], 5.degree. C-acclimated green sunfish-bluegill hybrid (Lepomis), 25.degree. C-acclimated green sunfish-bluegill hybrid goldfish, desert pupfish [Cyprinodon nevadensis], and rat. This correlated with increasing adaptation or body (i.e., cellular) temperatures of 0.degree., 5.degree., 25.degree., 34.degree. and 37.degree. C and suggested a partial compensation of membrane fluidity for environmental temperature that occurs over the evolutionary time period and during laboratory (seasonal) acclimation. Evolutionary adaptation of relatively stenothermal species to constant thermal environments resulted in a more complete compensation than laboratory (seasonal) acclimation. Each compensation is accompanied by differences in the saturation of membrane phosphoglycerides. At increased cellular temperatures the proportion of saturated fatty acids increased and the unsaturation index decreased; the correlation between these indices and the measured expression of membrane dynamic structure was highly significant. The homeoviscous compensation of synaptic membrane function is an important component of temperature adaptation.