THE EFFECTS OF SPONTANEOUS MUTATION ON QUANTITATIVE TRAITS .1. VARIANCES AND COVARIANCES OF LIFE-HISTORY TRAITS

We have accumulated spontaneous mutations in the absence of natural se lection in Drosophila melanogaster by backcrossing 200 heterozygous re plicates of a single high fitness second chromosome to a balancer stoc k for 44 generations. At generations 33 and 44 of accumulation, we ext racted samples of chromosomes and assayed their homozygous performance for female fecundity early and late in adult life, male and female lo ngevity, male mating ability early and late in adult life, productivit y (a measure of fecundity times viability) and body weight. The varian ce among lines increased significantly for all traits except male mati ng ability and weight. The rate of increase in variance was similar to that found in previous studies of egg-to-adult viability, when calcul ated relative to trait means. The mutational correlations among traits were all strongly positive. Many correlations were significantly diff erent from 0, while none was significantly different from 1. These dat a suggest that the mutation-accumulation hypothesis is not a sufficien t explanation for the evolution of senescence in D. melanogaster. Muta tion-selection balance does seem adequate to explain a substantial pro portion of the additive genetic variance for fecundity and longevity.