Gynogenesis, a form of

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 developmen ...

, 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. The egg cell of the organism is able to develop, unfertilized, into an adult using only maternal genetic material. Gynogenesis is often termed "sperm parasitism" in reference to the somewhat pointless role of male gametes. Gynogenetic species, "gynogens" for short, are unisexual, meaning they must mate with males from a closely related bisexual species that normally reproduces sexually. Gynogenesis is a disadvantageous mating system for males, as they are unable to pass on their DNA. The question as to why this reproductive mode exists, given that it appears to combine the disadvantages of both asexual and sexual reproduction, remains unsolved in the field of evolutionary biology. The male equivalent to this process is

Androgenesis Androgenesis occurs when a zygote is produced with only paternal nuclear genes. During standard sexual reproduction, one female and one male parent each produce haploid gametes(such as a sperm or egg cell, each containing only a single set of chr ...

where the father is the sole contributor of DNA.Androgenesis: where males hijack eggs to clone themselves
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Examples

Most gynogenetic species fall into the taxonomic groups of the fishes and the amphibians. Amazon mollies, ('' Poecilia formosa'') require the sperm of closely related male ''

Poecilia latipinna ''Poecilia'' is a genus of fishes in the family Poeciliidae of the order Cyprinodontiformes. These livebearers are native to fresh, brackish and salt water in the Americas, and some species in the genus are euryhaline. A few have adapted to liv ...

'' to engage in gynogenesis. Research has shown that the ''P. latipinna'' males prefer to mate with females of their own species, given the previously-discussed disadvantage for males in mating with gynogens. This presents a problem for ''P. formosa'', as they must compete for males with a preferred population. However, those ''P. formosa'' successful in finding a mate make up the deficit by producing twice as many female offspring as their competitors. The ant species '' Myrmecia impaternata'' is female-only, with its hybrid origin tracing back to '' Myrmecia banksi'' and ''

Myrmecia pilosula Myrmecia can refer to: * ''Myrmecia'' (alga), genus of algae associated with lichens * ''Myrmecia'' (ant), genus of ants called bulldog ants * Myrmecia (skin), a kind of deep wart on the human hands or feet See also * '' Copromorpha myrmecias'' ...

''. In ant species, sex is determined by the

haplodiploidy Haplodiploidy is a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid. Haplodiploidy is sometimes called arrhenotoky. Haplodiploidy determines the sex ...

system, where unfertilized eggs result in haploid males and fertilized eggs result in diploid females. In this species, the queen reproduces through sexual interaction, yet not fertilization, with allospecific males reared from "impaternate" (fatherless) eggs in impaternate nests. '' Ambystoma platineum'', a unisexual

mole salamander The mole salamanders ( genus ''Ambystoma'') are a group of advanced salamanders endemic to North America. The group has become famous due to the presence of the axolotl (''A. mexicanum''), widely used in research due to its paedomorphosis, an ...

species, are a result of the hybridization of sexually reproducing ''

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 ...

'' and '' A laterale''. ''A. platineum'' individuals normally live in proximity to either of these parent species, due to their need to use their sperm to facilitate reproduction.

Evolutionary origin

Two evolutionary pathways may be considered to explain how and why gynogenesis evolved. The single-step pathway involves multiple changes taking place simultaneously: meiosis must be interrupted, one gender's gametes eradicated, and a unisexual gender formation must arise. The second option involves multiple steps: a sexual generation is formed with a strongly biased sex ratio, and because of Haldane's Rule the species evolves towards loss of sexuality and selection that is preferential towards the gynogen. Experimenters who attempted unsuccessfully to induce ''P. formosa'' in a laboratory by hybridizing its genetic ancestors concluded that the evolutionary origin of ''P. formosa'' was not from the simple hybridization of two specific genomes, but the movement of certain alleles at certain loci that resulted in this evolutionary change to unisexuality.

References

{{Reflist Asexual reproduction in animals Zoology