Isogamy#Conjugation

{{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 cells, B) isogamy of non-motile cells, C) conjugation (isogamy in the broad sense)|270x270px]]

Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), and is found in most unicellular eukaryotes.{{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}} Because both gametes look alike, they generally cannot be classified as male or female.{{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}} Instead, organisms that reproduce through isogamy are said to have different mating types, most commonly noted as "+" and "−" strains.{{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}}

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.{{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}} The term isogamy was first used in the year 1891.{{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}}{{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}}

Characteristics of isogamous species

Isogamous species often have two mating types (heterothallism), but sometimes can occur between two haploid individuals that are mitotic descendents (homothallism). 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 basidiomycete species, a species can have thousands of mating types.{{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}}

Under the strict definition of isogamy, fertilization occurs when two gametes fuse to form a zygote.{{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}} Sexual reproduction between two cells that does not involve gametes (e.g. conjugation between two mycelia in basidiomycete fungi), is often called isogamy, although it is not technically isogametic reproduction in the strict sense.

Evolution

As the first stage in the evolution of sexual reproduction in all known lifeforms, isogamy is thought to have evolved just once, in a single unicellular eukaryote species, the common ancestor of all eukaryotes. It is generally accepted that isogamy is an ancestral state for anisogamy.{{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}} Isogamous reproduction evolved independently in several lineages of plants and animals into anisogamy (species with gametes of male and female types) and subsequently into oogamy (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.Dusenbery, David B. (2009). Living at Micro Scale, Chapter 20. Harvard University Press, Cambridge, Massachusetts {{ISBN|978-0-674-03116-6}}.

Since it appeared, isogamy has remained the norm in unicellular eukaryote species, and it is possible that isogamy is also evolutionarily stable in multicellular species.

Occurrence

Almost all unicellular eukaryotes are isogamous.{{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}} Among multicellular organisms, isogamy is restricted to fungi and eukaryotic algae.{{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}} Many species of green algae are isogamous. It is typical in the genera Ulva, Hydrodictyon, Tetraspora, Zygnema, Spirogyra, Ulothrix, and Chlamydomonas.{{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}} Many fungi are also isogamous, including single-celled species such as Saccharomyces cerevisiae and Schizosaccharomyces pombe.{{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}}

In some multicellular fungi, such as basidiomycetes, sexual reproduction takes place between two mycelia, but there is no exchange of gametes.

There are no known examples of isogamous metazoans, red algae or land plants.

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Notes

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Not to be confused with self-incompatibility in plants.

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References

{{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 }}

Category:Reproduction

Category:Germ cells

Category:Charophyta