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. Because both gametes look alike, they generally cannot be classified as male or female. Instead, organisms that reproduce through isogamy are said to have different mating types, most commonly noted as "+" and "−" strains.
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. The term isogamy was first used in the year 1891.
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.
Under the strict definition of isogamy, fertilization occurs when two gametes fuse to form a zygote. 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. 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.
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. Among multicellular organisms, isogamy is restricted to fungi and eukaryotic algae. Many species of green algae are isogamous. It is typical in the genera Ulva, Hydrodictyon, Tetraspora, Zygnema, Spirogyra, Ulothrix, and Chlamydomonas. Many fungi are also isogamous, including single-celled species such as Saccharomyces cerevisiae and Schizosaccharomyces pombe.
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.
See also
Biology
Social anthropology
- Hypergamy
- Hypogamy
Notes
- Not to be confused with self-incompatibility in plants.
References
- Lehtonen, Jussi; Kokko, Hanna; Parker, Geoff A. (2016-10-19). "What do isogamous organisms teach us about sex and the two sexes?". Philosophical Transactions of the Royal Society B: Biological Sciences. 371 (1706). doi:10.1098/rstb.2015.0532. ISSN 0962-8436. PMC 5031617. PMID 27619696.
- Sawada, Hitoshi; Inoue, Naokazu; Iwano, Megumi (2014). Sexual Reproduction in Animals and Plants. Springer. p. 216. ISBN 978-4-431-54589-7. Archived from the original on 2024-04-04. Retrieved 2021-07-24.
- Kumar R, Meena M, Swapnil P (2019). "Anisogamy". In Vonk J, Shackelford T (eds.). Anisogamy. Encyclopedia of Animal Cognition and Behavior. Cham: Springer International Publishing. pp. 1–5. doi:10.1007/978-3-319-47829-6_340-1. ISBN 978-3-319-47829-6.
- Encyclopedia of Evolutionary Biology. Vol. 2. Academic Press. 2016-04-14. p. 212. ISBN 978-0-12-800426-5. Archived from the original on 2023-10-06. Retrieved 2021-08-14.
- Hartog, M. (17 September 1891). "Isogamy, the union of gametes undistinguishable in size, form, and behaviour". Nature: 484.
- "Definition of ISOGAMOUS". www.merriam-webster.com. Archived from the original on 2021-09-14. Retrieved 2021-09-14.
- Casselton, L. A. (2002-02-01). "Mate recognition in fungi". Heredity. 88 (2): 142–147. doi:10.1038/sj.hdy.6800035. ISSN 1365-2540.
- Krumbeck, Yvonne; Constable, George W. A.; Rogers, Tim (2020-02-26). "Fitness differences suppress the number of mating types in evolving isogamous species". Royal Society Open Science. 7 (2): 192126. arXiv:1906.07117. Bibcode:2020RSOS....792126K. doi:10.1098/rsos.192126. ISSN 2054-5703. PMC 7062084. PMID 32257356.
- Pitnick, Scott S.; Hosken, Dave J.; Birkhead, Tim R. (2008-11-21). Sperm Biology: An Evolutionary Perspective. Academic Press. pp. 43–45. ISBN 978-0-08-091987-4. Archived from the original on 2023-10-06. Retrieved 2021-07-24.
- Dusenbery, David B. (2009). Living at Micro Scale, Chapter 20. Harvard University Press, Cambridge, Massachusetts ISBN 978-0-674-03116-6.
- Bell, Graham (2008). Selection: The Mechanism of Evolution. OUP Oxford. p. 439. ISBN 978-0-19-856972-5. Archived from the original on 2023-10-06. Retrieved 2023-03-19.
- Togashi, Tatsuya; Cox, Paul Alan (2011-04-14). The Evolution of Anisogamy: A Fundamental Phenomenon Underlying Sexual Selection. Cambridge University Press. p. 96. ISBN 978-1-139-50082-1. Archived from the original on 2023-10-06. Retrieved 2021-07-24.
- Sharma, O. P. (1986-01-01). Textbook of Algae. Tata McGraw-Hill Education. p. 130. ISBN 978-0-07-451928-8. Archived from the original on 2023-10-06. Retrieved 2021-07-24.
- Heitman, Joseph; Howlett, Barbara J.; Crous, Pedro W.; Stukenbrock, Eva H.; James, Timothy Yong; Gow, Neil A. R. (2020-07-10). The Fungal Kingdom. John Wiley & Sons. p. 149. ISBN 978-1-55581-958-3. Archived from the original on 2023-10-06. Retrieved 2021-07-24.
- Sa Geng; Peter De Hoff; James G. Umen (July 8, 2014). "Evolution of Sexes from an Ancestral Mating-Type Specification Parthway". PLOS Biology. 12 (7): e1001904. doi:10.1371/journal.pbio.1001904. PMC 4086717. PMID 25003332.
