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.{{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 }} 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.{{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.}}

The potential advantages of polyembryony in competing invasive plant species has been studied as well.{{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 }}

Armadillos are the most well studied vertebrate that undergoes polyembryony, with six species of armadillo in the genus Dasypus that are always polyembryonic.{{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}} 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. It is thought that nine banded armadillos evolved to be polyembryonic because of the latter.

File:Wasp colony.jpg

A more striking example of the use of polyembryony as a competitive reproductive tool is found in the parasitoid Hymenoptera, family Encyrtidae.{{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=978-0412074011|oclc=875319486}} 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. These latter larvae patrol the host and kill any other parasitoids they find with the exception of their siblings, usually sisters.

Obligately polyembryonic insects fall in two classes: Hymenoptera (certain wasps), and Strepsiptera.{{Cite book|title=Encyclopedia of Insects|last=Strand|first=Michael|publisher=Elsevier|year=2009|location=Oxford, UK|edition=2nd}} From one egg, these insects can produce over thousands of offspring. Polyembryonic wasps from the Hymenoptera group can be further subdivided into four families including Braconidae (Macrocentrus), Platygastridae (Platygaster), Encyrtidae (Copidosoma), and Dryinidae.

Polyembryony also occurs in Bryozoa.{{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|pages=e0170010|doi=10.1371/journal.pone.0170010|issn=1932-6203|pmid=28095467|bibcode=2017PLoSO..1270010J|doi-access=free}} Through genotype analysis and molecular data, it has been suggested that polyembryony happens in the entire bryozoan order Cyclostomatida.

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. In some plant taxa, the many embryos of polyembryony eventually gives rise to only a single offspring. 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. 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.

The genus Citrus has a number of species that undergo polyembryony, where multiple nucellar-cell-derived embryos exist alongside sexually-derived embryos.{{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 }}{{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}} Antonie van Leeuwenhoek first described polyembryony in 1719 when the seed in Citrus was observed to have two germinating embryos. In Citrus, polyembryony is genetically controlled by a shared polyembryony locus among the species, determined by single-nucleotide polymorphism in the genotypes sequenced. The variation within the species of citrus is based on the amount of embryos that develop, the impact of the environment, and gene expression. As with other species, due to the many embryos developing in close proximity, competition occurs, which can cause variation in seed success or vigor.

File:Syzygium Polyembryony seeds.jpg seeds with more than one embryo]]

• Monoembryony

{{reflist}}

• {{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