Population structure of plaice (Pleuronectes platessa L.) in northern Europe: a comparison of resolving power between microsatellites and mitochondrial DNA data

We used Single Strand Conformation Polymorphism (SSCP) of mtDNA control region to assess the population structure of the flatfish Pleuronectes platessa (plaice), to compare these data with a previous study based on microsatellite loci, and to test for possible sex-biased dispersal. From 461 individuals, 163 haplotypes were identified across 11 locations. Diversity was higher with mtDNA (h =0.776 to 0.981; π = 0.0178 to 0.0298) as compared to microsatellite loci using the same samples (He = 0.721 to 0.77). Genetic diversity was lower in samples from Iceland and Faroe, as compared to the continental shelf samples. Although both classes of markers revealed a relatively strong differentiation between shelf and off-shelf populations (θ = 0.1015 and θ = 0.0351, respectively), only the mtDNA data were able to detect differentiation within the continental shelf, i.e., a North Sea-Irish Sea group which was weakly distinguishable from Norway (θ = 0.0046), the Baltic (θ = 0.0136) and the Bay of Biscay (θ = 0.0162). No evidence was obtained for isolation by distance, nor for sex-biased dispersal. This study demonstrates the importance of using more than one class of markers, especially for species such as plaice, with large populations, high dispersal and recent colonisation histories.