DENSITY-DEPENDENT NATURAL-SELECTION IN DROSOPHILA - ADAPTATION TO ADULT CROWDING

The effects of adult crowding on two components of fitness were studie d in three sets of Drosophila melanogaster populations, subjected to l ife-stage-specific, density-dependent natural selection in the laborat ory for over 50 generations. Three days of crowding, early in adult li fe, were observed to increase mortality significantly during the episo de of crowding, as well as decrease subsequent fecundity. Populations selected for adaptation to high adult densities suffered significantly lower mortality during episodes of adult crowding, as compared to pop ulations selected specifically for adaptation to larval crowding, as w ell as control populations typically maintained at low larval and adul t densities. Moreover, populations adapted to larval crowding seemed t o be adversely affected by adult crowding to a greater extent than the controls, raising the possibility of trade-offs between adaptations t o larval and adult crowding, respectively. Preliminary evidence sugges ts that the populations adapted to adult crowding may have evolved a p ropensity to stay away from the food medium, which is where most death s occur when adults are crowded in culture vials.