|Abstract or Summary
- 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.