Parthenogenesis (from the
GreekGreek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical...
παρθένος
parthenos, "virgin", + γένεσις
genesis, "creation") is an asexual form of reproduction found in females where growth and development of embryos occurs without fertilization by a
maleMale refers to the sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
. In plants, parthenogenesis means development of an embryo from an unfertilized egg cell, and is a component process of
apomixisIn botany, apomixis is replacement of the normal sexual reproduction by asexual reproduction, without fertilization...
. The offspring produced by parthenogenesis are always female in species that use the
XY sex-determination systemThe XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects and some plants . In this system, females have two of the same kind of sex chromosome , and are called the homogametic sex...
.
Parthenogenesis occurs naturally in some
invertebrateAn invertebrate is an animal without a vertebral column. The group includes 95% of all animal species — all animals except those in the Chordate subphylum Vertebrata ....
animal species (e.g.
water fleaWater flea is a generic term for a number of small aquatic crustacea characterised by their jumping or jerky mode of swimming. The characteristic of the water flea is that the main part of the body is enclosed by a kind of shell...
s,
aphidAphids, also known as plant lice , are small plant-eating insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
s, nematodes, some
beeBees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
s, some Phasmida, some
scorpionScorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. There are about 2,000 species of scorpions, found widely distributed south of about 49° N, except New Zealand and Antarctica...
species, and
parasitic waspThe term Parasitoid wasp refers to a large evolutionary grade of hymenopteran superfamilies, mainly in the Apocrita. They are primarily parasitoids of other animals, mostly other arthropods...
s), and
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s (e.g. some
reptileReptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded" amniotes that generally have skin covered in scales or scutes. They are tetrapods and lay amniote eggs, whose embryos are surrounded by the amnion membrane...
s,
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
,
and very rarely
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s and
sharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs....
s) and this type of reproduction has been induced artificially in other species.
The term is sometimes used inaccurately to describe reproduction modes in
hermaphroditicIn a biological context, a hermaphrodite is an animal or plant that has both male and female reproductive organs.Many taxonomic groups of animals , do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both partners can...
species which can reproduce by themselves because they contain reproductive organs of both sexes.
Asexual reproduction
Parthenogenesis is a form of
asexual reproductionAsexual reproduction is reproduction which does not involve meiosis, ploidy reduction, or fertilization. Only one parent is involved in asexual reproduction. A more stringent definition is agamogenesis which refers to reproduction without the fusion of gametes...
in which females produce eggs that develop without fertilization. A parthenogenetic offspring is sometimes called a parthenogen. Parthenogenesis is seen to occur naturally in aphids,
daphniaDaphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...
, rotifers, nematodes and some other invertebrates, as well as in many plants.
Komodo dragonThe Komodo dragon is a species of lizard that inhabits the islands of Komodo, Rinca, Flores, and Gili Motang in Indonesia. A member of the monitor lizard family , it is the largest living species of lizard, growing to an average length of and weighing around...
s and the
hammerhead-The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna; some authorities...
and
blacktip sharkThe blacktip shark, Carcharhinus limbatus, is a species of requiem shark, family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the...
s 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). As with all types of
asexual reproductionAsexual reproduction is reproduction which does not involve meiosis, ploidy reduction, or fertilization. Only one parent is involved in asexual reproduction. A more stringent definition is agamogenesis which refers to reproduction without the fusion of gametes...
, there are both costs (low genetic diversity and therefore susceptibility to adverse mutations that might occur) and benefits (reproduction without the need for a male) associated with parthenogenesis.
The offspring of parthenogenesis will be all female if two like chromosomes determine the female sex (such as the
XY sex-determination systemThe XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects and some plants . In this system, females have two of the same kind of sex chromosome , and are called the homogametic sex...
), but they will be male if two like chromosomes determine the male sex (such as the
ZW sex-determination systemThe ZW sex-determination system is a system that determines the sex of offspring in birds, some fish, and some insects , and some reptiles, including Komodo dragons...
