Environmental influence on ovulation and embryonic development in Rana pipiens

Abstract

Environmental effects on ovulation and embryogenesis in Rana pipiens were assessed using both freshly-captured fall animals and laboratory-conditioned females which had undergone vitellogenesis in the laboratory. Frogs in both categories were divided into two groups. Ovulation was hormonally induced in one group of females prior to cold exposure and in the second group of animals following an 8-week-period at 4 degrees C with an 8L 16D photoperiod. The incidence of both ovulation and normal embryonic development was increased following exposure of the animals to low temperatures and short daylength. Those animals which only partially ovulated prior to cold treatment did not respond to hormone injections following the period of cold exposure. Examination of the ovaries of these females revealed a much greater degree of oocyte resorption than was found in frogs whose initial ovulation was induced only after exposure to cold temperatures. The administration of ovulation-inducing hormones prior to artificial hibernation may thus have initiated a phase of oocyte resorption which progressed even at 4 degrees C. The incidence of ovulation was similar in wild-caught and laboratory-conditioned females, but eggs from the latter showed a much lower percentage of development to Shumway stage 20. This effect may have been related to differences in the environmental factors to whcih the two groups were exposed during oogenesis.

Hormonal induction of spawning in 4 species of frogs by coinjection with a gonadotropin-releasing hormone agonist and a dopamine antagonist

“…The reason for this low success rate compared to the in-season breeding is currently unknown, but likely relates to the short hibernation period we induced. Perhaps a longer period of hibernation at 4°C would increase spawning success by promoting vitellogenesis in the females [50,51]. Nevertheless, the tadpoles grew and metamorphosed normally, although they resulted from spawnings in captivity that were approximately 6 months earlier that the expected time of natural spawning of L. pipiens in Eastern Ontario.…”

CURRENT STATUS OF AMPHIBIAN CULTURE WITH EMPHASIS ON NUTRITION, DISEASES AND REPRODUCTION OF THE BULLFROG, Rand catesbeiana

“…Obviously, t h i s l e v e l of response i s i n s u f f i c i e n t f o r large-scale culture purposes. Further, t h e University of Michigan personnel t e s t e d the p o s s i b i l i t y t h a t subjecting leopard frog females t o a simulated "hibernation" period (LD 8:16; 4OC) would improve the success of ovulat i o n (Lehman, 1977). Frogs not exposed t o cold temperatures produced very few eggs when ovulated, and only 0.3% of those produced were successfully f e r t i l i z e d .…”

Captive breeding in the endangered alpine tree frog, Litoria verreauxii alpina

“…It is also possible that the distinct egg masses represent partial ovulations for the females. Partial ovulation of mature eggs seems to be relatively rare in natural amphibian populations, but some captive breeders have experienced partial ovulation in female frogs particularly following hormone inductions ( Lehman, 1977 ; Jorgensen, 1984 ; Sive, Grainger & Harland, 2000 ). Egg clutches resulting from partial ovulation can result in poor fertilization success, reduced egg viability, or few tadpoles hatching ( Silla & Byrne, 2021 ).…”