Dioicy

Not to be confused with Dioecy.

Dioicy (/daɪˈoʊəsi/) is a sexual system in non-vascular plants where archegonia and antheridia are produced on separate gametophytes.^[1] It is one of the two main sexual systems in bryophytes, the other being monoicy. Both dioicous (/daɪˈoʊəkəs/) and monoicous gametophytes produce gametes in gametangia by mitosis rather than meiosis, so that sperm and eggs are genetically identical with their parent gametophyte.^[2]

Description

Dioicy promotes outcrossing.^[3] Sexual dimorphism is commonly found in dioicous species.^{[4]: 71 [2]: 378} Dioicy is correlated with reduced sporophyte production,^[5] due to spatial separation of male and female colonies, scarcity or absence of males.^[4]: 65

The term dioecy is inapplicable to bryophytes because it refers to the sexuality of vascular plant sporophytes.^[4]: 62 Nonetheless dioecy and dioicy are comparable in many respects.^[6]

Etymology

The words dioicous and di(o)ecious are derived from οἶκος or οἰκία and δι- (di-), twice, double. ((o)e is the Latin way of transliterating Greek οι, whereas oi is a more straightforward modern way.) Generally, the term and "dioicous" have been restricted to description of haploid sexuality (gametophytic sexuality), and are thus primarily to describe bryophytes in which the gametophyte is the dominant generation. Meanwhile, "dioecious" is used to describe diploid sexuality (sporophytic sexuality), and thus is used to describe tracheophytes (vascular plants) in which the sporophyte is the dominant generation.^[1][7]: 82

Occurrence

Sixty-eight percent of liverwort species,^[1] 57% to 60%^[8] of moss species, and 40% of hornwort species are dioicous.^[1] Dioicy also occurs in algae such as Charales and Coleochaetales.^[4]: 71It is also prevalent in brown algae.^{[9][clarification needed]}

In all cases sex determination is genetic.^[10]

Evolution of dioicy

Main article: Evolution of sexual reproduction

The ancestral sexual system in bryophytes is unknown but it has been suggested monoicy and dioicy evolved several times.^[11] It has also been suggested that dioicy is a plesiomorphic character for bryophytes.^[4]: 71 In order for dioicy to evolve from monoicy it needs two mutations, a male sterility mutation and a female sterility mutation.^[11]

Hornworts have gone through twice as many transitions from dioicy to monoicy than monoicy to dioicy.^[1]

Among moss species the transition from monoicy to dioicy is more common than dioicy to monoicy^[12] with there being at least 133 transitions from monoicy to dioicy in moss. Sexual specialization has been used as an explanation for this recurring evolution of dioicy in mosses.^[4]: 71

References

1. Villarreal, Juan Carlos; Renner, Susanne S. (2013-11-02). "Correlates of monoicy and dioicy in hornworts, the apparent sister group to vascular plants". BMC Evolutionary Biology. 13 (1): 239. doi:10.1186/1471-2148-13-239. ISSN 1471-2148. PMC 4228369. PMID 24180692.
2. Goffinet, Bernard (2008-10-30). Bryophyte Biology. Cambridge University Press. ISBN 978-1-107-37728-8.
3. Windsor, Jon and Lesley Lovett-Doust Professor of Biology the University of (1988-07-07). Plant Reproductive Ecology : Patterns and Strategies: Patterns and Strategies. Oxford University Press, USA. pp. 291–292. ISBN 978-0-19-802192-6.
4. Ramawat KG, Merillon JM, Shivanna KR (2016-04-19). Reproductive Biology of Plants. CRC Press. ISBN 978-1-4822-0133-8.
5. Windsor, Jon and Lesley Lovett-Doust Professor of Biology the University of (1988-07-07). Plant Reproductive Ecology : Patterns and Strategies: Patterns and Strategies. Oxford University Press, USA. p. 295. ISBN 978-0-19-802192-6.
6. Bisang, Irene; Ehrlén, Johan; Hedenäs, Lars (2006). "Reproductive effort and costs of reproduction do not explain female-biased sex ratios in the moss Pseudocalliergon trifarium (Amblystegiaceae)". American Journal of Botany. 93 (9): 1313–1319. doi:10.3732/ajb.93.9.1313. ISSN 1537-2197. PMID 21642196.
7. Buck WR & Goffinet B (2000). "Morphology and classification of mosses". In Shaw AJ & Goffinet B (ed.). Bryophyte Biology. New York: Cambridge University Press. ISBN 978-0-521-66794-4.
8. Rensing, Stefan (2016-03-23). "Genomes and Evolution of Charophytes, Bryophytes, Lycophytes and Ferns". Advances in Botanical Research. Vol. 78. Academic Press. p. 109. ISBN 978-0-12-801324-3.
9. Zhang, Jiaxun; Li, Yan; Luo, Shiju; Cao, Min; Zhang, Linan; Li, Xiaojie (2021-07-14). "Differential gene expression patterns during gametophyte development provide insights into sex differentiation in the dioicous kelp Saccharina japonica". BMC Plant Biology. 21 (1): 335. doi:10.1186/s12870-021-03117-z. ISSN 1471-2229. PMC 8278619. PMID 34261451.
10. Renner, Susanne S. (2014). "The relative and absolute frequencies of angiosperm sexual systems: Dioecy, monoecy, gynodioecy, and an updated online database". American Journal of Botany. 101 (10): 1588–1596. doi:10.3732/ajb.1400196. ISSN 1537-2197. PMID 25326608.
11. McDaniel, Stuart F.; Perroud, Pierre-François (2012). "Invited perspective: bryophytes as models for understanding the evolution of sexual systems". The Bryologist. 115 (1): 1–11. doi:10.1639/0007-2745-115.1.1. ISSN 0007-2745. JSTOR 41486736. S2CID 85943617.
12. Genomes and Evolution of Charophytes, Bryophytes, Lycophytes and Ferns. Academic Press. 2016-03-23. p. 109. ISBN 978-0-12-801324-3.