Divergence and molecular variation in common whelk B uccinum undatum ( G astropoda: B uccinidae) in I celand: a trans‐ A tlantic comparison

The dispersal and history of species affects their genetic population structure at both small and large geographical scales. The common whelk, B uccinum undatum , is a widespread subtidal gastropod in the N orth A tlantic that has no planktonic larvae and has thus limited dispersal capacity. The snail, which has been harvested by humans for centuries, is highly variable in morphology. To evaluate the population structure in the rich fishing grounds in western I celand and its divergence from samples across the A tlantic, genetic patterns based on sequence variation in two mitochondrial (mt) DNA genes ( COI and 16S ) and five microsatellites were studied and compared with variation in populations from both sides of the A tlantic. Significant differences in allele and haplotype frequencies were found among samples separated by short distances along the coast of I celand. Partition of the variation showed larger variance among samples obtained from distant regions than from neighbouring sites and genetic distances were correlated with geographical distance among populations in E urope. Phylogeographic patterns in mtDNA reveal different monophyletic lineages on both sides of the A tlantic, which predate the onset of the I ce Age and which may constitute cryptic species. Similar micro‐ and macrogeographical patterns were observed for the mtDNA and microsatellite markers, despite high frequencies of null alleles. B ayesian skyline reconstructions of the demographic history and mismatch distributions suggest that, although sizes of some populations were unaffected by I ce Age glaciations, others show signs of expansion after the Last Glacial Maximum. These phylogeographical patterns are consistent with patterns expected for low dispersal species that have survived in allopatric glacial refugial populations on both sides of the A tlantic and in deep‐sea refugia within each continent. The observed genetic structure has implications for conservation and sustainable management of the harvested populations. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society , 2014, 111 , 145–159.