Interspecific hybridization can disrupt canonical gametogenic pathways, leading to the emergence of clonal and hemiclonal organisms. Such gametogenic alterations usually include genome endoreplication and/or premeiotic elimination of one of the parental genomes. The hybrid frog Pelophylax esculentus exploits genome endoreplication and genome elimination to produce haploid gametes with chromosomes of only one parental species. To reproduce, hybrids coexist with one of the parental species and form specific population systems. Here, we investigated the mechanism of spermatogenesis in diploid P. esculentus from sympatric populations of P. ridibundus using fluorescent in situ hybridization. We found that the genome composition and ploidy of germ cells, meiotic cells, and spermatids vary among P. esculentus individuals. The spermatogenic patterns observed in various hybrid males suggest the occurrence of at least six diverse germ cell populations, each with a specific premeiotic genome elimination and endoreplication pathway. Besides co-occurring aberrant cells detected during meiosis and gamete aneuploidy, alterations in genome duplication and endoreplication have led to either haploid or diploid sperm production. Diploid P. esculentus males from mixed populations of P. ridibundus rarely follow classical hybridogenesis. Instead, hybrid males simultaneously produce gametes with different genome compositions and ploidy levels. The persistence of the studied mixed populations highly relies on gametes containing a genome of the other parental species, P. lessonae.

M etamorphosis is a crucial process in anuran ontogenesis, through which the larva (tadpole) develops its adult morphology. During the climax stage, the tadpole skeleton, internal organs, and skin restructure, the tail is totally resorbed, and the tadpole loses weight (mostly due to significant water loss) (Brown and Cai 2007). It is quite important that these processes progress quickly and be coordinated in order to shorten the highly vulnerable period of the meta-Unexpected Heterochrony in the Edible Frog, Pelophylax esculentus (Linnaeus 1758), and Pallas' Spadefoot, Pelobates vespertinus (Pallas 1771), in Eastern Ukraine

No abstract