Population differentiation of the shore crab Carcinus maenas (Brachyura: Portunidae) on the southwest English coast based on genetic and morphometric analyses

Abstract

Carcinus maenas has a planktonic larval phase which can potentially disperse over large distances. Consequently, larval transport is expected to play an important role in promoting gene flow and determining population structure. In the present study, population structuring on the southwest coast of England was analysed using molecular and morphometric approaches. Variation at eight microsatellite loci suggested that the individuals sampled within this region comprise a single genetic population and that gene now among them is not restricted. Nevertheless, the F-ST values estimated across loci for all populations suggested that the Tamar population was significantly different from the Exe, Camel and Torridge populations. This differentiation is not explained by isolation by distance, and coastal hydrological events that are apparently influencing larval flux might be the cause of this pattern. Morphometric analysis was also performed. Analysis of carapace and chela shape variation using landmark-based geometric morphometrics revealed extensive morphological variability, as the multivariate analysis of variance showed significant morphometric differences among geographic groups for both sexes. Thus, the morphological differentiation found may be a plastic response to habitat-specific selection pressures.

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