Morphological and histochemical studies of Bidder’s organ in Rhinella schneideri (Amphibia: Anura) males

Abstract Bufonids have an organ that produces female germ cells in both sexes, known as the Bidder’s organ (BO). In males, BO is located in the anterior pole of the testis and it has been compared to a rudimentary ovary. It has been demonstrated that in some species the bidderian follicles can accumulate vitellogenin in males, while in other species, the development of follicles is inhibited by the differentiation of the corresponding gonad. This study describes the anatomical, histochemical and ultrastructural aspects of the BO in males of the neotropical frog Rhinella schneideri during the breeding season. A topographic model has also been built using three-dimensional (3D) reconstruction. BO has an irregular shape with lobes varying in size and number. There is no physical barrier between the BO and male gonads and, for this reason, female cells are in intimate association with seminiferous locules. Histologically, two distinct regions are observed in the BO: the cortex, and medulla. In the cortex, bidderian oocytes are surrounded by follicle cells forming bidderian follicles, which are in pre-vitellogenic stage. The ooplasm of bidderian oocytes is rich in cytoplasmic organelles. Microvilosities are formed in the oolemma, where the follicular cells are juxtaposed with oocytes, and amorphous extracellular material is deposited. Lipofuscin and myelin bodies occur in the medulla as a result of the cellular degradation. Pigmented cells were also detected in the medullar region. The oogonias observed in the BO periphery, and the significant amount of degenerating oocytes in the cortex, showed the renewal capacity of BO cells in R. schneideri males. The BO anatomical pattern in R. schneideri is similar to that observed for most species of bufonids. This work describes for the first time specific aspects related to the morphological description with emphasis on architecture, morphometry and histochemistry.