| Summary: | Variation in morphology of shelled marine gastropods across small spatial scales may reflect restricted population connectivity, resulting in evolutionary or plastic responses to environmental heterogeneity. Species delimitation of shelled gastropods is often based solely on shell characteristics; therefore, morphological variation can lead to taxonomic confusion and inaccurate estimates of species diversity. A comprehensive delimitation approach based on both phenotypic and genotypic information is needed in the face of such taxonomic uncertainty. The common whelk Buccinum undatum, a subtidal gastropod ubiquitous in the North Atlantic, exhibits considerable spatial variation in shell morphology and color. The purpose of the current project was to perform a comprehensive analysis of phenotypic differentiation across the whelk’s distribution and compare with a revised analysis of molecular genetic differentiation among the populations. Phylogenetic reconstruction revealed monophyletic Eastern and Western North Atlantic whelk lineages, which diverged early in the Pleistocene glaciation (~2.1 Mya). Species screening indices indicated cryptic speciation as a result of allopatric divergence. Genetic distances between populations from the two continents were similar to or greater than interspecific genetic distances across several North Pacific and North Atlantic Buccinum species. Morphological differentiation in whelk populations across the North Atlantic reflected this genetic split. Concordant with observed genetic differentiation, Canadian and Icelandic whelk reared in a common garden experiment revealed consistent morphological differences between juveniles from the two continents. Finally, analysis of fine-scaled phenotypic variation of common whelk in Breiðafjörður, Iceland, revealed that shell color diversity, shape and proportion of striped individuals were all related to depth. Svæðisbundinn útlitsbreytileiki sjávarkuðunga ber oft vitni um lítinn samgang milli stofna og getur endurspeglað þróun aðskildra ...
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