View source for Isogamy

{{Short description|Sexual reproduction form involving gametes of the same size}}
{{Hatnote|Not to be confused with [[Isogyny]], marriage between people of similar status or age}}
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[[File:Isogamy.svg|thumb|Different forms of isogamy:
A) isogamy of [[Motile cell|motile cells]], B) isogamy of non-motile cells, C) conjugation (isogamy in the broad sense)|270x270px]]
'''Isogamy''' is a form of [[sexual reproduction]] that involves [[Gamete|gametes]] of the same [[Morphology (biology)|morphology]] (indistinguishable in shape and size), and is found in most [[Unicellular organism|unicellular eukaryotes]].<ref name="Lehtonen-2016">{{Cite journal|last1=Lehtonen|first1=Jussi|last2=Kokko|first2=Hanna|last3=Parker|first3=Geoff A.|date=2016-10-19|title=What do isogamous organisms teach us about sex and the two sexes?|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=371|issue=1706|doi=10.1098/rstb.2015.0532|issn=0962-8436|pmc=5031617|pmid=27619696}}</ref> Because both gametes look alike, they generally cannot be classified as [[male]] or [[female]].<ref>{{Cite book|last1=Sawada|first1=Hitoshi|url=https://books.google.com/books?id=Adm6BQAAQBAJ&q=isogamy+mating+types|title=Sexual Reproduction in Animals and Plants|last2=Inoue|first2=Naokazu|last3=Iwano|first3=Megumi|date=2014|publisher=Springer|isbn=978-4-431-54589-7|pages=216|language=en|access-date=2021-07-24|archive-date=2024-04-04|archive-url=https://web.archive.org/web/20240404062136/https://books.google.com/books?id=Adm6BQAAQBAJ&q=isogamy+mating+types#v=snippet&q=isogamy%20mating%20types&f=false|url-status=live}}</ref> Instead, organisms that reproduce through isogamy are said to have different [[Mating type|mating types]], most commonly noted as "+" and "&minus;" strains.<ref name="Kumar-20192">{{Cite encyclopedia |title=Anisogamy |entry=Anisogamy |encyclopedia=Encyclopedia of Animal Cognition and Behavior |publisher=Springer International Publishing |place=Cham |date=2019 |pages=1–5 |doi=10.1007/978-3-319-47829-6_340-1 |isbn=978-3-319-47829-6 |quote= |vauthors=Kumar R, Meena M, Swapnil P |veditors=Vonk J, Shackelford T}}</ref>
== Etymology ==
The [[etymology]] of isogamy derives from the Greek adjective ''isos'' (meaning equal) and the Greek verb ''gameo'' (meaning to have sex/to reproduce), eventually meaning "equal reproduction" which refers to a hypothetical initial model of equal contribution of resources by both gametes to a zygote in contrast to a later evolutional stage of [[anisogamy]].<ref>{{Cite book|url=https://books.google.com/books?id=_r4OCAAAQBAJ&q=isogamy+encyclopedia&pg=RA1-PA212|title=Encyclopedia of Evolutionary Biology|date=2016-04-14|publisher=Academic Press|isbn=978-0-12-800426-5|volume=2|pages=212|language=en|access-date=2021-08-14|archive-date=2023-10-06|archive-url=https://web.archive.org/web/20231006173122/https://books.google.com/books?id=_r4OCAAAQBAJ&q=isogamy+encyclopedia&pg=RA1-PA212|url-status=live}}</ref> The term isogamy was first used in the year 1891.<ref name="Hartog">{{cite journal |last1=Hartog |first1=M. |title=Isogamy, the union of gametes undistinguishable in size, form, and behaviour. |journal=Nature |date=17 September 1891 |page=484}}</ref><ref>{{Cite web|title=Definition of ISOGAMOUS|url=https://www.merriam-webster.com/dictionary/isogamous|access-date=2021-09-14|website=www.merriam-webster.com|language=en|archive-date=2021-09-14|archive-url=https://web.archive.org/web/20210914002001/https://www.merriam-webster.com/dictionary/isogamous|url-status=live}}</ref>
