THE ENERGETICS OF GROWTH IN DROSOPHILA-MELANOGASTER - EFFECT OF TEMPERATURE AND FOOD CONDITIONS

The relation between oxygen consumption rate and larval growth rate in Drosophila melanogaster at different temperatures and food levels was analyzed to investigate whether different larval growth rates and adu lt body sizes are the consequences of different costs of growth. Four isofemale lines from two populations collected from France and Tanzani a were compared. The rate of oxygen consumption per mg body weight inc reased with the relative rate of growth. Costs of growth (C-g), i.e., the increase in oxygen consumption due to growth, took 17.4% of the to tal energy invested in growth. No significant effect on C-g could be s hown of either temperature or food level. Basal metabolic rate (R-b), i.e., the rate of oxygen consumption in the absence of growth, increas ed with temperature and food level at the intermediate temperature. Th e two French lines showed a higher rate of growth, independent of the environmental conditions, leading to a larger final body size. The two Tanzanian lines show a reduced C-g as compared to the French lines at 27.5 degrees C, while showing no such difference at 17.5 degrees C an d 22.5 degrees C. Yet, these differences in C-g do not lead to clear d ifferences in growth efficiency between populations, indicating that d ifferences in absorption rate are the main cause of both environmental and genetic differences in growth rate.