Genetic differentiation of the bullhead Cottus gobio L. across watersheds in Central Europe: Evidence for two taxa

Starch gel electrophoresis and morphological characters were used to analyse the geographical variation of 16 populations of Cottus gobio, the bullhead, across three Central European drainage systems. Twenty out of 31 screened allozyme loci were polymorphic. Genetic variability differed considerably among populations (H(e) between 0.008 and 0.099). Populations of the Danube and Elbe were significantly less variable than the Rhine populations. This is interpreted as a consequence of the smaller population sizes of the bullhead within the parts of the Danube and Elbe investigated. An F(ST) value of 0.73 showed that the bullhead is one of the most highly structured freshwater fish species. High genetic distances and morphological differences indicated the existence of two well-defined taxa, one within the Rhine system and one within the Danube and Elbe systems. Genetic distance between these two taxa is about 0.24 (Nei's unbiased distance). Time estimates showed that the two taxa were probably originally separated by palaeogeographical events at the Pliocene/Pleistocene change.