Daphnia magna can tolerate short-term starvation without major changes in lipid metabolism

Daphnia magna is a common crustacean that is adapted to brief spells of fasting. Lipids are naturally a major component of their diet and are stored as energy reserves. However, there has been some controversy in the literature on the extent to which dietary lipids are used directly for complex lipid formation in Daphnia. We examined lipid metabolism in D. magna by labeling the animals using [1-14C]acetate and then followed the turnover of radiolabeled lipids during a pulse chase. Daphnia were either fed or maintained without food during the chase period. The decrease in radioactivity during the chase was relatively unaffected by feeding, although there were some differences in the distribution of radioactivity between lipid classes or individual FA. The polar lipids, which were four times better labeled than nonpolar lipids, contained the most radioactivity in the zwitterionic phosphoglycerides, PE and PC. Under the experimental conditions, the turnover of the polar membrane lipids was unaffected by feeding. Within nonpolar lipids, TAG accounted for up to about 80% of the label, followed by DAG. Overall, our data show that D. magna is capable of high rates of lipid radiolabeling de novo and, in addition, is able to use--and indeed may be dependent on--some dietary components such as the PUFA linoleate and alpha-linolenate. The results also clearly show that Daphnia is able to tolerate brief spells of fasting (24 h) with very little change to its lipid metabolism.