), 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. In many cases, parthenogenesis occurs when one gender (typically the male) is unavailable in the general vicinity. Once males are again available, the parthenogenesis-created females would be capable of mating with the males and creating normal offspring.
Parthenogenesis is distinct from artificial animal cloning, a process where the new organism is necessarily genetically identical to the cell donor. In cloning, the
nucleusIn cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as...
of a diploid cell from a donor organism is inserted into an enucleated egg cell and the cell is then stimulated to undergo continued
mitosisMitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two daughter nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two daughter cells containing...
, resulting in an organism that is genetically identical to the donor. Parthenogenesis is different, in that it originates from the genetic material contained within an egg cell. Egg cells may be produced via
meiosisIn biology, meiosis is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. As with mitosis, before meiosis begins, the DNA in the original...
or
mitosisMitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two daughter nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two daughter cells containing...
oogenesis. If by mitosis, the egg that undergoes parthenogenesis can be either haploid or diploid, leading to a number of possible outcomes in terms of the genetic fingerprint of the parthenogen. Whether the parthenogen is haploid or diploid, because meiosis was involved in forming the gamete that subsequently underwent parthenogenesis, incidence of
crossing overCrossing Over may refer to:* Chromosomal crossover, a cellular process* Crossing Over , a 1998 album by Hesperus* Crossing Over , a book by John Edward* Crossing Over , a 2009 film...
would effectively create a new genetic fingerprint; this would be of particular importance in the case of a haploid parthenogen, in which crossing over would drastically alter its single chromosome genotype. Because there are so many variables in parthenogenesis, there is little that can be said for sure unless the specific methods of the particular parthenogenetic tendencies of an organism are known.
A litter of offspring resulting from parthenogenesis may contain genetically unique siblings. In organisms possessing an XY chromosome system, parthenogenic offspring are always female, but they are not necessarily genetically identical to one another or to their mother (some chromosome segments may differ because of meiosis).
Parthenogenesis may be achieved through an artificial process as described below under the discussion of mammals.
Alternation between parthenogenesis and
sexual reproductionSexual reproduction is characterized by processes that pass a combination of genetic material to offspring, resulting in diversity. The main two processes are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the restoration...
is called
heterogamyHeterogamy has a number of biological definitions:*In reproductive biology, heterogamy is the alternation of differently organized generations, applied to the alternation between parthenogenetic and a sexual generation...
. A form of reproduction related to parthenogenesis, but that only requires the presence of sperm that do not fertilize an egg, is known as gynogenesis. In hybridogenesis the sperm fertilizes the egg, but its chromosomes are not carried to subsequent generations.
Insects
Parthenogenesis in insects can cover a wide range of mechanisms.
The different forms include:
- Thelytoky - parthenogenesis in which only female offspring are produced and no mating is observed
- Pseudogamy
Pseudogamy refers to aspects of reproduction. It has come to have different meanings in zoology and in botany.In zoology it is used for a type of parthenogenesis in which the sperm stimulates the egg cell to develop into an embryo, but no male inheritance is transmitted...
(or gynogenesis or sperm-dependent parthenogenesis) - here mating occurs and the eggs require activation by entry of sperm but only the maternal chromosomes are expressed
- Automixis - parthenogenesis in which the eggs underwent meiosis
In biology, meiosis is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. As with mitosis, before meiosis begins, the DNA in the original...
- Apomixis - parthenogenesis in which the eggs did not undergo meiosis
Polyembryony is another process that produces multiple clonal offspring from a single egg. This is known in some hymenopteran parasitoids and in strepsiptera.
In automictic species the offspring can be haploid or diploid. Diploids are produced by doubling or fusion of gametes after meiosis. Fusion is seen in the Phasmatodea, Hemiptera (Aleurodids and Coccidae), Diptera, and some Hymenoptera.
In addition to these forms is hermaproditism, where both the eggs and sperm are produced by the same individual. This is seen in three species of
Icerya scale insects.
