Parthenogenesis, first studied in 1740 by Charles Bonnet in aphids, is a phenomenon as rare as it is fascinating, observed in several animal species. If we turn to etymology, the term “parthenogenesis” comes from two Greek roots, which literally translate as “virgin creation.”
Uniform reproduction method
Parthenogenesis is indeed a single-parent mode of reproduction in which a mother’s cell fertilizes an egg to form an embryo. Unlike sexual reproduction, which involves an egg and a sperm, parthenogenesis allows the creation of genes normally provided by the sperm… but without the sperm.
Parthenogenesis is a mode of reproduction that should be clearly distinguished from other methods of reproduction such as artificial insemination or self-fertilization.
Interested in several types of animals
Parthenogenesis is common in small invertebrates such as bees, wasps, ants, and aphids that alternate between sexual and asexual reproduction, but instances of parthenogenesis occur in other species such as reptiles, fish, and, to a lesser extent, some birds.
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Regarding the latter, let’s cite for example the exceptional opening of the San Diego Zoo in the United States in November 2021: two maleless condor chicks were conceived there, which experts on this endangered species believe is the first. Thus, scientists found that the embryo developed without fertilization. The fact is all the more remarkable that female condors were in the presence of males. “We believe our results represent the first example of facultative avian parthenogenesis not associated with sexual segregation,” noted the researchers who studied this particular case.
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Other species breed without the help of a male, in particular some snakes. In 2015, a female yellow-bellied sea snake bred alone for two consecutive years at the Cape Girardeau Conservation Center in Missouri, USA.
Mandatory or facultative parthenogenesis
Thus, in most cases, parthenogenesis is not the only way an animal reproduces, then we are talking about “facultative” parthenogenesis: it occurs in females that usually reproduce sexually, such as sharks, Komodo dragons or our famous condors.
On the other hand, parthenogenesis is considered “obligatory” in some species that have no other choice to provide for their offspring: this is the case in species in which all individuals, without exception, are females. One can, for example, cite Aspidoscelis neomexicana, a species of lizards from the family Teiidae.
Two types of parthenogenesis
Within parthenogenesis, two sub-methods must be distinguished: so-called calf-parthenogenesis, the most common, occurs when a female gives birth to other females. The second form of parthenogenesis is called arrenotok and mainly affects insects, especially bees. In the latter, the female may or may not fertilize her eggs: to do this, she decides to open or close the seminal receptacle, which is located in her reproductive system and inside which she holds the male’s sperm. The picture is then quite classical: while an unfertilized egg always gives rise to a male, a fertilized egg systematically gives rise to a female.
What are the benefits of parthenogenesis?
One of the first benefits that comes to mind when thinking about this type of reproduction is the survival of the species, since parthenogenesis involves the transfer of genes without the need for a partner. It’s a mode of reproduction that can be interesting – even vital – in the case of endangered species.
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