SPONTANEOUS MUTATION FOR LIFE-HISTORY TRAITS IN DROSOPHILA-MELANOGASTER

Spontaneous mutations accumulated during 80 generations in 94 lines de rived from a completely homozygous population of Drosophila melanogast er, all of them maintained by a single brother-sister mating per gener ation. Three traits were evaluated: early productivity, late productiv ity, and longevity. Mutational heritabilities were similar for all tra its: 3.18 x 10(-3), 3.52 x 10(-3), and 3.38 x 10(-3), respectively. Ni ne lines were examined, their means being in the upper or lower tails of the distribution of line's means for at least two traits. Reciproca l crosses were made between each line and the control population to es timate line effects. The results can be summarised as follows: all lin es carried putative mutations affecting fitness traits; five lines aff ect the three traits scored; one affects exclusively early productivit y; and three affect exclusively late life-history traits (late product ivity and longevity). Most mutations were deleterious and recessive, e xcept one that favourably affected early-productivity and was dominant . Additional fitness traits were evaluated, indicating pleiotropy. We have not found mutations with antagonistic effects early and late in l ife; moreover, positive mutational correlation seems to be the rule.