Difference between revisions of "Parthenogenesis" - New World Encyclopedia

Latest revision as of 08:54, 18 November 2022

The asexual whiptail species Cnemidophorus neomexicanus (center) consists exclusively of females who reproduce via parthenogenesis. C. neomexicanus is flanked by the sexually reproducing species that hybridized to generate it: C. inornatus (left) and C. tigris (right).

Parthenogenesis is a form of asexual reproduction in which offspring develop from unfertilized eggs. A common mode of reproduction in arthropods, such as insects and arachnids, parthenogenesis also occurs in some species of fish, amphibians, and reptiles.

Parthenogenesis is part of the wide diversity of adaptations found in nature, securing the perpetuation of the lineage of organisms. Reproduction not only secures the individual purpose of the species survival, but also provides organisms for food chains. Most animals that engage in parthenogenesis also utilize sexual reproduction or sexual behaviors, reflecting the near universal mode of this form of reproduction among eukaryotes.

Overview

Parthenogenesis (which is derived from the Greek words for "virgin" and "creation") is more efficient than sexual reproduction because it does not always involve mating behaviors, which require energy and usually incur risks. Moreover, all members of an asexual population are capable of reproducing. The disadvantage, however, is that asexual reproduction, unlike its sexual counterpart, does not generate genotypic diversity, which is important for adapting to abiotic and biotic environmental changes.

Given the drawbacks of asexual reproduction for the long-term survival of the species, most species that engage in parthenogenesis also participate in sexual reproduction or sexual behaviors. Parthenogenesis, thus, typically serves as one available reproductive strategy, often a response to environmental or seasonal conditions, such as the amount of available resources. Aphids, for example, are parthenogenic in spring and summer, multiplying rapidly while conditions are favorable; during the winter months, they mate, and the females hatch fertilized eggs. In rare cases, however, parthenogenesis does not occur in combination with sexual reproduction or behaviors: The bdelloid rotifer Philodina roseola, for example, reproduces exclusively by parthenogenesis, and the species is believed to have avoided sexual reproduction for 85 million years (Judson 2002).

In addition to its reproductive role, parthenogenesis functions as part of a mechanism for determining sex in some species. In ants and most species of bees and wasps, females develop from unfertilized eggs and are referred to as haploid (possessing one set of chromosomes), while males develop from fertilized eggs and hence are diploid (possessing two sets of chromosomes, one from each parent). Thus, in species also capable of sexual reproduction, parthenogenesis can help to regulate the relative number of males and females in a population.

Sexual behavior

In some species, parthenogenesis requires a sexual act to trigger development of the egg, even though this behavior does not fertilize the egg. In parthenogenic ticks and mites, for example, the eggs develops only after the animals have mated, but the eggs remain unfertilized. Some species of beetles that have no males require sperm to trigger development; these beetles mate with males of closely related species. However, the sperm does not contribute genetic material.

In other parthenogenic species lacking males, females stimulate each other to activate the neuroendocrine mechanisms necessary for egg maturation. This phenomenon has been extensively studied in the New Mexico whiptail (genus Cnemidophorus), of which 15 species reproduce exclusively by parthenogenesis. One female plays the role of the male in closely related species, and mounts the female that is about to lay eggs. This behavior is due to the hormonal cycles of the females, which cause them to behave like males shortly after laying eggs, when levels of progesterone are high, and to take the female role in mating before laying eggs, when estrogen dominates. Lizards that act out the courtship ritual have greater fecundity than those kept in isolation, due to the increase in hormones that accompanies the mounting. So, although the populations lack males, they still require sexual stimuli for maximum reproductive success.

Determining sex

Parthenogenesis involves the inheritance and subsequent duplication of only a single sex chromosome. The unfertilized egg can thus be male or female depending on the chromosomal scheme of the species:

If two like chromosomes determine the female sex (such as the XY sex-determination system), the offspring will be female.
If two like chromosomes determine the male sex (such as the ZW sex-determination system), the offspring will be male.

In eusocial animals that engage in reproductive specialization, parthenogenesis can be a means of regulating the relative number of females and males in the group. One well-known example is the honeybee: Most females in the colony are sterile workers, but a few become fertile queens. After the queen mates, she possesses a supply of sperm that she controls, enabling her to produce either fertilized or unfertilized eggs. Thus, the queen determines when and how much of the colony’s resources are expended on the production of males (called drones).

