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Trioecy, or subdioecy, is a rare sexual system characterized by the coexistence of males, females, and hermaphrodites. It has been found in both plants and animals.[1][2] Trioecy is sometimes referred to as a mixed mating system alongside androdioecy and gynodioecy.[3]

Evolution of trioecy[edit]

Many speculate trioecy is a transient state[4] and is often associated with evolutionary transitioning from gynodioecy to dioecy.[5] Other studies show that trioecious populations originated from gonochoristic ancestors which were invaded by a mutant selfing hermaphrodite, creating a trioecious population.[1] It has been suggested that chromosomal duplication is an important part in the evolution of trioecy.[6]

Evolutionary stability[edit]

Trioecy is usually viewed as evolutionarily unstable, but its exact stability is unclear.[4] Like in brachiopod species trioecy usually breaks into androdioecy or gynodioecy.[7]

But one study found that trioecy can be stable under nucleocytoplasmic sex determination.[8] Another theoretical analysis indicates that trioecy could be evolutionary stable in plant species if a large amount of pollinators vary geographically.[9]


Trioecy is a relatively common sexual system in plants.[10] Trioecy has been estimated to occur in about 3.6% of flowering plant species,[8] although most reports of trioecy could be misinterpretations of gynodioecy.[11] It is rare as well as poorly understood in animals.[10]

Species that exhibit trioecy[edit]

The following species have been observed to exhibit a trioecious breeding system.



See also[edit]


  1. ^ a b c Chaudhuri, Jyotiska; Bose, Neelanjan; Tandonnet, Sophie; Adams, Sally; Zuco, Giusy; Kache, Vikas; Parihar, Manish; von Reuss, Stephan H.; Schroeder, Frank C.; Pires-daSilva, Andre (December 3, 2015). "Mating dynamics in a nematode with three sexes and its evolutionary implications". Scientific Reports. 5 (1): 17676. Bibcode:2015NatSR...517676C. doi:10.1038/srep17676. PMC 4668576. PMID 26631423.
  2. ^ Choe, Jae (2019-01-21). "Hermaphrodite Mating Systems". In Leonard, Janet (ed.). Encyclopedia of Animal Behavior. Vol. 4. Academic Press. pp. 584–589. ISBN 978-0-12-813252-4.
  3. ^ a b c Fusco, Giuseppe; Minelli, Alessandro (2019-10-10). The Biology of Reproduction. Cambridge University Press. pp. 134–135. ISBN 978-1-108-49985-9.
  4. ^ a b c d Kanzaki, Natsumi; Kiontke, Karin; Tanaka, Ryusei; Hirooka, Yuuri; Schwarz, Anna; Müller-Reichert, Thomas; Chaudhuri, Jyotiska; Pires-daSilva, Andre (2017-09-11). "Description of two three-gendered nematode species in the new genus Auanema (Rhabditina) that are models for reproductive mode evolution". Scientific Reports. 7 (1): 11135. Bibcode:2017NatSR...711135K. doi:10.1038/s41598-017-09871-1. PMC 5593846. PMID 28894108.
  5. ^ Kliman, Richard (2016). Encyclopedia of Evolutionary Biology. Vol. 2. Academic Press. p. 476. ISBN 978-0-12-800426-5. Archived from the original on 2016.
  6. ^ Fleming, Theodore H.; Valiente-Banuet, Alfonso (2002). Columnar Cacti and Their Mutualists: Evolution, Ecology, and Conservation. University of Arizona Press. p. 215. ISBN 978-0-8165-2204-0.
  7. ^ Subramoniam, Thanumalaya (2016-09-27). Sexual Biology and Reproduction in Crustaceans. Academic Press. p. 15. ISBN 978-0-12-809606-2.
  8. ^ a b Albert, Béatrice; Morand-Prieur, Marie-Élise; Brachet, Stéphanie; Gouyon, Pierre-Henri; Frascaria-Lacoste, Nathalie; Raquin, Christian (2013-10-01). "Sex expression and reproductive biology in a tree species, Fraxinus excelsior L". Comptes Rendus Biologies. 336 (10): 479–485. doi:10.1016/j.crvi.2013.08.004. ISSN 1631-0691. PMID 24246889.
  9. ^ Fleming, Theodore H.; Valiente-Banuet, Alfonso (2002). Columnar Cacti and Their Mutualists: Evolution, Ecology, and Conservation. University of Arizona Press. p. 214. ISBN 978-0-8165-2204-0.
  10. ^ a b c Oyarzún P, Nuñez J, Toro JE, Gardner J (2020). "Trioecy in the Marine Mussel Semimytilus algosus (Mollusca, Bivalvia): Stable Sex Ratios Across 22 Degrees of a Latitudinal Gradient". Frontiers in Marine Science. 7 (348): 1–10. doi:10.3389/fmars.2020.00348.
  11. ^ Geber, Monica A.; Dawson, Todd E.; Delph, Lynda F. (2012-12-06). Gender and Sexual Dimorphism in Flowering Plants. Springer Science & Business Media. p. 74. ISBN 978-3-662-03908-3.
  12. ^ Silva, C. A.; Oliva, M.; Vieira, M. F.; Fernandes, G. W. (October 27, 2008). "Trioecy in Coccoloba cereifera Schwacke (Polygonaceae), a narrow endemic and threatened tropical species". Brazilian Archives of Biology and Technology. 51 (5): 1003–1010. doi:10.1590/S1516-89132008000500017. S2CID 85673074.
  13. ^ Joseph KS, Murthy HN (2015). "Sexual system of Garcinia indica Choisy: geographic variation in trioecy and sexual dimorphism in floral traits". Plant Systematics and Evolution. 301 (3): 1065–1071. doi:10.1007/s00606-014-1120-y. S2CID 15926083.
  14. ^ Perry, Laura E.; Pannell, John R.; Dorken, Marcel E. (2012-04-19). "Two's Company, Three's a Crowd: Experimental Evaluation of the Evolutionary Maintenance of Trioecy in Mercurialis annua (Euphorbiaceae)". PLOS ONE. 7 (4): e35597. Bibcode:2012PLoSO...735597P. doi:10.1371/journal.pone.0035597. ISSN 1932-6203. PMC 3330815. PMID 22532862.
  15. ^ a b Avise, John C. (2011-03-18). Hermaphroditism: A Primer on the Biology, Ecology, and Evolution of Dual Sexuality. Columbia University Press. p. 55. ISBN 978-0-231-52715-6.
  16. ^ Fleming, Theodore H. (September 2000). "Pollination of Cacti in the Sonoran Desert: When closely related species vie for scarce resources, necessity is the mother of some pretty unusual evolutionary inventions". American Scientist. 88 (5): 432–439. doi:10.1511/2000.5.432. JSTOR 27858091.
  17. ^ Armoza-Zvuloni, Rachel; Kramarsky-Winter, Esti; Loya, Yossi; Schlesinger, Ami; Rosenfeld, Hanna (2014-06-01). "Trioecy, a Unique Breeding Strategy in the Sea Anemone Aiptasia diaphana and Its Association with Sex Steroids". Biology of Reproduction. 90 (6): 122. doi:10.1095/biolreprod.113.114116. ISSN 0006-3363. PMID 24790160.
  18. ^ Leonard, Janet L. (2013-10-01). "Williams' Paradox and the Role of Phenotypic Plasticity in Sexual Systems". Integrative and Comparative Biology. 53 (4): 671–688. doi:10.1093/icb/ict088. ISSN 1540-7063. PMID 23970358.