Ploidy-dependent survival of progeny arising from crosses between natural allotriploid Cobitis females and diploid C. taenia males (Pisces, Cobitidae)

Abstract

Crosses between 21 triploid hybrid Cobitis females and 19 C. taenia (2n = 48) males led to viable progeny; whereas no embryonic development was observed in crosses with tetraploid males (4n = 98). The ploidy status of 491 progenies randomly selected with flow cytometry (316) or chromosome analysis (175) revealed an average of 55.2 % triploids and 44.8 % tetraploids, but the ratio of 3n versus 4n fish did change during development. In the first 2 days after hatching, approximately 65.1 % of tetraploid larvae were observed. Their number decreased significantly to 30.8 and 6.2 % on average during 2-5 and 10-15 months of life, respectively. The karyotype of tetraploid progeny (4n = 98) included 3n = 74 chromosomes of the parental female and n = 24 of C. taenia male. The number of tetraploid progeny indicated indirectly that about 66 % of eggs from 3n females were fertilized with C. taenia. The rest of the eggs developed clonally via gynogenesis or hemiclonally via hybridogenesis into triploids of the same karyotype structure as parental females. We have documented for the first time that (at least under experimental conditions) tetraploids are commonly formed, but are less viable than triploids, and a ratio similar to what is found under natural conditions is finally attained. The current explanation concerning the ploidy and karyotype structure of the progeny confirms that the eggs of 3n Cobitis females are not only capable of maintaining all chromosomes but are also capable of incorporating the sperm genome, thus creating the potential to produce tetraploids.

Histological evidence that diploid hybrids of Cobitis taenia and C. elongatoides (Teleostei, Cobitidae) develop into fertile females and sterile males

“…For example, it has been proven that tetraploids of Iberian Squalius alburnoides (Steindachner, 1866) from populations in the Douro drainage resumed normal meiosis after undergoing intermediate processes of asexual reproduction to give rise to a new sexually reproducing polyploid species, which are better adapted to a new habitat (Cunha et al, 2008). Tetraploids of Cobitis in European populations are scarce, it was previously documented that triploid Cobitis females produce tetraploids in crosses with C. taenia males (Juchno et al, 2014). Even though such tetraploids are clearly less viable than simultaneously gynogenetically originated triploids, they can have an evolutionary future.…”

“…Artificial spawning was done in June, during the natural time for reproduction, but collected parental individuals were hormonally stimulated before crossing according to the routine fertilization method described in detail by Juchno et al (2014). Similar to the method described by Juchno et al (2016), the developing eggs were initially incubated in Petri dishes, and then in separate small aquaria with running water at 24°C under artificial light with a photoperiod similar to natural light conditions.…”

“…In order to investigate the reproductive capacity of diploid F1 hybrids, subsequent crossing experiments were performed by the routine fertilization method (Juchno et al, 2014). Two diploid F1 hybrid females (TE1, TE2) and four F1 (TE1, TE2 and ET1, ET2) three-year-old hybrid males were backcrossed with C. taenia (TT1) and C. elongatoides (EE1) males and with C. taenia (TT1, TT2, TT3, TT4) females, respectively according to following scheme: TE1 9 TT1, TE2 9 EE1; TT1 9 TE1, TT2 9 TE2, TT3 9 ET1, TT4 9 ET2.…”

Meiotic chromosome configurations in oocytes of Cobitis taenia and its polyploid hybrids

“…Some of them evolved via hybridization and polyploidization, and then they parted from bisexual reproducing diploids acquiring unisexual reproductive mode such as hybridogenesis and gynogenesis in diploids and triploids (Saitoh et al 2004), gynogenesis or bisexual reproduction in tetraploids (Boron 2003;Janko et al 2007Janko et al , 2012Saitoh et al 2010;Juchno et al 2014).…”

“…Experimental studies revealed that triploid females of Cobitis from populations in Poland produced unreduced triploid eggs, which were gynogenetically activated by sperm of Cobitis taenia to develop into viable triploid progeny, but simultaneously some of the eggs were fertilized to provide less viable tetraploid progeny (Juchno and Boroń 2006;Juchno et al 2014). The mechanisms responsible for unreduced gametogenesis have not been identified in polyploid Cobitis inhabiting Polish diploidpolyploid populations.…”