Parasitic bacteria like
WolbachiaWolbachia is a genus of inherited bacteria which infects arthropod species, including a high proportion of insects. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere...
have been noted to induce automictic thelytoky in many insect species with haplodiploid systems. They also cause gamete duplication in unfertilized eggs causing them to develop into female offspring.
An example of non-viable parthenogenesis is common among domesticated
honey beeHoney bees are a subset of bees, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...
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 AfricaThe Republic of South Africa is a country located at the southern tip of Africa, with a coastline on the Atlantic and Indian Oceans. To the north lie Namibia, Botswana and Zimbabwe, to the east are Mozambique and Swaziland, while Lesotho is an independent country surrounded by South Africa.Modern...
,
Apis mellifera capensisApis mellifera capensis, the Cape honey bee or Cape bee is a southern South African sub-species of the Western honey bee.Cape bee workers are uniquely able to lay diploid, female eggs, by means of thelytoky, whereas workers of other honey bee subspecies are able to lay only haploid, male eggs.The...
, 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
beeBees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
s may be truly parthenogenetic, for example, at least one species of small carpenter bee, in the genus
CeratinaThe cosmopolitan bee genus Ceratina, often referred to as small carpenter bees, is the sole lineage of the tribe Ceratinini, and closely related to the more familiar carpenter bees...
. Many
parasitic waspThe term Parasitoid wasp refers to a large evolutionary grade of hymenopteran superfamilies, mainly in the Apocrita. They are primarily parasitoids of other animals, mostly other arthropods...
s are known to be parthenogenetic, sometimes due to infections by
WolbachiaWolbachia is a genus of inherited bacteria which infects arthropod species, including a high proportion of insects. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere...
.
In
Cataglyphis cursor, a European
formicine antFormicinae is a subfamily within the Formicidae containing ants of moderate evolutionary development.Formicines retain some primitive features such as the presence of cocoons around pupae, the presence of ocelli in workers, and little tendency toward reduction of palp or antennal segmentation in...
, the queen can reproduce by parthenogenesis. The workers are fertile and can mate with the males in the colony.
In Central and South American
electric ants (aka little fire antsThe electric ant, also known as the little fire ant, Wasmannia auropunctata, is a tiny , light to golden brown social ant native to Central and South America, now spread to parts of Africa , North America and six Pacific Island groups The electric ant, also known as the little fire ant, Wasmannia...
),
Wasmannia auropunctata, queens produce more queens through parthenogenesis. Sterile workers usually are produced from eggs fertilized by males. In some of the eggs fertilized by males, however, the fertilization can cause the female genetic material to be ablated from the zygote, in a process called ameiotic parthenogenesis. In this way, males pass on only their genes to become fertile male offspring. This type of reproduction results in a complete separation of the gene pools for females and males. This is the first recognized example of an animal species where both females and males can reproduce clonally resulting in a complete separation of male and female gene pools.
Crustaceans
Crustacean reproduction varies both across and within species. The
water fleaWater flea is a generic term for a number of small aquatic crustacea characterised by their jumping or jerky mode of swimming. The characteristic of the water flea is that the main part of the body is enclosed by a kind of shell...
DaphniaDaphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...
pulex alternates between sexual and parthenogenetic reproduction . Among the better-known large
decapodThe decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers.-Anatomy:...
crustaceans, some crayfish reproduce by parthenogensis. "
MarmorkrebsMarmorkrebs or marbled crayfish are parthenogenetic crayfish that were discovered in the pet trade in Germany in the 1990s . The location of natural populations of this species is unknown. Information provided by one of the original pet traders as to where they were obtained was deemed "totally...
" are parthenogenetic
crayfishCrayfish, crawfish, or crawdads — members of the superfamilies Astacoidea and Parastacoidea — are freshwater crustaceans resembling small lobsters, to which they are related...
that were discovered in the
pet tradeFishkeeping is a popular hobby concerned with keeping fish in a home aquarium or garden pond.- Types of fishkeeping :The hobby can be broadly divided into three specific disciplines, freshwater, brackish, and marine fishkeeping....
in the 1990s . Offspring are genetically identical to the parent, indicating it reproduces by
apomixisIn botany, apomixis is replacement of the normal sexual reproduction by asexual reproduction, without fertilization...
