As a part of studies on the reproduction of laboratory maintained frogs, wild-caught Rana pipiens were ovulated and maintained a t 22-27Β°C for up to 18 months. Vitellogenic oocytes were periodically staged and counted, and a "maturity index" was calculated to assess the progress of the vitellogenic cycle. The initial cycle was similar to that of wild frogs except that the first oocytes to reach stage 5 (mature eggs) usually began to degenerate before later starting oocytes became mature. In addition, a second cycle began before the first was completed. After more than 1 year at room temperature, abnormal cycles were common. Ovaries of such animals contained very few mature eggs. Many of their oocytes were in early stages of vitellogenesis or, if pigmented, had begun to degenerate. These deficiencies were partially corrected in females placed in 4Β°C for 4-6 weeks. The average number of mature eggs increased 15-fold and ovary weights more than doubled. Oviduct weights almost doubled. Although the rates of cooling, photoperiod, and nutritional status could be important influences, the results imply that cold treatment alone increases estrogen secretion. We suggest that low estrogen secretion may account for the reproductive deficiencies seen in R. pipiens cultured a t room temperature.
Recent declines in natural populations of the leopard frog, Rana pipiens (Rittschof, '75; Hine et al., '811, as well as a decline in the quality of eggs obtained from wild-caught frogs (Nace, '76, '77; Lehman, '771, have lent urgency to the establishment of a reproducing laboratory colony of this valuable amphibian. However, egg production in laboratory-maintained frogs has proved to be unpredictable (Kemp, '53; Cairns et al., '67; Nace, '68; Mohanty-Hejmadi et al., '781, and the eggs that are produced do not always support normal development (Lehman, '77). The present work was undertaken at the Amphibian Facility of the University of Michigan (Nace, '68) to study the course of vitellogenesis in laboratory maintained females of R. pipiens and to try and understand and correct any abnormalities that occur in this process.