The annual variations in reproductive characteristics of the female frog Rana perezi have been studied. In natural populations of this species, spawning takes place in early spring with the maximum development of the ovary and oviduct. After the female has mated, her ovary and oviduct are regressed, and the remaining mature ovarian follicles become completely resorbed, remaining in the ovary as atretic follicles. The ovarian follicular growth begins at the end of summer and continues throughout the autumn and winter. We have found pronounced seasonal changes in fat body development. The seasonal proflile of fat body weight is inversely related to ovary and oviduct seasonal cycles. Plasma levels of 17β-estradiol showed a significant seasonal variation with maximal values occurring from late winter to the breeding time. After the mating the hormonal level drops to a minimum in summer.
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Delgado et al. (1990) studied this question.