GENETIC-VARIATION FOR TOTAL FITNESS IN DROSOPHILA-MELANOGASTER

We measured the heterozygous effects on net fitness of a sample of 12 wild-type third chromosomes in D. melanogaster. Effects on fitness wer e assessed by competing the wild-type chromosomes against balancer chr omosomes, to prevent the production of recombinants. The measurements were carried out in the population cage environment in which the life history had been evolving, in an undisturbed population with overlappi ng generations, and replicated measurements were made on each chromoso me to control for confounding effects such as mutation accumulation. W e found significant variation among the wild type chromosomes in their additive genetic effect on net fitness. The system provides an opport unity to obtain an accurate estimate of the distribution of heterozygo us effects on net fitness, the contribution of different fitness compo nents including male mating success, and the role of intra-chromosomal epistasis in fitness variation.