Graduate Thesis Or Dissertation
 

Role of male mating behavior in the induction of ovulation in rough-skinned newts, Taricha granulosa

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  • To determine whether meiotic maturation of ovarian follicles, ovulation, and oviposition are influenced by male mating behaviors, female rough-skinned newts (Taricha granulosa) were captured prior to contact with males and maintained in simulated pond conditions. Females were either exposed to male courtship and inseminated or were isolated from male contact. Follicular maturation was accelerated after only 10 hours of amplexus. Further, as determined by the presence of oviducal eggs, only mated females ovulated, and this occurred 11 to 32 days after exposure of the female to male courtship and insemination. To determine whether male mating behaviors or insemination causes ovulation, cloacae were occluded in half of the females that were paired with nuptial males. Neither females that were exposed to male courtship but were not inseminated, nor unmated controls ovulated. In contrast, a high percentage of inseminated females both ovulated and oviposited. Progesterone is known to play an integral role in the stimulation of meiotic maturation and ovulation in amphibians. Unmated females injected with exogenous gonadotropin, ovine LH, were sacrificed at various intervals following injections, and plasma progesterone concentrations were measured by radioimmunoassay. LH induced ovulation. Further, ovulation, induced by injections of exogenous LH, was associated with an increase in plasma progesterone levels: Progesterone concentration was highest one day prior to the onset of ovulation. Plasma progesterone levels were measured in females sacrificed at various intervals during and following mating, and also in unmated control females. There was no significant difference in plasma progesterone concentrations in mated and unmated females during the first 4 days following initiation of mating behaviors. A significant difference between mated and unmated females was found 13 days after pairing. These results support the hypothesis that male mating behaviors stimulate the release of gonadotropin which acts on the ovary to facilitate the production of a steroid, probably progesterone, capable of inducing maturation and ovulation. Furthermore, male courtship with insemination induces ovulation in T. granulosa. This is the first documentation of induced ovulation in any species of amphibians.
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