Ovarian cycle in the frog Rana cyanophlyctis: a quantitative study of follicular kinetics in relation to body mass, oviduct, and fat body cycles

Abstract

In Rana cyanophlyctis, all stages of oocyte development are present throughout the year owing to continuous and asynchronous gametogenetic activity, but quantitative differences occur in the frequency distribution of the first growth phase (FGP) and second growth phase (SGP) oocytes. The number of SGP oocytes influences ovarian weight; therefore, seasonal changes in the number of SGP oocytes and ovarian mass are correlated. Mean ovarian weight and gonadosomatic index follow comparable changes during the annual cycle. The body mass of the frog undergoes only minor seasonal variations. Also, the body mass does not influence the number of oocytes in the frog. Small FGP oocytes always formed the dominant type in the ovary. Only 20-0% of FGP oocytes were recruited to SGP stage during the prebreeding months (March-April). The breeding season extends over 2- months (July-September) and an adult R. cyanophlyctis spawns 3,000-,500 eggs of 1,300-1,350 µm diameter in size. The breeding is not followed by any resting period, and therefore oogonial proliferation and recruitment of FGP oocytes start soon after the breeding months (October-December). Atretic oocytes are present in all months but their number is greatest during prebreeding and breeding months. The frequency distribution of oocytes in the right and the left ovaries is identical. The oviducts undergo seasonal changes that are correlated with ovarian weight, whereas the fat body cycle is inversely related to ovarian weight.