L'hybridation naturelle entre le barbeau commun et le barbeau méridional en France : compte rendu de dix années de recherche

Abstract

The aim of this publication is double: one is to gather all the different studies concerning the hybridization between the common barbel and the Mediterranean barbel for setting off the mechanisms of this hybridization; second is to collect from different searchers unpublished data about these two species in order to have an idea of the extent of this hybridization in France. These two species, Barbus barbus and Barbus meridionalis, are quite different morphologically (figure 1) and ecologically. The former lives in large rivers with a strong current whereas the second one can live in small mountain tributaries. In southern France, hybridization occurs in few rivers. The sampled fish were analysed by electrophoresis on horizontal starch gels at ten diagnostic loci. A genetic hybrid index (GI) corresponding conventionally to the percentage of meridionalis genes in an individual or a population was calculated. A hybrid zone has been identified in the Lergue river, near Montpellier, by the presence of enzymatic clines (figure 3). The presence of sharp enzymatic clines and linkage disequilibrium indicate that this hybrid zone is a tension zone, in which a balance between selection and dispersal maintains the clines. Parasitical studies, using a natural specific parasite of Barbus meridionalis as genetic marker, have demonstrated the importance of the behaviour of fish for being infested or not, and so, for hybrid zone stability. Other studies in natura or in aquaria have shown too the existence of ecological differences between the two species and their hybrids. Paleontological evidences suggest that the two species only came into contact since last glaciation, date of the arrival from the nearest catchment area of Barbus barbus in Hérault basin. A map showing the extent of hybridization between the two species in France is given (figure 2). All these results are used for trying to understand how this hybridization is functioning.