Geographic extent of introgression in and its effect on genetic population structure.

Genetic population structure is often used to identify management units in exploited species, but the extent of genetic differentiation may be inflated by geographic variation in the level of hybridization between species. We identify the genetic population structure of and investigate possible introgression within the genus by analyzing 13 microsatellites in 2,562 redfish specimens sampled throughout the North Atlantic. The data support an historical divergence between the "shallow" and "deep" groups, beyond the Irminger Sea where they were described previously. A third group "slope," has an extended distribution on the East Greenland Shelf, in addition to earlier findings on the Icelandic slope. Furthermore, from the Northeast Arctic and Northwest Atlantic waters are genetically different populations. In both areas, interspecific introgression may influence allele frequency differences among populations. Evidence of introgression was found for almost all the identified gene pools, but to a much lower extent than suggested earlier. Greenland waters appear to be a sympatric zone for many of the genetically independent groups. This study illustrates that the identified groups maintain their genetic integrity in this region despite introgression.