Most animals store energy as long-chain triacylglycerols (lcTAGs). Trace amounts of acetylated triacylglycerols (acTAGs) have been reported in animals, but are not accumulated, likely because they have lower energy density than lcTAGs. Here we report that acTAGs comprise 36% of the neutral lipid pool of overwintering prepupae of the goldenrod gall fly, Eurosta solidaginis, while only 17% of the neutral lipid pool is made up of typical lcTAGs. These high concentrations of acTAGs, present only during winter, appear to be synthesized by E. solidaginis and are not found in other freeze-tolerant insects, nor in the plant host. The mixture of acTAGs found in E. solidaginis has a significantly lower melting point than equivalent lcTAGs, and thus remains liquid at temperatures at which E. solidaginis is frozen in the field, and depresses the melting point of aqueous solutions in a manner unusual for neutral lipids. We note that accumulation of acTAGs coincides with preparation for overwintering and the seasonal acquisition of freeze tolerance. This is the first observation of accumulation of acTAGs by an animal, and the first evidence of dynamic interconversion between acTAGs and lcTAGs during development and in response to stress.
↵* Present address: Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
↵‡ Present address: Grenfell Campus, Memorial University, Corner Brook, NL A2H 5G4, Canada.
K.E.M., A.R. and B.J.S. designed the research. K.E.M., R.H.T., A.R., E.K.Y.C. and J.C.L.B. performed the research. R.H.T., J.C.L.B. and E.K.Y.C. contributed new reagents or analytic tools. K.E.M., R.H.T., A.R., E.K.Y.C., J.C.L.B., E.R.G. and B.J.S. analyzed the data. K.E.M. and B.J.S. wrote the paper.
The authors declare no competing financial interests.
This research is supported by a Natural Sciences and Engineering Research Council (NSERC) post-graduate scholarship to K.E.M., and NSERC Discovery grants to B.J.S. and E.R.G.
Supplementary material available online at http://jeb.biologists.org/lookup/suppl/doi:10.1242/jeb.099838/-/DC1
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