. The Louisiana red swamp crayfish (
Procambarus clarkiiProcambarus clarkii is a freshwater crayfish species, native to the Southeastern United States, but found also on other continents, where it is often an invasive pest. It is known variously as the red swamp crawfish, red swamp crayfish, Louisiana crawfish or Louisiana crayfish.-Range and range...
), which normally reproduces sexually, has also been suggested to reproduce by parthenogenesis
Snails
Parthenogenetic Thiarid snails have slender cone shaped shells. They live in muddy stream bottoms and feed on detritus and algae.
Reptiles
Most reptiles reproduce sexually, but parthenogenesis has been observed to occur naturally in certain species of
whiptailCnemidophorus is a genus of lizards which belong to the family of Teiidae, which are commonly referred to as Whiptail Lizards or Racerunners. Note that the nomenclature for this genus has recently been re-examined by T. W. Reeder et al. in 2002...
s,
geckoThe Mourning Gecko or Common Smooth-Scaled Gecko Lepidodactylus lugubris is a species of gecko.-Distribution:Taiwan, China, Sri Lanka, India , Myanmar, West Malaysia , Vietnam The Mourning Gecko or Common Smooth-Scaled Gecko Lepidodactylus lugubris is a species of gecko.-Distribution:Taiwan, China,...
s,
rock lizardDarevskia is a genus of wall lizards of the family Lacertidae.-Species:*Darevskia alpina*Darevskia armeniaca*Darevskia bendimahiensis*Darevskia brauneri*Darevskia caucasica*Darevskia clarkorum*Darevskia daghestanica...
s,
blindsnakeRamphotyphlops braminus is a harmless blind snake species found mostly in Africa and Asia, but has been introduced in many other parts of the world. Completely fossorial, they are often mistaken for earthworms, except that they are not segmented. The specific name is a Latinized form of the word...
s and
Komodo dragonThe Komodo dragon is a species of lizard that inhabits the islands of Komodo, Rinca, Flores, and Gili Motang in Indonesia. A member of the monitor lizard family , it is the largest living species of lizard, growing to an average length of and weighing around...
s.
Parthenogenesis has been studied extensively in the
New Mexico whiptailThe New Mexico Whiptail is a species of lizard found in the southern United States in New Mexico and Arizona, and in northern Mexico in Chihuahua...
(genus
CnemidophorusCnemidophorus is a genus of lizards which belong to the family of Teiidae, which are commonly referred to as Whiptail Lizards or Racerunners. Note that the nomenclature for this genus has recently been re-examined by T. W. Reeder et al. in 2002...
), of which 15 species reproduce exclusively by parthenogenesis. These lizards live in the dry and sometimes harsh climate of the southwestern
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
and northern
MexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. 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.
An interesting aspect to reproduction in these asexual lizards is that mating behaviors 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 who act out the courtship ritual have greater
fecundityFecundity, derived from the word fecund, generally refers to the ability to reproduce. In biology and demography, fecundity is the potential reproductive capacity of an organism or population, measured by the number of gametes , seed set or asexual propagules. Fecundity is under both genetic and...
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 behavioral stimuli for
maximum reproductive success.
Recently, the
Komodo dragonThe Komodo dragon is a species of lizard that inhabits the islands of Komodo, Rinca, Flores, and Gili Motang in Indonesia. A member of the monitor lizard family , it is the largest living species of lizard, growing to an average length of and weighing around...
, which normally reproduces sexually, was found also to be able to reproduce asexually by parthenogenesis. Because the genetics of sex determination in Komodo Dragons uses the
ZW systemThe ZW sex-determination system is a system that determines the sex of offspring in birds, some fish, and some insects , and some reptiles, including Komodo dragons...
