Molecular methods for assessing temporal adaptive changes in fish populations: a case study employing historical analysis of Pan I in cod (Gadus morhua)

We investigated temporal genetic differentiation at the Pan I locus in four cod populations from the southeastern part of the species distribution: the Baltic Sea, the North Sea, the Faeroe Plateau and the Faeroe Bank. Historical otolith collections enabled investigation of allele frequency variation over time periods up to 69 years employing Pan I primers specifically designed for partially degraded DNA. Small and nonsignificant temporal changes in Pan I allele frequencies were observed in the four populations. Simultaneous microsatellite analysis revealed similar temporal genetic stability with temporal Fst飐 ranging from 0 - 0.006 suggesting limited demographic changes. Sea surface temperature (SST), which has been suggested as the primary driver for the geographical distribution of Pan I alleles in cod, showed no long-term trend although temperature has increased since the mid-1990s. Our study demonstrates that populations in the southeastern part of the species range has been characterized by very high frequencies of the Pan IA allele for many decades.