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Dioecy (Greek: διοικία "two households"; adjective form: dioecious) is a characteristic of a species, meaning that it has distinct individual organisms that produce male and female gametes, either directly (in animals) or indirectly (in plants). Dioecious reproduction is biparental reproduction. Dioecy has costs, since only about half the population directly produces offspring. It is one method that excludes self-fertilization and promotes allogamy (outcrossing), and thus tends to reduce the expression of recessive deleterious mutations present in a population. Flowering plants have several other methods of excluding self-fertilization, such as self-incompatibility.

In zoology[edit]

Physalia physalis, Portuguese man o' war, is a marine colonial animal that is dioecious; the reproductive medusae within a colony such as this are all of the same sex.[1]

In zoology, dioecious species may be opposed to hermaphroditic species, meaning that an individual is either male or female, in which case the synonym gonochory is more often used.[2] Dioecy may also describe colonies within a species, such as the colonies of Siphonophorae (Portuguese man-of-war), which may be either dioecious or monoecious.[3]

Most animal species are dioecious (gonochoric).[4] It is estimated that 95% of animal species are dioecious.[5]

In botany[edit]

Land plants (embryophytes) differ from animals in that they have alternation of generations. In animals, typically an individual produces gametes of one kind, either sperms or egg cells. A sperm and an egg cell fuse to form a new individual. In land plants, by contrast, one generation – the sporophyte generation – consists of individuals that produce spores rather than gametes. Spores do not fuse, but divide to give rise to individuals which produce gametes – the gametophyte generation. A male gamete and a female gamete must then fuse to produce a new sporophyte.[6] In bryophytes (mosses, liverworts and hornworts), the gametophytes are fully independent plants,[7] whereas in seed plants (spermatophytes), the male gametophytes are contained within pollen produced by stamens, and the female gametophytes are contained within ovules produced by carpels.[6]

Alternation of generation in plants: the sporophyte generation produces spores that give rise to the gametophyte generation, which produces gametes that fuse to give rise to the sporophyte generation.

The sporophyte generation is called dioecious when each sporophyte plant has only one kind of spore-producing organ, all of whose spores give rise either to male gametophytes, which produce only male gametes (sperm), or to female gametophytes, which produce only female gametes (egg cells). A single flowering plant – a sporophyte - of a fully dioecious species has either flowers with functional stamens producing pollen containing male gametes (staminate or 'male' flowers), or flowers with functional carpels producing female gametes (carpellate or 'female' flowers), but not both.[8][9] The sporophyte generation is called monoecious when each sporophyte plant has both kinds of spore-producing organ, so ultimately produces both male and female gametophytes and hence gametes. A single flowering plant of a monoecious species has both functional stamens and carpels, either in separate flowers[8] or in the same flower.[10] (See Plant reproductive morphology for further details, including more complex cases.)

Slightly different terms, dioicous and monoicous, may be used for the gametophyte generation, although dioecious and monoecious are also used.[11][12] A dioicous gametophyte produces only male gametes (sperm) or female gametes (egg cells).

Dioecy occurs in a wide variety of plant families. However it is more common in woody plants,[13] and heterotrophic species.[14] 65% of gymnosperms are dioecious.[15] About 6 percent of angiosperm species are entirely dioecious and about 7% of angiosperm genera contain some dioecious species.[16] Examples of dioecious plant species include ginkgos, willows, cannabis and African teak. There is a consensus that dioecious flowers evolved from monoecious ancestors with flowers containing both functional stamens and carpels.[17][18]

Certain algae are dioecious.[19]

In most dioecious plants, whether male or female gametophytes are produced is determined genetically, but in some cases it can be determined by the environment, as in Arisaema species.[20]

In mycology[edit]

Monoecy and dioecy in fungi refer to the donor and recipient roles in mating, where a nucleus is transferred from one haploid hypha to another, and the two nuclei then present in the same cell merge by karyogamy to form a zygote.[21] The definition avoids reference to male and female reproductive structures, which are rare in fungi.[21] An individual of a dioecious fungal species not only requires a partner for mating, but performs only one of the roles in nuclear transfer, as either the donor or the recipient. A monoecious fungal species can perform both roles, but may not be self-compatible.[21]

Adaptive benefit[edit]

Dioecy has a demographic disadvantage compared with hermaphroditism: only about half of reproductive adults are able to produce offspring. It is commonly assumed that dioecious species must therefore have fitness advantages to compensate for this cost through increased survival, growth, or reproduction. Dioecy excludes self-fertilization and promotes allogamy (outcrossing), and thus tends to reduce the expression of recessive deleterious mutations present in a population.[22] In trees, compensation is realized mainly through increased seed production by females. This in turn is facilitated by a lower contribution of reproduction to population growth, which results in no demonstrable net costs of having males in the population compared to being hermaphroditic.[23] Dioecy may also accelerate or retard lineage diversification in angiosperms. Dioecious lineages are more diversified in certain genera, but less in others. An analysis suggested that dioecy neither consistently places a strong brake on diversification, nor strongly drives it.[24]

See also[edit]


