In the Bangalore population of Bufo melanostictus the ovarian cycles in individual toads are characterized by synchronous growth of the vittellogenic oocytes and by asynchrony with respect to stage in the ovarian cycle among the toads. However, late ovarian cycles predominated during the period of August-October. The incidence of atresia, as observed in the ovaries sampled throughout the year, suggests that about two thirds of the toads preparing for spawning are primiparous, leaving only one third to represent iteroparity within the population. Body size varied greatly at first maturation, when somatic growth declined or stopped. The greatly varying body size is consistent with a seasonal timing of sexual maturation preparing for the main breeding season, which coincides with the height of the monsoon rains during August-October.

https://www.jstor.org/stable/info/3565838

Body size, reproduction and growth in a tropical toad, Bufo melanostictus, with a comparison of ovarian cycles in tropical and temperate zone anurans

Typhlonectes compressicauda is an aquatic gymnophionan amphibian living in South America. Its breeding cycle is linked to seasons, characterized by a regular alternation of rainy and dry seasons. During a complex biennial cycle, the female genital tract undergoes a series of alternations of increasing and decreasing, governed by equilibrium of proliferation and apoptotic phenomena. Immunohistochemical methods were used to visualize cell proliferation with the detection of Ki67 antibody, a protein present in proliferative cells; terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and Apostain were performed to detect apoptotic cells on sections of ovaries and oviducts. In ovaries, both phenomena affect the germinal nests and follicles according to the cycle period. In the oviduct, the balance was in favor of proliferation during preparation for reproduction, and in favor of apoptosis when genital ducts regress. Apoptosis and proliferation are narrowly implicated in the remodeling of the genital tract and they are accompanied by the differentiation of tissues according to the phase of the breeding cycle. These variations permit the capture of oocytes at ovulation, always at the same period, and the parturition after 6–7 months of gestation, at a period in which the newborns live with their mother, protected in burrows in the mud. During the intervening year of sexual inactivity, the female reconstitutes body reserves.

https://www.mdpi.com/1422-0067/18/1/16/pdf

Patterns of Apoptosis and Proliferation throughout the Biennial Reproductive Cycle of Viviparous Female Typhlonectes compressicauda (Amphibia, Gymnophiona)

Developing oocytes in adult Rana tigerina can be divided into six stages based on size, color and histology. The stage I oocyte (50-350 µm) is characterized by translucent cytoplasm and a smooth nuclear membrane. The major portion of its cytoplasm contains a large quantity of free ribosomes. Cytoplasmic organelles confined to the peripheral part of oocyte include a few mitochondria, Golgi apparatus, primary and secondary lysosomes, and a few lipid droplets. The stage II oocyte (360-550 µm) contains alcian-blue positive cortical alveoli at the periphery and large central nucleoli in the nucleus. The stage III oocyte (560-900 µm) is characterized by the deposition of yolk platelets and formation of pigmented granules. The cortical alveoli are greatly increased in number as well as in size. Endocytotic activity on the surface of oocyte can be observed. The stage IV oocyte (910-1300 µm) is characterized by a large number of main yolk bodies, cortical alveoli and melanin granules. High endocytotic activities are observed. In the stage V oocyte (1310-1500 µm), most of the melanin granules migrate to the animal pole, while the cortical granules are concentrated underneath the oolemma. The stage VI or fully grown oocyte (1510-1700 µm) is characterized by a complete absence of melanin granules in the vegetal pole and by the cessation of endocytotic activity. Studying the development of ovaries in frogs at various ages reveals that definitive ovaries are formed in the one-month-old frog. Ovaries of two- to four-month-old frogs contain only stage I oocytes, while the ovaries of twelve-month- old frogs contain oocytes of all stages, which indicate the maturity of female frogs. Studying the seasonal variation of ovaries throughout the year reveals that there are no stage VI oocytes in ovaries collected from November to February, while these oocytes are present during the period from March to October.

