The evolution of age-specific mortality rates in Drosophila melanogaster: Genetic divergence among unselected lines

Age-specific effects of spontaneous mutations on mortality rates in Drosoph ila are inferred from three large demographic experiments. Data were collec ted from inbred lines that were allowed to accumulate spontaneous mutations for 10, 19, and 47 generations. Estimates of age-specific mutational varia nce for mortality were based on data from all three experiments, totalling similar to 225,000 flies, using a model developed for genetic analysis of a ge-dependent traits (the character process model). Both within- and among g eneration analyses suggest that the input of genetic variance is greater fo r early life mortality rates than for mortality at older ages. In females, age-specific mutational variances ranged over an order of magnitude from 5. 96 X 10(-9) at 2 wk posteclosion to 0.02 X 10(-3) at 7 wk. The male data sh ow a similar pattern. Age-specific genetic variances were substantially les s at generation 47 than at generation 19-an unexplained observation that is likely due to block effects. Mutational correlations among mortality rates at different ages tend to increase with the accumulation of new mutations. Comparison of the mutation-accumulation lines at generations 19 and 47 wit h their respective control lines suggests little age-specific mutational bi as.