{{Short description|Development of more than one embryo from a single egg}} '''Polyembryony''' is the phenomenon of two or more embryos developing from a single fertilized egg.<ref name=":1">{{Cite journal|last1=Filonva|first1=L. H.|last2=von Arnold|first2=S.|last3=Daniel|first3=G.|last4=Bozhkov|first4=P. V.|year=2002|title=Programmed cell death eliminates all but one embryo in a polyembryonic plant seed|journal=Nature|volume=9|issue=10|pages=1057–1062|doi=10.1038/sj.cdd.4401068|pmid=12232793|doi-access=free}}</ref><ref name=":3">{{Cite journal|last1=Craig|first1=Sean F.|last2=Slobodkin|first2=Lawrence B.|last3=Wray|first3=Gregory A.|last4=Biermann|first4=Christiane H.|date=1997-03-01|title=The 'paradox' of polyembryony: A review of the cases and a hypothesis for its evolution|journal=Evolutionary Ecology|language=en|volume=11|issue=2|pages=127–143|doi=10.1023/A:1018443714917|bibcode=1997EvEco..11..127C |s2cid=5556785|issn=0269-7653}}</ref><ref name=":7">{{Cite journal|last1=Batygina|first1=T. B.|last2=Vinogradova|first2=G. Iu|date=2007-05-01|title=[Phenomenon of polyembryony. Genetic heterogeneity of seeds]|journal=Ontogenez|volume=38|issue=3|pages=166–191|issn=0475-1450|pmid=17621974}}</ref> Due to the embryos resulting from the same egg, the embryos are identical to one another, but are genetically diverse from the parents.<ref name=":1" /><ref name=":3" /> The genetic difference between the offspring and the parents, but the similarity among siblings, are significant distinctions between polyembryony and the process of budding and typical sexual reproduction.<ref name=":3" /> Polyembryony can occur in humans, resulting in identical twins, though the process is random and at a low frequency.<ref name=":1" /> Polyembryony occurs regularly in many species of vertebrates, invertebrates, and plants.
== Evolution of polyembryony == The evolution of polyembryony and the potential evolutionary advantages that may entail have been studied. In parasitoid wasps, there are several hypotheses surrounding the evolutionary advantages of polyembryony, one of them being that it allows female wasps that are small in size to increase the number of potential offspring in comparison to wasps that are mono embryonic.<ref name=":9">{{Cite journal |last1=Segoli |first1=M. |last2=Harari |first2=A. R. |last3=Rosenheim |first3=J. A. |last4=Bouskila |first4=A. |last5=Keasar |first5=T. |date=September 2010 |title=REVIEW: The evolution of polyembryony in parasitoid wasps: The evolution of polyembryony |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2010.02049.x |journal=Journal of Evolutionary Biology |language=en |volume=23 |issue=9 |pages=1807–1819 |doi=10.1111/j.1420-9101.2010.02049.x|pmid=20629853 |s2cid=22573370 |url-access=subscription }}</ref> There are limitations to monoembryony, but with this method of development, multiple embryos can be derived from each of the individual eggs that are laid.<ref name=":10">{{Citation |last=Strand |first=Michael R. |title=Chapter 208 - Polyembryony |date=2009-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780123741448002174 |encyclopedia=Encyclopedia of Insects (Second Edition) |pages=821–825 |editor-last=Resh |editor-first=Vincent H. |place=San Diego |publisher=Academic Press |language=en |isbn=978-0-12-374144-8 |access-date=2022-04-10 |editor2-last=Cardé |editor2-first=Ring T.}}</ref><ref name=":9" />
The potential advantages of polyembryony in competing invasive plant species has been studied as well.<ref name=":11">{{Cite journal |last1=Blanchard |first1=Megan L. |last2=Barney |first2=Jacob N. |last3=Averill |first3=Kristine M. |last4=Mohler |first4=Charles L. |last5=DiTommaso |first5=Antonio |date=February 2010 |title=Does polyembryony confer a competitive advantage to the invasive perennial vine Vincetoxicum rossicum (Apocynaceae)? |url=http://doi.wiley.com/10.3732/ajb.0900232 |journal=American Journal of Botany |language=en |volume=97 |issue=2 |pages=251–260 |doi=10.3732/ajb.0900232|pmid=21622385 |url-access=subscription }}</ref>