Recent examples

The Komodo dragon, which normally engages in sexual reproduction, was recently found to be able to reproduce asexually via parthenogenesis (Highfield 2006; Watts 2006). Because the genetics of sex determination in Komodo dragons uses the WZ system (where WZ is female, ZZ is male, and WW is inviable), the offspring of parthenogenesis will be male (ZZ) or inviable (WW), with no females being born. It has been postulated that this strategy might give the Komodo dragon an advantage in the colonization of islands, where a single female could theoretically have male offspring asexually, then switch to sexual reproduction to maintain a higher level of genetic diversity than asexual reproduction alone could produce.

In 2001, a bonnethead (a type of small hammerhead shark) was thought to have produced a pup in captivity at a zoo in Nebraska. The tank contained three female hammerheads and no males. DNA testing showed that the pup's DNA matched only one female living in the tank, and that no male DNA was present in the pup. The pup was not a twin or clone of the mother; rather, it contained only half her DNA (a process called automictic parthenogenesis). The type of reproduction exhibited had been seen before in bony fish but never in cartilaginous fish such as sharks (Sample 2007). Another apparent parthenogenic shark birth occurred in 2002, when two white-spotted bamboo sharks were born at the Belle Isle Aquarium in Detroit. The birth baffled experts as the mother shared an aquarium with only one other female shark.

The repercussions of self-fertilization in sharks, which reduces the genetic diversity of the offspring, is a matter of concern for shark experts, taking into consideration conservation management strategies for this species, particularly in areas where there may be a shortage of males due to fishing or environmental pressures. Unlike Komodo dragons, which have a WZ chromosome system and produce male (ZZ) offspring by parthenogenesis, sharks have an XY chromosome system, so they produce only female (XX) offspring by parthenogenesis. As a result, sharks cannot restore a depleted male population through parthenogenesis, so an all-female population must come in contact with an outside male before normal sexual reproduction can resume.

Parthenogenesis differs from cloning

Parthenogenesis is distinct from artificial animal cloning, a process in which the new organism is identical to the cell donor. Parthenogenesis is truly a reproductive process that creates a new individual or individuals from the naturally varied genetic material contained in the eggs of the mother. However, in animals with an XY chromosome system where parthenogenic offspring (called parthenogens) are female, the offspring of a parthenogen all are genetically identical to each other and to the mother, as a parthenogen is homozygous (possessing two identical sets of genes).

References
ISBN links support NWE through referral fees

Highfield, R. 2006. No sex please, we're lizards. Daily Telegraph. Retrieved July 28, 2007.
Judson, O. 2002. Dr. Tatiana’s Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex. New York: Metropolitan Books. ISBN 0805063315
Purves, W., D. Sadava, G. Orians, and C. Heller. 2004. Life: The Science of Biology, 7th edition. Sunderland, MA: Sinauer. ISBN 0716766728
Sample, I. 2007. Study confirms virgin birth of zoo shark pup. The Guardian. Retrieved August 6, 2007.
Watts, P. C., et al. 2006. Parthenogenesis in Komodo dragons. Nature 444: 1021.

External links

All links retrieved November 18, 2022.

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History of "Parthenogenesis"

