Hybridogenesis is a hemiclonal reproductive strategy in diploid and triploid hybrids. Our study model is a frog P. esculentus (diploid RL and triploids RLL and RRL), a natural hybrid between P. lessonae (LL) and P. ridibundus (RR). Hybridogenesis relies on elimination of one genome (L or R) from gonocytes (G) in tadpole gonads during prespermatogenesis, but not from spermatogonial stem cells (SSCs) in adults. Here we provide the first comprehensive study of testis morphology combined with chromosome composition in the full spectrum of spermatogenic cells. Using genomic in situ hybridization (GISH) and FISH we determined genomes in metaphase plates and interphase nuclei in Gs and SSCs. We traced genomic composition of SSCs, spermatocytes and spermatozoa in individual adult males that were crossed with females of the parental species and gave progeny. Degenerating gonocytes (24%-39%) and SSCs (18%-20%) led to partial sterility of juvenile and adult gonads. We conclude that elimination and endoreplication not properly completed during prespermatogenesis may be halted when gonocytes become dormant in juveniles. After resumption of mitotic divisions by SSCs in adults, these 20% of cells with successful genome elimination and endoreplication continue spermatogenesis, while in about 80% spermatogenesis is deficient. Majority of abnormal cells are eliminated by cell death, however some of them give rise to aneuploid spermatocytes and spermatozoa which shows that hybridogenesis is a wasteful process.

Amphibian Biology Group Department of Evolutionary Biology and Conservation of Vertebrates Faculty of Biological Sciences University of Wrocław Wrocław Poland

Department of Medicine Biology The Cardinal Wyszyński National Institute of Cardiology Warsaw Poland

Laboratory of Non Mendelian Evolution Institute of Animal Physiology and Genetics Czech Academy of Sciences Liběchov Czech Republic

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Arioli M., Jakob C., Reyer H.-U. (2010). Genetic diversity in water frog hybrids (Pelophylax esculentu s) varies with population structure and geographic location. Mol. Ecol. 19 (9), 1814–1828. 10.1111/j.1365-294X.2010.04603.x PubMed DOI

Bartmańska J., Ogielska M. (1999). Development of testes and differentiation of germ cells in water frogs of the Rana esculenta - complex (Amphibia, Anura). Amphib. Reptil. 20 (3), 251–263. 10.1163/156853899X00286 DOI

Berger L. (1976). Hybrids of B2 generation of European water frogs (Rana esculenta complex). Ann. Zoologici Warsaw 33, 201–214.

Berger L. (1968). Morphology of the F1 generation of various crosses within Rana esculenta complex. Acta Zool. Cracoviensia 3, 301–324.

Berger L., Roguski H., Uzzell T. (1978). Triploid F2 progeny of water frogs (Rana esculenta complex). Folia Biol. 26 (3), 135–152. PubMed

Berger L., Rybacki M., Hotz H. (1994). Artificial fertilization of water frogs. Amphib. Reptil. 15, 408–413. 10.1163/156853894x00452 DOI

Berger L., Rybacki M. (1994). Sperm competition between two species of European water frogs (Rana ridibunda and Rana lessonae). Zool. Pol. 39, 281–291.

Berger L., Rybacki M. (1992). Sperm competition in European water frogs. Alytes 10, 113–116.

Berger L. (1973). Systematics and hybridization in European green frogs of Rana esculenta complex. J. Herpetology 7 (1), 1–10. 10.2307/1562822 DOI

Berger L., Uzzell T. (1977). Vitality and growth of progeny from different egg size classes of Rana esculenta L. (Amphibia, Salientia). Zool. Pol. 26 (3-4), 291–317.

Bi K., Bogart J. P. (2006). Identification of intergenomic recombinations in unisexual salamanders of the genus Ambystoma by genomic in situ hybridization (GISH). Cytogenet. Genome Res. 112 (3–4), 307–312. 10.1159/000089885 PubMed DOI

Biriuk O. V., Shabanov D. A., Korshunov A. V., Borkin L. J., Lada G. A., Pasynkova R. A., et al. (2016). Gamete production patterns and mating systems in water frogs of the hybridogenetic Pelophylax esculentus complex in north-eastern Ukraine. J. Zool. Syst. Evol. Res. 54 (3), 215–225. 10.1111/jzs.12132 DOI

Blin N., Stafford D. W. (1976). A general method for isolation of high molecular weight DNA from eukaryotes. Nucleic Acids Res. 3 (9), 2303–2308. 10.1093/nar/3.9.2303 PubMed DOI PMC

