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 another and a control group, using 14 allozyme loci. All groups showed a similar and high degree of genetic variability. Overall, the percentage of polymorphic loci (P < 0.99 criterion) was 66.7%, the mean observed (and expected) heterozygosity (±S.D.) was 0.222±0.087 (0.223±0.087), and the mean number of alleles per locus (±S.D.)was 2.5 ± 0.6. While selection for increased whole weight does not appear to have significantly diminished genetic variation of the two generations of the selected breeding line relative to the controls, there were some significant allele frequency differences among groups (n = 100 per group). Unexpectedly, the allele frequencies from the third-generation sample was more similar to those of the control sample than the second-generation sample, due to sampling error in the latter samples. This was reflected in estimated effective population numbers 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 cases were similar to numbers expected if allele loss occurred through genetic drift or sampling variation only. © 2001 Elsevier Science B.V.