Genetic structure of the flounders Platichthys flesus and P. stellatus at different geographic scales

The genetic structure of the flounders #Platichthys flesus$ L. and #P. stellatus$ Pallas was investigated on different spatial scales trough analysis of allozyme variation at 7 to 24 polymorphic loci in samples collected from different regions (Baltic Sea, North Sea, Brittany, Portugal, western Mediterranean, Adriatic Sea, Aegean Sea and Japan) in 1984 to 1987. No geographic variation was evident within a region. Some pattern of differentiation by distance was infered within the Atlantic, while the Mediterranean comprised three geographically isolated populations and was itself geographycally isolated from the Atlantic (fixed allele differences at up to three loci were found among #P. flesus$ populations from the Atlantic, the western Mediterranean, the Adriatic Sea, the Aegean Sea and also #P. stellatus$ from the coast of Japan). Sea temperature during the reproductive period probably acts as a barrier to gene flow between populations. Genetic distances among European flounder populations (#P. flesus$) were higher than, or of the same magnitude as, the genetic distance between Pacific (#P. stellatus$) and European flounder populations, suggesting that #P. flesus$ is paraphyletic and/or there is no phylogenetic basis to recognising #P. stellatus$ as a different species. The divergence between #P. flesus$ and #P. stellatus$ was thus inferred to be more recent than the divergence between the present #P. flesus$ populations from the NE Atlantic and eastern Mediterranean. The eastern Mediterranean populations are thought to originate from the colonisation of the Mediterranean by a proto-#P. flesus$/#P. stellatus$ ancestor, whereas the present western Mediterranean population has undergone a more recent colonisation event by #P. flesus$... (D'après résumé d'auteur