The purpose of this work is to identify previously unknown molecular mechanisms by which insects deal with low temperatures. The freeze tolerant midge, Belgica antarctica, and the freeze intolerant flesh fly, Sarcophaga crassipalpis, were chosen as model organisms to test for membrane restructuring and metabolic change. An analysis of the membrane lipids from flesh flies revealed that diapause and rapid cold-hardening both dramatically altered the composition of fatty acids in cell membranes. Both physiological conditions increased oleic acid levels, which promotes cellular survival to low-temperatures by widening the window by which cell membranes maintain their liquid crystalline state. In addition, phosphatidycholines were replaced by phosphatidylethanolamines, which also lowers the temperature window by which cell membranes maintain homeostasis. In short, membrane restructuring appears to contribute to low-temperature survival in the flesh fly.
A metabolomic analysis of whole-body metabolites isolated from flesh flies in diapause and rapid cold-hardening revealed wide-spread alterations in metabolism. Rapid cold-hardening produced an increase in glycerol concentration, but this increase was also coupled with the increase of sorbitol. Rapid cold-hardening produced elevations in many other metabolites that have been previously unknown to be increased, most notably alanine, glutamine and pyruvate. With these metabolic changes, flesh flies experiencing rapid cold-hardening are well-equipped to survive low-temperature stress. Increases in glycerol, alanine, and pyruvate were also seen for diapause, but unlike rapid cold-hardening, diapause produced a metabolic profile consistent with a disruption of Krebs cycle activity.
A metabolomic analysis of the freeze tolerant midge, Belgica antarctica, revealed that freezing increased a number of different polyols in whole-body extracts, including glycerol, mannitol, and erythritol. Freezing also increased alanine, asparagine, and glycine. Larvae accumulated Krebs cycle intermediates, indicating that aerobic respiration is considerably slowed. A comparison of the metabolic responses of this midge to heat, freezing and desiccation revealed that freezing and desiccation produced similar results, supporting the hypothesis that the cellular response to these two stressors is related. In conclusion, numerous physiological mechanisms by which insects survive low-temperatures have yet to be discovered, but the richness of these mechanisms is clearly displayed in the present work using only two model species.
|School:||The Ohio State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||Cold, Fatty acid, Insect, Membrane, Metabolism|
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