A case of hybridization in loaches (osteichthies: Cobitidae: Cobitis) determining genetic instability and expansion

Abstract

Monitoring of a hybrid community of spined loaches carried out during a six-year period represents a description of a unique case of reproductive interaction of Danube triploid females C. 2 elongatoides-“tanaitica” spontaneously introduced into the Irpen’ River (Middle Dnieper River basin) with local diploid males C. taenia. The obtained results show that, even during similar “crosses,” the restricted incorporation of C. taenia genetic material into the C. 2 elongatoides-“tanaitica” hybrid genome takes place. As a result, the progeny undergo modifications of the electrophoretic hybrid spectrum of the Aat-1 locus that can be interpreted as the development of genetic instability. During two years, genetically modified progeny not only completely displaced normal Danube triploids from the Irpen’ River, but also sharply increased the representation of introgressants in the basin. As a consequence, the community of spined loaches of this river at present consists of more than one-half modified Danube triploids. During subsequent gynogenetic “crosses” of already modified triploid females C. 2 elongatoides-“tanaitica” with C. taenia males, tetraploid recombinants and backcrosses appeared in the population, which have never been observed in the Dnieper spined loach populations. The fact of directional genome transformations during gynogenetic crosses proves that initiation of ovum cleavage by a spermatozoon is not a genetically neutral event.