(where ZW is female, ZZ is male, and WW is inviable) the offspring of this process will be ZZ (male) or WW (inviable), with no ZW females being born. A case has been documented of a Komodo Dragon switching back to sexual reproduction after a known parthenogenetic event. It has been postulated that this gives an advantage to colonization of islands, where a single female could theoretically have male offspring asexually, then switch to sexual reproduction with them to maintain higher level of genetic diversity than asexual reproduction alone can generate.
Parthenogenesis may also occur naturally when males and females are both present, explaining why the wild Komodo dragon population is approximately 75 percent male.
Sharks
A
bonnetheadThe bonnethead shark or shovelhead, Sphyrna tiburo, is a member of the hammerhead shark genus Sphyrna. The Greek word sphyrna translates as hammer, referring to the shape of this shark's head - tiburo is the Taino word for shark.- Appearance :Characterized by a broad, smooth, spade-like head, they...
, a type of small
hammerhead sharkThe hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna; some authorities...
, was found to have produced a pup, born live on the 14th December, 2001 at
Henry Doorly ZooThe Henry Doorly Zoo is a zoo in Omaha, Nebraska, located at 3701 South 13th Street.It is accredited by the Association of Zoos and Aquariums and a member of the World Association of Zoos and Aquariums . Its mission is conservation, research, recreation, and education.Henry Doorly Zoo is...
in Nebraska, in a tank containing three female hammerheads, but no males. The pup was thought to have been conceived through parthenogenic means. The shark pup was apparently killed by a
stingrayThe stingrays are a family—Dasyatidae—of rays, cartilaginous fishes related to sharks. They are common in coastal tropical and subtropical marine waters throughout the world, but the family also includes species found in warmer temperate oceans such as Dasyatis thetidis, and species entirely...
within days of birth. The investigation of the birth was conducted by the research team from Queen's University Belfast, Southeastern University in Florida, and Henry Doorly Zoo itself, and it was concluded after DNA testing that the reproduction was parthenogenic. The testing showed the female pup's DNA matched only one female who lived in the tank, and that no male DNA was present in the pup. The pup was not a twin or clone of her mother, but rather, contained only half of her mother's DNA ("automictic parthenogenesis"). This type of reproduction had been seen before in bony fish, but never in cartilaginous fish such as sharks, until this documentation.
In 2002, two
white-spotted bamboo sharkThe whitespotted bamboo shark, Chiloscyllium plagiosum, is a carpet shark with an adult size that approaches one metre in length This small, mostly nocturnal species is harmless to humans. The whitespotted bamboo shark is occasionally kept as a pet in larger home aquariums...
s were born at the
Belle Isle AquariumThe Belle Isle Aquarium, located on Belle Isle Park in Detroit, Michigan, was the oldest continually-operating aquarium in North America. Designed by noted architect Albert Kahn, it opened on August 18, 1904. It was completely outfitted in tile from the Pewabic Pottery which covers the vaulted...
in Detroit. They hatched 15 weeks after being laid. The births baffled experts as the mother shared an aquarium with only one other shark, which was female. The female bamboo sharks had laid eggs in the past. This is not unexpected, as many animals will lay eggs even if there is not a male to fertilize them. Normally, the eggs are assumed to be inviable and are discarded. This batch of eggs was left undisturbed by the curator as he had heard about the previous birth in 2001 in Nebraska and wanted to observe whether they would hatch.
Other possibilities had been considered for the birth of the Detroit bamboo sharks including thoughts that the sharks had been fertilized by a male and stored the sperm for a period of time (a phenomenon known as
superfecundityFecundity, derived from the word fecund, generally refers to the ability to reproduce. In biology and demography, fecundity is the potential reproductive capacity of an organism or population, measured by the number of gametes , seed set or asexual propagules. Fecundity is under both genetic and...
), as well as 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, but that is not confirmed.
