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Dioecy (/daɪˈiːsi/ dy-EE-see;[1] from Ancient Greek διοικία dioikía 'two households'; adj. dioecious, /daɪˈiːʃ(i)əs/ dy-EE-sh(ee-)əs)[2][3] is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduction is biparental reproduction. Dioecy has costs, since only the female part of the population directly produces offspring. It is one method for excluding self-fertilization and promoting allogamy (outcrossing), and thus tends to reduce the expression of recessive deleterious mutations present in a population. Plants have several other methods of preventing self-fertilization including, for example, dichogamy, herkogamy, and self-incompatibility.

In zoology

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Physalia physalis, Portuguese man o' war, is a dioecious colonial marine animal; the reproductive medusae within the colony are all of the same sex.[4]
Further information: Gonochorism

In zoology, dioecy means that an animal is either male or female, in which case the synonym gonochory is more often used.[5][page needed] Most animal species are gonochoric, almost all vertebrate species are gonochoric, and all bird and mammal species are gonochoric.[6] Dioecy may also describe colonies within an animal species, such as the colonies of Siphonophorae (Portuguese man-of-war), which may be either dioecious or monoecious.[7]

In botany

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Land plants (embryophytes) differ from animals in that their life cycle involves alternation of generations. In animals, typically an individual produces gametes of one kind, either sperm or egg cells. The gametes have half the number of chromosomes of the individual producing them, so are haploid. Without further dividing, a sperm and an egg cell fuse to form a zygote that develops into a new individual. In land plants, by contrast, one generation – the sporophyte generation – consists of individuals that produce haploid spores rather than haploid gametes. Spores do not fuse, but germinate by dividing repeatedly by mitosis to give rise to haploid multicellular individuals, the gametophytes, which produce gametes. A male gamete and a female gamete then fuse to produce a new diploid sporophyte.[8]

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

In bryophytes (mosses, liverworts and hornworts), the gametophytes are fully independent plants.[9] Seed plant gametophytes are dependent on the sporophyte and develop within the spores, a condition known as endospory. In flowering plants, the male gametophytes develop within pollen grains produced by the sporophyte's stamens, and the female gametophytes develop within ovules produced by the sporophyte's carpels.[8]

The sporophyte generation of a seed plant is called "monoecious" when each sporophyte plant has both kinds of spore-producing organ but in separate flowers or cones. For example, a single flowering plant of a monoecious species has both functional stamens and carpels, in separate flowers.[10]

The sporophyte generation of seed plants 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). For example, a single flowering plant sporophyte of a fully dioecious species like holly 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.[10][11] There are other, more complex reproductive schemes such as gynodioecy and androdioecy.

Slightly different terms, dioicous and monoicous, may be used for the gametophyte generation of non-vascular plants, although dioecious and monoecious are also used.[12][13] A dioicous gametophyte either produces only male gametes (sperm) or produces only female gametes (egg cells). About 60% of liverworts are dioicous.[14]: 52 

Dioecy occurs in a wide variety of plant groups. Examples of dioecious plant species include ginkgos, willows, cannabis and African teak. As its specific name implies, the perennial stinging nettle Urtica dioica is dioecious,[15]: 305  while the annual nettle Urtica urens is monoecious.[15]: 305  Dioecious flora are predominant in tropical environments.[16]

About 65% of gymnosperm species are dioecious,[17] but almost all conifers are monoecious.[18] In gymnosperms, the sexual systems dioecy and monoecy are strongly correlated with the mode of pollen dispersal, monoecious species are predominantly wind dispersed (anemophily) and dioecious species animal-dispersed (zoophily).[19]

About 6 percent of flowering plant species are entirely dioecious and about 7% of angiosperm genera contain some dioecious species.[20] Dioecy is more common in woody plants,[21] and heterotrophic species.[22] 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.[23]

  • In dioecious holly, some plants only have 'male' flowers with stamens producing pollen.
    In dioecious holly, some plants only have 'male' flowers with stamens producing pollen.
  • Other holly plants only have 'female' flowers that produce ovules.
    Other holly plants only have 'female' flowers that produce ovules.
  • Each bisexual (perfect) tulip flower has both stamens and carpels.
    Each bisexual (perfect) tulip flower has both stamens and carpels.

