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The frequency of degenerating germ cells in the ovaries of water frogs (Pelophylax esculentus complex)


Pelophylax esculentus is the fertile hybrid of P. ridibundus and P. lessonae. During gametogenesis, one of the parental genomes is removed from the germ line cells, whereas the other one is clonally transmitted to the gametes. In hybrids, development of gonads is delayed in comparison with parental species. This may result from complex processes of genome elimination in female tadpoles at Gosner stages 28–46, potentially responsible for increased degeneration of germ cells in developing gonads from the very beginning of sexual differentiation to ovaries with diplotene oocytes, respectively. In this work, we revealed that germ cells died by apoptosis, as detected by expression of active caspase-3 using immunohistochemical method. The main group of degenerating germ cells was primary oogonia, however, in P. lessonae and P. ridibundus also secondary oogonia and diplotene oocytes were found. The number of degenerating germ cells was significantly higher in ovaries of P. esculentus. In hybrids, positive correlations were demonstrated between Gosner stage and gonadal volume, Gosner stage and the number of degenerating germ cells, gonadal volume and number of degenerating germ cells. These observations suggest that increased rate of apoptosis in germ cells, probably as the result of improper genome elimination, may be responsible for delayed maturation of ovaries in P. esculentus.

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This study was supported by the grant from Polish National Science Center No. 2012/07/B/NZ3/02563. Translation of publication was supported by Wrocław Centre of Biotechnology programme, the Leading National Research Centre (KNOW) for the years 2014–2018. We are grateful to Mrs. Ewa Serwa for help in immunohistochemical processing.

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Correspondence to Magdalena Chmielewska.

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The authors declare that they have no conflict of interest.

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All applicable international, national and/or institutional guidelines for the care and use of animals were followed. To carry out the research, consent was obtained from the local ethical commission in Wroclaw No. 7/2013. The acquisition of specimens of the species was accepted by license number DOP-oz.6401.02.2.2013.JRO.

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Paweł Szydłowski and Magdalena Chmielewska have contributed equally to this work.

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Szydłowski, P., Chmielewska, M., Rozenblut-Kościsty, B. et al. The frequency of degenerating germ cells in the ovaries of water frogs (Pelophylax esculentus complex). Zoomorphology 136, 75–83 (2017).

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  • Hybridogenesis
  • Pelophylax esculentus
  • Germ cells
  • Apoptosis
  • Ovaries