{{Short description|Form of sexual reproduction}} thumb|Oogamy in animals: small, motile sperm on the surface of an ovum
'''Oogamy''' is a type of sexual reproduction where the gametes differ greatly in both size and form. In oogamy in animals the large female gamete (also known as the ovum) is immotile, while the small male gamete (also known as a sperm) is mobile.<ref>{{Cite book |last1=Fusco |first1=Giuseppe |url=https://books.google.com/books?id=AKGsDwAAQBAJ|title=The Biology of Reproduction |last2=Minelli |first2=Alessandro |date=2019-10-10 |publisher=Cambridge University Press |isbn=978-1-108-49985-9 |pages=111–112 |language=en |author-link2=Alessandro Minelli (biologist)|access-date=29 March 2021}}</ref> Most sexually reproducing species – animals, land plants and some algae, are oogamous. It is generally accepted that isogamy is the ancestral state, from which oogamy evolved at least twenty times via anisogamy. Once oogamy evolves, males and females typically differ in various aspects. Internal fertilization may have originated from oogamy, although some studies suggest certain species may have evolved before the transition from external to internal fertilization. In streptophytes, oogamy occurred before the split from green algae.
== Occurrence == Oogamy is found in almost all animal species that reproduce sexually.<ref>{{Cite book|last=Bell|first=Graham|url=https://books.google.com/books?id=Xzv3DwAAQBAJ&q=the+evolution+of+sexual+reproduction+is+important+to+the+evolution+of+sex|title=The Masterpiece of Nature: The Evolution and Genetics of Sexuality|date=2019-11-28|publisher=Routledge|isbn=978-1-000-49744-1|page=63|language=en|author-link=Graham Bell (biologist)}}</ref><ref name="Dusenbery-2009">{{Cite book|last=Dusenbery|first=David B.|url=https://books.google.com/books?id=9hgtEAAAQBAJ&dq=oogamy+and+internal+fertilization&pg=PA326|title=Living at Micro Scale: The Unexpected Physics of Being Small|date=2009|publisher=Harvard University Press|isbn=978-0-674-06021-0|page=32|language=en}}</ref> There are exceptions, such as the opiliones that have immobile sperm.<ref>{{Cite book|last1=Leonard|first1=Janet|url=https://books.google.com/books?id=wmlnDAAAQBAJ&dq=oogamy+in+animals&pg=PA18|title=The Evolution of Primary Sexual Characters in Animals|last2=Cordoba-Aguilar|first2=Alex|date=2010-07-19|publisher=Oxford University Press, USA|isbn=978-0-19-532555-3|pages=18–19|language=en}}</ref>
Oogamy is found in all land plants,<ref>{{Cite book|last=Simpson|first=Michael G.|url=https://books.google.com/books?id=dj8KRImgyf4C&dq=oogamy+common+in+land+animals.&pg=PA58|title=Plant Systematics|date=2010-07-19|publisher=Academic Press|isbn=978-0-08-092208-9|page=58|language=en}}</ref> and in some red algae, brown algae and green algae.<ref name="Raven-2005">{{Cite book|last1=Raven|first1=Peter H.|url=https://books.google.com/books?id=8tz2aB1-jb4C&q=Oogamy|title=Biology of Plants|last2=Evert|first2=University Ray F.|last3=Evert|first3=Ray F.|last4=Eichhorn|first4=Susan E.|last5=Eichhorn|first5=University Susan E.|date=2005|publisher=W. H. Freeman|isbn=978-0-7167-1007-3|language=en}}</ref>{{rp|309}} Oogamy is favored in land plants because only one gamete has to travel through harsh environments outside the plant.<ref name="Raven-2005" />{{rp|376}} Oogamy is also present in oomycetes.<ref name="Buaya-2020">{{cite journal |first1=Anthony T. |last1=Buaya |first2=Marco |last2=Thines |journal=Philippine Journal of Systematic Biology |volume=14 |issue=1 |page=1-20 |date=2020 |title=An overview on the biology and phylogeny of the early-diverging oomycetes |doi=10.26757/pjsb2020a14004 |doi-access=free }}</ref>
== Etymology == The term oogamy was first used in the year 1888.<ref>{{Cite web|title=Definition of OOGAMY|url=https://www.merriam-webster.com/dictionary/oogamy|access-date=2021-09-14|website=Merriam-Webster |language=en}}</ref> It derives from the Greek noun "oon" (ΩΟΝ = egg) and the Greek verb "gameo" (ΓΑΜΕΩ → ΓΑΜΩ = to have sex/to reproduce) and eventually means "reproduction through eggs".
== Evolution == {{Main|Evolution of sexual reproduction}} The ancestral state of sexual reproduction is probably isogamy, in which both gametes are identical, from which oogamy is thought to have evolved multiple times<ref name="Wolpert-2002">{{cite journal |last1=Wolpert |first1=L |last2=Szathmáry |first2=E |title=Multicellularity: evolution and the egg |journal=Nature |volume=420 |page=745 |doi=10.1038/420745a }}</ref> through anisogamy.<ref>{{Cite book|last1=Pitnick|first1=Scott S.|url=https://books.google.com/books?id=kctYNbO1fE0C&q=evolution+of+anisogamy|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=43–44|language=en}}</ref><ref>{{Cite book|last=Kumar|first=Awasthi & Ashok|url=https://books.google.com/books?id=r0h1DwAAQBAJ&dq=isogamy+generally+accepted&pg=PA363|title=Textbook of Algae|publisher=Vikas Publishing House|isbn=978-93-259-9022-7|page=363|language=en}}</ref><ref name="Dusenbery-2009" />{{rp|309}}<ref>{{Cite journal|last1=Hörandl|first1=Elvira|last2=Hadacek|first2=Franz|date=August 2020|title=Oxygen, life forms, and the evolution of sexes in multicellular eukaryotes|journal=Heredity|language=en|volume=125|issue=1|pages=1–14|doi=10.1038/s41437-020-0317-9|pmid=32415185|issn=1365-2540|pmc=7413252}}</ref> When oogamy has evolved, males and females typically differ in many aspects. Oogamy evolved before the transition from external to internal fertilization.<ref name=Nozaki-2014>{{cite journal |last1=Nozaki |first1=H |last2=Yamada |first2=TK |last3=Takahashi |first3=F |last4=Matsuzaki |first4=R |last5=Nakada |first5=T |date=2014 |title=New "missing link" genus of the colonial volvocine green algae gives insights into the evolution of oogamy |journal=BMC Evolutionary Biology |volume=14 |issue=1 |page=37 |doi=10.1186/1471-2148-14-37 |doi-access=free |pmid=24589311 |pmc=4015742 |bibcode=2014BMCEE..14...37N }}</ref>{{rp|37}}<ref name="Dusenbery-2009" />{{rp|326}}
In streptophytes, oogamy occurred before the split from green algae.<ref>{{Cite journal|last1=Geng|first1=Sa|last2=De Hoff|first2=Peter|last3=Umen|first3=James G.|date=2014-07-08|title=Evolution of Sexes from an Ancestral Mating-Type Specification Pathway|journal=PLOS Biology|volume=12|issue=7|article-number=e1001904|doi=10.1371/journal.pbio.1001904|issn=1544-9173|pmc=4086717|pmid=25003332 |doi-access=free }}</ref>
== References == {{Reflist}}
{{Eggs}}
Category:Reproductive system Category:Germ cells