HOW DAMS ON THE RIVER DANUBE MIGHT HAVE CAUSED HYBRIDIZATION AND INFLUENCED THE APPEARANCE OF A NEW CYPRINID TAXON

When a new species is found, or a known one collected outside its recognized distribution, most people either assume that the species has been overlooked in the past or that it has recently invaded the area in question from elsewhere. While other, more evolutionary explanations are possible, these are nearly always ignored, in spite of the common perception that animals are constantly in states of change. Recent findings in the Danube River are used as examples for such alternative interpretations. The case of two forms of Vimba - short and long snouted - which live in sympatry in the upper Danube is dispelled, as one of them is identified as a hybrid between female V. vimba and male Blicca bjoerkna. Frequent occurrences of this hybrid (and a few of its backcrosses) in recent times are explained by man-induced alteration of reproductive isolation between their parent species, caused by the impoundment of the river by dams built as part of the Rhein-Main-Donau Kanal. These impoundments, however, might be responsible not only for the creation of hybrids but also for direct speciation, as the case of Gobio albipinnatus may represent. The ability for epigenetic creation of two alternative life-history states (as part of the theory of alprehost) and the survival of an alternative state when environmental conditions change might be ultimately responsible for the appearance of a new taxon.