In 2008, a Hungarian aquarium had another case of parthenogenesis after its lone female shark produced a pup without ever having come into contact with a male shark. In the same year, a female
Atlantic blacktip sharkThe blacktip shark, Carcharhinus limbatus, is a species of requiem shark, family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the...
in Virginia reproduced via parthenogenesis.
The repercussions of parthenogenesis in sharks, which fails to increase 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. Although parthenogenesis may help females who cannot find mates, it does reduce genetic diversity.
On Friday, Oct. 10, 2008, Scientists confirmed the second case of a virgin birth in a shark. The Journal of Fish Biology reported a study in which scientists said DNA testing proved that a pup carried by a female Atlantic blacktip shark in the Virginia Aquarium & Marine Science Center contained no genetic material from a male.
Unlike
Komodo dragonThe Komodo dragon is a species of lizard that inhabits the islands of Komodo, Rinca, Flores, and Gili Motang in Indonesia. A member of the monitor lizard family , it is the largest living species of lizard, growing to an average length of and weighing around...
s, which have a WZ chromosome system and produce even 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 sexual reproduction resulting in males can occur.
Birds
There were early claims of parthenogenesis in birds but this can be attributed to non-scientific reasoning and motivation. According to one Giraldus Cambrensis, or Gerald of Wales, who along with Irish counterpart Conor O'Cathfai, wrote an account of the history and topography of Ireland following several visits in the latter part of the 12th century, the Barnacle goose reproduces without mating. Upon closer examination one realises that this classification means the bishops and religious men of Ireland may eat it without sin during periods of fasting. Since it is not the progeny of flesh, it cannot be considered flesh itself. This then was the reason for the classification and has no basis in fact.
More recently:
According to Kathrin P. Lampert of the University of Bochum "...isolated cases of parthenogenetic development have been reported in all vertebrate groups. Facultative parthenogenesis
http://russlings.blogspot.com/2006/03/facultative-parthenogenesis.html in vertebrates has only been found in captive animals but might simply have been overlooked in natural populations. Even though its evolutionary impact is hard to determine and very likely varies depending on the ploidy restoration mechanisms and sex-determining mechanisms involved, facultative parthenogenesis is already discussed in conservation biology and medical research."
http://www.online.karger.com/ProdukteDB/produkte.asp?Aktion=ShowAbstract&ArtikelNr=195678&Ausgabe=244226&ProduktNr=231547#OLN
Parthenogenesis occurs in turkeys through doubling of haploid cells, and the rate at which this occurs could be increased by selective breeding. The offspring produced by parthenogenesis were healthy, and as doubled haploids they were
homogameticHomogametic sex refers to the sex of a species in which both sex chromosomes are identical. For example, in humans, females having two X sex chromosomes would be referred to as the homogametic sex while males, with an X and a Y sex chromosome, would be referred to as the heterogametic sex...
, and consequently all were male.
Mammals
There are no known cases of naturally-occurring mammalian parthenogenesis in the wild. However, in 1936,
Gregory Goodwin PincusDr. Gregory Pincus was American biologist and researcher who co-invented the combined oral contraceptive pill. -Birth and education:...
reported
successfully inducing parthenogenesis in a rabbit.
In April 2004, scientists at
Tokyo University of Agriculture, officially , is one of the 47 prefectures of Japan and is located on the eastern side of the main island Honshū. The twenty-three special wards of Tokyo, each governed as a city, cover the area that was once the city of Tokyo in the eastern part of the prefecture, totaling over 8 million people....
used parthenogenesis successfully to create a fatherless mouse.
It is highly doubtful that artificial human parthenogenesis would be used to reproduce humans, due to technical concerns. Use of an electrical or chemical stimulus can produce the beginning of the process of parthenogenesis in the asexual development of viable offspring.
