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

This is the authors' abstract. We don't add key points for this paper.

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 × 106 sperm/ml 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.