Quantitative changes in breeding groups of Lebistes after irradiation.

Abstract

Neonatal guppies of a wild-coloured inbred strain were X-irradiated with 1000 R, corresponding to early oogonia and spermatogonia. At sexual maturity the irradiated fish and their sham-treated controls were mated to unirradiated guppies of another stock. The proportions of the body shape and the number of vertebrae of the F1 and F2 generations were determined. The quantitative characters controlled by polygenes in both experimental and control groups showed that the number of vertebrae increased in the F1 and decreased in the F2. The changes in body proportions reveal a trend towards a more compact type after ancestral irradiation. The variability coefficient was greater among females of the irradiated series. Shifts in the mean values were combined with alterations of viability revealing an increase in postnatal mortality and a reduction of litter size in the backcross generation. An increase in litter size and a decrease in postnatal mortality appeared in the F1 and F2 generations where radiation-induced detrimental mutations were less likely to become homozygous.