Mitochondrial DNA analysis reveals gene drift and structuring in the declining European piddock Pholas dactylus (L., 1758) confirming high vulnerability

Abstract

Pholas dactylus is a historically valuable species with a relevant role in both environmental and biotechnological fields. It has become scarce in Europe due to habitat destruction and human overuse. This species is currently undergoing steep population declines, which have caused local extinction and/or distribution range contraction. Six different localities were sampled between the southern central region of the Bay of Biscay (Spain) and the Black Sea (Bulgaria and Romania) with the aim of describing for the first time its genetic variation patterns and assisting its conservation. Analyses using the mitochondrial Cytochrome Oxidase I gene revealed a high number of unique haplotypes in the Atlantic and Black Sea areas and significant genetic structuring (FST=0.15495 p<0.001,ΦST=0.36501 p<0.001). Significant differences were found between the regions since higher haplotype and nucleotide diversities were found in the Bay of Biscay (Dh=0.913, π=0.97%) than in the Black Sea (Dh=0.732, π=0.30%) and three different genetic units were discovered based on significant ΦCT values (western Bay of Biscay, Villaviciosa (the easternmost locality sampled within the Bay of Biscay) and the Black Sea) (ΦcT=0.41076 p<0.05). Globally, it seems that after different origins, gene drift has been acting on the species in its European geographical distribution. Results from this study reinforce the need for more efforts on obtaining data for this species and for a careful protection of its habitats.