A study of ovarian foilicular kinetics, oviduct, fat body, and liver mass cycles in laboratory-maintained Rana cyanophlyctis in comparison with wild-caught frogs

Abstract

Ovarian follicular dynamics and fluctuations in fat body, oviducal, and liver masses were studied in captive Rana cyanophlyctis in comparison with wild-caught frogs, sampled at monthly intervals over a period of 12 months. In both the captive and wil-dcaught frogs first growth phase (FGP) and second growth phase (SGP) or vitellogenic oocytes were produced throughout the period examined; however, changes in ovarian and oviducal weights were less marked in the former group. In the captive frogs SGP oocyte production was reduced by 50%, and, maximum ovarian weight and SGP oocyte number were attained 2-3 months earlier than in wild-caught controls. The FGP oocyte pool in laboratory-maintained frogs, however was comparable with that of the corresponding wild-caught frogs. Captivity caused a threefold increase in atresia and reduced the number of oocytes reaching SGP. The depletion of fat stores in fat bodies during the later phases of captivity suggests that the deposition of lipids into oocytes (for SGP) was given priority over storage in the fat bodies. The low oviducal weights of captive frogs was correlated with a reduced number of SGP oocytes, which are the source of estrogen. On the other hand, liver weight remained high, indicating adequate hepatic vitellogenin synthesis. Possible reduction in its output was not detected, possibly due to the reduced number of follicles reaching SGP. The findings indicate that stress of captivity decreases gonadotrophins and estrogen levels. Oviducal growth is reduced in captive frogs. It is hypothesized that in the frog oviducts respond to estrogen in a threshold-dependent manner, whereas the liver responds to it in relation to the length of exposure.