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@@ Line 1: / Line 1: @@
-{{Claimed}}
+{{Approved}}{{Images OK}}{{Submitted}}{{Paid}}{{copyedited}}
-[[Image:Cnemidophorus-ThreeSpecies.jpg|thumb|260px|right|The asexual whiptail species ''[[Cnemidophorus neomexicanus]]'' (center) with the sexual species that hybridized to form it, ''[[Cnemidophorus inornatus|C. inornatus]]'' (left) and ''[[Cnemidophorus tigris|C. tigris]]'' (right).]]
+[[Image:Cnemidophorus-ThreeSpecies.jpg|thumb|260px|right|The asexual whiptail species ''[[Cnemidophorus neomexicanus]]'' (center) consists exclusively of females who reproduce via parthenogenesis. ''C. neomexicanus'' is flanked by the sexually reproducing species that hybridized to generate it: ''[[Cnemidophorus inornatus|C. inornatus]]'' (left) and ''[[Cnemidophorus tigris|C. tigris]]'' (right).]]
-'''Parthenogenesis''' (from the [[Greek language|Greek]] παρθένος ''parthenos'', "virgin", + γένεσις ''genesis'', "creation") is the growth and development of an [[embryo]] or [[seed]] without [[fertilization]] by a [[male]]. Parthenogenesis occurs naturally in some species, including lower [[plant]]s, [[invertebrate]]s (e.g. [[water flea]]s, [[aphid]]s, some [[bee]]s and [[parasitic wasp]]s), and [[vertebrate]]s (e.g. some
+'''Parthenogenesis''' is a form of [[reproduction#asexual reproduction|asexual reproduction]] in which offspring develop from unfertilized eggs. A common mode of [[reproduction]] in [[arthropod]]s, such as [[insect]]s and [[arachnid]]s, parthenogenesis also occurs in some species of [[fish]], [[amphibian]]s, and [[reptile]]s.
-[[reptile]]s,<ref name="reptiles">{{cite book
+{{toc}}
-  | last = Halliday
+Parthenogenesis is part of the wide diversity of [[adaptation]]s found in nature, securing the perpetuation of the lineage of organisms. Reproduction not only secures the individual purpose of the species survival, but also provides organisms for [[food chain]]s. Most animals that engage in parthenogenesis also utilize [[sexual reproduction]] or sexual behaviors, reflecting the near universal mode of this form of reproduction among [[eukaryote]]s.
-  | first = Tim R.
-  | coauthors = Kraig Adler (eds.)
-  | title = Reptiles & Amphibians
-  | publisher = Torstar Books
-  |date= 1986
-  | pages = p. 101
-  | id = ISBN 0-920269-81-8 }}</ref>
-[[fish]],
-and, very rarely, [[bird]]s<ref>{{cite web|last = Savage
-  | first = Thomas F.
-  | title = A Guide to the Recognition of Parthenogenesis in Incubated Turkey Eggs
-  | work = Oregon State University
-  |date= September 12, 2005
-  | url=http://oregonstate.edu/Dept/animal-sciences/poultry/index.html
-  | accessdate = 2006-10-11 }}</ref> and [[shark]]s<ref>[http://www.washingtonpost.com/wp-dyn/content/article/2007/05/22/AR2007052201405.html "Female Sharks Can Reproduce Alone, Researchers Find"], Washington Post, Wednesday, May 23, 2007; Page A02</ref>). It is sometimes also used to describe reproduction modes in hermaphroditic species which can self-fertilize.
-==Parthenogenesis==
+==Overview==
-'''Parthenogenesis''' is a form of [[asexual reproduction]] in which females produce eggs that develop without fertilization. Parthenogenesis is seen in [[aphids]], [[daphnia]], [[rotifers]], and some other invertebrates, as well as in some plants. [[Komodo dragon]]s and sharks have recently been added to the list of vertebrates—along with several genera of fish, amphibians, and reptiles—that exhibit differing forms of asexual reproduction, including true parthenogenesis, gynogenesis, and hybridogenesis (an incomplete form of parthenogenesis).
-The offspring of parthenogenesis will be all female if two like chromosomes determine the female sex (such as the [[XY sex-determination system]]), but male if two like chromosomes determine the male sex (such as the [[ZW sex-determination system]]), because the process involves the inheritance and subsequent duplication of only a single sex chromosome. The offspring may be capable of sexual reproduction, if this mode exists in the species. A parthenogenetic offspring is sometimes called a '''parthenogen'''. As with all types of [[asexual reproduction]], there are both costs (reduced genetic diversity generated and susceptibility to adverse mutation) and benefits (reproduction without the need for a mate) associated with parthenogenesis.
+Parthenogenesis (which is derived from the [[Greek language|Greek]] words for "virgin" and "creation") is more efficient than [[sexual reproduction]] because it does not always involve mating behaviors, which require energy and usually incur risks. Moreover, all members of an asexual population are capable of reproducing. The disadvantage, however, is that asexual reproduction, unlike its sexual counterpart, does not generate genotypic diversity, which is important for [[adaptation|adapting]] to abiotic and biotic environmental changes.
