Differential response of lipid metabolism and membrane physical state by an actively and passively overwintering planktonic crustacean

Abstract

Abstract Phospholipid (PL) composition, fatty acid (FA) composition of total and major individual PL as well as the physical state of isolated PL were investigated in relation to temperature exposure by freshwater planktonic crustaceans, Cyclops vicinus and Daphnia magna. C. vicinus , adapted to warm water, accumulated appreciable amounts of docosahexaenoic acid in its PL within 3 days when the temperature was decreased from 20 C to 10 C. Docosahexaenoic acid was preferentially esterified to phosphatidylethanolamine (PE). Docosapolyenoic FA were absent in PL of D. magna and this species did not increase polyenoic acid level under identical temperature treatment. The level of PE was elevated, however, in both species in response to decreased environmental temperature. Two characteristic breaks were observed in ln S vs 1/T plots of 5‐doxyl stearic acid spin probs. These were at 19 C and 13 C for C. vicinus and at 20 C and 7 C for D. magna. C. vicinus shifted both the upper and lower phase‐separation temperatures of its PL to lower temperatures when exposed to cold. Differences between the onset and completion of phase‐separation temperatures equalled that in environmental temperature (10 C). The phase‐separation temperatures of D. magna were unchanged under identical experimental conditions. Results are interpreted as a complete temperature adaptation of membrane transitional state by C. vicinus but not by D. magna . Researchers have postulated that one of the reasons the latter species cannot overwinter in an active form as does C. vicinus , but instead overwinters as resting eggs, involves its failure to adapt membrane PL composition and physical state to temperature.