Certain algae, such as some species of Polysiphonia, are dioecious.[24] Dioecy is prevalent in the brown algae (Phaeophyceae) and may have been the ancestral state in that group.[25]

Evolution of dioecy

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For evolution in animals, see Gonochorism § Evolution.

In plants, dioecy has evolved independently multiple times[26] either from hermaphroditic species or from monoecious species. A previously untested hypothesis is that this reduces inbreeding;[27] dioecy has been shown to be associated with increased genetic diversity and greater protection against deleterious mutations.[28] Regardless of the evolutionary pathway the intermediate states need to have fitness advantages compared to cosexual flowers in order to survive.[29]

Dioecy evolves due to male or female sterility,[30] although it is unlikely that mutations for male and female sterility occurred at the same time.[31] In angiosperms unisexual flowers evolve from bisexual ones.[32] Dioecy occurs in almost half of plant families, but only in a minority of genera, suggesting recent evolution.[33] For 160 families that have dioecious species, dioecy is thought to have evolved more than 100 times.[34]

In the family Caricaceae, dioecy is likely the ancestral sexual system.[35]

From monoecy

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Dioecious flowering plants can evolve from monoecious ancestors that have flowers containing both functional stamens and functional carpels.[36] Some authors argue monoecy and dioecy are related.[37]

In the genus Sagittaria, since there is a distribution of sexual systems, it has been postulated that dioecy evolved from monoecy[38] through gynodioecy mainly from mutations that resulted in male sterility.[39]: 478  However, since the ancestral state is unclear, more work is needed to clarify the evolution of dioecy via monoecy.[39]: 478 

From hermaphroditism

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Dioecy usually evolves from hermaphroditism through gynodioecy but may also evolve through androdioecy,[40] through distyly[41] or through heterostyly.[28] In the Asteraceae, dioecy may have evolved independently from hermaphroditism at least 5 or 9 times. The reverse transition, from dioecy back to hermaphroditism has also been observed, both in Asteraceae and in bryophytes, with a frequency about half of that for the forward transition.[42]

In Silene, since there is no monoecy, it is suggested that dioecy evolved through gynodioecy.[43]

In mycology

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Very few dioecious fungi have been discovered.[44]

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.[45] The definition avoids reference to male and female reproductive structures, which are rare in fungi.[45] 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.[45]

Adaptive benefit

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Dioecy has the demographic disadvantage compared with hermaphroditism that only about half of reproductive adults are able to produce offspring. 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.[46] 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.[47] 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.[48]

See also

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References

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Bibliography

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Dioecy

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from Grokipedia
Dioecy is a characterized by the separation of reproductive organs into distinct individuals, with males producing only male gametes (e.g., or ) and s producing only gametes (e.g., ova or eggs). In flowering , this manifests as separate male bearing staminate flowers and bearing pistillate flowers, promoting obligatory to ensure fertilization. While most prevalent and studied in , dioecy also occurs in animals and some fungi. This sexual strategy occurs in approximately 6% of angiosperm , though it is represented in about 40% of families containing unisexual-flowered taxa, highlighting its sporadic but recurrent evolution across plant lineages. Dioecy has arisen independently over 100 times from hermaphroditic ancestors, frequently through transitional states like (where females coexist with hermaphrodites) or (separate male and female flowers on the same plant), driven by genetic mechanisms such as mutations in floral development genes and the emergence of with suppressed recombination. It is more common among woody perennials, wind-pollinated , and those with animal-dispersed , potentially due to selective pressures favoring reduced selfing and enhanced in such ecological niches. Notable examples of dioecious plants include the (Carica papaya), which exhibits an XY sex chromosome system; (Cannabis sativa), often wind-pollinated; and members of the family, where nearly half the species are dioecious. Other well-documented cases encompass the (Phoenix dactylifera), hollies (Ilex spp.), and willows (Salix spp.), illustrating dioecy's prevalence in both tropical and temperate flora. While dioecy can impose costs like pollen limitation for females and biased sex ratios, it confers benefits such as avoidance of and resolution of over resource allocation.

