parthenogenesis

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The parthenogenesis ( ancient Greek παρθενογένεσις parthenogenesis of, παρθένος parthenos " Virgin " and γένεσις genesis "birth", "Origin"), even parthenogenesis , or virgin birth called, is a form of unisexual reproduction . The offspring are created from individual, unfertilized egg cells. The phenomenon was first described in the 18th century by the Geneva biologist and Enlightenment philosopher Charles Bonnet .

Some plants and female animals such as B. aphids and water fleas , but also some fish and lizard species, snails and the flowerpot snake can reproduce unisexually, i.e. without being fertilized by a male conspecific: Certain hormones simulate a fertilization situation for the unfertilized egg cell, which then divides begins and matures into an organism. Parthenogenesis can either be preceded by meiosis with egg cell formation or it can take place directly via diploid germline cells . In the latter there is no recombination and the resulting offspring are clones of their mother. So only females are born.

Occurrence

According to the current state of knowledge, parthenogenesis is regarded as difficult or even impossible for higher mammals and marsupials . The reason for this is the so-called imprinting , which probably makes it inevitable that a male and a female chromosome set is available for the complete development of an embryo . However, research is being carried out into obtaining human stem cell lines from unfertilized egg cells.

So far, parthenogenesis, which naturally leads to fully developed organisms, has been proven in many animal species, including:

Forms of parthenogenesis

Mandatory and optional parthenogenesis

In parthenogenesis, a distinction is made between mandatory and facultative forms. In contrast to the obligatory parthenogenesis, there are species in the facultative parthenogenesis in which both unisexual and bisexual populations are known (scorpions, aphids , gall wasps ). All transitions to normal bisexual species occur: males can be a little rarer than females, their number can be very low, or they may only appear in exceptional situations. If one type of parthenogenetically generated and sexually generated generations alternate regularly, one speaks of heterogony .

Thelytokia: females as offspring

As a rule, parthenogenetic reproduction does not produce asexual individuals, but rather females with all the usual anatomical and cytological characteristics of this sex, which as a rule cannot be easily distinguished from females of separate sexes or populations with normal (diplodiploid) fertilization. This most common form of parthenogenesis is also called thelytokia (from ancient Greek thelys = 'female' and tokos = 'birth'; name after Carl von Siebold ). In rare cases, these females mate with males of closely related forms without the male genome being passed on (“pseudogamy”), but mating usually does not take place. In addition, a distinction is made between:

Automictic parthenogenesis

In automictic parthenogenesis, also called automixis , the reduction division of meiosis occurs quite normally. Afterwards, however, the nuclei are not distributed among daughter cells, but two nuclei merge again immediately. This restores the old diploid state and gives rise to female individuals. In these species, males can be created by eliminating an X chromosome set, but this can often be omitted. ( Butterfly mosquitoes , whiteflies )

Apomictic parthenogenesis

In apomictic parthenogenesis, there is no reduction division (meiosis) in the oocyte , the egg cells are generated by mitotic division. The offspring all have the same set of chromosomes as the mother. There are the following variants:

Parthenogenesis from infection with Wolbachia

Bacteria of the genus Wolbachia , which live in the sex cells of their hosts, are known to be able to massively manipulate the sex determination of the offspring. In numerous species it has been observed that species or populations infected with Wolbachia produce exclusively parthenogenetic females. The mechanism of feminization is the (asexual) duplication of the genome, which results in females in haplodiploid inheritance. In some parthenogenetic weevil species, triploid females are created in this way. Infection with Wolbachia is not an exotic exception. It is assumed that a large proportion (possibly up to three quarters) of insects and a previously unpredictable proportion of other arthropods are infected with Wolbachia .

