Allozyme variation in three generations of selection for whole weight in Sydney rock oysters (Saccostrea glomerata)

Genetic variability in second and third generations of a selective breeding line of Sydney rock oysters (Saccostrea glomerata) was compared with one a nother and a control group. using 14 allozyme loci, All groups showed a sim ilar and high degree of genetic variability. Overall, the percentage of pol ymorphic loci (P < 0.99 criterion) was 66.7%, the mean observed land expect ed) heterozygosity (+/- S.D.) was 0.222 +/- 0.087 (0.223 +/- 0.087), and th e mean number of alleles per locus (+/- S.D.) was 2.5 +/- 0.6, While select ion for increased whole weight does not appear to have significantly dimini shed genetic variation of the two generations of the selected breeding line relative to the controls, there were some significant allele frequency dif ferences among groups (n = 100 per group). Unexpectedly, the allele frequen cies from the third-generation sample was more similar to those of the cont rol sample than the second-generation sample, due to sampling error in the latter samples, This was reflected in estimated effective population number s of 41.4 +/- 14.0 for the second-generation line and 383.8 +/- 249 for the third-generation lines, when compared to the control group, and 7.5 +/- 2 for the third generation when compared to the second generation. Numbers of alleles remaining in all eases were similar to numbers expected if allele loss occurred through genetic drift or sampling variation only. (C) 2001 El sevier Science B.V. All rights reserved.