Impact of 10 dietary sterols on growth and reproduction of Daphnia galeata.

In crustaceans, cholesterol is an essential nutrient, which they must directly obtain from their food or by bioconversion from other dietary sterols. Eukaryotic phytoplankton contain a great variety of sterols that differ from cholesterol in having additional substituents or different positions and/or number of double bonds in the side chain or in the sterol nucleus. In this study, we investigated to what extent these structural features affect the growth and reproduction of Daphnia galeata in standardized growth experiments with the cyanobacterium Synechococcus elongatus supplemented with single sterols as food source. The results indicated that delta 5 (sitosterol, stigmasterol, desmosterol) and delta 5.7 (7-dehydrocholesterol, ergosterol) sterols meet the nutritional requirements of the daphnids, while the delta 7 sterol lathosterol supports somatic growth and reproduction to a significantly lower extent than cholesterol. Dihydrocholesterol (delta 0) and lanosterol (delta 8) did not improve the growth of D. galeata, and growth was adversely affected by the delta 4 sterol allocholesterol. Sterols seem to differ in their allocation to somatic growth and reproduction. Thus, structural differences of dietary sterols have pronounced effects on life-history traits of D. galeata.