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Haploid parthenogenesis has been achieved experimentally in
Parthenogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
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
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
, where fertilization occurs, but the paternal DNA is not passed on. Among amphibians, it is seen in numerous frog
A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...
and salamander
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
species, but has not been recorded in caecilians.
Artificial parthenogenesis
Haploid parthenogenesis has been achieved experimentally in amphibians
Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbore ...
, through approaches that could be considered artificial gynogenesis Gynogenesis, a form of parthenogenesis, is a system of asexual reproduction that requires the presence of sperm without the actual contribution of its DNA for completion. The paternal DNA dissolves or is destroyed before it can fuse with the egg. Th ...
. Oscar Hertwig
Oscar Hertwig (21 April 1849 in Friedberg – 25 October 1922 in Berlin) was a German embryologist and zoologist known for his research in developmental biology and evolution. Hertwig is credited as the first man to observe sexual reproduction ...
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
''Pelophylax nigromaculatus'' (formerly ''Rana nigromaculata''), is a species of true frog found in East Asia, first described in 1861. This widespread and common frog has many common names, including dark-spotted frog, black-spotted pond frog, a ...
'' by pricking an egg with a needle. This method produced tadpole
A tadpole is the larval stage in the biological life cycle of an amphibian. Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial. Tadpoles have some fish-like features that may not be found i ...
s which metamorphosed into adult frogs, some of which were albino.
'' Rana japonica'', ''Pelophylax nigromaculatus
''Pelophylax nigromaculatus'' (formerly ''Rana nigromaculata''), is a species of true frog found in East Asia, first described in 1861. This widespread and common frog has many common names, including dark-spotted frog, black-spotted pond frog, a ...
'' and ''Lithobates pipiens
''Lithobates pipiens''Integrated Taxonomic Information System nternet2012''Lithobates pipiens'' pdated 2012 Sept; cited 2012 Dec 26Available from: www.itis.gov/ or ''Rana pipiens'', commonly known as the northern leopard frog, is a species of l ...
'' have all produced viable haploid adults as a result of artificial parthenogenesis.
Parthenogenesis in nature
Origins
Salamanders
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
are the oldest known parthenogenic vertebrates. Molecular methods date the origins of unisexual salamanders to the Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pelophylax esculentus'', the edible frog, is the product of crosses between ''
Pelophylax lessonae
The pool frog (''Pelophylax lessonae'') is a European frog in the family Ranidae. Its specific name (zoology), specific name was chosen by the Italian Herpetology, herpetologist Lorenzo Camerano in 1882, in order to honour his master Michele Less ...
'' and ''Pelophylax ridibundus
The marsh frog (''Pelophylax ridibundus'') is a species of water frog native to Europe and parts of western Asia.
Description
The marsh frog is the largest type of frog in most of its range, with males growing to a size around 100 mm (3.9 ...
''. Similarly, ''Ambystoma laterale
The blue-spotted salamander (''Ambystoma laterale'') is a mole salamander native to the Great Lakes region, Great Lakes states and northeastern United States, and parts of Ontario and Quebec in Canada. Their range is known to extend to James Bay ...
'', ''Ambystoma jeffersonianum
The Jefferson salamander (''Ambystoma jeffersonianum'') is a mole salamander native to the northeastern United States, southern and central Ontario, and southwestern Quebec. It was named after Jefferson College in Pennsylvania.
It is typically ...
'', ''Ambystoma texanum
The small-mouth salamander (''Ambystoma texanum'') is a species of mole salamander found in the central United States, from the Great Lakes region in Michigan to Nebraska, south to Texas, and east to Tennessee, with a population in Canada, in P ...
'' and '' Ambystoma tigrinum'' have been identified as extant parent species to unisexual salamanders within the same genus. However, mitochondrial evidence suggests that the origins of hybrid '' Ambystoma'', on the maternal line, lie in a relative of '' Ambystoma barbouri''. In spite of this, all extant unisexual species of ''Ambystoma'' share no nuclear DNA with ''Ambystoma barbouri''.
Polyploidy in unisexual amphibians
Polyploidy
Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei ( eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contain ...