== Characteristics of isogamous species ==
Isogamous species often have two [[Mating type|mating types]] ([[heterothallism]]), but sometimes can occur between two [[Ploidy|haploid]] individuals that are mitotic descendents ([[homothallism]]).<ref name="Lehtonen-2016" /><ref group=Note name=Note01/> Some isogamous species have more than two mating types, but the number is usually lower than ten. In some extremely rare cases, such as in some [[Basidiomycota|basidiomycete]] species, a species can have thousands of mating types.<ref>{{Cite journal |last=Casselton |first=L. A. |date=2002-02-01 |title=Mate recognition in fungi |url=https://www.nature.com/articles/6800035 |journal=Heredity |language=en |volume=88 |issue=2 |pages=142–147 |doi=10.1038/sj.hdy.6800035 |issn=1365-2540}}</ref>
Under the strict definition of isogamy, [[fertilization]] occurs when two [[Gamete|gametes]] fuse to form a [[zygote]].<ref>{{Cite journal|last1=Krumbeck|first1=Yvonne|last2=Constable|first2=George W. A.|last3=Rogers|first3=Tim|date=2020-02-26|title=Fitness differences suppress the number of mating types in evolving isogamous species|journal=Royal Society Open Science|volume=7|issue=2|page=192126|arxiv=1906.07117|bibcode=2020RSOS....792126K|doi=10.1098/rsos.192126|issn=2054-5703|pmc=7062084|pmid=32257356}}</ref> Sexual reproduction between two cells that does ''not'' involve gametes (e.g. conjugation between two [[Mycelium|mycelia]] in basidiomycete fungi), is often called isogamy, although it is not technically isogametic reproduction in the strict sense.<ref name="Lehtonen-2016" />
== Evolution ==
{{Main|Evolution of sexual reproduction}}
It is generally accepted that isogamy is an ancestral state for [[Anisogamy|anisogamy]]<ref name="Lehtonen-2016"/><ref>{{Cite book|last1=Pitnick|first1=Scott S.|url=https://books.google.com/books?id=kctYNbO1fE0C&q=anisogamy+defines+the+sexes|title=Sperm Biology: An Evolutionary Perspective|last2=Hosken|first2=Dave J.|last3=Birkhead|first3=Tim R.|date=2008-11-21|publisher=Academic Press|isbn=978-0-08-091987-4|pages=43–45|language=en|access-date=2021-07-24|archive-date=2023-10-06|archive-url=https://web.archive.org/web/20231006173121/https://books.google.com/books?id=kctYNbO1fE0C&q=anisogamy+defines+the+sexes|url-status=live}}</ref> and that isogamy was the first stage in the evolution of [[sexual reproduction]]. Isogamous reproduction [[Convergent evolution|evolved independently]] in several lineages of plants and animals to [[anisogamy|anisogamous]] species with [[gamete]]s of male and [[female]] types and subsequently to [[oogamy|oogamous]] species in which the female gamete is much larger than the male and has no ability to move. This pattern may have been driven by the physical constraints on the mechanisms by which two gametes get together as required for [[sexual reproduction]].<ref>Dusenbery, David B. (2009). ''Living at Micro Scale'', Chapter 20. Harvard University Press, Cambridge, Massachusetts {{ISBN|978-0-674-03116-6}}.</ref>
Isogamy is the norm in [[Unicellular organism|unicellular eukaryote species]], although it is possible that isogamy is evolutionarily stable in multicellular species.<ref name="Lehtonen-2016"/>
== Occurrence ==
