Decrease of the effective population size during maintenance of the guppy strain

The change of gene frequencies at the AA T-1* and PGM-1* loci was examined in the two guppy strains, S and S3, which had been maintained as a closed c olony for a period of 16 years. These strains had been separated from an or iginal strain in 1981. In the S strain, the *a allele frequency at AAT-1* l ocus changed from 0.282 in 1981 to 0.602 in 1997, and the *a allele at the PGM-1* locus changed from 0.772 to 0.430. On the other hand, in the S3 stra in, the *a allele frequency at the AAT-1* locus changed to 0.395 in 1997, a nd the *a allele at the PGM-1* locus changed to 0.528. The effective population size (Ne) during the maintenance period of the gup py strain was estimated based on the magnitude of the random drift in the g ene frequency. The estimated Ne was initially 623 in the S strain and 413 i n the S3 strain. The decrease of Ne over a period of 16 years was demonstra ted to be 18 in the S strain and 24 in the S3 strain, and these phenomenon may be led by the sampling of mature fish.