GEOGRAPHIC-VARIATION IN COMPETITIVE ABILITY IN DROSOPHILA-MELANOGASTER

The aim of this study was to examine the latitudinal variation in prea dult competitive ability of Drosophila melanogaster. Two pairs of popu lations from Queensland and Tasmania, Australia, were examined. Queens land flies are genetically smaller and develop more slowly than the Ta smanian flies. Survival and body size of flies raised at different tem peratures and densities were compared when larvae were challenged with a common competitor. No latitudinal variation in larval survival was detected. Body size (measured as wing length) decreased with increasin g temperature and larval density. Flies from the Tasmanian populations were more sensitive to the effects of temperature and density and to the joint effect of increased temperature and density. This could expl ain the evolution of greater growth efficiency and larger body size at lower temperatures.