, a numerical change in the number of chromosomes, is common in parthenogenic amphibians. Triploidy (having three sets of chromosomes), tetraploidy (four sets of chromosomes) and pentaploidy (five sets of chromosomes) are common in salamanders. In unisexual salamanders these different levels of polyploidy are a result of multiple hybridization events, involving two to four species. '' Ambystoma nothagenes'' is a unisexual, triploid hybrid of ''Ambystoma laterale
The blue-spotted salamander (''Ambystoma laterale'') is a mole salamander native to the Great Lakes region, Great Lakes states and northeastern United States, and parts of Ontario and Quebec in Canada. Their range is known to extend to James Bay ...
'', ''Ambystoma texanum
The small-mouth salamander (''Ambystoma texanum'') is a species of mole salamander found in the central United States, from the Great Lakes region in Michigan to Nebraska, south to Texas, and east to Tennessee, with a population in Canada, in P ...
'' and '' Ambystoma tigrinum'', while hybrids of '' Ambystoma platineum'' and ''Ambystoma texanum
The small-mouth salamander (''Ambystoma texanum'') is a species of mole salamander found in the central United States, from the Great Lakes region in Michigan to Nebraska, south to Texas, and east to Tennessee, with a population in Canada, in P ...
'' have been found to be tetraploid. Most '' Ambystoma'' hybrids are described by how many haploid sets of chromosomes they contain from each of their parent species, reflecting their level of ploidy.
Mortality
Embryonic mortality in parthenogenic amphibians is high. Hatching rates for North American salamander species have ranged from 19.5% to 30.5%. It is speculated that intergenomic exchanges, like crossing over duringmeiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
, may play a role. Intergenomic exchanges are often lethal due to the fact that chromosomes in unisexual species are homeologous (similar, but less so than homologous chromosomes
A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points alon ...
from within a species). Homologous chromosomes are largely identical, in this case as a result of the chromosome replication.
Modes of parthenogenesis and parthenogenetic-like reproduction in amphibians
Gynogenesis
Gynogenesis Gynogenesis, a form of parthenogenesis, is a system of asexual reproduction that requires the presence of sperm without the actual contribution of its DNA for completion. The paternal DNA dissolves or is destroyed before it can fuse with the egg. Th ...
is a form of parthenogenesis where an egg begins to divide only after being pricked by a sperm cell, but without the genetic material of the sperm being used. There are two known mechanisms of gynogenesis. The first is an endomitotic event prior to meiosis, where the number of chromosomes in a cell doubles without cell division taking place. After meiosis each egg has the same ploidy (number of chromosomes) as the mother. This particular parthenogentic mechanism has been observed in unisexual '' Ambystoma'' species as well as '' Glandirana rugosa''. The second potential mechanism is apomixis
In botany, apomixis is asexual reproduction without fertilization. Its etymology is Greek for "away from" + "mixing". This definition notably does not mention meiosis. Thus "normal asexual reproduction" of plants, such as propagation from cuttin ...
, which produces a complete set of chromosomes through mitotic replication. This method has not been observed in any amphibious species.
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.
Hybridogenesis
Inhybridogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
, 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. Just prior to meiosis, during mitotic division, spindle fibers attach to the maternal chromosomes, leaving the paternal chromosomes in the cytoplasm. The paternal chromosomes are therefore excluded from nascent eggs, without recombination having typically occurred. 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.
Hybridogenesis can be described as a parthenogenetic-like mode of reproduction, since there is no continuing heredity in the paternal line . It has been documented in the European water frog complex of the genus ''Pelophylax
''Pelophylax'' is a genus of true frogs widespread in Eurasia, with a few species ranging into northern Africa. This genus was erected by Leopold Fitzinger in 1843 to accommodate the green frogs of the Old World, which he considered distinct fro ...
'', which includes three hybridogenic forms.
Kleptogenesis
Kleptogenesis
In biology, a klepton (abbr. kl.) and synklepton (abbr sk.) is a species that requires input from another biological taxon (normally from a species which is closely related to the kleptonic species) to complete its reproductive cycle. Specific typ ...
is a sexually parasitic form of reproduction in unisexual organisms, that is often associated with species that are also capable of gynogenetic reproduction. 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'', and is implicated in the exceptional genetic diversity that exists in those animals.
References
{{reflist, 2 Vertebrate parthenogenesis Amphibians