Cold adaptations in Drosophila. Qualitative changes of triacylglycerols with relation to overwintering.

Triacylglycerols are the major fuel for basal metabolism during the winter in temperate species of the Drosophila melanogaster species group. Differential scanning calorimetry analysis revealed that the transition temperatures of triacylglycerols were lower in diapausing adults than in reproducing ones, and also lower in species or strains adapted to cooler climates than those adapted to warmer climates. These phenomena were correlated to the fatty acid compositions of the triacylglycerols; the proportion of unsaturated fatty acids in the triacylglycerols was higher in the diapausing individuals, and in the species or strains adapted to cooler climates. Furthermore, in the temperate species of the montium species subgroup (D. subauraria, D. biauraria, D. triauraria, and D. rufa), the amount of saturated triacylglycerols was smaller than the value expected on the assumption that fatty acids are randomly distributed in the triacylglycerols, suggesting the nonrandom distribution of unsaturated fatty acids among triacylglycerols. This may facilitate the lowering of the transition temperature of triacylglycerols, and hence may be related to the ability of Drosophila to cope with temperate climates.