INVESTIGATION OF THE GENETIC STRUCTURE OF THE PACIFIC OYSTER (CRASSOSTREA GIGAS) IN EUROPE USING A HIGH DENSITY SNP ARRAY
David L.J. Vendrami1, Luca Telesca2, Joseph I. Hoffman1
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1 Department of Animal Behavior, University of Bielefeld, Postfach 100131, 33615 Bielefeld, Germany
2 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
The pacific oyster Crassostrea gigas is a shellfish native to the pacific coast of Asia that was introduced into Europe in the 1960’ and that is now considered invasive. Previous studies of this choice edible species showed little in terms of genetic differentiation among European populations, but were based on small numbers of genetic markers. Here we employed a high density SNP array to genotype 128 C. gigas, sampled along the European latitudinal gradient and including individuals from the source populations in Japan and British Columbia, at over 30,000 Single Nucleotide Polymorphisms, resulting in the very first study of European oysters that employs such a large number of genetic markers.
Results from a variety of different approaches, allowed us to produce a robust picture of the genetic structure of C. gigas populations in Europe as well as to study their relationship with the populations they originated from. Samples from the northern part of the Iberian Peninsula to the Netherlands, corresponding to the area where C. gigas was initially introduced, form a separate genetic cluster that do not differ from samples collected from the two source populations. Other separate clusters were found in northern Europe, in the Mediterranean and in the south of Portugal, where another cupped oyster of uncertain taxonomic identity is found (C. angulata).
Finally, farmed populations were genetically different from each other and from all of the other populations, supporting the hypothesis that aquaculture practices can quickly shift allele frequencies of animal populations. Furthermore, a significant correlation between latitude and genetic diversity was found, with samples from higher latitudes showing greater levels of heterozygosity and, interestingly, farmed samples showing the highest values. Our results, coming from the analysis of a dataset with unprecedented resolution power, provided new insights into the adaptive genetic structure of the keystone invader C. gigas in Europe.