Bucci S., Ragghianti M., Mancino G., Berger L., Hotz H., Uzzell T. (1990). Lampbrush and mitotic chromosomes of the hemiclonally reproducing hybridRana esculenta and its parental species. J. Exp. Zool. 255 (1), 37–56. 10.1002/jez.1402550107 PubMed DOI

Chmielewska M., Dedukh D., Haczkiewicz K., Rozenblut-Kościsty B., Kaźmierczak M., Kolenda K., et al. (2018). The programmed DNA elimination and formation of micronuclei in germ line cells of the natural hybridogenetic water frog Pelophylax esculentus. Sci. Rep. 8 (1), 7870. 10.1038/s41598-018-26168-z PubMed DOI PMC

Christiansen D. G., Fog K., Pedersen B. V., Boomsma J. J. (2005). Reproduction and hybrid load in all-hybrid populations of Rana esculenta water frogs in Denmark. Evolution 59 (6), 1348–1361. 10.1111/j.0014-3820.2005.tb01784.x PubMed DOI

Christiansen D. G. (2009). Gamete types, sex determination and stable equilibria of all-hybrid populations of diploid and triploid edible frogs (Pelophylax esculentus). BMC Evol. Biol. 9 (1), 135. 10.1186/1471-2148-9-135 PubMed DOI PMC

Christiansen D. G., Jakob C., Arioli M., Roethlisberger S., Reyer H. U. (2010). Coexistence of diploid and triploid hybrid water frogs: Population differences persist in the apparent absence of differential survival. BMC Ecol. 10 (1), 14. 10.1186/1472-6785-10-14 PubMed DOI PMC

Christiansen D. G., Reyer H.-U. (2009). From clonal to sexual hybrids: Genetic recombination via triploids in all-hybrid populations of water frogs. Evolution 63 (7), 1754–1768. 10.1111/j.1558-5646.2009.00673.x PubMed DOI

Christiansen D. G. (2005). A microsatellite-based method for genotyping diploid and triploid water frogs of the Rana esculenta hybrid complex. Mol. Ecol. Notes 5 (1), 190–193. 10.1111/j.1471-8286.2004.00869.x DOI

Czarniewska E., Pabijan M., Rybacki M. (2011). Large eggs and ploidy of green frog populations in Central Europe. Amphib. Reptil. 32 (2), 149–158. 10.1163/017353710X546495 DOI

Dawley R. M., Bogart J. P. (1989). Evolution and ecology of unisexual vertebrates, 4. New YorkAlbany: New York State Museum Publications.

De Storme N., Geelen D. (2013). Sexual polyploidization in plants – cytological mechanisms and molecular regulation. New Phytol. 198 (3), 670–684. 10.1111/nph.12184 PubMed DOI PMC

Dedukh D., Altmanová M., Klima J., Kratochvil L. (2022a). Premeiotic endoreplication is essential for obligate parthenogenesis in geckos. Development 149 (7), dev200345. 10.1242/dev.200345 PubMed DOI

Dedukh D., Litvinchuk J., Svinin A., Litvinchuk S., Rosanov J., Krasikova A. (2019). Variation in hybridogenetic hybrid emergence between populations of water frogs from the Pelophylax esculentus complex’, PLoS ONE . PLoS One 14 (11), e0224759. 10.1371/journal.pone.0224759 PubMed DOI PMC

Dedukh D., Litvinchuk S., Rosanov J., Mazepa G., Saifitdinova A., Shabanov D., et al. (2015). Optional endoreplication and selective elimination of parental genomes during oogenesis in diploid and triploid hybrid European water frogs. PLoS ONE 10, e0123304. 10.1371/journal.pone.0123304 PubMed DOI PMC

Dedukh D., Litvinchuk S., Rosanov J., Shabanov D., Krasikova A. (2017). Mutual maintenance of di- and triploid Pelophylax esculentus hybrids in R-E systems: Results from artificial crossings experiments’, BMC Evolutionary Biology . BMC Evol. Biol. 17 (1), 220. 10.1186/s12862-017-1063-3 PubMed DOI PMC

Dedukh D., Majtánová Z., Marta A., Psenicka M., Kotusz J., Klima J., et al. (2020a). Parthenogenesis as a solution to hybrid sterility: The mechanistic basis of meiotic distortions in clonal and sterile hybrids. Genetics 215 (4), 975–987. 10.1534/genetics.119.302988 PubMed DOI PMC

