Cytonuclear discordance in the marbled crab, Pachygrapsus marmoratus (Fabricius, 1787) along the Mediterranean coasts of turkey

The marbled crab, Pachygrapsus marmoratus is a common species in the Mediterranean and along the coasts of Turkey. Its global distribution extends to the north-eastern part of the Atlantic Ocean. In this study, a total of 384 specimens from 32 sites were collected from around coasts of Turkey, and genetically examined in mitochondrial CO1 gene and five nuclear microsatellites for a better understanding of its evolutionary history. High levels of genetic differentiation was found between populations of P. marmoratus distributed all around the Turkish coasts (Population C) and those constrained to the Mediterranean coasts (Population M). Both populations, however, shared the same or have very similar mtDNA CO1 haplotypes. Different scenarios are discussed referring to the biogeographical history of the Mediterranean for explaining this pattern. Two alternative explanations for the cytonuclear discordance as retention of ancestral polymorphisms or gene flow after secondary contact could not be distinguished. The use of complementary mitochondrial markers with faster mutation rates than CO1 subunit in addition to microsatellites, and sampling individuals from the rest of the Mediterranean and from the Atlantic Ocean can be useful in resolving the observed pattern.