Basic Concepts

Definition of Dioecy

Dioecy is a reproductive system characterized by the presence of distinct male and female individuals within a species, where males produce small, motile gametes such as sperm or pollen, and females produce larger, provisioned gametes such as eggs or ovules. This unisexual condition represents a form of sexual dimorphism at the organismal level, with sexes spatially separated across individuals rather than combined within them. The term "dioecy" derives from the Greek "di-" (two) and "oikos" (house), alluding to the division of reproductive functions into separate "households." A fundamental characteristic of dioecy is the promotion of obligate , as the separation of sexes necessitates mating between s and s, thereby minimizing self-fertilization and in most cases. This system typically arises following the evolution of , a dimorphism in size and investment where smaller s prioritize quantity and mobility, while larger s emphasize quality and nourishment, setting the stage for the specialization of entire individuals into or roles. In biological terminology, dioecy is the standard term applied to plants and fungi exhibiting this unisexual organization, whereas the analogous condition in animals is more commonly referred to as gonochorism. This distinction reflects domain-specific conventions in describing separate-sex systems, though the underlying principle of individual-level sex separation remains consistent across kingdoms. Dioecy is characterized by the strict separation of male and female reproductive functions across distinct individuals, each producing only one type of gamete, in contrast to monoecy, where a single individual bears both male and female reproductive structures in separate flowers or inflorescences. Monoecious plants, such as maize (Zea mays), produce staminate (male) flowers in tassels and pistillate (female) flowers in ears on the same plant, enabling both self-pollination and outcrossing depending on environmental and genetic factors. This arrangement in monoecy allows for greater flexibility in mating but differs from dioecy by not requiring sexual dimorphism at the individual level. Hermaphroditism, the most common sexual system in flowering plants, involves individuals with both male and female reproductive organs either within the same flower (cosexual or perfect flowers) or across the plant, occurring simultaneously or sequentially over time. Unlike dioecy's unisexual individuals, hermaphroditic plants, such as tomatoes (Solanum lycopersicum), can readily self-fertilize, though many promote through mechanisms like . This contrasts sharply with dioecy, where self-fertilization is impossible due to the absence of opposite-sex organs on any individual. Mixed or subdioecious systems, such as gynodioecy, represent polymorphic populations containing both female individuals (producing only ovules) and hermaphroditic individuals (producing both gametes), serving as potential evolutionary intermediates between hermaphroditism and full dioecy. In gynodioecious species like wild strawberry (Fragaria virginiana), females often achieve higher seed production, while hermaphrodites contribute pollen, enhancing overall outcrossing rates without the complete separation seen in dioecy. These systems highlight transitional dynamics but maintain some degree of sexual overlap absent in pure dioecy. The following table summarizes key distinctions among these sexual systems based on gamete production, individual structure, and outcrossing potential:
Sexual SystemGamete ProductionIndividual StructureOutcrossing Potential
HermaphroditismBoth sperm and ova per individualBisexual flowers or combined organsVariable; selfing possible but often reduced by incompatibility
Separate male (sperm) and female (ova) flowersUnisexual flowers on the same individualPromoted but selfing feasible via
DioecyMales: sperm only; females: ova onlyEntirely unisexual individualsObligate; requires inter-individual mating
Females: ova only; hermaphrodites: bothPopulation mix of unisexual females and bisexual individualsEnhanced relative to pure hermaphroditism; partial selfing in hermaphrodites

