Fertility of females of sturgeon hybrids obtained from species with different levels of ploidy (Acipenser ruthenus and A. dauricus) and their cloning

Main purpose of this work is the identification of females of artificial sturgeon hybrids capable to produce unreduced oocytes. The importance of this task is due to the ability to receive clonal all-female lines. Experiments were performed on the previously obtained reciprocal hybrids of sterlet, Acipenser ruthenus (S) with similar to 120 chromosomes and kaluga, Acipenser dauricus (K) with similar to 260 chromosomes. Karyotypes of backcross hybrids of (S x K) female (obtained by crossing sterlet female with kaluga male) and sterlet male included 180 - 190 chromosomes. This means that (S x K) female produced eggs with similar to 125 chromosomes and its karyotype consisted of similar to 250 chromosomes. This number was confirmed by a comparative analysis of erythrocyte size in this female and species with different ploidy. Karyotype with similar to 250 chromosomes can occur in (S x K) female only as a result of fertilization of a diploid sterlet egg (120 chromosomes) with kaluga haploid sperm (similar to 130 chromosomes). Eggs of hybrid fertile (S x K) female, inseminated with inactivated sperm of Amur sturgeon and sterlet, developed into viable gynogenetic offspring, confirmed by the analysis of five microsatellite loci in this progeny, (S x K) female, and males used for UV-inactivated sperm. These data allow us to propose a method for obtaining fertile females of sturgeon hybrids from species with different ploidy. For this, experimentally obtained diploidized eggs from diploid 120-chromosome species must be fertilized by 250-270-chromosome male. Karyotypes of backcross hybrids of (K x S) female (obtained by crossing kaluga female with sterlet male) and sterlet male included similar to 250 chromosomes and hybrids of this female with kaluga male had similar to 320 chromosomes. These results proved an ability of hybrid (K x S) female to produce unreduced eggs, resulting in triploid backcrosses. The absence of reduction during egg development is well known in clonal forms (species) of vertebrates, which are of hybrid origin, and in artificially created fish hybrids. However, this has not been reported previously for sturgeons. Insemination of eggs of (K x S) female with UV-inactivated sperm of sterlet and Amur sturgeon led to offspring generation for which the genetic identity to their mother was proved using microsatellite analysis. That is, clonal inheritance was observed. These results suggest the possibility of developing a technology to produce all-female offspring. Artificial production of clonal lines in hybrid vertebrates can be also considered as experimental reproduction of the first stages of reticular speciation in nature.

Automated summary

The study focuses on the identification of female artificial sturgeon hybrids capable of producing unreduced oocytes, with experiments showing the potential to obtain all-female clonal lines. The results provide insight into the possibility of developing a technology to produce all-female offspring, which could have implications for experimental reproduction of reticular speciation in nature.