Dedukh D., Marta A., Janko K. (2021). Challenges and costs of asexuality: Variation in premeiotic genome duplication in gynogenetic hybrids from Cobitis taenia complex. Int. J. Mol. Sci. 22 (22), 12117. 10.3390/ijms222212117 PubMed DOI PMC

Dedukh D., Riumin S., Chmielewska M., Rozenblut-Kościsty B., Kolenda K., Kaźmierczak M., et al. (2020b). Micronuclei in germ cells of hybrid frogs from Pelophylax esculentus complex contain gradually eliminated chromosomes. Sci. Rep. 10 (1), 8720. 10.1038/s41598-020-64977-3 PubMed DOI PMC

Dedukh D., Riumin S., Kolenda K., Chmielewska M., Rozenblut-Kościsty B., Kaźmierczak M., et al. (2022b). Maintenance of pure hybridogenetic water frog populations: Genotypic variability in progeny of diploid and triploid parents. PLOS ONE 17 (7), e0268574. 10.1371/journal.pone.0268574 PubMed DOI PMC

Doležálková M., Sember A., Marec F., Rab P., Plotner J., Choleva L. (2016). Is premeiotic genome elimination an exclusive mechanism for hemiclonal reproduction in hybrid males of the genus Pelophylax? BMC Genet. 17 (1), 100. 10.1186/s12863-016-0408-z PubMed DOI PMC

Doležálková-Kaštánková M., Mazepa G., Jeffries D. L., Perrin N., Plotner M., Plotner J., et al. (2021). Capture and return of sexual genomes by hybridogenetic frogs provide clonal genome enrichment in a sexual species. Sci. Rep. 11 (1), 1633. 10.1038/s41598-021-81240-5 PubMed DOI PMC

Dufresnes C., Mazepa G. (2020). “Hybridogenesis in water frogs,” in eLS (New Jersey, United States: Wiley; ), 718–726. 10.1002/9780470015902.a0029090 DOI

Endoh M., Shima F., Havelka M., Asanuma R., Yamaha E., Fujimoto T., et al. (2020). Hybrid between Danio rerio female and Danio nigrofasciatus male produces aneuploid sperm with limited fertilization capacity’. PLoS One 15 (5), e0233885. 10.1371/journal.pone.0233885 PubMed DOI PMC

Fedorova A., Pustovalova E. (2021). What the distribution of sperm size can tell about the stability of spermatogenesis in hybrid frogs Pelophylax esculentus. J. V. N. Karazin Kharkiv Natl. Univ. Ser. “Biology” 37, 70–78. 10.26565/2075-5457-2021-37-6 DOI

Graf J. D., Müller W. P. (1979). Experimental gynogenesis provides evidence of hybridogenetic reproduction in the Rana esculenta complex. Experientia 35 (12), 1574–1576. 10.1007/BF01953200 PubMed DOI

Gregory T. R. (2001). Coincidence, coevolution, or causation? DNA content, cell size, and the C-value enigma. Biol. Rev. Camb. Philos. Soc. 76 (1), 65–101. 10.1017/S1464793100005595 PubMed DOI

Günther R. (1990). Die wasserfrösche europas (Anura-froschlurche). Ziemsen: Wittenberg-Lutherstadt, 1–288.

Günther R. (1975). Untersuchungen der Meiose bei Männchen von Rana ridibunda Pall., Rana lessonae Cam. und deren Bastardform “Rana esculenta” L. (Anura). Biol. Zentralblatt 94 (3), 277–294.

Haczkiewicz K., Ogielska M. (2013). Gonadal sex differentiation in frogs: How testes become shorter than ovaries. Zool. Sci. 30 (2), 125–134. 10.2108/zsj.30.125 PubMed DOI

Haczkiewicz K., Rozenblut-Kościsty B., Ogielska M. (2017). Prespermatogenesis and early spermatogenesis in frogs. Zoology 122, 63–79. 10.1016/j.zool.2017.01.003 PubMed DOI

Hauswaldt J. S., Hoer M., Ogielska M., Christiansen D. G., Dziewulska-Szwajkowska D., Czernicka E., et al. (2012). A simplified molecular method for distinguishing among species and ploidy levels in European water frogs (Pelophylax). Mol. Ecol. Resour. 12 (5), 797–805. 10.1111/j.1755-0998.2012.03160.x PubMed DOI

