Lizards, Lipids, and Dietary Links to Animal Function

Abstract

Our experiments were designed to test the hypotheses that dietary lipids can affect whole-animal physiological processes in a manner concordant with changes in the fluidity of cell membranes. We measured (1) the lipid composition of five tissues, (2) body temperatures selected in a thermal gradient (T(sel)), (3) the body temperature at which the righting reflex was lost (critical thermal minimal [CTMin]), and (4) resting metabolic rate (RMR) at three body temperatures in desert iguanas (Dipsosaurus dorsalis) fed diets enriched with either saturated or unsaturated fatty acids. The composition of lipids in tissues of the lizards generally reflected the lipids in their diets, but the particular classes and ratios of fatty acids varied among sampled organs, indicating the conservative nature of some tissues (e.g., brain) relative to others (e.g., depot fat). Lizards fed the diet enriched with saturated fatty acids selected warmer nighttime body temperatures than did lizards fed a diet enriched with unsaturated fatty acids. This difference is concordant with the hypothesis that the composition of dietary fats influences membrane fluidity and that ectotherms may compensate for such changes in fluidity by selecting different body temperatures. The CTMin of the two treatment groups was indistinguishable. This may reflect the conservatism of some tissues (e.g., brain) irrespective of diet treatment. The RMR of the saturated treatment group nearly doubled between 30 degrees and 40 degrees C. Here, some discrete membrane domains in the lizards fed the saturated diet may have been in a more-ordered phase at 30 degrees C and then transformed to a less-ordered phase at 40 degrees C. In contrast, the RMR of the unsaturated treatment group exhibited temperature independence in metabolic rate from 30 degrees to 40 degrees C. Perhaps the unsaturated diet resulted in membranes that developed a higher degree of disorder (i.e., a certain phase) at a lower temperature than were membranes of lizards fed the saturated diet. Our study demonstrates links between dietary fats and whole-animal physiology; however, the mechanistic basis of these links, and the general knowledge of lipid metabolism in squamate reptiles, remain poorly understood and warrant further study.

Nutritional ecology of essential fatty acids: an evolutionary perspective

“…Thermoregulation temperature. Almost twenty years ago Geiser and colleagues reported the fascinating finding that diet fatty acid composition influenced the preferred body temperature that lizards select and this was later confirmed by other investigators (Simandle et al 2001). All species investigated selected a lower preferred body temperature when fed a PUFA-enriched diet than when fed an SFA-enriched diet (Geiser et al 1992;1994).…”

Glycogen, not dehydration or lipids, limits winter survival of side-blotched lizards (Uta stansburiana)

“…Thus, it may not be absolute amounts of lipid stores that are important but composition of those stores. However, we know of no studies that have reported the fatty acid composition or patterns of utilization of lizards during winter (but see Simandle et al, 2001;McCue, 2008). A third possibility is that lizards sequester lipids primarily for subsequent (i.e.…”

Postprandial thermophily in the Danube crested newt, Triturus dobrogicus

“…Moreover, fasting newts preferred similar temperatures during both behavioural states and thus the conflict between postprandial thermophily and preference of lower temperatures for LI did not exist in this species. However, dietary fat composition affected postprandial temperature preferences during LA and LI in a desert iguana (Simandle et al, 2001). Newts prey upon a variety of invertebrates (Griffiths and Mylotte, 1987) that may differ in their fatty acids composition.…”