Pattern and rate of ovary differentiation with reference to somatic development in anuran amphibians

The rate of somatic development of anuran amphibians is only roughly correlated with the rate of gonad differentiation and varies among species. The somatic stage of a tadpole often does not reflect its age, which seems to be crucial for gonad differentiation rate. We compared the morphology and differentiation of developing ovaries at the light and electron microscopy level, with reference to somatic growth and age of a female. Our observations were performed on 12 species of six families (Rana lessonae, R. ridibunda, R. temporaria, R. arvalis, R. pipiens, R. catesbeiana, Bombina bombina, Hyla arborea, Bufo bufo. B. viridis, Xenopus laevis, Pelobates fuscus) and compared with the results obtained by other authors. This allowed us to describe the unified pattern of anuran female gonad differentiation. Ovary differentiation was divided into 10 stages: I-III, undifferentiated gonad; IV, sexual differentiation; V, first nests of meiocytes; VI, first diplotene oocytes; VII-IX, increasing number of diplotene oocytes and decreasing number of oogonia and nests; X, fully developed ovary composed of diplotene oocytes with rudimental patches of oogonia. We distinguished three types of ovary differentiation rate: basic (most species), retarded (genus Bufo), and accelerated (green frogs of the subgenus Pelophylax genus Rana).