Untitled

Abstract

The respective status of the Portuguese oyster, Crassostrea angulata, and the Pacific oyster, Crassostrea gigas, has long been a matter of controversy. Morphological and physiological similarities, homogeneity of allozyme allelic frequencies between populations of the two taxa and the demonstration of hybridization lead most authors to suggest that they should be regrouped within the same species. The risk of introgression and the present expansion of C. gigas aquaculture in Europe raises the question of the need for preservation of C. angulata in Europe, as only a few populations remain. We studied European and Asian populations of C. gigas and C. angulata using microsatellite and mitochondrial DNA markers to estimate their genetic diversity and differentiation. The analysis of genetic distances and the distribution of allelic and haplotype frequencies revealed significant genetic differences between taxa, showing two clusters: (1) C. gigas French and Japanese populations and (2) C. angulata Portuguese and Taiwanese populations. The Asian origin of the Crassostrea angulata taxa is therefore confirmed. Unlike previous studies based on allozymes, significant nuclear genome differences were noted between C. angulata and C. gigas. Despite the presumed history of the introduction of C. angulata into Southern Europe, these populations did not show any significant reduction of variability compared to Taiwanese populations. Any conservation plans for European C. angulata populations should take its non-native origin into account. They represent a valuable genetic resources for European breeding program.

Detailed insights into pan‐European population structure and inbreeding in wild and hatchery Pacific oysters (Crassostrea gigas) revealed by genome‐wide SNP data

“…Our comprehensive sampling design coupled with high‐resolution genomic data allowed us to resolve patterns of genetic differentiation over both broad and fine geographic scales. Specifically, we found clear support for a northern and southern European group, with the latter being virtually identical to the Japanese and Canadian source populations, consistently with previous studies (Huvet, Lapegue, Magoulas, & Boudry, ; Moehler et al, ; Rohfritsch et al, ). We furthermore resolved substantial genetic differences between wild populations and hatcheries and compared genomic inbreeding coefficients to show that some of the sampled hatchery cohorts have higher levels of inbreeding than wild populations.…”

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

“…This might be the case for the Pacific oyster C. gigas, 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 [23,84]. Hence our results confirm an absence of detection of clear differences between the source population and the French populations of C. gigas as several other studies did even with a far higher number of markers [21,42,50,61,85,86]. We failed at detecting differences between Asian and European populations within each species [42] because our 80 SNPs panel was not well adapted for detecting such structure if it exists.…”

“…We failed at detecting differences between Asian and European populations within each species [42] because our 80 SNPs panel was not well adapted for detecting such structure if it exists. However this panel allowed detecting the difference observed between the southern group of European C. gigas populations and the northern group [21,30,42,50,61,86,87] here represented by the Danish sample (LIM). Hence several outlier loci between the two groups identified in [50] had been included in this panel.…”

Temperature modulate disease susceptibility of the Pacific oyster Crassostrea gigas and virulence of the Ostreid herpesvirus type 1

“…Quality of RNA and quantity were determined using a NanoDrop 2000 (Thermo Scientific). First strand cDNA synthesis was performed using the iScript™ cDNA Synthesis Kit (BIO-RAD) with 1µg of RNA [29]. A no reverse transcription was performed after each DNAse treatment using real time PCR to control for the absence of oyster and virus genomic DNA.…”