Dietary modification of membrane composition mimics characteristics of thermal acclimation in the eastern newt (<i>Notophthalmus viridescens</i>)

Acclimation in response to seasonal temperature fluctuations is well described across animal taxa. Our previous studies on adult eastern red spotted newts have demonstrated that winter- or cold-acclimated newts prefer lower cloacal temperatures, have higher standard metabolic rates (SMRs), exhibit higher skeletal muscle cytochrome c oxidase (CCO) and citrate synthase (CS) activity, and possess membranes composed of elevated polyunsaturated fatty acid (PUFA) content compared with skeletal muscle of summer- or warm-acclimated newts. Acclimation to cold also results in partial compensation of locomotor performance. Additionally, northern populations have higher CS and CCO activity and a higher degree of membrane unsaturation compared with southern populations regardless of acclimation conditions. In the present study, we tested the hypothesis that modification of membrane fatty acid composition mimics characteristics of thermal acclimation. We modified membrane composition in newts independent of environmental temperature by feeding them diets differing in fatty acid composition (saturated, monounsaturated, and n3 or n6 PUFA diets) and measured CCO and CS activity, SMR, preferred cloacal temperature, locomotor performance and thermal tolerance. Here, we present data suggesting that a diet-mediated elevation of PUFA in tissue membranes results in lower preferred body temperature, increased metabolic rate, increased burst speed at low temperature and decreased burst speed at high temperature. This introduces an ectothermic vertebrate model system that acclimates characteristics across levels of biological organization in which we can effectively uncouple membrane composition from environmental temperature or light cycle, and further suggests that diet may be an important component of thermal acclimation in nature.