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]
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]
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. [7] [8]: 82
Sixty-eight percent of liverwort species, [1] 57% to 60% [9] of moss species, and 40% of hornwort species are dioicous. [1] Dioicy also occurs in algae such as Charales and Coleochaetales. [4]: 71 It is also prevalent in brown algae. [10][ clarification needed]
In all cases sex determination is genetic. [11]
The ancestral sexual system in bryophytes is unknown but it has been suggested monoicy and dioicy evolved several times. [12] 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. [12]
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 [13] 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
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]
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]
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. [7] [8]: 82
Sixty-eight percent of liverwort species, [1] 57% to 60% [9] of moss species, and 40% of hornwort species are dioicous. [1] Dioicy also occurs in algae such as Charales and Coleochaetales. [4]: 71 It is also prevalent in brown algae. [10][ clarification needed]
In all cases sex determination is genetic. [11]
The ancestral sexual system in bryophytes is unknown but it has been suggested monoicy and dioicy evolved several times. [12] 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. [12]
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 [13] 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