Genetic Characterization of Cupped Oyster Resources in Europe Using Informative Single Nucleotide Polymorphism (SNP) Panels

Abstract

The Pacific oyster, Crassostrea gigas, was voluntarily introduced from Japan and British Columbia into Europe in the early 1970s, mainly to replace the Portuguese oyster, Crassostrea angulata, in the French shellfish industry, following a severe disease outbreak. Since then, the two species have been in contact in southern Europe and, therefore, have the potential to exchange genes. Recent evolutionary genomic works have provided empirical evidence that C. gigas and C. angulata exhibit partial reproductive isolation. Although hybridization occurs in nature, the rate of interspecific gene flow varies across the genome, resulting in highly heterogeneous genome divergence. Taking this biological property into account is important to characterize genetic ancestry and population structure in oysters. Here, we identified a subset of ancestry-informative makers from the most differentiated regions of the genome using existing genomic resources. We developed two different panels in order to (i) easily differentiate C. gigas and C. angulata, and (ii) describe the genetic diversity and structure of the cupped oyster with a particular focus on French Atlantic populations. Our results confirm high genetic homogeneity among Pacific cupped oyster populations in France and reveal several cases of introgressions between Portuguese and Japanese oysters in France and Portugal.

Genetic diversity and connectivity of the Ostreid herpesvirus 1 populations in France: a first attempt to phylogeographic inference for a marine mollusc disease

“…Given that the fate of new genetic variants is largely determined by host selection, one hypothesis to explain the lower diversity in the Bay of Brest and Thau Lagoon is that oyster populations there exert a bottleneck on viral diversity imported from Marennes-Oléron. However, several studies conducted in Europe to document oyster genetic variability and population structure have revealed a high level of genetic diversity, but no genetic differentiation between French populations (Lapegue et al, 2020; Rohfritsch et al, 2013; Vendrami et al, 2019). This lack of differentiation suggests that selection pressure exerted by oysters is not sufficient to explain differences in viral genetic diversity between farming areas.…”

“…Indeed, it can be speculated that some OsHV-1 variations imported from Marennes- Oléron have not found oysters with a genetic background compatible with their replication and survival. However, several studies conducted in Europe to document oyster genetic variability and population structure have revealed a high level of genetic diversity, but no genetic differentiation between French populations (Lapegue et al, 2020; Rohfritsch et al, 2013; Vendrami et al, 2019). This lack of differentiation suggests that selection pressure exerted by oysters is not sufficient to explain differences in viral genetic diversity between farming areas.…”

Population genetic structure of macrozoobenthic invertebrates: Its implications for coastal resource management

“…This might be the case for the Pacific oyster for which several repeated introductions from Canada and Japan of adults, but also high quantities of spat, happened by the end of the 1960s in Europe, especially in France and the Netherlands. This phenomenon led to a failure detection of genetic differences between Asian and European populations within the Pacific cupped oyster species [41]. High levels of gene flow were also reported in three squat lobster Munida species in the southwest Pacific Ocean, suggesting among population leading to panmixia or recent demographic expansion [37].…”

One in a Million: Genetic Diversity and Conservation of the Reference Crassostrea angulata Population in Europe from the Sado Estuary (Portugal)

“…Concerning their taxonomy, cupped oysters belong to two identified sister species [2]: the Pacific oyster Crassostrea gigas (Thunberg, 1793) and the Portuguese oyster Crassostrea angulata (Lamarck 1819), both introduced in Europe from their native ranges in the Northwestern Pacific [2].…”

“…The taxonomic classification of cupped oysters has been debated for almost two decades, being identified as a single species or two depending on their cross-fertilization and the genetic variation estimated by different molecular markers-for a complete list of references, see [2]. Recent genomic studies [2,3] have reinforced the hypothesis of two genetically similar but differentiated species.…”