DENSITY-DEPENDENT NATURAL-SELECTION IN DROSOPHILA - TRADE-OFFS BETWEEN LARVAL FOOD ACQUISITION AND UTILIZATION

Natural selection at high densities has often been postulated to favou r the evolution of greater efficiency of food use. Contrary to this ex pectation, a previous study suggested the existence of a trade-off bet ween larval feeding rate and efficiency at using food to complete larv al development in populations of Drosophila melanogaster subjected to crowding for many generations. In this paper, we confirm the generalit y of such a density-dependent trade-off between food acquisition and u tilization by demonstrating its occurrence in a new set of Drosophila populations subjected to extreme larval crowding. We suggest that such trade-offs between food acquisition and food use may represent a gene ral phenomenon in organisms exhibiting scramble competition. We test a nd reject the possible mechanistic explanation that decreased efficien cy of food use in faster-feeding larvae may merely be a consequence of a faster passage of food through the gut, leading to incomplete assim ilation of nutrients and energy.