Almost all unicellular eukaryotes are isogamous.<ref>{{Cite book|last=Bell|first=Graham|url=https://books.google.com/books?id=jS0TDAAAQBAJ|title=Selection: The Mechanism of Evolution|date=2008|publisher=OUP Oxford|isbn=978-0-19-856972-5|pages=439|language=en|author-link=Graham Bell (biologist)|access-date=2023-03-19|archive-date=2023-10-06|archive-url=https://web.archive.org/web/20231006173121/https://books.google.com/books?id=jS0TDAAAQBAJ|url-status=live}}</ref> Among multicellular organisms, isogamy is restricted to [[fungi]] and eukaryotic [[algae]].<ref>{{Cite book|last1=Togashi|first1=Tatsuya|url=https://books.google.com/books?id=5eOvRTIuLXMC&q=isogamy+in+fungi|title=The Evolution of Anisogamy: A Fundamental Phenomenon Underlying Sexual Selection|last2=Cox|first2=Paul Alan|date=2011-04-14|publisher=Cambridge University Press|isbn=978-1-139-50082-1|pages=96|language=en|access-date=2021-07-24|archive-date=2023-10-06|archive-url=https://web.archive.org/web/20231006173122/https://books.google.com/books?id=5eOvRTIuLXMC&q=isogamy+in+fungi|url-status=live}}</ref> Many species of green algae are isogamous. It is typical in the genera ''[[Ulva (alga)|Ulva]]'', ''[[Hydrodictyon]]'', ''[[Tetraspora]]'', ''[[Zygnema]]'', ''[[Spirogyra]]'', ''[[Ulothrix]]'', and ''[[Chlamydomonas]]''.<ref name="Lehtonen-2016" /><ref>{{Cite book|last=Sharma|first=O. P.|url=https://books.google.com/books?id=hOa74Hm4zDIC&q=isogamy&pg=PA130|title=Textbook of Algae|date=1986-01-01|publisher=Tata McGraw-Hill Education|isbn=978-0-07-451928-8|pages=130|language=en|access-date=2021-07-24|archive-date=2023-10-06|archive-url=https://web.archive.org/web/20231006173123/https://books.google.com/books?id=hOa74Hm4zDIC&q=isogamy&pg=PA130|url-status=live}}</ref> Many fungi are also isogamous, including single-celled species such as [[Saccharomyces cerevisiae|''Saccharomyces cerevisiae'']] and ''[[Schizosaccharomyces pombe]]''.<ref name="Lehtonen-2016"/><ref>{{Cite book|last1=Heitman|first1=Joseph|url=https://books.google.com/books?id=VILwDwAAQBAJ&q=most+fungi+are+isogamous&pg=PA149|title=The Fungal Kingdom|last2=Howlett|first2=Barbara J.|last3=Crous|first3=Pedro W.|last4=Stukenbrock|first4=Eva H.|last5=James|first5=Timothy Yong|last6=Gow|first6=Neil A. R.|date=2020-07-10|publisher=John Wiley & Sons|isbn=978-1-55581-958-3|pages=149|language=en|access-date=2021-07-24|archive-date=2023-10-06|archive-url=https://web.archive.org/web/20231006173122/https://books.google.com/books?id=VILwDwAAQBAJ&q=most+fungi+are+isogamous&pg=PA149|url-status=live}}</ref>
In some multicellular fungi, such as [[Basidiomycota|basidiomycetes]], sexual reproduction takes place between two [[Mycelium|mycelia]], but there is no exchange of gametes.<ref name="Lehtonen-2016" />
There are no known examples of isogamous [[Animal|metazoans]], [[red algae]] or [[land plants]].<ref name="Lehtonen-2016" />
==See also==
===Biology===
* [[Anisogamy]]
* [[Evolution of sexual reproduction]]
* [[Gamete]]
* [[Mating in fungi]]
* [[Meiosis]]
* [[Oogamy]]
* [[Sex]]
===Social anthropology===
* [[Hypergamy]]
* [[Hypogamy]]
== Notes ==
{{reflist|group=Note|refs=
<ref name=Note01>Not to be confused with [[self-incompatibility]] in plants.</ref>
}}
==References==
{{Reflist}}
*{{cite journal|journal=PLOS Biology|volume=12 |issue=7 |pages=e1001904 |author1=Sa Geng |author2=Peter De Hoff |author3=James G. Umen |date=July 8, 2014|doi=10.1371/journal.pbio.1001904|pmid=25003332 |pmc=4086717 |title=Evolution of Sexes from an Ancestral Mating-Type Specification Parthway |doi-access=free }}
{{Sex (biology)}}
[[Category:Reproduction]]
[[Category:Germ cells]]
[[Category:Charophyta]]