POPULATION-STRUCTURE OF THE DOVER SOLE, SOLEA-SOLEA L., IN A BACKGROUND OF HIGH GENE FLOW

To investigate the genetic population structure of the Dover sole, Sol ea solea L., allozyme electrophoresis was performed on 303 fish collec ted from seven locations ranging from Cumbria, Great Britain, to Greec e. A total of 22 enzyme systems were analysed, coded by 33 loci. Of th ese, 27 loci were polymorphic using the P-99 criterion. A phenogram us ing Prevosti's Distance generated by the Wagner method exhibited a geo graphic pattern in the clustering of populations. Estimates of N-m (ef fective number of migrants per generation between populations) were su fficiently high to imply near-panmixia between the North Sea, Bay of B iscay and the Irish Coast populations, indicating a probable movement of migrants through the English Channel. However, despite this high le vel of gene flow, striking patterns of geographic differentiation were observed at a few loci. Allele frequencies ar: loci ACOH, EST-I-1, PE P-I-2 exhibited genetic patchiness on both local and range-wide (withi n the northern and southern European basins) scales. This pattern of g enetic patchiness could be the result of localised selection, genetic drift or single-generation sampling effects.. Estimates of mean hetero zygosity (H) were inversely related to latitude. Evolutionary processe s such as genetic drift and founder effect, and/or selection, may have produced the observed difference in the number of alleles between the basins. Moreover, the absence of isolation by distance provides suppo rt for a model of geographic isolation. Such a pattern of genetic patc hiness, revealing a slight reduction of genetic variability in the nor thern European basin, may suggest a population bottleneck, or local re duction in population size. Various physical parameters, especially wa ter temperature during the reproductive period, vary within the range of the species, and may produce or maintain this genetic differentiati on. These results indicate the role of both ecological and evolutionar y structuring mechanisms in determining the genetic population structu re of S. solea. (C) 1998 Elsevier Science B.V. ALI lights reserved.