Lipids and buoyancy in Southern ocean pteropods.
The lipids of Clione limacina, a Southern Ocean pteropod (order Gymnosomata), contain 28% diacylglyceryl ether (DAGE) (as percentage of total lipid) whereas the pteropod Limacina helicina (order Thecosomata) lacks DAGE. The alkyl glyceryl ether diols (1-O-alkyl glycerols, GE) of Clione DAGE are dominated by 16:0 (60%) and 15:0 (21%), in contrast with deep-sea shark liver DAGE, which is dominated by 18:1 GE. The fatty acid profiles of Clione and Limacina are similar (28-32% polyunsaturated, 26-34% monounsaturated) as are the sterols, which include 24-methylenecholesterol, transdehydrocholesterol, cholesterol, and desmosterol. This finding probably reflects the fact that Limacina is the major food source for Clione. Spongiobranchaea australis, another Southern Ocean pteropod (order Gymnosomata), has 0.9-1.7% DAGE, but has less lipid (3.3-4.8 mg/g lipid, wet weight) than Clione (50.8 mg/g lipid, wet weight). We propose a buoyancy role for DAGE in Clione since Limacina has bubbles for flotation which Clione lack; DAGE provides 23% more uplift than triacylglycerol at a concentration of 1.025 g/mL seawater.
Phleger
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Department of Biology, San Diego State University, California 92182, USA. phleger@sunstroke.sdsu.edu
Nichols
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Virtue
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D000818:Animals; D004075:Diglycerides / Q000032:analysis*; D005227:Fatty Acids / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry; D008974:Mollusca / Q000737:chemistry*; D013261:Sterols / Q000032:analysis*
D004075:Diglycerides; D005227:Fatty Acids; D013261:Sterols