Genetic variability for growth was analysed in three populations of Ostrea edulis, selected for
resistance to the protozoan parasite Bonamia ostreae. This study was undertaken first to determine
the potential for selection for growth in populations that have never been selected for this
character, and second to estimate heterosis versus inbreeding depression. Growth was monitored in
culture for 10 months. The selected populations (namely S85-G3, S89I-G2 and S89W-G2), their
crossbred population and a control population were composed of full-sib families whose parents
were already genotyped using five microsatellite markers. This genotyping allowed the estimation
of genetic relatedness among pairs of parents. The parents' relatedness was then correlated with
the growth performance of their offspring within each of the three populations, and inbreeding
depression was estimated. The population effect for growth was highly significant, with the
crossbred population having the highest growth rate, followed by S89I-G2 and S89W-G2, S85-G3
and the control population. The within-populations family effect was also highly significant,
indicating, as well as the high value for heritability at the family level (between 0·57 and 0·92), that
a potential for a further selection for growth still exists within the three populations. Estimates of
inbreeding depression (relative to the mean, for complete inbreeding) were high (1 for S891-G2,
0·44 for S89W-G2 and between 0·02 and 0·43 for S85-G3), which correlates with the apparent
heterosis for growth observed in the crossbred population. These results are discussed in the
context of the future management of the selected populations.
Influence of parentage upon growth in Ostrea edulis: evidence for inbreeding depression