-Parthenogenesis is distinct from artificial [[animal cloning]], a process where the new organism is identical to the cell donor.  Parthenogenesis is truly a reproductive process which creates a new individual or individuals from the naturally varied genetic material contained in the eggs of the mother. A litter of animals resulting from parthenogenesis may contain all genetically unique siblings without any twins or multiple numbers from the same genetic material. In animals with an XY chromosome system where parthenogenic offspring are female, parthenogenic offspring of a parthenogen are, however, all genetically identical to each other and to the mother, as a parthenogen is [[homozygous]].
+Given the drawbacks of asexual reproduction for the long-term survival of the species, most species that engage in parthenogenesis also participate in sexual reproduction or sexual behaviors. Parthenogenesis, thus, typically serves as one available reproductive strategy, often a response to environmental or seasonal conditions, such as the amount of available resources. [[Aphid]]s, for example, are parthenogenic in spring and summer, multiplying rapidly while conditions are favorable; during the winter months, they mate, and the females hatch fertilized eggs. In rare cases, however, parthenogenesis does not occur in combination with sexual reproduction or behaviors: The bdelloid [[rotifer]] ''Philodina roseola,'' for example, reproduces exclusively by parthenogenesis, and the species is believed to have avoided sexual reproduction for 85 million years (Judson 2002).
-The alternation between parthenogenesis and [[sexual reproduction]] is called '''[[heterogamy]]'''.  Forms of reproduction related to parthenogenesis but that require the presence of sperm are known as '''[[Parthenogenesis#Gynogenesis|gynogenesis]]''' and '''[[Parthenogenesis#Hybridogenesis|hybridogenesis]]'''.
+In addition to its reproductive role, parthenogenesis functions as part of a mechanism for determining sex in some species. In [[ant]]s and most species of [[bee]]s and [[wasp]]s, females develop from unfertilized eggs and are referred to as [[haploid]] (possessing one set of [[chromosome]]s), while males develop from fertilized eggs and hence are [[diploid]] (possessing two sets of chromosomes, one from each parent). Thus, in species also capable of sexual reproduction, parthenogenesis can help to regulate the relative number of males and females in a population.
-===Examples===
+==Sexual behavior==
-====Reptiles====
+In some species, parthenogenesis requires a sexual act to trigger development of the egg, even though this behavior does not fertilize the egg. In parthenogenic [[tick]]s and [[mite]]s, for example, the eggs develops only after the animals have mated, but the eggs remain unfertilized. Some species of [[beetle]]s that have no males require [[sperm]] to trigger development; these beetles mate with males of closely related species. However, the sperm does not contribute genetic material.
-Most reptiles reproduce sexually, but parthenogenesis has been observed in certain species of [[Cnemidophorus|whiptail]]s, [[gecko]]s, [[Darevskia|rock lizard]]s<ref name="reptiles"/>, and [[Komodo dragon]]s.
-Parthenogenesis has been extensively studied in the [[Cnemidophorus neomexicanus|New Mexico whiptail]] (genus ''[[Cnemidophorus]]''), of which 15 species reproduce exclusively by parthenogenesis.  These lizards live in the dry and sometimes harsh climate of the southwestern [[United States]] and northern [[Mexico]].  All these asexual species appear to have arisen through the hybridization of two or three of the sexual species in the genus leading to [[polyploid]] individuals.  The mechanism by which the mixing of chromosomes from two or three species can lead to parthenogenetic reproduction is unknown.  Because multiple hybridization events can occur, individual parthenogenetic whiptail species can consist of multiple independent asexual lineages. Within lineages, there is very little genetic diversity, but different lineages may have quite different genotypes.
+In other parthenogenic species lacking males, females stimulate each other to activate the neuroendocrine mechanisms necessary for egg maturation. This phenomenon has been extensively studied in the [[Cnemidophorus neomexicanus|New Mexico whiptail]] (genus ''[[Cnemidophorus]]''), of which 15 species reproduce exclusively by parthenogenesis. One female plays the role of the male in closely related species, and mounts the female that is about to lay eggs. This behavior is due to the [[hormone|hormonal]] cycles of the females, which cause them to behave like males shortly after laying eggs, when levels of [[progesterone]] are high, and to take the female role in mating before laying eggs, when estrogen dominates.  [[Lizard]]s that act out the courtship ritual have greater [[fecundity]] than those kept in isolation, due to the increase in hormones that accompanies the mounting. So, although the populations lack males, they still require sexual stimuli for maximum reproductive success.
