AGE-SPECIFIC PROPERTIES OF SPONTANEOUS MUTATIONS AFFECTING MORTALITY IN DROSOPHILA-MELANOGASTER

An analysis of the effects of spontaneous mutations affecting age-spec ific mortality was conducted using 29 lines of Drosophila melanogaster that had accumulated spontaneous mutations for 19 generations. Diverg ence among the lines was used to estimate the mutational variance for weekly mortality rates and the covariance between weekly mortality rat es at different ages. Significant mutational variance was observed in both males and females early in life (up to similar to 30 days of age) . Mutational variance was not significantly different from zero for mo rtality rates at older ages. Mutational correlations between ages sepa rated by 1 or 2 wk were generally positive, but they declined monotoni cally with increasing separation such that mutational effects on early -age mortality were uncorrelated with effects at later ages. Analyses of individual lines revealed several instances of mutation-induced cha nges in mortality over a limited range of ages. Significant age-specif ic effects of mutations were identified in early and middle ages, but surprisingly, mortality rates at older ages were essentially unaffecte d by the accumulation procedure. Our-results provide strong evidence f or the existence of a class of polygenic mutations that affect mortali ty rates on an age-specific basis. The patterns of mutational effects measured here relate directly to recently published estimates of stand ing genetic variance for mortality in Drosophila, and they support mut ation accumulation as a viable mechanism for the evolution of senescen ce.