Evidence for a maternal origin of spontaneous autopolyploidy in cultured white sturgeon (Acipenser transmontanus)

Gille DA.Famula TR.May BP.Schreier AD.

Sturgeons (order Acipenseriformes) are members of an ancient evolutionary lineage that has experienced multiple rounds of whole-genome duplication. As a result, most extant species are polyploid and possess more than two complete sets of chromosomes. While interspecific variation in ploidy and overall genome size is common within this order, recent studies have also documented intraspecific variation in some captive bred sturgeon species, most notably in white sturgeon (Acipenser transmontanus). The unintentional duplication of one or more complete sets of chromosomes in a single species in the absence of hybridization is known as spontaneous autopolyploidization. The mechanism and the effects on viability and reproductive development of spontaneous autopolyploidy, however, are poorly understood. Sturgeons are valuable aquacultural species for production of boneless meat and caviar, and incidence of spontaneous autopolyploidy could have negative economic implications. In this study, we wished to determine whether there was a maternal or paternal origin of spontaneous autopolyploidy. We used flow cytometry to identify spontaneous autopolyploids and microsatellite genotyping to track the transfer of unique maternal and paternal alleles from broodstock to offspring across multiple full-sibling families in two populations of cultured white sturgeon. In all families, we found that the probability of transfer success of unique maternal alleles was greater than that of unique paternal alleles in spontaneous autopolyploid white sturgeon, indicating a maternal origin of spontaneous autopolyploidy. Secondly, as no spontaneous autopolyploid progeny shared all the same microsatellite alleles as the respective dam as would be expected with premeiotic endomitosis or apomixis, we believe that failure to extrude the second polar body in meiosis II is the most likely cause of spontaneous autopolyploidy in cultured white sturgeon.