Genome size variation estimated by flow cytometry in Acipenser mikadoi, Huso dauricus in relation to other species of Acipenseriformes

In Acipenseriformes, extant species can be categorized into three ploidy groups based on their genome size inferred from chromosome numbers and / or nuclear DNA content. However, genome size is still inconclusive in some sturgeon species. Here, we reported genome size of Acipenser mikadoi, Huso dauricus, other seven sturgeon and one paddlefish species quantified by nuclear DNA content flow cytometry. We also measured DNA content of artificially propagated progenies of A. mikadoi and H. dauricus, and progenies from several hybrids using eggs of the two sturgeon species and the hybrid bester. Nuclear DNA content of A. mikadoi was 8.2 pg and thus this species was categorized into functional tetraploid or evolutionary octaploid species like closely related A. medirostris. Although H. dauricus has been considered to be functional diploid or evolutionary tetraploid species based on previous results, this species had 8.3 pg DNA content and was classified into the functional tetraploid or evolutionary octaploid group which includes A. mikadoi. Among artificially propagated A. mikadoi, high frequencies of triploid individuals (45%) and a little portion of tetraploid individuals (1.5%) were detected. The occurrence of polyploid larvae was also detected in hybrid progenies using eggs of A. mikadoi. All 1-year-old survivors (n = 3) of artificially propagated H. dauricus were triploid. The spontaneous occurrence of such genetic triploid and tetraploid progenies suggests that polyploidization event presumably occurs even at present and may cause intraspecific variation of genome size in Acipenseridae.