Influence of parentage upon growth in Ostrea edulis: evidence for inbreeding depression
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.(Received May 12 1999)
(Revised November 1 1999)
(Revised February 25 2000)
c1 Corresponding author. Conservatoire et Jardin botaniques, 1 chemin de l'Impératrice, Case Postale 60, CH-1292 Chambésy, Genève, Switzerland. Tel: +41 22 418 5165/5218. Fax: +41 22 418 5101. email Yamama.Naciri-Graven@cjb.ville-ge.ch
p1 Current address: Laboratoire de Génétique des Poissons, INRA, 78352 Jouy-en-Josas, France.