Mechanisms of Polyploid Evolution in Fish: Polyploidy in Sturgeons

Possible ways of polyploid speciation in fish are analysed. According to this analysis, the autopolyploid origin of bisexual species seems to be practically improbable, whereas their allopolyploid origin is quite probable, as it has been confirmed by data on reticular speciation in vertebrates and experimental crossings in fish. The most probable hybrid origin of polyploid sturgeon species is confirmed by various data. The species with 120-chromosomes belong to the ancient tetraploids, but they have passed through significant diploidization that has resulted in their practically functional diploid state. Therefore two scales of ploidy levels should be distinguished in Acipenseriformes: the 'evolutionary scale', which presumes diploid-tetraploid-octoploid-12-ploid relationships among these species, and the 'recent scale', which presumes diploid-tetraploid-hexaploid relationships. At least three independent polyploidization events have taken place in sturgeon evolution, but in fact there seem to have been many more.