Parthenogenesis in amphibians
caecilians.
Artificial parthenogenesis
Haploid parthenogenesis has been achieved experimentally in
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.[1] Parthenogenesis has also been induced in Pelophylax nigromaculatus by pricking an egg with a needle.[2] This method produced tadpoles which metamorphosed into adult frogs, some of which were albino.[2]
Lithobates pipiens have all produced viable haploid adults as a result of artificial parthenogenesis.[1]
Parthenogenesis in nature
Origins
Salamanders are the oldest known parthenogenic vertebrates.[3] Molecular methods date the origins of unisexual salamanders to the Pliocene, from between 3.9 million[4] to approximately 5 million years ago.[5]
All known parthenogenic amphibians have been the result of hybridization events between closely related species.
Polyploidy in unisexual amphibians
Ambystoma hybrids are described by how many haploid sets of chromosomes they contain from each of their parent species, reflecting their level of ploidy.[4]
Mortality
Embryonic mortality in parthenogenic amphibians is high. Hatching rates for North American salamander species have ranged from 19.5%
Modes of parthenogenesis and parthenogenetic-like reproduction in amphibians
Gynogenesis
Glandirana rugosa.[12] The second potential mechanism is apomixis, which produces a complete set of chromosomes through mitotic replication.[8] This method has not been observed in any amphibious species.[8]
Courtship behavior between females of the same species has been observed in Ambystoma platineum, and has been posited to induce either oviposition of ovulation, though the precise utility of the behavior is unknown.[13]
Hybridogenesis
In
hybridogenesis, females of a unisexual species mate with a male of a related species and utilize their genetic material in order to produce offspring. However, in spite of this requirement, the genetic material of the male is not passed on to the next generation.[8] Just prior to meiosis, during mitotic division, spindle fibers attach to the maternal chromosomes, leaving the paternal chromosomes in the cytoplasm.[14] The paternal chromosomes are therefore excluded from nascent eggs, without recombination having typically occurred.[8] In some cases, such as Pelophylax esculentus, there is also endomeiosis prior to cell division, which means that the maternal chromosomes are duplicated and each egg contains identical pairs of chromosomes.[8]
Hybridogenesis can be described as a parthenogenetic-like mode of reproduction, since there is no continuing heredity in the paternal line .[8] It has been documented in the European water frog complex of the genus Pelophylax, which includes three hybridogenic forms.
Kleptogenesis
Kleptogenesis is a sexually parasitic form of reproduction in unisexual organisms, that is often associated with species that are also capable of gynogenetic reproduction.[8] In this reproductive mode unisexual females mate with sympatric males of related species, and genetic material in the paternal line recombines with the maternal DNA and thus is passed on. This mode of reproduction can be seen in numerous, though not all, species of unisexual salamander, particularly salamanders in the genus Ambystoma,[3] and is implicated in the exceptional genetic diversity that exists in those animals.[7]
References
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- ^ a b c Graf, J.D.; Pelaz, M.P. (1989). "Evolution and Genetics of Unisexual Vertebrates". In Dawley, R.M.; Bogart, J.P. (eds.). Evolutionary Genetics of the Rana esculenta complex. New York: New York State Museum.
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- ^ Ichikawa, Y; Miura, I.; Ohtani, H. (1997). "Early gonadal development of the genetic ZZ males and XX females produced by gynogenesis in Rana rugosa". Zoological Science. 14: 73.
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