Sex ratios of triploids and gynogenetic diploids induced in the hybrid sturgeon, the bester (Huso huso female x Acipenser ruthenus male)

Omoto N, Maebayashi M, Adachi S, Arai K, Yamauchi K.

The sex ratios of triploids and gynogenetic diploids in the hybrid sturgeon, the bester (Huso huso female×Acipenser ruthenus male), have been investigated to confirm the possibilities of sex control by chromosome manipulation in sturgeon. Viable gynogenetic diploids were produced by activating eggs with ultraviolet-irradiated bester sperm followed by heatshock treatment. Triploids were induced by the same method after fertilization of eggs with normal bester sperm. A total of 380 progeny individuals were analyzed by flow cytometry, and classified into 217 diploids (2n) and 163 triploids (3n). The percentages of females are 40–55% in control diploid, 60.0–73.3% in triploid and 70.0–80.0% in gynogenetic groups. Since these progeny reared under same environmental conditions, the presence of males in gynogenetic progeny groups derived from five different pairs suggested the involvement of a female heterogametic {ZW (female)/ZZ (male)} sex-determination system in bester. The percentage of males in each groups most closely approximated the percentages expected when the sex-determining element on the W chromosome segregates independently of the centromere during meiosis in females. If the WW “super”-female is viable in sturgeon, such females would be produce all female progeny when crossed to normal ZZ males. Moreover, inducing gynogenetic diploid in endangered sturgeon population with genetically inactivated “donor” sperm from other sturgeon species is likely to offer a useful method for restoration, since both sexes and not just an all-female population would be predicted.