Arrhenotocia: females or males depending on fertilization

In arrhenotocia , females produce egg cells and eggs in the usual way (via meiosis ). Unfertilized eggs develop into haploid males, and fertilized eggs become diploid females. This occurs among insects e.g. B. in fringed winged lice , plant lice , but especially in hymenoptera , typical example are the honey bees , whose drones are created by this form of parthenogenesis. The somatic cells of the males produced in this way usually remain haploid. In most hymenoptera, certain cells or cell lines can regain the diploid set of chromosomes through polyploidy, so cells in the intestinal and muscle tissue or the Malpighian vessels are diplo- or even polyploid in almost all hymenoptera (including honeybees). Occasionally, diploid sperm are even found. A rarer form of arrhenotocia is characterized by the fact that males are initially created in the usual way and with a diploid genome. After fertilization, however, the paternal genome is eliminated and only the maternal genome is passed on. With regard to the transmission of genes, there is no difference to the haplodiploid inheritance. This form of arrhenotocia has been studied primarily in scale insects .

Amphitocia: females and males as offspring

In amphitocous or mixed parthenogenesis, both (diploid) females and (haploid) males develop from unfertilized eggs. Amphitocia is very rare, it has mainly been observed in some species of Wood Wasp .

Demarcation

The conception of young animals without male sexual partners present can also take place through the storage of sperm in the female body in a receptaculum seminis , or birth occurs much later after a dormancy . In such cases of doubt, often only a genetic comparison between dam and offspring can demonstrate actual parthenogenesis.

See also

Web links

Individual evidence

  1. ^ C. Moritz (1983): Parthenogenesis in the Endemic Australian Lizard Heteronotia binoei (Gekkonidae). Science 220 (4598): 735-737. doi: 10.1126 / science.220.4598.735
  2. ↑ Parthenogenesis in the Komodo dragon . In: Naturwissenschaftliche Rundschau. Stuttgart 2007 (60) 5, pp. 257-258. ISSN  0028-1050
  3. ↑ Snakes: Virgin generation also happens in the wild Spiegel Online
  4. ^ TVM Groot, E. Bruins, JAJ Breeuwer: Molecular genetic evidence for parthenogenesis in the Burmese python, Python molurus bivittatus . Heredity Vol. 90, 2003, pp. 130-135.
  5. ↑ Virgin generation: Sharks can reproduce without males Spektrum.de
  6. ↑ Demian D. Chapman et al: Virgin birth in a hammerhead shark. In: Biology Letters. London 3.2007, 4, pp. 425-427. PMID 17519185 ISSN  1744-9561 Virgin generation: Hammerheads master single trick Spiegel Online
  7. ↑ Demian D. Chapman et al. a .: Parthenogenesis in a large-bodied requiem shark, the blacktip Carcharhinus limbatus Parthenogenesis in a large-bodied requiem shark, the blacktip Carcharhinus limbatus. In: Journal of Fish Biology. Oxford 73.2008, 6, pp. 1473-1477. doi : 10.1111 / j.1095-8649.2008.02018.x ISSN  0022-1112
    How the shark comes to a child . In: Wissenschaft.de. October 10, 2008, accessed September 8, 2019 .
  8. ↑ Leipzig Zoo achieves breeding success with sharks that is unique in Europe ( Memento from February 22, 2014 in the Internet Archive ) Sächsische Zeitung
  9. ↑ Switch from sexual to parthenogenetic reproduction in a zebra shark (Christine L. Dudgeon, Laura Coulton, Ren Bone, Jennifer R. Ovenden & Severine Thomas) published January 16, 2017 (Eng.)
  10. ↑ maiden births "at sawfishing scinexx.de
  11. ^ MW Olsen: Avian parthenogenesis. USDA publication, Agricultural Research Service, ARS-NE 65, Beltsville (MD) 1975, pp. 1-82. KE Nestor (2009): The Tremendous Turkey. Parthenogenesis in turkeys. ( Memento of July 14, 2010 on the Internet Archive ) The Ohio State University (website copy of the Internet Archive )
    Can turkeys reproduce when young? zeit.de
  12. ↑ Serge Aron, Ludivine de Menten, Dirk R. Van Bockstaele, Stephan M. Blank, Yves Roisin (2005): When Hymenopteran Males Reinvented Diploidy. In: Current Biology. Volume 15, Number 9, pp. 824-827. doi : 10.1016 / j.cub.2005.03.017
  13. ↑ G. Herrick & J. Seger (1999): Imprinting and paternal genome elimination in insects. In: R. Ohlsson (editor): Genomic imprinting: An interdisciplinary approach. Springer, pp. 41-71.