Incorporation of [1‐¹⁴C] acetate into fatty acids of the crustaceansDaphnia magna andCyclops strenus in relation to temperature

Abstract

Daphnia magna andCyclops strenus were maintained in aquaria containing sodium [1‐14C] acetate and the effect of temperature on labeling of their lipids was investigated. Incorporation of radioactivity in total lipids was slowed by a factor of 4 in cold‐exposed (5C) specimens compared to those incubated at 25 C. There was no significant difference in the distribution of label in the lipid classes of animals incubated at the two extreme temperatures. Decrease of the temperature from 25 to 5 C brought about a considerable reduction in the formation of palmitic and stearic acids and an increase in labeling of monounsaturated (18∶1) fatty acids inD. magna. Docosapolyenoic acids were absent from lipids of this crustacean.C. strenus directed a higher proportion of radioactivity into both oleic and docosahexaenoic acids upon cold exposure. In response to decrease of the temperature,D. magna formed a less unsaturated fatty acid population, as judged from dpm ratios of total saturated to total unsaturated fatty acids, thanC. strenus. Inability to form and accumulate docosapolyenoic fatty acids byD. magna might be related to their poor survival at reduced temperatures.

Effect of temperature on the fatty acid composition and temporal trajectories of fatty acids in fasting Daphnia pulex (Crustacea, cladocera)

“…Short-term (48 h) exposure to cold temperatures (4-5°C) did not cause appreciable changes in HUFA levels of D. pulex (8) or D. magna (9). These observations indicate either that Daphnia exposed to cold temperatures must be highly dependent on dietary HUFA, or that enzymes involved in the HUFA synthesis need longer adaptation periods to reach full activity.…”

“…However, Daphnia appear unable to accumulate large amounts of docosahexaenoic acid (DHA; 22:6n3), which they readily convert to EPA (6,8). Daphnia can use α-linolenic acid (ALA; 18:3n3) and linoleic acid (LIN; 18:2n6) as precursors for the synthesis of EPA and ARA, respectively (6,9,10). However, de novo rates of FA synthesis in Daphnia have been shown to be less than 2% (11).…”

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

“…In contrast, Farkas et al (17) showed that some copepods, namely, Cyclops strenuus and D. magna, showed substantial FA synthesis rates. Their calculations indicated that 0.9% of the total FA were renewed in 1 h in D. magna, and they suggested that the bulk of FA accumulated in both species could be synthesized by the animals.…”

“…Their calculations indicated that 0.9% of the total FA were renewed in 1 h in D. magna, and they suggested that the bulk of FA accumulated in both species could be synthesized by the animals. They also showed that incorporation of radioactivity from labeled acetate into total lipids was greatly affected by temperature, with large changes in the pattern of FA labeled in D. magna (17). Various other external (e.g., UV light, salinity, dissolved oxygen concentration, pH, water transparency, stressors) and internal (e.g., reproductive condition) factors may also influence zooplankton lipid composition and biosynthesis (13,(18)(19)(20).…”

“…We used this radiolabeled precursor because it is regarded as a good compound with which to examine de novo FA biosynthesis and to allow comparison with the previous work referred to above (15)(16)(17). Daphnia magna represents freshwater cladocerans, which are important in the structure of the zooplankton community.…”