Abstract
The soft-shell clam Mya arenaria 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. Strong population structure was detected, with Bayesian cluster analysis identifying four groups located in the Mediterranean, Celtic Sea, along the continental coast of the North Sea and in Scotland. Multivariate analysis of shell shape uncovered a significant effect of collection site but no associations with any other variables. Shell thickness did not vary significantly with either latitude or genotype, although PR thickness and calcification were positively associated with latitude, while CCL thickness showed a negative association. Our study provides new insights into the population structure of this species and sheds light on factors influencing shell shape, thickness and microstructure.
Highlights
The soft-shell clam Mya arenaria Linnaeus, 1758, is a marine bivalve that occurs in numerous intertidal infaunal communities across Europe and North America
Radiocarbon dating of shells found along the coast of the North Sea suggests that M. arenaria was subsequently reintroduced into Europe by the Vikings during the 13th to 15th centuries [8,9], making it one of the oldest marine invaders of European coasts [10]
This study found clear evidence for genetic differentiation at microsatellites but not mitochondrial DNA (mtDNA) [27], implying that population genetic structure may be present over a broader scale in Europe
Summary
The soft-shell clam Mya arenaria Linnaeus, 1758, is a marine bivalve that occurs in numerous intertidal infaunal communities across Europe and North America. While this species has a relatively high dispersal potential during the planktonic larval stage and as juveniles [1], the contemporary geographic distribution of M. arenaria appears to have been largely influenced by human-mediated translocations. Following recolonization from the North Sea and probable further man-mediated introductions, the soft-shell clam can nowadays be found around most of the continent, including in the Mediterranean Sea [11,12], on the Iberian Peninsula [13], along the Atlantic coast of France [14], around the British Isles [15,16] and in the North Sea [1,17,18]
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