Biochemical Aspects of Climatic Adaptations inDrosophila curviceps,D. immigrans,andD. albomicans(Diptera: Drosophilidae)

Abstract

Qualitative and quantitative changes in phospholipids and energy reserves (triacylglycerols and glycogen) were studied in relation to temperature adaptations in a temperate species, Drosophila curviceps Okada & Kurokawa, and its subtropical relatives, D. immigrans Sturtevant and D. albomicans Duda. Cold and heat tolerance were negatively correlated among the study species: D. curviceps was the most tolerant to cold but the least tolerant to heat, D. albomicans was the least tolerant to cold but the most tolerant to heat, and D. immigrans had intermediate tolerance to cold and heat. In these species, the percentages of monoenoic acids in phospholipids generally increased but the percentages of dienoic acids decreased with the enhancement of cold tolerance. Concomitantly, the percentage of fatty acids containing 16 carbon atoms increased, while that of fatty acids with 18 carbon atoms decreased. It is considered that these changes in fatty acid composition play important roles in the acquisition of cold tolerance in these Drosophila species. In the species studied, triacylglycerols were major energy reserves. The concentration of triacylglycerols and the percentage of unsaturated fatty acids in triacylglycerols were slightly higher in the subtropical species than in the temperate species. In addition, lower rearing temperature elevated the degree of unsaturation of triacylglycerols in D. albomicans, but did not in D. curviceps and D. immigrans. Thus, the notion that insects adapted to cooler climates have a mechanism to lower the transition temperature of triacylglycerols does not fit for these species.