PRUITT, NL; Colgate University: Seasonal Changes in Membrane Lipids Associated with Freeze Tolerance in Eurosta solidaginis

Third instar larvae of the goldenrod gall fly Eurosta solidaginis (Diptera: Tephritidae) are freeze-tolerant in winter. Cell membranes must compensate for both low temperature and dehydration during freezing. Documented adaptations to low temperature include increased fatty acid unsaturation and enrichment of conical phosphatides, both of which prevent formation of gel phase lipid domains. These changes are inconsistent with adaptations known to prevent formation of the H_II phospholipid phase at low water activities, namely increased fatty acid saturation and increased proportions of cylindrical phosphatides. Changes in phospholipid composition and class-specific fatty acid composition were studied from August to November, 2002. A transient and significant increase in cylindrical phosphatides, mostly PC, occurred during the first week in October, a period that coincides with the transition from freeze-susceptible to freeze-tolerant in this population. While both PC and PE accumulated monoenes with the onset of freeze-tolerance, PC did so at a significantly higher rate than PE. PC accumulated the most unsaturated acid detected in this species, 18:3(n-3), to a significantly greater extent than PE. This combination of changes, wherein the cylindrical PC becomes more unsaturated than the conical PE, may represent a finely tailored response to both low temperatures and to freeze-induced dehydration.