Reproductive system of females of the Magdalena river endemic stingray Potamotrygon magdalenae: Anatomical and functional aspects

Abstract

We studied anatomical and functional aspects of the reproductive system of females of the Magdalena river stingray Potamotrygon magdalenae using microscopic and macroscopic analysis of each organ. Although the reproductive tract was fully functional on both side, the left organs possibly have a greater contribution to reproductive success, because left ovary and uterus were more developed and had higher number of oocytes and embryos, respectively, than the right ones. This species has histotrophic viviparity given by the presence of uterine trophonemata and by glandular character in pregnant and postpartum females. We suggest that the epigonal organ is involved in the degradation of components of atretic follicles and the embryos begin to develop surrounded by a gelatinous tertiary envelope produced by the oviducal gland. This latter organ is composed by three zones in mature females, club, papillary, and baffle zone, as described for other elasmobranchs. From the anatomical observations, a maturity scale comprising six sexual maturity stages (Immature I, Immature II, early mature, pregnant, post-partum, and regenerating) was established for female P. magdalenae, and it can be useful as basis for reproductive studies of other potamotrygonid species. Finally, we propose a continuous reproductive cycle for P. magdalenae.

A review on the morphology of ovarian follicles in elasmobranchs: A case study inRhizoprionodon taylori

“…TeWinkel () reported these structures as “special atretic follicles.” The author suggested these structures were formed from the atresia of non‐yolky oocytes no larger than 2 mm and that they were a potential source of steroids. More recently, Galíndez et al () have also reported APF as having apoptotic nuclei, enlargement of the vitelline membrane, and disorganization of both the theca and granulosa cells, while Pedreros‐Sierra et al () reported hypertrophy of the theca cells, fibrous connective tissue and invasion of the central cavity by granulosa cells. Despite the potential importance of these APF as a temporary endocrine gland, no other report of these structures were found in the elasmobranch literature.…”

“…The occurrence of APF has only been described in a few species (e.g., S. laticaudus , Guraya, ; M. canis , TeWinkel, ; Dasyatis bleekeri , Chatchavalvanich and Visuttipat, ; Potamotrygon magdalenae , Pedreros‐Sierra et al, ). The APF of R. taylori resemble those of M. canis (TeWinkel, ) in regards to the granulosa arrangement, scarcity of granules and presence of distinct thecal tubes.…”

“…At the beginning of atresia, the vitellogenic follicle loses its vitelline membrane and basement membrane. The granulosa layer, which may be filled with granulocytes and lymphocytes (Pedreros‐Sierra et al, ), folds forming villi, while small granulosa cells grow in length becoming taller and skinnier like a column, large granulosa cells degenerate (Chieffi and Botte, ; TeWinkel, ; Chieffi Baccari et al, ). The theca layer, formed by theca cells, connective tissue and blood vessels, intrude on these villosities forming a well‐vascularized stroma (TeWinkel, ; Chieffi Baccari et al, ).…”

“…Shortly after the onset of atresia, the granulosa cells start an active process of yolk phagocytosis, where the villi continue to lengthen and anastomise, resulting in a reduction of the central cavity (Chieffi and Gualà, ; Galíndez et al, ; Lance and Callard, ; Chatchavalvanich and Visuttipat, ). In addition, blood cells have also been reported to phagocytise yolk platelets (Pedreros‐Sierra et al, ). When phagocytosis is complete the nuclei of granulosa cells migrate from the basal to apical pole of the cells.…”

“…Similar to other viviparous and oviparous elasmobranchs, the granulosa cells actively ingest yolk from the central cavity. As in the early stages of AVF in some viviparous (lecithotropic: T. marmorata , Chieffi and Gualà, ; S. acanthias , Lance and Callard, ; P. magdalenae , Pedreros‐Sierra et al, ; placental viviparous: M. canis , TeWinkel, ) and oviparous elasmobranchs ( S. stellaris , Chieffi, ), the granulosa cells of R. taylori actively ingest the yolk abundantly present in the central cavity. The theca layer, carrying abundant blood vessels, infiltrates through the folds of the granulosa.…”