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 Because both gametes look alike they generally cannot be classified as male or female Instead organisms that reproduce through isogamy are said to have different mating types most commonly noted as and strains Different forms of isogamy A isogamy of motile cells B isogamy of non motile cells C conjugation isogamy in the broad sense EtymologyThe 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 The term isogamy was first used in the year 1891 Characteristics of isogamous speciesIsogamous 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 Under the strict definition of isogamy fertilization occurs when two gametes fuse to form a zygote 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 EvolutionAs 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 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 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 OccurrenceAlmost all unicellular eukaryotes are isogamous Among multicellular organisms isogamy is restricted to fungi and eukaryotic algae Many species of green algae are isogamous It is typical in the genera Ulva Hydrodictyon Tetraspora Zygnema Spirogyra Ulothrix and Chlamydomonas Many fungi are also isogamous including single celled species such as Saccharomyces cerevisiae and Schizosaccharomyces pombe 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 See alsoBiology Anisogamy Evolution of sexual reproduction Gamete Mating in fungi Meiosis Oogamy SexSocial anthropology Hypergamy HypogamyNotesNot to be confused with self incompatibility in plants ReferencesLehtonen Jussi Kokko Hanna Parker Geoff A 2016 10 19 What do isogamous organisms teach us about sex and the two sexes Philosophical Transactions of the Royal Society B Biological Sciences 371 1706 doi 10 1098 rstb 2015 0532 ISSN 0962 8436 PMC 5031617 PMID 27619696 Sawada Hitoshi Inoue Naokazu Iwano Megumi 2014 Sexual Reproduction in Animals and Plants Springer p 216 ISBN 978 4 431 54589 7 Archived from the original on 2024 04 04 Retrieved 2021 07 24 Kumar R Meena M Swapnil P 2019 Anisogamy In Vonk J Shackelford T eds Anisogamy Encyclopedia of Animal Cognition and Behavior Cham Springer International Publishing pp 1 5 doi 10 1007 978 3 319 47829 6 340 1 ISBN 978 3 319 47829 6 Encyclopedia of Evolutionary Biology Vol 2 Academic Press 2016 04 14 p 212 ISBN 978 0 12 800426 5 Archived from the original on 2023 10 06 Retrieved 2021 08 14 Hartog M 17 September 1891 Isogamy the union of gametes undistinguishable in size form and behaviour Nature 484 Definition of ISOGAMOUS www merriam webster com Archived from the original on 2021 09 14 Retrieved 2021 09 14 Casselton L A 2002 02 01 Mate recognition in fungi Heredity 88 2 142 147 doi 10 1038 sj hdy 6800035 ISSN 1365 2540 Krumbeck Yvonne Constable George W A Rogers Tim 2020 02 26 Fitness differences suppress the number of mating types in evolving isogamous species Royal Society Open Science 7 2 192126 arXiv 1906 07117 Bibcode 2020RSOS 792126K doi 10 1098 rsos 192126 ISSN 2054 5703 PMC 7062084 PMID 32257356 Pitnick Scott S Hosken Dave J Birkhead Tim R 2008 11 21 Sperm Biology An Evolutionary Perspective Academic Press pp 43 45 ISBN 978 0 08 091987 4 Archived from the original on 2023 10 06 Retrieved 2021 07 24 Dusenbery David B 2009 Living at Micro Scale Chapter 20 Harvard University Press Cambridge Massachusetts ISBN 978 0 674 03116 6 Bell Graham 2008 Selection The Mechanism of Evolution OUP Oxford p 439 ISBN 978 0 19 856972 5 Archived from the original on 2023 10 06 Retrieved 2023 03 19 Togashi Tatsuya Cox Paul Alan 2011 04 14 The Evolution of Anisogamy A Fundamental Phenomenon Underlying Sexual Selection Cambridge University Press p 96 ISBN 978 1 139 50082 1 Archived from the original on 2023 10 06 Retrieved 2021 07 24 Sharma O P 1986 01 01 Textbook of Algae Tata McGraw Hill Education p 130 ISBN 978 0 07 451928 8 Archived from the original on 2023 10 06 Retrieved 2021 07 24 Heitman Joseph Howlett Barbara J Crous Pedro W Stukenbrock Eva H James Timothy Yong Gow Neil A R 2020 07 10 The Fungal Kingdom John Wiley amp Sons p 149 ISBN 978 1 55581 958 3 Archived from the original on 2023 10 06 Retrieved 2021 07 24 Sa Geng Peter De Hoff James G Umen July 8 2014 Evolution of Sexes from an Ancestral Mating Type Specification Parthway PLOS Biology 12 7 e1001904 doi 10 1371 journal pbio 1001904 PMC 4086717 PMID 25003332
