HIEBERT , S.M.; PANNORFI, R.; LEININGER, E.; LE, L.; HUNERYAGER, R.; PIKE, E.; Swarthmore College; Swarthmore College; Swarthmore College; Swarthmore College; Swarthmore College; Swarthmore College; ; : Dietary lipids, temperature and melatonin: behavioral preference adjustments in hamsters consistent with the membrane homeoviscosity model
For hibernators, seasonal changes in the lipid composition of membranes are considered an important adaptation for maintaining homeoviscosity of cell membranes during periods when body temperature is low. The lower body temperatures and metabolic rates achieved by hibernators consuming a diet rich in unsaturated fatty acids (as compared with hibernators consuming a diet rich in saturated fatty acids) is consistent with the homeoviscosity model. Studies in our laboratory demonstrate that Djungarian hamsters, daily heterotherms that are induced to enter spontaneous daily torpor by exposure to short days, are able to make the reverse adjustment—when they are exposed to different environmental temperatures and given a choice between diets rich in saturated or unsaturated fatty acids, they adjust their preference for these diets in the direction predicted by the homeoviscous adaptation model. Furthermore, they make this behavioral adjustment even when they are chronically normothermic, either in short or long days. Although exposure to cold alone is capable of inducing a greater preference for dietary unsaturated fatty acids, short days and melatonin treatments timed to mimic short days are each sufficient to induce the same change in preference in the absence of a reduction in ambient temperature. Additional experiments have shown that when given a choice of temperatures close to thermoneutrality, hamsters fed a highly unsaturated fatty diet exhibit a greater preference for the warmer nest location than hamsters fed a highly saturated fatty diet. Together, these results suggest a suite of behavioral adjustments that could assist in the regulation of cell membrane and depot fat fluidity.