Patterns of morphological and genetic variability in UK populations of the shore crab, Carcinus maenas Linnaeus, 1758 (Crustacea: Decapoda: Brachyura)

Abstract

Previous research has identified extensive inter-population variability in the morphology of the shore crab (Carcinus maenas L.). To determine the source of this variation (genetic or environmental), morphological and genetic data were analysed from crabs collected from eight sites around the coast of the UK. Ten morphometric traits were measured from over 800 crabs and the degree of morphological similarity among sites calculated using multivariate techniques. Allozyme electrophoresis was used to investigate patterns of genetic similarity. Extensive morphological variability was detected; eight out of the ten morphometric traits analysed were useful when discriminating between crabs from each site. Discriminant function analysis revealed that over 35% of individuals could be classified to their site of origin on the basis of their morphology. In contrast, the allozyme analysis revealed low levels of genetic variability, both within the meta-population and among the crab population at each site. Pairwise comparisons revealed a moderate correlation between the degree of morphological and genetic similarity of crabs at each site, which suggests that the observed phenotypic variability has a genetic component. However, only around 20% of the phenotypic variability detected was associated with the patterns of genetic similarity. This means that patterns of morphological variability in this species are largely determined by the local environmental conditions: local factors could have a within-generation selective influence on mean trait values or C. maenas may exhibit phenotypic plasticity.

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

“…This morphometric variability and population differentiation is in accordance with studies already carried out in the UK with this species (e.g. Brian, 2005;Brian et al, 2006). Brian et al (2006) also showed that the relationship between the phenotypic characteristics and patterns of genetic similarity was not strong.…”

“…Brian, 2005;Brian et al, 2006). Brian et al (2006) also showed that the relationship between the phenotypic characteristics and patterns of genetic similarity was not strong. The results achieved in the current study, in accordance with Brian et al (2006), suggest that genetic and phenotypic characters are in some way independent, and that environmental factors, such as habitat, wave action, predation, food supply and salinity can play an important role in the patterns of shape variability.…”

“…Two aspects of the life history of the shore crab may have led to the evolution of plastic responses : due to its pelagic larval stage, high levels of genetic homogeneity are expected, so there is limited opportunity for local adaptation (Roman and Palumbi, 2004); and post-settlement movements can occur, particularly in response to predator pressures, even though settling megalopae have swimming and habitat-selection ability (Moksnes et al, 1998). Furthermore, the morphology of C. maenas may respond plastically to site-specific selection pressures, causing changes in the expression of a particular morphological trait (Brian et al, 2006).…”

“…Brian, 2005;Todd et al, 2006). Given that population divergence is prevented by gene flow, patterns of phenotypic variability are likely to reflect differences between the local environmental conditions, as was suggested by Brian et al (2006). Phenotypic plasticity (i.e.…”

Morphometry of the stone crayfish (Austropotamobius torrentium) in the Czech Republic: allometry and sexual dimorphism

“…In this study, most observed morphological traits showed a wide range of variability. This variability is an evolutionary strategy based on various genotypes (Brian et al, 2006, Henryon et al, 1989Jones et al, 2000;Lutz and Wolters, 1989) or variations of the same genotype (Ghia et al, 2006) allowing an organism to alter its morphology or behaviour (Haddaway et al, 2012). In the Czech Republic, we should consider more than only one genetic lineage; together with isolated populations from the Danube or Elbe watersheds, a special position is occupied by the stone crayfish population from Luční brook in the Giant Mountains which probably was introduced from the Balkan Peninsula (Pešek, 2013).…”