POLYGENIC MUTATION IN DROSOPHILA-MELANOGASTER - GENOTYPE X ENVIRONMENT INTERACTION FOR SPONTANEOUS MUTATIONS AFFECTING BRISTLE NUMBER

A highly inbred line of Drosophila melanogaster was subdivided into re plicate sublines that were subsequently maintained independently with 10 pairs of parents per generation. The parents were randomly sampled for 19 'unselected' sublines, and artificially selected for high or lo w abdominal or sternopleural bristle number for 12 'selected' sublines (with 3 replicate selection lines/trait/direction of selection). Dive rgence in mean bristle number among the unselected sublines, and respo nse of the selected sublines to selection, are attributable to the acc umulation of new mutations affecting bristle number. The input of muta tional variance per generation, V-M, can be estimated from the magnitu de of response or divergence, assuming neutrality of mutations affecti ng the bristle traits. We reared unselected lines at generations 222 a nd 224, and selected lines at generations 182-184 of mutation accumula tion at each of three temperatures (18 degrees C, 25 degrees C, 28 deg rees C), and estimated the mutational variance common to all environme nts and the mutational variance from genotype x environment interactio n. For sternopleural bristle number, the mutational interaction varian ce was 26% of the mutational variance common to all temperatures, and the interaction variance was due to temperature x line interaction. Fo r abdominal bristle number, the mutational interaction variance was 14 2% of the mutational variance common to all temperatures, and the inte raction variance was due to interactions of temperature x line, sex x line, and temperature x sex x line. It is possible that segregating va riation for bristle number is maintained partly by genotype x environm ent interaction, but information on the fitness profiles of mutations affecting bristle number in each environment will be necessary to eval uate this hypothesis quantitatively.