Heppich S., Tunner H. G., Greilhuber J. (1982). Premeiotic chromosome doubling after genome elimination during spermatogenesis of the species hybrid Rana esculenta . Theor. Appl. Genet. 61 (2), 101–104. 10.1007/BF00273874 PubMed DOI

Jenkins G., Hasterok R. (2007). BAC “landing” on chromosomes of Brachypodium distachyon for comparative genome alignment. Nat. Protoc. 2 (1), 88–98. 10.1038/nprot.2006.490 PubMed DOI

Kierzkowski P., Kosiba P., Rybacki M., Socha M., Ogielska M. (2013). Genome dosage effect and colouration features in hybridogenetic water frogs of the Pelophylax esculentus complex. Amphib. Reptil. 34 (4), 493–504. 10.1163/15685381-00002904 DOI

Kierzkowski P., Pasko L., Rybacki M., Socha M., Ogielska M. (2011). Genome dosage effect and hybrid morphology - the case of the hybridogenetic water frogs of the Pelophylax esculentus complex. Ann. Zool. Fenn. 48, 56–66. 10.5735/086.048.0106 DOI

Kolenda K., Pietras-Lebioda A., Hofman S., Ogielska M., Pabijan M. (2017). Preliminary genetic data suggest the occurrence of the Balkan water frog, Pelophylax kurtmuelleri, in southwestern Poland. Amphib. Reptil. 38 (2), 187–196. 10.1163/15685381-00003103 DOI

Kuroda M., Fujimoto T., Murakami M., Yamaha E., Arai K. (2019). Aberrant meiotic configurations cause sterility in clone-origin triploid and inter-group hybrid males of the dojo loach, Misgurnus anguillicaudatus . Cytogenet. Genome Res. 158 (1), 46–54. 10.1159/000500303 PubMed DOI

Lamatsch D., Stöck M. (2009). “Sperm-dependent parthenogenesis and hybridogenesis in teleost fishes,” in Lost sex. The evolutionary Biology of parthenogenesis. Editors Schön I., Martens K., Dijk P. (Dordrecht Heidelberg London New York: Springer Netherlands; ), 399–432. 10.1007/978-90-481-2770-2 DOI

Majtánová Z., Dedukh D., Choleva L., Adams M., Ráb P., Unmack P., et al. (2021). Uniparental genome elimination in Australian carp gudgeons. Genome Biol. Evol. 13 (6), evab030. 10.1093/gbe/evab030 PubMed DOI PMC

Marracci S., Michelotti V., Guex G. D., Hotz H., Uzzell T., Ragghianti M. (2011). RrS1-like sequences of water frogs from central Europe and around the aegean sea: Chromosomal organization, evolution, possible function. J. Mol. Evol. 72 (4), 368–382. 10.1007/s00239-011-9436-5 PubMed DOI

Mazin A. L., Borkin L. J. (1979). Nuclear DNA content in green frogs of the GenusRana. Mitt. Mus. Nat. Kd. Berl. Zool. Reihe. 55 (1), 217–224. 10.1002/mmnz.4830550119 DOI

Ogielska M., Bartmańska J. (2009). “Spermatogenesis and male reproductive system in Amphibia-Anura,” in Reproduction of Amphibians. Enfield (NH). Editor Ogielska M. (Jersey, Plymouth: Science Publishers; ), 34–99.

Ogielska M., Kierzkowski P., Rybacki M. (2005). DNA content and genome composition of diploid and triploid water frogs belonging to the Rana esculenta complex ( Amphibia, Anura ). Can. J. Zool. 82, 1894–1901. 10.1139/Z04-188 DOI

Ogielska M. (1994). Nucleus-like bodies in gonial cells of Rana esculenta [Amphibia, Anura] tadpoles—A putative way of chromosome elimination. Zool. Pol. 39, 461–474.

Ogielska M., Rozenblut B., Augustyńska R., Kotusz A. (2010). Degeneration of germ line cells in amphibian ovary. Acta Zool. 91 (3), 319–327. 10.1111/j.1463-6395.2009.00411.x DOI

Plötner J. (2005). Die westpaläarktischen wasserfrösche. Beih. Z. für Feldherpetologie 9, 1–160.