/pdf/classification-of-developing-oocytes-ovarian-development-and-1xh7mgv9w7.pdf

Classification of Developing Oocytes, Ovarian Development and Seasonal Variation in Rana tigerina

We describe the ultrastructural organization of the vitellogenic follicle stages in two caecilian species. Monthly samples of slices of ovary of Ichthyophis tricolor and Gegeneophis ramaswamii from the Western Ghats of India were subjected to transmission electron-microscopic analysis, with special attention to the follicle cell/oocyte interface. In order to maintain uniformity of the stages among the amphibians, all the stages in the caecilian follicles were assigned to stages I–VI, the vitellogenic and post-vitellogenic follicles being assigned to stages III–VI. Stage III commences with the appearance of precursors of vitelline envelope material in the perivitelline space. Stages IV and V have been assigned appropriate substages. During the transition of stage III to stage VI oocytes, a sequential change occurs in the manifestations of follicle cells, perivitelline space, vitelline envelope and oocyte cortex. The vitelline envelope becomes a tough coat through the tunnels of which the macrovilli pass to interdigitate between the microvilli. The oocyte surface forms pinocytic vesicles that develop into coated pits and, later, coated vesicles. Contributions of the oocyte cortex to the vitelline envelope and of the follicle cells to yolk material via synthesis within them are indicated. The follicle cell/oocyte interface of vitellogenic follicles of these two caecilians resembles that in anurans and urodeles, with certain features being unique to caecilians. Thus, this paper throws light on the possible relationships of caecilians to anurans and urodeles with special reference to ovarian follicles.

/pdf/stages-in-follicle-cell-oocyte-interface-during-4woey24dbx.pdf

Stages in follicle cell/oocyte interface during vitellogenesis in caecilians Ichthyophis tricolor and Gegeneophis ramaswamii: a transmission electron-microscopic study.

Though much is known about various aspects of reproductive biology of amphibia, there is little information on the cellular and mechanistic basis of assembly of ovarian follicles in this group. This is especially true of the caecilians. Therefore, taking advantage of the abundant distribution of caecilians in the Western Ghats of India, two species of caecilians, Ichthyophis tricolor and Gegeneophis ramaswamii, were subjected to light and transmission electron microscopic analysis to trace the sequential changes during the assembly of ovarian follicles. The paired ovaries of these caecilians are elongated sac-like structures each including numerous vitellogenic follicles. The follicles are connected by a connective tissue stroma. This stroma contains nests of oogonia, primary oocytes and pregranulosa cells as spatially separated nests. During assembly of follicles the oocytes increase in size and enter the meiotic prophase when the number of nucleoli in the nucleus increases. The mitochondrial cloud or Balbiani vitelline body, initially localized at one pole of the nucleus, disperses through out the cytoplasm subsequently. Synaptonemal complexes are prominent in the pachytene stage oocytes. The pregranulosa cells migrate through the connective tissue fibrils of the stroma and arrive at the vicinity of the meiotic prophase oocytes. On contacting the oocyte, the pregranulosa cells become cuboidal in shape, wrap the diplotene stage oocyte as a discontinuous layer and increase the content of cytoplasmic organelles and inclusions. The oocytes increase in size and are arrested in diplotene when the granulosa cells become flat and form a continuous layer. Soon a perivitelline space appears between the oolemma and granulosa cells, completing the process of assembly of follicles. Thus, the events in the establishment of follicles in the caecilian ovary are described.

Assembly of ovarian follicles in the caecilians Ichthyophis tricolor and Gegeneophis ramaswamii: light and transmission electron microscopic study.

Oogenesis in the toad is of continuous type occurring throughout the year. The prefollicular cells divide mitotically to increase their number, to surround the developing follicles. The vitellogenesis begins from periphery and progresses towards the centre. The theca and granulosa layers in the mature follicles cannot be clearly differentiated. Binuclear oocytes are rarely found.The ovarian cycle of the toad can be broadly classified into prespawning (April-May), spawning (June-August) and postspawning-cum-preparatory period (September-March). The classification is based on the seasonal changes in the gonadosomatic index, diameter of the largest oocytes and ovarian histology. The breeding activity of the toad coincides with the rainy months of monsoon.

S. K. Saidapur

Papers

Pattern of ovarian activity in the Indian toad. Bufo melanostictus (Schn.)