-An interesting aspect to reproduction in these asexual lizards is that mating behaviours are still seen, although the populations are all female. One female plays the role played by the male in closely related species, and mounts the female that is about to lay eggs. This behaviour is due to the hormonal cycles of the females, which cause them to behave like males shortly after laying eggs, when levels of progesterone are high, and to take the female role in mating before laying eggs, when estrogen dominates.  Lizards that act out the courtship ritual have greater [[fecundity]] than those kept in isolation, due to the increase in hormones that accompanies the mounting.  So, although the populations lack males, they still require sexual stimuli for maximum reproductive success.
+==Determining sex==
+Parthenogenesis involves the inheritance and subsequent duplication of only a single sex [[chromosome]]. The unfertilized egg can thus be male or female depending on the chromosomal scheme of the species:
+*If two like chromosomes determine the female sex (such as the [[XY sex-determination system]]), the offspring will be female.
+*If two like chromosomes determine the male sex (such as the [[ZW sex-determination system]]), the offspring will be male.
-Recently, the [[Komodo dragon]] which normally reproduces sexually was found to also be able to reproduce asexually by parthenogenesis.<ref>[http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/12/21/ndragon21.xml "No sex please, we're lizards"], Roger Highfield, Daily Telegraph, 21 December 2006</ref><ref>[http://www.nature.com/nature/journal/v444/n7122/full/4441021a.html "Parthenogenesis in Komodo dragons"]Watts PC, et al. . ''Nature'' 444, p1021, 2006.</ref> Because the genetics of sex determination in Komodo Dragons uses the WZ system (where WZ is female, ZZ is male, WW is inviable) the offspring of this process will be ZZ (male) or WW (inviable), with no WZ females being born. A case has been documented of a Komodo Dragon switching back to sexual reproduction after a parthenogenetic event. <ref name="The Hindu">[http://www.hindu.com/2007/01/25/stories/2007012506101400.htm Virgin birth of dragons], The Hindu, 25 January 2007, Retrieved 3 February 2007 </ref> It has been postulated that this gives an advantage to colonisation of islands, where a single female could theoretically have male offspring asexually, then switch to sexual reproduction to maintain higher level of genetic diversity than asexual reproduction alone can generate.<ref name="The Hindu"/> Parthenogenesis may also occur when males and females are both present, as the wild Komodo dragon population is approximately 75 percent male.
+In [[eusocial]] animals that engage in reproductive specialization, parthenogenesis can be a means of regulating the relative number of females and males in the group. One well-known example is the [[honeybee]]: Most females in the colony are sterile workers, but a few become fertile queens. After the queen mates, she possesses a supply of [[sperm]] that she controls, enabling her to produce either fertilized or unfertilized eggs. Thus, the queen determines when and how much of the colony’s resources are expended on the production of males (called drones).
-====Insects====
+==Recent examples==
-An example of non-viable parthenogenesis is common among domesticated [[Western honey bee|honey bee]]s.  The queen bee is the only fertile female in the hive; if she dies without the possibility for a viable replacement queen, it is not uncommon for the worker bees to lay eggs.  Worker bees are unable to mate, and the unfertilized eggs produce only drones (males), which can only mate with a queen.  Thus, in a relatively short period, all the worker bees die off, and the new drones follow.  In one subspecies from [[South Africa]], ''[[Apis mellifera capensis]]'', workers are capable of producing [[diploid]] eggs parthenogenetically, and thus the queen can be replaced if she dies. It is believed that a few other [[bee]]s may be truly parthenogenetic, for example, at least one species of small carpenter bee, in the genus ''[[Ceratina]]''.  Many [[parasitic wasp]]s are known to be parthenogenetic, sometimes due to infections by ''[[Wolbachia]]''.