Induced parthenogenesis in mice and monkeys often results in abnormal development. This is because mammals have imprinted genetic regions, where either the maternal or the paternal chromosome is inactivated in the offspring in order for development to proceed normally. A mammal created by parthenogenesis would thus have double doses of maternally imprinted genes and lack paternally imprinted genes, leading to developmental abnormalities if any were present in the genes of the mother. As a consequence, research on human parthenogenesis is focused on the production of embryonic stem cells for use in medical treatment, not as a reproductive strategy.
On June 26, 2007 International Stem Cell Corporation (ISCC), a California based stem cell research company, announced that their lead scientist, Dr. Elena Revazova, and her research team were the first to intentionally create human stem cells from unfertilized human eggs using parthenogenesis. The process may offer a way for creating stem cells that are genetically matched to a particular woman for the treatment of degenerative diseases that might affect her.
On August 2, 2007, after much independent investigation, it was revealed that discredited South Korean scientist,
Hwang Woo-SukHwang Woo-suk is a South Korean veterinarian researcher. He was a professor of theriogenology and biotechnology at Seoul National University who became infamous for fabricating a series of experiments, which appeared in high profile journals, in the field of stem cell research...
, unknowingly produced the first human embryos resulting from parthenogenesis. Initially, Hwang claimed he and his team had extracted stem cells from cloned human embryos, a result which was later found to be fabricated. Further examination of the chromosomes of these cells show indicators of parthenogenesis in those extracted stem cells, similar to those found in the mice created by Tokyo scientists in 2004. Although Hwang deceived the world about being the first to create artificially cloned human embryos, he did contribute a major breakthrough to stem cell research by creating human embryos using parthenogenesis.
Although the truth about the results of Hwang's work were just discovered, those embryos were created by him and his team before February 2004, making Hwang the first, although unknowingly, to perform the process of parthenogenesis to create a human embryo and ultimately a human parthenogenetic stem cell line successfully. In 2006, a group of Italian researchers announced they had achieved the same feat, but have yet to publish their results.
On December 18, 2007 Dr. Revazova and ISC published an on-line article in the journal Cloning and Stem Cells illustrating a breakthrough in the use of parthenogenesis to produce human stem cells that are homozygous in the
"HLA"The human leukocyte antigen system is the name of the major histocompatibility complex in humans. The superlocus contains a large number of genes related to immune system function in humans. This group of genes resides on chromosome 6, and encode cell-surface antigen-presenting proteins and many...
region of the
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
. These stem cells are called HLA homozygous parthenogenetic human stem cells (hpSC-Hhom) and have unique characteristics that will allow derivatives of these cells to be implanted into millions of people without immune rejection. With proper selection of oocyte donors according to HLA
haplotypeThe term haplotype is a contraction of the term 'haploid genotype'. In genetics, a haplotype is a combination of alleles at multiple loci that are transmitted together on the same chromosome...
, it is possible to generate a bank of cell lines, whose tissue derivatives collectively, could be MHC-matched with a significant number of individuals within the human population.
Oomycetes
Apomixis can apparently occur in
PhytophthoraPhytophthora is a genus of plant-damaging Oomycetes , whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems...
, an Oomycete.
OosporeAn oospore is a thick-walled sexual spore that develops from a fertilized oosphere in some algae and fungi....
s derived after an experimental cross were germinated, and some of the progeny were genetically identical to one or other parent, which would imply that meiosis did not occur and the oospores developed by parthenogenesis.
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 merely be stimulated by the
presence of
spermThe term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species are all female, activation of their eggs requires mating with males of a closely related species for the needed stimulus. Some
salamanderSalamander is a common name of approximately 500 species of amphibians. They are typically characterized by their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant species are grouped together as the Urodela...
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 rare fertilization of eggs by males, introducing new material to the gene pool, which may result from perhaps only one mating out of a million.
Hybridogenesis
In hybridogenesis reproduction is not completely asexual, but instead hemiclonal: half the genome is passed intact to the next generation, while the other half is discarded. It occurs in some animals that are themselves hybrids between two different species.