Dioecy in Animals

Characteristics and Prevalence

In animals, dioecy is referred to as , a sexual system in which individuals develop as either male or female and remain so throughout their lives, producing only one type of —sperm in males or ova in females. This system contrasts with hermaphroditism, where individuals possess both male and female reproductive organs, and is characterized by distinct sex-specific reproductive strategies that often lead to in morphology, physiology, or behavior. For instance, males typically invest less in gamete production, generating numerous small, mobile , while females allocate more resources to fewer, larger ova, frequently coupled with in many species. Sex determination in gonochoristic occurs through diverse mechanisms, including genetic factors like sex , hormonal influences, or environmental cues. In mammals, the XY system predominates, where the presence of a Y chromosome triggers male development via the SRY , resulting in 100% gonochorism across the class. Birds and some reptiles employ the ZW system, with heterogametic females (ZW) and homogametic s (ZZ), also yielding fully gonochoristic populations. Many fish and reptiles exhibit (ESD), such as temperature-dependent , though the vast majority retain fixed sexes post-determination. Hormones like testosterone and further differentiate secondary , such as larger body sizes in mammals or brighter in birds, often linked to . Gonochorism is the predominant across the animal kingdom, occurring in approximately 94–95% of , with hermaphroditism confined to about 5–6%. It is nearly ubiquitous in , comprising roughly 99% of in this , including all mammals, over 98% of fishes (the largest vertebrate group), and most reptiles and birds. In Chordata, prevalence exceeds 95%, reflecting stable genetic systems like XY or ZW. In contrast, arthropods show more variability, with dominant in most crustaceans and (over 90% in many orders), though alternatives like in maintain separate sexes while altering inheritance. overall exhibit higher rates of non-gonochoric reproduction, such as in some , but remains the ancestral and most common mode. Reproductive biology in gonochoristic animals emphasizes cross-fertilization, with mating behaviors like displays or territorial defense ensuring pairing between sexes and reducing self-fertilization risks. This often results in , where traits enhancing mate attraction or competition evolve, such as exaggerated ornaments in male birds or aggressive behaviors in male reptiles.

Notable Examples

Dioecy, or gonochorism, is prevalent among vertebrates, where separate sexes facilitate diverse reproductive strategies. In mammals, humans exemplify this system through the XX/XY chromosomal mechanism, in which females possess two X chromosomes and males have one X and one Y chromosome, determining sex at fertilization via the presence or absence of the Y chromosome. This genetic basis ensures strict separation of male and female roles in reproduction across mammalian species. Similarly, birds demonstrate dioecy via the ZW system, as seen in domestic chickens (Gallus gallus domesticus), where males are homogametic (ZZ) and females heterogametic (ZW), with sex determined by the inheritance of Z or W chromosomes from parents. In reptiles, dioecy manifests through both genetic and environmental cues; for instance, many turtle species like the red-eared slider (Trachemys scripta elegans) exhibit temperature-dependent sex determination (TSD) alongside genetic factors, where incubation temperatures during a critical embryonic period bias offspring toward male or female development, though some populations show underlying chromosomal influences. Among invertebrates, marine bivalves such as clams (family ) display , with individuals maintaining fixed male or female sexes throughout life and lacking , enabling broadcast spawning in aquatic environments. In the order , produces dioecy-like separation, as observed in honeybees (Apis mellifera), where unfertilized eggs develop into haploid males (drones) and fertilized eggs into diploid females (queens and workers). , representing elasmobranch fishes, exhibit strict dioecy with , where males use claspers to transfer sperm directly to females, enhancing reproductive efficiency in mobile oceanic species like the great white shark ( carcharias). In contrast, clownfish (Amphiprioninae) employ , starting as males and changing to female if the dominant female dies, highlighting an adaptive alternative to fixed dioecy in anemone-dwelling reef habitats. Ecological contexts further illustrate dioecy's role in animal diversity, particularly in challenging environments. Deep-sea fishes, such as dragonfishes (family ), maintain despite sparse populations, where low densities and vast distances complicate mate location, often relying on bioluminescent cues or opportunistic encounters to ensure . These examples underscore how dioecy supports specialized behaviors and adaptations across animal taxa, from terrestrial vertebrates to abyssal .

