The aim of this investigation was to compare the genetic responses of two common cyprinids, chub (Leuciscus cephalus) and roach (Rutilus rutilus), to various habitat and pollution regimes within the same river basin, the Rhone, using allozyme data. Over the three main portions of the River Rhone, lower genetic polymorphism and lower heterozygosity were detected for the chub in the Saone, which is characterized by lower environmental diversity than in the Lower and Upper Rhone. On a local scale, no detectable decrease in polymorphism or heterozygosity was observed in populations of both species living in heavily polluted sites of the Rhone's Chemical Corridor. Significant differentiation was detected between populations of both chub and roach localized upstream and downstream from the dams of Donzère Mondragon, which were erected 45 years ago. The F statistics and neighbor-joining analysis of genetic distances suggested that the Upper Rhone populations were unique in comparison with the other populations for both species; this situation could be the result of historical factors and (or) a selective pressure in a variable environment. Isolation by distance was observed for chub in the less perturbed river system over a range of 100 km. By contrast, there was no relationship between geographic distance and genetic distance for roach, whatever the subsystem tested.
Investigation into Adaptation in Genes Associated with Response to Estrogenic Pollution in Populations of Roach (Rutilus rutilus) Living in English Rivers
