Gonadal Differentiation and Development in the Snouted Treefrog, Scinax fuscovarius (Amphibia, Anura, Hylidae)

Accurate descriptions of gonadogenesis are necessary to have a baseline to detect abnormalities during development and to assess the time a species may be more vulnerable to the action of pesticides, endocrine disruptors, and pharmaceuticals to which abnormal conditions have been attributed. Here, I describe the histomorphological changes during gonadal differentiation in the Snouted Treefrog Scinax fuscovarius. I sexed and measured a total of 302 tadpoles between Gosner stages 26-46 and 21 juvenile and adults. The results show that 1) the species possesses the undifferentiated type of gonadal differentiation-ovaries differentiate much earlier (at stage 26) than testes (stage 36); 2) oogenesis begins almost simultaneously with ovarian differentiation; and 3) ovaries and testes exhibit different rates of gonadal differentiation with respect to somatic development-the ovaries have an accelerated rate (the ovarian cavity differentiates early during larval development and previtellogenic oocytes develop at early premetamorphic stages), whereas the testes have a decelerated rate (seminiferous tubules differentiate at the juvenile stage). The comparison of these characteristics with those of other co-occurring anuran species reveals important interspecific variation in the relative timing of gonadogenesis. Finally, and as a byproduct of the extensive sampling, I describe several cases of gonadal malformations.