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Dietary lipid quality affects temperature-mediated reaction norms of a freshwater key herbivore
(2012)
Temperature-mediated plasticity in life history traits strongly affects the capability of ectotherms to cope with changing environmental temperatures. We hypothesised that temperature-mediated reaction norms of ectotherms are constrained by the availability of essential dietary lipids, i.e. polyunsaturated fatty acids (PUFA) and sterols, as these lipids are involved in the homeoviscous adaptation of biological membranes to changing temperatures. A life history experiment was conducted in which the freshwater herbivore Daphnia magna was raised at four different temperatures (10, 15, 20, 25A degrees C) with food sources differing in their PUFA and sterol composition. Somatic growth rates increased significantly with increasing temperature, but differences among food sources were obtained only at 10A degrees C at which animals grew better on PUFA-rich diets than on PUFA-deficient diets. PUFA-rich food sources resulted in significantly higher population growth rates at 10A degrees C than PUFA-deficient food, and the optimum temperature for offspring production was clearly shifted towards colder temperatures with an increased availability of dietary PUFA. Supplementation of PUFA-deficient food with single PUFA enabled the production of viable offspring and significantly increased population growth rates at 10A degrees C, indicating that dietary PUFA are crucial for the acclimation to cold temperatures. In contrast, cumulative numbers of viable offspring increased significantly upon cholesterol supplementation at 25A degrees C and the optimum temperature for offspring production was shifted towards warmer temperatures, implying that sterol requirements increase with temperature. In conclusion, essential dietary lipids significantly affect temperature-mediated reaction norms of ectotherms and thus temperature-mediated plasticity in life history traits is subject to strong food quality constraints.
We investigated the effects of temperature (4 degrees C, 8 degrees C, and 12 degrees C) on structural and storage dynamics, as measured by changes in fatty acids (FA) associated with cell membrane phospholipids (PL) and triacylglycerols (TAG), respectively, as well as on body weight and survival of a freshwater calanoid copepod (Eudiaptomus gracilis) during fasting (10 d) and refeeding (10 d) with two algae of differing nutritional quality (Cryptomonas ozolinii and Scenedesmus obliquus). Fasting led to 50% loss in body weight, a near total depletion of TAG, and a drastic decrease of the polyunsaturated FA (PUFA) in TAG and PL, indicating their preferential utilization and alterations in membrane function, respectively. Higher temperatures accelerated the decrease of body weight and of PUFA in PL and TAG, and decreased survival. After 10 d of refeeding, copepods partially recovered their initial lipid stores and cell membrane composition. The effects of food quality were temperature dependent: Cryptomonas promoted better recovery (i.e., return to or close to the levels at the beginning of the experiment) of both body weight and TAG at only the two higher temperatures (8 degrees C and 12 degrees C), whereas no recovery was observed at 4 degrees C. Higher temperatures and refeeding on Cryptomonas also had a positive, but minor, influence on the recovery of membrane FA composition. Survival differed among treatments but was lowest at the intermediate temperature (8 degrees C) for both diets. We conclude that temperature changes on the order of 4-8 degrees C significantly influence TAG and PL during fasting periods and interact with food quality to determine the extent of recovery in copepod lipids.