Phylogeographical structure of the Dover sole Microstomus pacificus: the larval retention hypothesis and genetic divergence along the deep continental slope of the northeastern Pacific Ocean

Population genetic variability and phylogeographical structure of the Dover sole, Microstomus pacificus (Teleostei: Pleuronectidae), were examined along the continental slope of the north-eastern Pacific Ocean using sequences of the left domain of the mitochondrial DNA (mtDNA) control region. Six sites were sampled in three primary biogeographical provinces (based on surface water temperatures), ranging from the subarctic to the warm temperate zones. Many haplotypes were discerned, totalling 90 for 110 individuals. Neighbour joining and parsimony analyses of the entire data set showed that some groups of haplotypes of adult Dover sole were widely distributed, suggesting either panmixia or homoplasy and reversals. However, a substantial number of groups of related haplotypes were geographically circumscribed, and there were significant differences among sites in the distribution of restricted haplotypes (based on a reduced number of characters), supporting geographical structure. Geographical differentiation of populations appeared to be consistent with the member-vagrant hypothesis for retention of the pelagic larvae in currents and recruitment to adult habitats, reducing long-distance dispersal. Results of this study indicate phylogeographical structure among some populations, despite extended pelagic larval periods, and apparent environmental homogeneity in the adult habitats along the continental slope.