Résumé
Originating from the north eastern Asia, Crassostrea gigas has been introduced and translocated, mainly for aquaculture purpose, into several European countries (from Norway to Portugal and in the Mediterranean Sea) (1). Although highly variable, the invasiveness pattern of C. gigas has been demonstrated in several countries and therefore considered as a pest or a noxious species in those areas (2 and 3). Our project aims at identifying the characteristics of such a flourishing species: can its success be explained by chance and/or global warming only or does it exhibit a more important potential of adaptation than other species? Therefore we developed a population genomics approach, known as "genome scan". It corresponds to the study of numerous loci spread through the genome, in order to quantify the part of the genome affected by a molecular signature that takes the form of a valley of diversity centred on the selected mutation (selective sweep) (see example in Figure 1a) and/or the form of an unexpected level of population differentiation (see example in Figure 1b). The genome scan is performed with AFLPs (Amplified Fragment Length Polymorphisms) as this technique allows obtaining a considerable number of loci over a large number of genomic regions which is a pre-requisite for studying the genetic basis of adaptation using genome scan method. We are genotyping different "colonizing" populations (Charente Maritime, Brittany and Herault – France, Denmark, Netherlands, Sweden), and a "native" population (Japan). Equilibrium models are then used to evaluate outliers to help focus research on genomic regions of interest. In addition, we are mapping on a reference population the candidate outliers and quantifying the part of the genome affected by a loss of diversity. We present and discuss here the first results.