Fertilization of Frog Body-Cavity Eggs: Rana pipiens Eggs and Rana clamitans Sperm

Abstract

Ovulated amphibian eggs that have not been coated with jelly in the oviduct are known as body-cavity eggs. Body-cavity eggs are usually not fertilized when placed with sperm. However, a low frequency of fertilization of body-cavity eggs of the frog Rana pipiens was obtained when the eggs were inseminated by high concentrations of R. pipiens sperm in the presence of a water extract of jellied eggs (egg-water). The frequency of fertilization was not predictable from the sperm concentration. Although most of the resulting embryos had difficulty completing gastrulation, a few were raised to metamorphosis. ‘When R. pipiens body cavity eggs were inseminated in R. pipiens egg_water by sperm of the frog R. clamitans, high frequencies of fertilization were obtained. Sperm concentrations greater than 2.5 x 10#{176} sperm/nil generally led to frequencies of fertilization greater than 60%. Most of the resulting embryos were diploid, and all arrested at gastrulation, a characteristic of the pipiens-clamitans hybrid cross. These results indicated that the R. clamitans sperm penetrated into the R. pipiens body-cavity egg and that syngamy occurred. The results demonstrate that R. pipiens eggs need not pass down the oviduct or acquire a jelly coat in order to be fertilizable.