== Vertebrates ==
Armadillos are the most well studied vertebrate that undergoes polyembryony, with six species of armadillo in the genus ''Dasypus'' that are always polyembryonic.<ref name=":4">{{cite journal|jstor=27857027|title=Polyembryony in Armadillos: An unusual feature of the female nine-banded armadillo's reproductive tract may explain why her litters consist of four genetically identical offspring|first1=W. J.|last1=Loughry|first2=Paulo A.|last2=Prodöhl|first3=Colleen M.|last3=McDonough|first4=John C.|last4=Avise|date=1 January 1998|volume=86|issue=3|pages=274–279|doi=10.1511/1998.25.824|journal=American Scientist}}</ref> The nine banded armadillo, for instance, always gives birth to four identical young. There are two conditions that are expected to promote the evolution of polyembryony: the mother does not know the environmental conditions of her offspring as in the case of parasitoids, or a constraint on reproduction.<ref name=":3" /> It is thought that nine banded armadillos evolved to be polyembryonic because of the latter.<ref name=":4" />
Chondrichthyans, namely the skates ''Beringraja binoculata'' and ''Beringraja pulchra'', in addition to spotted catsharks, have exhibited multiple embryos in a single egg case.<ref>{{Cite journal |last=Gayford |first=Joel Harrison |date=2025-04-30 |title=The adaptability of facultative parthenogenesis and 'multiple embryos per eggcase' as alternative reproductive strategies in Chondrichthyes |url=https://royalsocietypublishing.org/doi/10.1098/rsos.242030 |journal=Royal Society Open Science |volume=12 |issue=4 |article-number=242030 |doi=10.1098/rsos.242030 |doi-access=free|pmc=12040468}}</ref>
== Invertebrates == thumb|A colony of wasps
A more striking example of the use of polyembryony as a competitive reproductive tool is found in the parasitoid Hymenoptera, family Encyrtidae.<ref name=":2">{{Cite book|url=https://books.google.com/books?id=v44RlnM9ncQC&q=Parasites+and+pathogens:+effects+on+host+hormones+and+behavior+precocious+larvae&pg=PA42|title=Parasites and pathogens: effects on host hormones and behavior|last=E.|first=Beckage, Nancy|date=1997-01-01|publisher=Chapman & Hall|isbn=978-0-412-07401-1|oclc=875319486}}</ref> The progeny of the splitting embryo develop into at least two forms, those that will develop into adults and those that become a type of soldier, called precocious larvae.<ref name=":2" /> These latter larvae patrol the host and kill any other parasitoids they find with the exception of their siblings, usually sisters.<ref name=":2" />
Obligately polyembryonic insects fall in two classes: Hymenoptera (certain wasps), and Strepsiptera.<ref name=":0">{{Cite book|title=Encyclopedia of Insects|last=Strand|first=Michael|publisher=Elsevier|year=2009|location=Oxford, UK|edition=2nd}}</ref> From one egg, these insects can produce over thousands of offspring.<ref name=":0" /> Polyembryonic wasps from the Hymenoptera group can be further subdivided into four families including Braconidae (''Macrocentrus''), Platygastridae (''Platygaster''), Encyrtidae (''Copidosoma''), and Dryinidae.<ref name=":0" />
Polyembryony also occurs in Bryozoa.<ref name=":3" /><ref name=":5">{{Cite journal|last1=Jenkins|first1=Helen L.|last2=Waeschenbach|first2=Andrea|last3=Okamura|first3=Beth|last4=Hughes|first4=Roger N.|last5=Bishop|first5=John D. D.|date=2017-01-17|title=Phylogenetically Widespread Polyembryony in Cyclostome Bryozoans and the Protracted Asynchronous Release of Clonal Brood-Mates|pmc=5240946|journal=PLOS ONE|volume=12|issue=1|article-number=e0170010|doi=10.1371/journal.pone.0170010|issn=1932-6203|pmid=28095467|bibcode=2017PLoSO..1270010J|doi-access=free}}</ref> Through genotype analysis and molecular data, it has been suggested that polyembryony happens in the entire bryozoan order Cyclostomatida.<ref name=":5" />
== Plants ==