  1. ^ "Animal Diversity Web". Retrieved 27 April 2014.
  2. ^ Kliman, Richard (2016). Encyclopedia of Evolutionary Biology. Academic Press. ISBN 978-0-12-800426-5. Archived from the original on May 6, 2021. Alternative archive URL
  3. ^ Dunn, C.W.; Pugh, P.R.; Haddock, S.H.D. (2005). "Molecular Phylogenetics of the Siphonophora (Cnidaria), with Implications for the Evolution of Functional Specialization". Systematic Biology. 54 (6): 916–935. doi:10.1080/10635150500354837. PMID 16338764.
  4. ^ David, J.R. (2001). "Evolution and development: some insights from evolutionary theory". Anais da Academia Brasileira de Ciências. 73 (3): 385–395. doi:10.1590/s0001-37652001000300008.
  5. ^ Sabath, Niv; Goldberg, Emma E.; Glick, Lior; Einhorn, Moshe; Ashman, Tia-Lynn; Ming, Ray; Otto, Sarah P.; Vamosi, Jana C.; Mayrose, Itay (2016). "Dioecy does not consistently accelerate or slow lineage diversification across multiple genera of angiosperms". New Phytologist. 209 (3): 1290–1300. doi:10.1111/nph.13696. ISSN 1469-8137.
  6. ^ a b Mauseth (2014), pp. 204–205.
  7. ^ Mauseth (2014), p. 487.
  8. ^ a b Mauseth (2014), p. 218.
  9. ^ Hickey, M. & King, C. (2001). The Cambridge Illustrated Glossary of Botanical Terms. Cambridge University Press.
  10. ^ Beentje (2010), p. 72.
  11. ^ Lepp, Heino (2007). "Case studies : -oicy : Dioicous, dioecious, monoicous and monoecious". Australian Bryophytes. Australian National Botanic Gardens and Australian National Herbarium. Retrieved 2021-06-21.
  12. ^ Stearn, W.T. (1992). Botanical Latin: History, grammar, syntax, terminology and vocabulary, Fourth edition. David and Charles.
  13. ^ Matallana, G.; Wendt, T.; Araujo, D.S.D.; Scarano, F.R. (2005), "High abundance of dioecious plants in a tropical coastal vegetation", American Journal of Botany, 92 (9): 1513–1519, doi:10.3732/ajb.92.9.1513, PMID 21646169CS1 maint: uses authors parameter (link)
  14. ^ Nickrent D.L., Musselman L.J. (2004). "Introduction to Parasitic Flowering Plants". The Plant Health Instructor. doi:10.1094/PHI-I-2004-0330-01. Archived from the original on 2016-10-05. Retrieved 2017-01-10.
  15. ^ "Sexual systems in gymnosperms: A review". Basic and Applied Ecology. 31: 1–9. 2018-09-01. doi:10.1016/j.baae.2018.05.009. ISSN 1439-1791.
  16. ^ Renner, S. S.; R. E. Ricklefs (1995). "Dioecy and its correlates in the flowering plants". American Journal of Botany. 82 (5): 596–606. doi:10.2307/2445418. JSTOR 2445418.
  17. ^ Núñez-Farfán, Juan; Valverde, Pedro Luis (2020-07-30). Evolutionary Ecology of Plant-Herbivore Interaction. Springer Nature. p. 177. ISBN 978-3-030-46012-9.
  18. ^ K. S. Bawa (1980). "Evolution of Dioecy in Flowering Plants". Annual Review of Ecology and Systematics. 11: 15–39. doi:10.1146/annurev.es.11.110180.000311. JSTOR 2096901.
  19. ^ Maggs, C.A. and Hommersand, M.H. 1993. Seaweeds of the British Isles Volume 1 Rhodophyta Part 3A Ceramiales. The Natural History Museum, London. ISBN 0-11-310045-0
  20. ^ Fusco, Giuseppe; Minelli, Alessandro (2019-10-10). The Biology of Reproduction. Cambridge University Press. p. 329. ISBN 978-1-108-49985-9.
  21. ^ a b c Esser, K. (1971). "Breeding systems in fungi and their significance for genetic recombination". Molecular and General Genetics. 110 (1): 86–100. doi:10.1007/bf00276051.
  22. ^ Charlesworth D, Willis JH (2009). "The genetics of inbreeding depression". Nat. Rev. Genet. 10 (11): 783–96. doi:10.1038/nrg2664. PMID 19834483.
  23. ^ Bruijning, Marjolein; Visser, Marco D.; Muller-Landau, Helene C.; Wright, S. Joseph; Comita, Liza S.; Hubbell, Stephen P.; de Kroon, Hans; Jongejans, Eelke (2017). "Surviving in a Cosexual World: A Cost-Benefit Analysis of Dioecy in Tropical Trees". The American Naturalist. 189 (3): 297–314. doi:10.1086/690137. hdl:2066/168955. ISSN 0003-0147.
  24. ^ Sabath, Niv; Goldberg, Emma E.; Glick, Lior; Einhorn, Moshe; Ashman, Tia-Lynn; Ming, Ray; Otto, Sarah P.; Vamosi, Jana C.; Mayrose, Itay (2016). "Dioecy does not consistently accelerate or slow lineage diversification across multiple genera of angiosperms". New Phytologist. 209 (3): 1290–1300. doi:10.1111/nph.13696. PMID 26467174.