Relative ages of present populations of Barbus barbus and Barbus meridionalis (Cyprinidae) in southern France: preliminary considerations

Abstract

The biogeographic history of French freshwater fish is poorly defined, and fishery managers donot currently take into account the only functional level, that of genetic stocks. The aim of the present paper is to provide a contribution for filling this gap. It surveys existing knowledge and previous studies of the genus Barbus in France. A first part chronicles the populations of the two French species according to ancient (tertiary) and recent (pre- and post-glacial, and contemporary) history. Thus, the Barbus meridionalis lineage seems to have been present in this country for 5 million years at least (Upper Miocene), but the present populations of the Rhône Valley seem to be the result of recent recolonization by populations restricted to a Languedoc-Roussillon sanctuary during the glaciations. B. barbus has its origin in the Danube drainage basin. It is a more recent invader in Western Europe. Its immigration may have occurred during the Pliocene interconnections between the Rhône, the Rhine and the Danube basins (and perhaps even that of the Loire), or even more recently. If the first assumption is correct, the present populations of the Rhône are presumably descended from populations that found a shelter in the southern tributaries of the right bank of the river, or even in the tributaries of the right bank of the River Saône. In the Rhine basin, the sanctuarymay have been the tributaries of the left bank, the Meuse and the Mosel Rivers, from which probablydescend the populations of Eastern England. The present occurrence of B. barbus in the Garonne catchment and perhaps also the Seine catchment seems to be due to man. The second part of the paper considers the genetic point of view, but the lack of data make it possible to discuss only the status of B. meridionalis. A synthesis of the available enzymatic data, compared with the hypotheses expressed in the first part, reveals a good agreement between the two approaches. In particular, the French an Spanish populations are well differentiated from one another, confirming the ancient settlement of the species in these countries. Moreover, the homogeneity of the French populations, and the higher polymorphism of the Roussillon population, agree with the presumption of a survival in this province during the glaciations. For instance, the first results on B. barbus show a very low polymorphism and a very high homogeneity throughout the different catchments examined (Rhône, Meuse, Garonne, Hérault). Based on this work, a historical diagram is proposed, with the aim of ordinating the hypotheses for future research on the genetics of this group.