EFFECT OF ADULT COHORT DENSITY ON AGE-SPECIFIC MORTALITY IN DROSOPHILA-MELANOGASTER

Mortality rates decelerate at older ages in experimental populations o f Drosophila. It is unclear whether this reflects a real slow-down in the aging process, or an artifact of declining density. Mortality was studied in age-synchronized cohorts of four inbred lines at three init ial densities that varied 10-fold. A total of 70,000 flies of both sex es were studied. There were large line x density, line, and sex effect s, but no systematic relationship between density and life span was de tected. Mortality curves level off at older ages in 23 out of 24 sex-g enotype combinations, irrespective of initial cohort density. Density has only second-order effects on the pattern of oldest-old mortality o ver the range of densities studied here. The dramatic departure from G ompertz-type mortality dynamics at older ages is not an artifact of de clining density in Drosophila.