Pruvost N. B. M., Hoffmann A., Reyer H.-U. (2013). Gamete production patterns, ploidy, and population genetics reveal evolutionary significant units in hybrid water frogs ( Pelophylax esculentus ). Ecol. Evol. 3 (9), 2933–2946. 10.1002/ece3.687 PubMed DOI PMC

Pui H. P., Saga Y. (2017). Gonocytes-to-spermatogonia transition initiates prior to birth in murine testes and it requires FGF signaling. Mech. Dev. 144, 125–139. 10.1016/j.mod.2017.03.002 PubMed DOI

Pustovalova E., Choleva L., Shabanov D., Dedukh D. (2022). The high diversity of gametogenic pathways in amphispermic water frog hybrids from Eastern Ukraine. PeerJ 10, e13957. 10.7717/peerj.13957 PubMed DOI PMC

Ragghianti M., Bucci S., Casola C., Marracci S., Mancino G. (2004). Molecular investigations in Western palearctic water frogs. Italian J. Zoology 71 (2), 17–23. 10.1080/11250000409356601 DOI

Ragghianti M., Bucci S., Marracci S., Casola C., Mancino G., Hotz H., et al. (2007). Gametogenesis of intergroup hybrids of hemiclonal frogs. Genet. Res. 89 (1), 39–45. 10.1017/S0016672307008610 PubMed DOI

Ragghianti M., Guerrini F., Bucci S., Mancino G., Hotz H., Uzzell T., et al. (1995). Molecular characterization of a centromeric satellite DNA in the hemiclonal hybrid frog Rana esculenta and its parental species. Chromosome Res. 3 (8), 497–506. 10.1007/BF00713965 PubMed DOI

Rello-Varona S., Lissa D., Shen S., Niso-Santano M., Senovilla L., Marino G., et al. (2012). Autophagic removal of micronuclei. Cell Cycle 11 (1), 170–176. 10.4161/cc.11.1.18564 PubMed DOI

Reyer H.-U., Niederer B., Hettyey A. (2003). Variation in fertilisation abilities between hemiclonal hybrid and sexual parental males of sympatric water frogs ( Rana lessonae, R. esculenta, R. ridibunda ). Behav. Ecol. Sociobiol. 54 (3), 274–284. 10.1007/s00265-003-0635-y DOI

Roco Á. S., Ruiz-García A., Bullejos M. (2021). Testis development and differentiation in Amphibians. Genes 12 (4), 578. 10.3390/genes12040578 PubMed DOI PMC

Rozenblut B., Ogielska M. (2005). Development and growth of long bones in European water frogs (Amphibia: Anura: Ranidae), with remarks on age determination. J. Morphol. 265 (3), 304–317. 10.1002/jmor.10344 PubMed DOI

Rozenblut-Kościsty B., Piprek R., Pecio A., Bartmanska J., Szymura J. M., Ogielska M. (2017). The structure of spermatogenic cysts and number of Sertoli cells in the testes of Bombina bombina and Bombina variegata (Bombinatoridae, Anura, Amphibia). Zoomorphology 136 (4), 483–495. 10.1007/s00435-017-0362-y DOI

Rybacki M., Berger L. (2001). Types of water frog populations (Rana esculenta complex) in Poland. Zoosyst. Evol. 77 (1), 51–57. 10.1002/mmnz.20010770109 DOI

Scali V., Passamonti M., Marescalchi O., Mantovani B. (2003). Linkage between sexual and asexual lineages: Genome evolution in Bacillus stick insects. Biol. J. Linn. Soc. Lond. 79 (1), 137–150. 10.1046/j.1095-8312.2003.00172.x DOI

Schindelin J., Arganda-Carreras I., Frise E., Kaynig V., Longair M., Pietzsch T., et al. (2012). Fiji: An open-source platform for biological-image analysis. Nat. Methods 9 (7), 676–682. 10.1038/nmeth.2019 PubMed DOI PMC

Schmidt D. J., Bond N. R., Adams M., Hughes J. M. (2011). Cytonuclear evidence for hybridogenetic reproduction in natural populations of the Australian carp gudgeon (Hypseleotris: Eleotridae). Mol. Ecol. 20 (16), 3367–3380. 10.1111/j.1365-294X.2011.05206.x PubMed DOI

Schultz R. J. (1969). Hybridization, unisexuality, and polyploidy in the teleost Poeciliopsis (poeciliidae) and other vertebrates. Am. Nat. 103 (934), 605–619. 10.1086/282629 DOI

Schwarzacher T., Heslop-Harrison P. (2000). Practical in situ hybridization. Oxford: Bios.