The term is also used in botany to describe the phenomenon of multiple seedlings emerging from one embryo. Around 20 genera of gymnosperms undergo polyembryony, termed "cleavage polyembryony," where the original zygote splits into many identical embryos.<ref name=":1" /><ref name=":7" /> In some plant taxa, the many embryos of polyembryony eventually gives rise to only a single offspring.<ref name=":1" /> The mechanism underlying the phenomenon of a resulting single (or in some cases a few) offspring is described in ''Pinus sylvestris'' to be programmed cell death (PCD), which removes all but one embryo.<ref name=":1" /> Originally, all embryos have equal opportunity to develop into full seeds, but during the early stages of development, one embryo becomes dominant through competition, and therefore the now dormant seed, while the other embryos are destroyed through PCD.<ref name=":1" />
The genus ''Citrus'' has a number of species that undergo polyembryony, where multiple nucellar-cell-derived embryos exist alongside sexually derived embryos.<ref name=":6">{{Cite journal|last1=Nakano|first1=Michiharu|last2=Shimada|first2=Takehiko|last3=Endo|first3=Tomoko|last4=Fujii|first4=Hiroshi|last5=Nesumi|first5=Hirohisa|last6=Kita|first6=Masayuki|last7=Ebina|first7=Masumi|last8=Shimizu|first8=Tokurou|last9=Omura|first9=Mitsuo|date=2012-02-01|title=Characterization of genomic sequence showing strong association with polyembryony among diverse Citrus species and cultivars, and its synteny with Vitis and Populus|journal=Plant Science|volume=183|pages=131–142|doi=10.1016/j.plantsci.2011.08.002|issn=1873-2259|pmid=22195586|bibcode=2012PlnSc.183..131N }}</ref><ref name=":8">{{Cite journal|last1=Kishore|first1=Kundan|last2=N.|first2=Monika|last3=D.|first3=Rinchen|last4=Lepcha|first4=Boniface|last5=Pandey|first5=Brijesh|date=2012-05-01|title=Polyembryony and seedling emergence traits in apomictic citrus|journal=Scientia Horticulturae|volume=138|pages=101–107|doi=10.1016/j.scienta.2012.01.035|bibcode=2012ScHor.138..101K |doi-access=free}}</ref> Antonie van Leeuwenhoek first described polyembryony in 1719 when the seed in ''Citrus'' was observed to have two germinating embryos.<ref name=":7" /> In ''Citrus'', polyembryony is genetically controlled by a shared polyembryony locus among the species, determined by single-nucleotide polymorphism in the genotypes sequenced.<ref name=":6" /> The variation within the species of citrus is based on the amount of embryos that develop, the impact of the environment, and gene expression.<ref name=":8" /> As with other species, due to the many embryos developing in close proximity, competition occurs, which can cause variation in seed success or vigor.<ref name=":8" />
[[File:Syzygium Polyembryony seeds.jpg|thumb|Syzygium seeds with more than one embryo]]
==See also== *Monoembryony
== References == {{reflist}}
== External links == * {{cite web |title=Chapter 26 — Largest Parasitoid Brood |url=http://entnemdept.ifas.ufl.edu/walker/ufbir/chapters/chapter_26.shtml |author=Juan Manuel Alvarez A. |publisher=University of Florida |date=15 April 1997 |work=Book of Insect Records }} * {{cite journal |url=http://jcs.biologists.org/cgi/content/abstract/s2-63/250/175 |author=J. Bronté Gatenby |title=Memoirs: Polyembryony in Parasitic Hymenoptera: A Review |journal=Quarterly Journal of Microscopical Science |volume=s2-63 |pages=175–196 |year=1918}} * {{cite journal |url=http://jcs.biologists.org/content/s2-63/250/161.short |author=J. Bronté Gatenby |title=The Segregation of the Germ-cells in ''Trichogramma evanescens'' |journal=Quarterly Journal of Microscopical Science |volume=s2-63 |pages=161–174 |year=1918}} *{{cite journal | last1 = Craig | first1 = S.F. | last2 = Slobodkin | first2 = L.B. | last3 = Wray | first3 = G. | year = 1997 | title = The 'Paradox' of Polyembryony: A review of the cases and a hypothesis for its evolution | journal = Evolutionary Ecology | volume = 11 | issue = 2| pages = 127–143 | doi=10.1023/A:1018443714917| bibcode = 1997EvEco..11..127C | s2cid = 5556785 }}
Category:Plant reproduction Category:Embryology Category:Insect physiology