Sturgeons are pretty polyploid: hybrid and ploidy diversity in sturgeons. International meeting on the genetics of polyploids

Symonová R. Flajšhans M. Gela D. Rodina M. Pelikanova Š. Rabova M. Rab P

Sturgeons, shovelnoses and paddlefishes (Acipenseriformes with families Polyodontidae and Acipenseridae) include three evolutionary (paleo) ploidy levels: tetraploid (4n, ~120 chromosomes), octaploid (8n, ~240 chromosomes) and also dodecaploid (12n, ~360 chromosomes in A. brevirostrum). While paleotetraploid level is present in Polyodontidae, the elevated ploidy levels are confined to several species of sturgeons of the genus Acipenser. Sturgeons are also notoriously known to hybridise irrespective to ploidy level producing progeny of intermediate ploidy levels. Larger screening of ploidy level in several European hatcheries revealed a number of such ploidy intermediates indicating uninformed hatchery practices in artificial reproduction of sturgeons. To unravel hybrid and ploidy diversity of sturgeons, we systematically mated pure 4n (A. ruthenus) and 8n (A. gueldenstaedtii, A. baerii) individuals as controls with males and/or females of 6n (~180 chromosomes), 10n (~300 chromosomes) and 12n ploidy levels that were identified in breeding stocks of A. ruthenus, A. gueldenstaedtii and A. baerii. The respective progenies were reared up to check ploidy level using flow cytometry, image cytometry of erythrocyte nuclear dimensions and direct karyotyping. Each crossing between different ploidy level individuals unambiguously confirmed intermediate ploidy levels in progenies resulting in production of 5n (~150 chromosomes), 6n (~180chromosomes), 7n (~210 chromosomes), 9n (~270 chromosomes) and 10n (~300 chromosomes). A part of such progenies is reared up to verify expected fertility. The evident ploidy plasticity of sturgeons with apparent multiples of about 30 chromosomes might suggest that these semi-haploid units (n = 60, n/2 = 30) still reflect original haploid genome of extinct sturgeon paleodiploid ancestor and reinforce the hypothesis of Vasil´ev regarding hybrid origin of sturgeons through the reticulate speciation.