Sessions S. K. (1982). Cytogenetics of diploid and triploid salamanders of the Ambystoma jeffersonianum complex. Chromosoma 84 (5), 599–621. 10.1007/BF00286329 DOI

Stenberg P., Saura A. (2013). Meiosis and its deviations in polyploid animals. Cytogenet. Genome Res. 140 (2–4), 185–203. 10.1159/000351731 PubMed DOI

Stöck M., Lamatsch D. K., Steinlein C., Epplen J. T., Grosse W. R., Hock R., et al. (2002). A bisexually reproducing all-triploid vertebrate. Nat. Genet. 30 (3), 325–328. 10.1038/ng839 PubMed DOI

Stöck M., Ustinova J., Betto-Colliard C., Schartl M., Moritz C., Perrin N. (2012). Simultaneous Mendelian and clonal genome transmission in a sexually reproducing, all-triploid vertebrate. Proc. Biol. Sci. 279 (1732), 1293–1299. 10.1098/rspb.2011.1738 PubMed DOI PMC

Svinin A., Dedukh D. V., Borkin L. J., Ermakov O., Ivanov A., Litvinchuk J., et al. (2021). Genetic structure, morphological variation, and gametogenic peculiarities in water frogs ( Pelophylax ) from northeastern European Russia. J. Zool. Syst. Evol. Res. 59 (3), 646–662. 10.1111/jzs.12447 DOI

Szydłowski P., Chmielewska M., Rozenblut-Kościsty B., Ogielska M. (2016). The frequency of degenerating germ cells in the ovaries of water frogs (Pelophylax esculentus complex). Zoomorphology 136, 75–83. 10.1007/s00435-016-0337-4 DOI

Tunner H. G., Heppich S. (1981). Premeiotic genome exclusion during oogenesis in the common edible frog, Rana esculenta . Naturwissenschaften 68, 207–208. 10.1007/BF01047207 PubMed DOI

Tunner H. G., Heppich-Tunner S. (1991). Genome exclusion and two strategies of chromosome duplication in oogenesis of a hybrid frog. Naturwissenschaften 78, 32–34. 10.1007/bf01134041 DOI

Uzzell T., Berger L., Günther R. (1975). Diploid and triploid progeny from a diploid female of Rana esculenta (Amphibia salientia). Proc. Acad. Nat. Sci. Phila. 127, 81–91.

Uzzell T., Hotz H., Berger L. (1980). Genome exclusion in gametogenesis by an interspecific Rana hybrid: Evidence from electrophoresis of individual oocytes. J. Exp. Zool. 214 (3), 251–259. 10.1002/jez.1402140303 DOI

Veregina A. O., Biriuk O. W., Shabanov D. A. (2014). Comparison of spermatogenesis stability in hemiclonal interspecific hybrid Pelophylax esculentus and parental species Pelophylax ridibundus (Amphibia, Anura). Праці українського герпетологічного товариства 5, 20–28.

Vinogradov A. E., Borkin L. J., Gunter R., Rosanov J. M. (1990). Genome elimination in diploid and triploid Rana esculenta males: Cytological evidence from DNA flow cytometry. Genome 33 (5), 619–627. 10.1139/g90-092 PubMed DOI

Vinogradov A. E., Borkin L. J., Gunter R., Rosanov J. M. (1991). Two germ cell lineages with genomes of different species in one and the same animal. Hereditas 114 (3), 245–251. 10.1111/j.1601-5223.1991.tb00331.x PubMed DOI

Wang J., Liu Q., Luo K., Chen X., Xiao J., Zhang C., et al. (2016). Cell fusion as the formation mechanism of unreduced gametes in the gynogenetic diploid hybrid fish. Sci. Rep. 6 (1), 31658. 10.1038/srep31658 PubMed DOI PMC

Weibel E. R. (1979). “Stereological methods,” in Practical methods for biological morphometry (London: Academic Press; ), 1, 51–60.

Zaleśna A., Choleva L., Ogielska M., Rabova M., Marec F., Rab P. (2011). Evidence for integrity of parental genomes in the diploid hybridogenetic water frog Pelophylax esculentus by genomic in situ hybridization. Cytogenet. Genome Res. 134 (3), 206–212. 10.1159/000327716 PubMed DOI

Gradual chromosomal lagging drive programmed genome elimination in hemiclonal fishes from the genus Hypseleotris

Inheritance patterns of male asexuality in hybrid males of a water frog Pelophylax esculentus

Cytogenetics of the Hybridogenetic Frog Pelophylax grafi and Its Parental Species Pelophylax perezi

Karyotypes of water frogs from the Pelophylax esculentus complex: results of cross-species chromosomal painting