Hybridogenetic females can mate with males of a "donor" species and both will contribute genetic material to the offspring. When each female offspring produces her own eggs, however, the eggs will contain no genetic material from her father (the donor), only the chromosomes from her 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 has half new genetic material from the father's side. This form of reproduction is seen in some live-bearing fish of the genus
PoeciliopsisPoeciliopsis is a genus of fish in the Poeciliidae family.Species include:* Poeciliopsis infans – Lerma Livebearer* Poeciliopsis monacha* Poeciliopsis occidentalis – charalito...
as well as in the waterfrog
Rana esculenta.
A graphical representation of this can be seen
through this link.
Automictic parthenogenesis
This is defined as a reproduction resulting when the set of chromosomes acquired from the mother, pairs with an exact copy of itself, which can be described as "half a clone". The animal still is unique and not a clone of her mother. In typical parthenogenesis the individual offspring differ from one another and their mother.
See also
- Apomixis
In botany, apomixis is replacement of the normal sexual reproduction by asexual reproduction, without fertilization...
for a similar process in plants
- Parthenocarpy
In botany and horticulture, parthenocarpy is the natural or artificially induced production of fruit without fertilization of ovules. The fruit is therefore seedless. Stenospermocarpy may also produce apparently seedless fruit, but the seeds are actually aborted while still small...
plants with seedless fruit
- Arrhenotoky
Arrhenotoky or arrhenotokous parthenogenesis is a form of parthenogenesis in which unfertilized eggs develop into haploid males.This form is observed in some marine invertebrates, beetles, scorpions, mites, bees, etc....
- Thelytoky
Thelytoky comes from the Greek thely, meaning "female", and tok, meaning "birth". Thelytokous parthenogenesis is a type of parthenogenesis in which females are produced from unfertilized eggs. It is rare in the animal kingdom and has only been reported in about 1500 species. It is more common in...
- Komodo Dragon, virgin birth recorded in Komodo dragon
- Jacques Loeb
Jacques Loeb was a German-born American physiologist and biologist.-Biography:...
was able to cause the eggs of sea urchinSea urchins or urchins are small, spiny, globular animals that compose part of class Echinoidea. They are found in oceans all over the world. Their shell, or "test", is round and spiny, typically from 3 to 10 cm across. Common colors include black and dull shades of green, olive, brown, purple,...
s to begin embryonic development without sperm
- Gregory Goodwin Pincus
Dr. Gregory Pincus was American biologist and researcher who co-invented the combined oral contraceptive pill. -Birth and education:...
experimented with parthenogenesis
- Charles Bonnet
Charles Bonnet , Swiss naturalist and philosophical writer, was born at Geneva, of a French family driven into Switzerland by the religious persecution in the 16th century.-Life and work:Bonnet's life was uneventful...
conducted a series of experiments establishing what is now termed parthenogenesis in aphides or tree-lice
- Kaguya, a mouse created in 2004 by induced parthogenesis
- Virgin birth (mythology)
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.
- Fangerau H. (2005). Can Artificial Parthenogenesis sidestep ethical pitfalls in human therapeutic cloning? A historical perspective, Journal of Medical Ethics 31, 733-735
- Futuyma, Douglas J. & Slatkin, Montgomery. (1983). Coevolution. Sunderland, Mass: Sinauer Associates. ISBN 0-87893-228-3.
- Maynard Smith, John. (1978). The Evolution of Sex. Cambridge: Cambridge University Press. ISBN 0-521-29302-2.
- Michod, Richard E. & Levin, Bruce R. (1988). The Evolution of Sex. Sunderland, Mass: Sinauer Associates. ISBN 0-87893-459-6.
- Phillip C. Watts, Kevin R. Buley, Stephanie Sanderson, Wayne Boardman, Claudio Ciofi and Richard Gibson. (2006). Parthenogenesis in Komodo dragons. Nature 444, 1021-1022
- 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.
- Stearns, Stephan C. (1988). The Evolution of Sex and Its Consequences (Experientia Supplementum, Vol. 55). Boston: Birkhauser. ISBN 0-8176-1807-4.
External links