Wax esters in two species of freshwater zooplankton

Livid classes were determined in three Lake Michigan hypolimnetic calanoid copepods, Limnocalanus macrurus, Diaptomus sicilis, and Senecella calanoides. Limnocalanus macrurus and S. calanoides contained large stores of wax esters (57–80% of total lipid). Wax esters in this amount have not previously been reported for freshwater zooplankton. Diaptomus sicilis exhibits a typical freshwater lipid profile and contains triacylglycerols as its lipid reserves. Lipid storage sites are morphologically different in the copepods. Limnocalanus macrurus and S. calanoides store their wax esters in a large sac that surrounds the intestine, whereas D. sicilis maintains lipid droplet morphology typical of freshwater “triacylglycerol‐storing” zooplankton. Limnocalanus macrurus and S. calanoides are “glacial relicts,” which may explain the origin of their typically marine wax ester lipid class.