Dioecy in Plants

Characteristics and Distribution

In dioecious , reproductive structures are unisexual, with male individuals bearing staminate flowers that produce via stamens and female individuals bearing pistillate flowers that contain ovules within carpels, ensuring separate sexes on distinct plants. This separation often accompanies morphological dimorphisms, including differences in plant size, leaf shape, or floral traits, such as larger, more colorful bracts on female plants in some species to enhance . For instance, in the family, male plants tend to be taller with more slender leaves compared to more robust female counterparts. Dioecy occurs in approximately 6% of angiosperm , affecting around 15,600 across diverse lineages, with higher prevalence in families like where nearly all are dioecious. In gymnosperms, dioecy is more common, present in about 65% of , particularly in non-conifer groups such as cycads and gnetophytes, while show a mixture, with approximately half of being dioecious, though large families like are predominantly monoecious. Phylogenetically, dioecy is unevenly distributed, being more frequent in wind-pollinated lineages and island floras, such as Hawaiian Schiedea adapted to dry habitats. It spans ecological zones from tropical rainforests, where animal pollination predominates, to temperate regions with wind dispersal. Pollination in dioecious typically involves or vectors, with male producing abundant lightweight for dispersal, while females invest in fewer but larger flowers to capture it efficiently. Females subsequently develop fruits for , often via animals or gravity, contrasting with males that lack this function. Sex ratios in dioecious populations are frequently near 1:1, as predicted by evolutionary stability models, but environmental factors like proximity to male can skew them toward female bias by influencing competition during fertilization.

Evolutionary Development

Dioecy in has evolved independently numerous times within the angiosperms, with phylogenetic analyses indicating over a thousand origins since the group's emergence around 140 million years ago during the . Fossil evidence for unisexual flowers in early angiosperms is limited, but estimates and comparative suggest that dioecy arose in lineages shortly after the diversification of flowering plants, potentially as early as 100-120 million years ago in basal clades. Higher frequencies of dioecy are observed in phylogenetic lineages characterized by small, numerous flowers in compact inflorescences, which may facilitate the evolutionary lability of sex expression from ancestral hermaphroditism. In early angiosperms, sex expression was likely labile, allowing transitions from hermaphroditic ancestors through intermediate states such as —where females coexist with hermaphrodites—or , featuring males alongside hermaphrodites. The gynodioecious pathway is considered more common in plants, often initiated by the spread of female individuals that allocate resources away from costly male function, eventually leading to the loss of female function in hermaphrodites and the establishment of separate sexes. , though rarer, has been documented as a transient stage in some lineages, such as certain species, before full dioecy. These pathways reflect adaptive shifts in , with dioecy stabilizing once males and females reach equilibrium frequencies around 50% in populations. Key mechanisms underlying these transitions include cytoplasmic male sterility (CMS), where maternally inherited mitochondrial genes disrupt pollen production, promoting the initial invasion of females into hermaphroditic populations and facilitating gynodioecy. Nuclear restorer genes can evolve to counteract CMS, but incomplete restoration often leads to stable dimorphism and eventual dioecy. In some species, genetic control shifts to sex chromosomes; for example, in Silene latifolia, an XY system has evolved rapidly from a pair of autosomes approximately 10-11 million years ago, with the Y chromosome accumulating suppressors of recombination and degenerative mutations that reinforce male heterogamety. This system exemplifies how chromosomal differentiation can lock in sexual dimorphism after initial genetic conflicts. Ecological factors promoting the of dioecy in include differential herbivory pressures, particularly on , which favor female specialization by selecting for individuals that invest heavily in and protection over production. In lineages exposed to high , females gain a fitness advantage through enhanced maternal , driving the separation of sexes. Additionally, efficiency plays a role, as dioecy is more prevalent in wind-pollinated or generalist-insect-pollinated lineages where specialized floral traits reduce selfing and enhance , though animal can impose selection for unisexuality in certain habitats.