+*The [[Komodo dragon]], which normally engages in [[sexual reproduction]], was recently found to be able to reproduce asexually via parthenogenesis (Highfield 2006; Watts 2006). Because the genetics of sex determination in Komodo dragons uses the WZ system (where WZ is female, ZZ is male, and WW is inviable), the offspring of parthenogenesis will be male (ZZ) or inviable (WW), with no females being born. It has been postulated that this strategy might give the Komodo dragon an advantage in the colonization of islands, where a single female could theoretically have male offspring asexually, then switch to sexual reproduction to maintain a higher level of genetic diversity than asexual reproduction alone could produce.
-In ''[[Cataglyphis cursor]]'', a European [[Formicinae|formicine ant]], the queen can reproduce by parthenogenesis. The workers are fertile and can mate with the males.<ref>[http://www.sciencemag.org/cgi/content/full/306/5702/1780 "Conditional Use of Sex and Parthenogenesis for Worker and Queen Production in Ants"] Pearcy M, et al. ''Science'' 306:1780, 2004.</ref>
+*In 2001, a bonnethead (a type of small [[hammerhead shark]]) was thought to have produced a pup in captivity at a zoo in Nebraska. The tank contained three female hammerheads and no males. DNA testing showed that the pup's DNA matched only one female living in the tank, and that no male DNA was present in the pup. The pup was not a twin or clone of the mother; rather, it contained only half her DNA (a process called ''automictic parthenogenesis''). The type of reproduction exhibited had been seen before in bony fish but never in cartilaginous fish such as sharks (Sample 2007). Another apparent parthenogenic shark birth occurred in 2002, when two [[white-spotted bamboo shark]]s were born at the Belle Isle Aquarium in Detroit. The birth baffled experts as the mother shared an aquarium with only one other female shark.
+The repercussions of self-fertilization in sharks, which reduces the genetic diversity of the offspring, is a matter of concern for shark experts, taking into consideration conservation management strategies for this species, particularly in areas where there may be a shortage of males due to fishing or environmental pressures. Unlike Komodo dragons, which have a WZ chromosome system and produce male (ZZ) offspring by parthenogenesis, sharks have an XY chromosome system, so they produce only female (XX) offspring by parthenogenesis. As a result, sharks cannot restore a depleted male population through parthenogenesis, so an all-female population must come in contact with an outside male before normal sexual reproduction can resume.
-In [[Wasmannia|little fire ants]], ''[[Wasmannia auropunctata]]'', queens produce more queens through parthenogenesis. Usually, eggs fertilized by the males will develop into sterile workers. In some eggs, males cause the female genetic material to be ablated from the zygote, in a process called ameiotic parthenogenesis. In this way, males can pass on their genes by cloning themselves. This is the first example of an animal species where both females and males can clone themselves.<ref>[http://www.nature.com/nature/journal/v435/n7046/full/nature03705.html "Clonal reproduction by males and females in the little fire ant"] Fournier D, et al. ''Nature'' 435:1230, 2005.</ref>
+==Parthenogenesis differs from cloning==
+Parthenogenesis is distinct from artificial [[animal cloning]], a process in which the new organism is identical to the cell donor. Parthenogenesis is truly a reproductive process that creates a new individual or individuals from the naturally varied genetic material contained in the eggs of the mother. However, in animals with an XY chromosome system where parthenogenic offspring (called ''parthenogens'') are female, the offspring of a parthenogen all are genetically identical to each other and to the mother, as a parthenogen is [[homozygous]] (possessing two identical sets of genes).
-====Mammals====
+==References==
-There are no known cases of mammalian parthenogenesis in the wild.
+*Highfield, R. 2006. [http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/12/21/ndragon21.xml No sex please, we're lizards.] ''Daily Telegraph''. Retrieved July 28, 2007.
+*Judson, O. 2002. ''Dr. Tatiana’s Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex''. New York: Metropolitan Books. ISBN 0805063315
-In April [[2004]], scientists at [[Tokyo|Tokyo University of Agriculture]] used parthenogenesis to successfully create fatherless mice: see [[Kaguya]].
+*Purves, W., D. Sadava, G. Orians, and C. Heller. 2004. ''Life: The Science of Biology,'' 7th edition. Sunderland, MA: Sinauer. ISBN 0716766728
+*Sample, I. 2007. [http://www.guardian.co.uk/science/2007/may/23/uknews.sciencenews Study confirms virgin birth of zoo shark pup.] ''The Guardian''. Retrieved August 6, 2007.
