Genome size variation estimated by nuclear DNA content Flow Cytometry in ten sturgeon species and several interspecific hybrids reared in Japan

Zhou H. Fujimoto T. Adachi S. Yamaha E. Arai K.

Based on evolutionary ploidy level inferred from nuclear DNA content and karyotype of somatic cells, sturgeon species have been categorized to three genome size groups, A (diploid or tetraploid, 3.2-4.5 pg/N), B (tetraploid or octaploid, 6.1-9.6 pg/N) and C (hexaploid or dodecaploid, 13.1-14.2 pg/N). Generally, it is difficult to compare these results on genome size from various previous studies by different authors, because different methods and standards were used in these measurements. To the best of our knowledge, kaluga Huso dauricus and mikado sturgeon Acipenser medirostris mikadoi specimens obtained from coasts of Hokkaido, Japan have not been flow-cytometrically examined. In the present study, we attempted to determine genome size of these two Pacific species by nuclear DNA content on fin-clip or blood specimens collected from adult individuals, artificially propagated pure species larvae and hybrid larvae from crosses using kaluga, Mikado sturgeon and bester (hybrid sturgeon, Huso huso × Acipenser ruthenus). For comparison of genome sizes among sturgeon species, specimens of other eight sturgeon species and bester were also flow-cytometrically measured.

Our intensive flow-cytometry revealed that spontaneous polyploid event giving rise to intra-specific genome size variation still occurs in sturgeon species at present. Such an on-going elevation of ploidy level might complicate problems related to taxonomy, phylogeny and genetics of sturgeon species.