Macronutrient balance has a strong influence on fitness in insects. Previous studies have revealed that altering the concentrations of yeast and sugar in the semi-synthetic diet has a profound impact on lifespan and fecundity in Drosophila melanogaster, indicating the role of dietary protein:carbohydrate (P:C) balance in determining these two key components of fitness. However, since yeast contains not only proteins but also other macro- and micronutrients, this lifespan-determining role of dietary P:C balance needs to be corroborated using a chemically defined diet. In this study, the effects of dietary P:C balance on lifespan and fecundity were investigated in female D. melanogaster flies on one of eight isocaloric synthetic diets differing in P:C ratio (0:1, 1:16, 1:8, 1:4, 1:2, 1:1, 2:1 or 4:1). Lifespan and dietary P:C ratio were related in a convex manner, with lifespan increasing to a peak at the two intermediate P:C ratios (1:2 and 1:4) and falling at the imbalanced ratios (0:1 and 4:1). Ingesting nutritionally imbalanced diets caused flies to start ageing earlier and senesce faster. Egg production increased progressively as the dietary P:C ratio rose from 0:1 to 4:1. Long-lived flies at the intermediate P:C ratios(1:2 and 1:4) stored a greater amount of lipids than those short-lived ones at the two imbalanced ratios (0:1 and 4:1). These findings provide a strong support to the notion that dietary P:C balance is a critical determinant of lifespan and fecundity in D. melanogaster.

• Taehwan Jang(School of Agricultural Biotechnology, Seoul National University)
• Myung Suk Rho(School of Agricultural Biotechnology, Seoul National University)
• Kwang Pum Lee(School of Agricultural Biotechnology, Seoul National University)