-The beginnings of artificial human parthenogenesis has been performed in the lab.<ref>http://news.bbc.co.uk/1/hi/sci/tech/4228992.stm</ref>  In theory, the process could be used to reproduce humans, but this is unlikely due to ethical concerns.  Parthenogenesis in mice and monkeys often results in abnormal development.  This high level of birth defects, plus the fact that parthenotes have only half the genetic diversity of their parent, means that research on human parthenogenesis is focused on the production of [[embryonic stem cells]] for use in medical treatment, not as a reproductive strategy.
+*Watts, P. C., et al. 2006. [http://www.nature.com/nature/journal/v444/n7122/full/4441021a.html Parthenogenesis in Komodo dragons.] ''Nature'' 444: 1021.
-====Sharks====
-<ref>http://www.msnbc.msn.com/id/18809674/</ref>
-<ref>http://news.bbc.co.uk/2/hi/science/nature/6681793.stm</ref>
-<ref>http://news.nationalgeographic.com/news/2002/09/0925_020925_virginshark.html</ref>
-<ref>http://www.livescience.com/animals/070522_asexual_sharks.html</ref>
-<ref>http://www.peteducation.com/article.cfm?cls=0&cat=1967&articleid=2710</ref>
-<ref>http://www.nytimes.com/2007/05/23/science/23shark.html Female Shark Reproduced Without Male DNA, Scientists Say</ref>
-In 2001 a bonnethead, a type of small [[hammerhead shark]] was thought to have produced a pup, born live on the 14th December 2001, in captivity in a tank containing three female hammerheads but no males; thought to be through parthenogenic means at [[Henry Doorly Zoo]] in Nebraska.  The shark pup was apparently killed by a [[stingray]] within three days of birth.<ref>http://edition.cnn.com/2007/TECH/science/05/23/virgin.sharks.ap/index.html</ref> The investigation of the birth was conducted by the research team from Queen's University Belfast, the Southeastern University in Florida, and Henry Doorly Zoo itself and concluded after DNA testing that the reproduction took place under parthenogenic circumstances. The testing showed the pup's DNA matched only one female that lived in the tank, and that no male DNA was present in the pup.  The pup was not a twin or clone of the mother, but rather contained only half her DNA ("[[#Automictic parthenogenesis|automictic parthenogenesis]]"). The type of reproduction exhibited had been seen before in bony fish but never in cartilaginous fish such as sharks.
-In 2002, two [[white-spotted bamboo shark]]s were born at the [[Belle Isle Aquarium]] in Detroit after hatching 15 weeks after laying. The birth baffled experts as the mother shared an aquarium with only one other female shark. The female bamboo sharks had laid eggs in the past. This is not unexpected, as many animals will lay infertile eggs even if there is not a male to mate with. Normally, the eggs are assumed to be infertile and are discarded. This batch was left alone by the curator as he had heard about the previous birth in 2001 in Nebraska.
-Other possibilities had been considered for the birth of the Detroit bamboo sharks included thoughts that the sharks had been fertilized by a male and stored the sperm for a period of time and also the possibility that the Belle Isle bamboo shark is a hermaphrodite, harboring both male and female sex organs, and capable of fertilizing its own eggs.
-The repercussions of self fertilization in sharks, which reduces the genetic diversity of the offspring, is a matter of concern for shark experts, taking into consideration conservation management strategies for this species, particularly in areas where there may be a shortage of males due to fishing or environmental pressures.
-Unlike [[Komodo dragon]]s, which have a WZ chromosome system and produce male (ZZ) offspring by parthenogenesis, sharks have an XY chromosome system, so they produce only female (XX) offspring by parthenogenesis.  As a result, sharks cannot restore a depleted male population through parthenogenesis, so an all-female population must come in contact with an outside male before normal sexual reproduction can resume.
-==Gynogenesis==
-A form of asexual reproduction related to parthenogenesis is '''gynogenesis'''. Here offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg be stimulated by the presence of [[sperm]] in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species lack males, activation of the egg requires mating with males of a closely related species. Some [[salamander]]s of the genus ''[[Ambystoma]]'' are gynogenetic and appear to have been so for over a million years. It is believed that the success of those salamanders may be due to the rare (perhaps only one mating out of a million) actual fertilization of eggs by a male, introducing new material to the gene pool.
-==Hybridogenesis==
-In '''hybridogenesis''' reproduction is not completely asexual but instead '''hemiclonal''': half the genome passes intact to the next generation while the other half is discarded.
