Oleic acid is elevated in cell membranes during rapid cold-hardening and pupal diapause in the flesh fly, Sarcophaga crassipalpis.

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The integrity of cellular membranes is critical to the survival of insects at low temperatures, thus there is tremendous advantage conferred to insects that can adjust their composition of membrane fatty acids (FA’s). Such changes, known as homeoviscous adaptation, allow cellular membranes to maintain a liquid-crystalline state at temperatures that are normally low enough to cause the membrane to enter the gel state and lose the ability to maintain homeostasis. Flesh flies (Sarcophaga crassipalpis) were subjected to two experimental conditions that elicit low temperature tolerance: rapid cold-hardening and diapause. FA’s were isolated and analyzed using gas chromatography-mass spectrometry. FA’s changed in response to both rapid cold-hardening and diapause. In response to rapid cold-hardening, the proportion of oleic acid (18:1n-9) in pharate adults increased from 30% to 47% of the total fatty acid pool. The proportion of almost every other FA was reduced. Diapausing pupae experienced an even greater increase in oleic acid proportion to 58% of the total FA pool. Oleic acid not only increases membrane fluidity at low temperature, but also allows the cell membrane to maintain a liquid crystalline state should the temperature increase. This is the first demonstration of homeoviscous adaptation in a cold-hardy insect with a pupal diapause.



homeoviscous adaptation, membrane fluidity, gas chromatography