Population Genetic Structure is Unrelated to Shell Shape, Thickness and Organic Content in European Populations of the Soft-Shell Clam .

The soft-shell clam is one of the most ancient invaders of European coasts and is present in many coastal ecosystems, yet little is known about its genetic structure in Europe. We collected 266 samples spanning a latitudinal cline from the Mediterranean to the North Sea and genotyped them at 12 microsatellite loci. In parallel, geometric morphometric analysis of shell outlines was used to test for associations between shell shape, latitude and genotype, and for a selection of shells we measured the thickness and organic content of the granular prismatic (PR), the crossed-lamellar (CL) and the complex crossed-lamellar (CCL) layers.