Environmental effects on Segregation-distorter in Drosophila melanogaster: Irradiation of SD-72 at the onset of spermatogenesis

To ascertain the effect of irradiation at the onset of spermatogenesis on Segregation-distorter, irradiation treatments were administered to very late third instar male SD larvae. Part of the experimental and control groups were stored. The first four daily broods from unstored irradiated males exhibited depressed k values and aberration products. The percentage of aberrations observed per sperm batch is inversely correlated with the k values exhibited. The SD mechanism appeared to be most sensitive to irradiation prior to or at Prophase I. Using aberration products as an index, stored males transfer few sperm which were in meiotic or premeiotic stages at the time of treatment. The induction of these aberrations affected the action of the SD mechanism very little. The SD-bearing exceptional chromosomes were 0.9 of the total exceptions recovered. Lack of mating activity depressed the drive of SD in both irradiated and control groups. Prolongation of spermiogenesis may allow recovery of SD+ gametes which were rendered temporarily dysfunctional.