Phylogeographic structure of a protogynous hermaphrodite species, the ballan wrasse Labrus bergylta, in Ireland, Scotland, and Norway, using mitochondrial DNA sequence data

The ballan wrasse, Labrus bergylta, is a protogynous hermaphrodite marine fish species that inhabits coastal waters of the eastern North Atlantic. Sequential hermaphrodite species tend to be characterized by a skewed sex ratio, which is thought to lead to marked population structuring due to a reduced effective number of breeders. Furthermore, due to its large body size (compared with other wrasse species) and its peculiar feeding behaviour, this species has been identified as a candidate cleaner fish to be used in parasite control of farmed finfish. In the present study, we used mitochondrial DNA (control region) sequence data to investigate the genetic diversity and population structuring of ballan wrasse in waters around the British Isles and southern Norway. Ballan wrasse in southern Norway showed lower levels of genetic diversity than around the British Isles, which appear to be the result of historical demographic events (population bottleneck followed by expansion). Analysis of mismatch distributions and the presence of two highly divergent clades unevenly represented in Atlantic and Scandinavian regions suggest distinct recolonization patterns in these two regions. These results provide a first insight on the status of wild populations of ballan wrasse in the eastern North Atlantic, with implications for conservation and management.