Conséquences génétiques de la production intensive de larves d'huîtres en écloserie : étude des processus de dérive et de sélection liés aux pratiques d'élevage.

In order to study the genetic influence of intensive production of the larval stage in commercial hatcheries, two types of specific selective processes were examined: the effects of discarding the smallest larvae and temperature. A mixed-family approach was used in order to infer the genetic composition of the larvae. The results show that our mixed-family approach, combined with microsatellite-based family assignment, is a powerful tool for the study of bivalve larvae genetics. Selective sieving is an advantageous practice at a phenotypic scale, but also represents a substantial risk for diversity loss. The culled larvae are important for the minimization of the variability in reproductive success and the maximization of broodstock genetic diversity. These results corroborate the variability estimations on broodstocks from commercial hatcheries that show lower allelic polymorphisms relative to natural populations. Temperature exerts an influence on the timing of genetic variability expression. A temperature of 26°C, coupled with selective sieving could amplify the selective effect. Furthermore, selection of fast growing larvae has proven to counteract the expression of genetic load at this stage. Genetic effects of intensive rearing conditions are significant and should be taken into account in hatchery practices, especially in terms of genetic diversity management.