EFFECT OF DENSITY ON AGE-SPECIFIC MORTALITY IN DROSOPHILA - A DENSITYSUPPLEMENTATION EXPERIMENT

Age-specific mortality rates were studied at two adult density levels in four inbred lines of Drosophila melanogaster. In experimental popul ations, adult densities were maintained at constant levels throughout the experiment by replacing dead flies with live, marked mutants. In c ontrol populations, densities declined naturally as the cohorts aged. For all experimental populations the best mortality model is the two-s tage Gompertz model, with slower mortality acceleration at older ages. Flies in the experimental populations generally lived longer than fli es in control populations, regardless of sex, genotype, or initial den sity level. The data demonstrate that deceleration of age-specific mor tality rates at older ages is not caused by declining cohort densities . Mortality deceleration is a real phenomenon that raises serious ques tions about the evolution of senescence.