Loss of genetic variability in the sub-strains which were established from one strain of the guppy Poecilia reticulata

The changes of gene frequencies and genetic variabilities in sub-strains which were experimentally subdivided from the same strain of the guppy Poecilia reticulata was examined. Each sub-strain was established by a small number of pairs (3-10) and maintained as a closed colony at a size of 200-500 individuals per aquarium. Of the 30 loci scored, variations were observed at three loci, Aat-1, Pgm-1 and Pgm-2. At these three polymorphic loci, the allele frequencies of each sub-strain fluctuated around the allele frequency of the original strain. However, there were no significant differences between the allele frequency of the original strain and the mean allele frequency of sub-strains at each locus. Average heterozygosities of each sub-strain also fiuctuated and were less than that of the original strain. There was no correlation between the decrease of the average heterozygosity and the initial number of pairs in each sub-strain, and the time after subdivision. These results suggest that the change of allele frequencies and loss of genetic variability would be determined by the genetic constitution of initial individuals of sub-strains