-Hybridogenetic females can mate with males of a "donor" species and both will contribute genetic material to the offspring. When the female offspring produce their own eggs, however, the eggs will contain no genetic material from their father, only the chromosomes from the offspring's own mother; the set of genes from the father is invariably discarded. This process continues, so that each generation is half (or hemi-) clonal on the mother's side and half new genetic material from the father's side.  This form of reproduction is seen in some livebearing fish of the genus ''[[Poeciliopsis]]'' and in the waterfrog ''[[Rana esculenta]]'' and the donor waterfrog species ''[[Rana lessonae]]''.
-A graphical representation of this can be seen [http://www.tolweb.org/notes/?note_id=579 here].
-==Automictic parthenogenesis==
-The set of chromosomes acquired from the mother pairs with a copy of itself, which can be described as "half a clone".<ref>Milius, S. (2007) Virgin Birth: Shark has daughter without a dad, ''Science News'' vol 171, pp 323-324. ([http://www.sciencenews.org/articles/20070526/fob2ref.asp references])</ref>
-==See also==
-* [[Apomixis]] for a similar process in plants
-* [[Parthenocarpy]]
-* [[Arrhenotoky]]
-* [[Thelytoky]]
-* [[Komodo Dragon#Parthenogenesis|Komodo Dragon]], virgin birth recorded in Komodo dragon
-* [[Jacques Loeb]]
-* [[Gregory Goodwin Pincus]]
-==Notes==
-<references/>
 ==Further reading==
-* Dawley, Robert M. & Bogart, James P. (1989). ''Evolution and Ecology of Unisexual Vertebrates''. Albany, New York: New York State Museum. ISBN 1-55557-179-4.
+* Dawley, R. M., and J. P. Bogart. 1989. ''Evolution and Ecology of Unisexual Vertebrates''. Albany, New York: New York State Museum. ISBN 1555571794
-* Futuyma, Douglas J. & Slatkin, Montgomery. (1983). ''Coevolution''. Sunderland, Mass: Sinauer Associates. ISBN 0-87893-228-3.
+* Futuyma, D. J., and M. Slatkin. 1983. ''Coevolution''. Sunderland, MA: Sinauer Associates. ISBN 0878932283
-* Maynard Smith, John. (1978). ''The Evolution of Sex''. Cambridge: Cambridge University Press. ISBN 0-521-29302-2.
+* Maynard Smith, J. 1978. ''The Evolution of Sex''. Cambridge: Cambridge University Press. ISBN 0521293022
-* Michod, Richard E. & Levin, Bruce R. (1988). ''The Evolution of Sex''. Sunderland, Mass: Sinauer Associates.  ISBN 0-87893-459-6.
+* Michod, R. E., and B. R. Levin. 1988. ''The Evolution of Sex''. Sunderland, MA: Sinauer Associates.  ISBN 0878934596
-* Schlupp, I. (2005) The evolutionary ecology of gynogenesis. Annu. Rev. Ecol. Evol. Syst. 36: 399-417.
+* Schlupp, I. 2005. The evolutionary ecology of gynogenesis. ''Annu Rev Ecol Evol Syst'' 36: 399-417.
-* Simon, Jean-Christophe, Rispe, Claude & Sunnucks, Paul. (2002). Ecology and evolution of sex in aphids. ''Trends in Ecology & Evolution, 17'', 34-39.
+* Simon, J., C. Rispe, and P. Sunnucks. 2002. Ecology and evolution of sex in aphids. ''Trends in Ecology & Evolution'' 17: 34-39.
-* Stearns, Stephan C. (1988). ''The Evolution of Sex and Its Consequences'' (Experientia Supplementum, Vol. 55). Boston: Birkhauser. ISBN 0-8176-1807-4.
+* Stearns, S. C. 1988. ''The Evolution of Sex and Its Consequences.'' Experientia Supplementum, Vol. 55. Boston: Birkhauser. ISBN 0817618074
-* Phillip C. Watts, Kevin R. Buley, Stephanie Sanderson, Wayne Boardman, Claudio Ciofi and Richard Gibson. (2006). Parthenogenesis in Komodo dragons. ''Nature'' 444, 1021-1022
+* Watts, P.C., K. R. Buley, S. Sanderson, W. Boardman, C. Claudio, and R. Gibson. 2006. Parthenogenesis in Komodo dragons. ''Nature'' 444: 1021-1022.
 ==External links==
-*[http://www.nature.com/news/2004/040419/pf/040419-8_pf.html Parthenogenesis of Mice at Nature.com]
+All links retrieved November 18, 2022.
+*[http://news.bbc.co.uk/2/hi/science/nature/6196225.stm BBC NEWS: 'Virgin births' for giant lizards (Komodo dragon)].
-*[http://www.utexas.edu/research/crewslab/index.html Reproductive behavior in whiptails at Crews Laboratory]
+*[http://www.nbcnews.com/id/18809674/ns/technology_and_science-science/t/female-sharks-capable-virgin-birth/#.XD9uZVxKiUk Female sharks capable of virgin birth].
-*[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AsexualReproduction.html Types of asexual reproduction]
-*[http://oregonstate.edu/Dept/animal-sciences/poultry/ Parthenogenesis in Incubated Turkey Eggs] from Oregon State University
-*[http://news.nationalgeographic.com/news/2006/12/061220-virgin-dragons.html National Geographic NEWS: Virgin Birth Expected at Christmas — By Komodo Dragon]
-*[http://news.bbc.co.uk/2/hi/science/nature/6196225.stm BBC NEWS: 'Virgin births' for giant lizards (Komodo dragon)]
-*[http://today.reuters.co.uk/news/articlenews.aspx?type=&storyid=2007-01-24T113157Z_01_L2438229_RTRIDST_0_OUKOE-UK-BRITAIN-DRAGONS.XML&src=/UK_DskTopTkr/GetContent REUTERS: Komodo dragon proud mum (and dad) of five]
-*[http://www.msnbc.msn.com/id/18809674/ Female sharks capable of virgin birth]
 [[Category:Life sciences]]
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