Parthenogenesis in amphibians

Parthenogenesis is a form of reproduction where eggs develop without fertilization, resulting in unisexual species. This phenomenon is closely related with reproductive modes such as hybridogenesis, where fertilization occurs, but the paternal DNA is not passed on. Among amphibians, it is seen in numerous frog and salamander species, but has not been recorded in caecilians.

Haploid parthenogenesis has been achieved experimentally in amphibians, through approaches that could be considered artificial gynogenesis. Oscar Hertwig first achieved artificial parthenogenesis in frogs in 1911, using eggs fertilized by irradiated sperm. The radiation destroyed the DNA within the sperm, but nearly normal embryos were still produced. Gunther Hertwig repeated this experiment in 1924, using crosses between different frogs. A cross between a toad, Amietophrynus regularis, and a frog, Rana fusca, would not produce a viable embryo, but fertilization of a toad egg by an irradiated frog sperm would produce a haploid larva. Parthenogenesis has also been induced in Pelophylax nigromaculatus by pricking an egg with a needle. This method produced tadpoles which metamorphosed into adult frogs, some of which were albino.Rana japonica, Pelophylax nigromaculatus and Lithobates pipiens have all produced viable haploid adults as a result of artificial parthenogenesis.

Salamanders are the oldest known parthenogenic vertebrates. Molecular methods date the origins of unisexual salamanders to the Pliocene, from between 3.9 million to approximately 5 million years ago.

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