A piece of rotting fruit may not look particularly appetizing to us, but to Drosophila, it's almost pure heaven; they like nothing more than settling down for a good feast on the decaying flesh. However, packed full of acetic acid and ethanol, decaying fruit poses a toxic threat to its guests. Fortunately, fruit fly populations in high latitudes seem to be well defended against the effects of acetic acid and ethanol, while tropical populations are less so. How these geographically distinct populations maintain their ethanol resistance puzzled Kristi Montooth, Kyle Siebenthall and Andrew Clark. Knowing that ethanol disrupts membranes, and that a key factor (dSREBP -Drosophila sterol regulatory element binding protein) regulating membrane composition also regulates the final stage of ethanol and acetic acid detoxification, the team decided to investigate to effects of temperature on the insect's ethanol detoxification and membrane physiology(p. 3837).

Working with fruit flies from tropical north eastern Australia and temperate Tasmania, the team found that both alcohol dehydrogenase and acetyl-CoA synthetase expression and activity were increased in the Tasmanian and warm acclimated insects, contributing to their enhanced ethanol tolerance. Temperature had upregulated the essential enzymes to increase the Tasmanian insect's ethanol tolerance. Looking at the effects of cold temperatures on the insect's membrane structure, the team found that at low temperatures, the flies had increased levels of lipid biosynthetic enzymes such as phospholipase D to counteract the membrane's increased rigidity. Montooth also points out that phospholipase D utilizes ethanol, possibly contributing to the insect's ethanol tolerance. And when the team suddenly dropped the temperatures, the insect's ethanol tolerance improved too. Montooth suspects that the high-latitude insect's ability to counteract increased membrane rigidity at low temperatures protects them from the damaging effects of ethanol, improving their tolerance.

So temperature influences Drosophila's ethanol and acetic acid tolerance by altering both the detoxification pathways and membrane physiology. Montooth explains that fruit flies probably experience both temperature and toxin stresses simultaneously and frequently, so Drosophila could teach us how `physiological pathways and mechanisms evolve in the face of multiple selection pressures in nature' she adds.

References

Montooth, K. L., Siebenthall, K. T. and Clark, A. G.(
2006
). Membrane lipid physiology and toxin catabolism underlie ethanol and acetic acid tolerance in Drosophila melanogaster.
J. Exp. Biol.
209
,
3837
-3850.