Dioecy in Fungi

Characteristics and Mating Types

In fungi, dioecy manifests as a mating system characterized by distinct compatibility types that segregate sexual functions across individuals, analogous to separate sexes in higher organisms. Unlike the gamete-based dioecy in animals and plants, fungal dioecy relies on heterothallism, where sexual reproduction requires fusion between hyphae of compatible mating types, typically denoted as + and – or controlled by mating type (MAT) loci. Fungi lack true motile gametes; instead, compatible mating initiates plasmogamy (cytoplasmic fusion without nuclear fusion), leading to spore production via meiosis. This system contrasts with homothallism, where a single individual can self-mate due to the presence of both mating types within the same mycelium, often through genetic mechanisms like mating-type switching or pseudohomothallism. Mating type loci in fungi encode regulatory genes, pheromones, and receptors that determine compatibility, with systems ranging from simple biallelic (two types) to highly multiallelic configurations. In the , many species exhibit a tetrapolar (bifactorial) system with two unlinked MAT loci (often A for homeodomain proteins and B for pheromone-receptor interactions), enabling extensive compatibility to promote . For instance, the Schizophyllum commune possesses over 23,000 distinct due to multiple alleles at these loci (81 specificities at the B locus from nine α and nine β subloci, and 288 combinations of 9 α and 32 β at the A locus). Post-, a forms, in which unfused nuclei from each parent coexist in shared hyphae, maintaining until () occurs during formation. Heterothallism is widespread in the , encompassing groups like rusts, smuts, and mushrooms, where it enforces and is the dominant mode, whereas it is less prevalent in the , which more frequently exhibit or unifactorial (bipolar) systems with a single locus. Overall, heterothallic comprise a significant portion of fungi, reflecting an evolutionary balance between and reproductive assurance. In the reproductive cycle of heterothallic , the dikaryotic hyphae develop clamp connections—specialized septal structures that ensure synchronous nuclear division and migration, preserving the binucleate state. Fruiting bodies then produce and disperse meiotic spores (basidiospores) from basidia, mimicking the spatial separation of and ovules in dioecious by relying on or vectors for cross-fertilization.

Examples in Fungal Species

In basidiomycete fungi, dioecy manifests through distinct that enforce , as exemplified by species in the genus , commonly known as ink caps. Coprinus disseminatus exhibits a bipolar mating system, where compatibility is governed by a single locus with multiple alleles, ensuring that only individuals with different alleles can fuse and form a for fruiting body development. Similarly, the pathogen maydis demonstrates a tetrapolar system with two unlinked loci, a and b, each containing multiple alleles; successful mating requires differing alleles at both loci to enable cell fusion, dikaryon formation, and subsequent infection of maize hosts. Among ascomycetes, serves as a model for dioecious-like mating via two non-homologous idiomorphs, mat A and mat a, which act as without morphological sex differentiation. These idiomorphs encode transcription factors that regulate sexual development, permitting only opposite-type fusions to produce perithecia and ascospores, thus promoting . In lichen-forming ascomycetes, true dioecy is rare, but similar to those in free-living relatives occur, as seen in species like where distinct alleles control compatibility in the fungal partner, influencing symbiotic formation with algal photobionts. Pathogenic basidiomycetes, such as rust fungi in the genus , illustrate dioecy through that drive life cycle alternation between hosts. In graminis, pycnia on the barberry host produce pycniospores of two or more ; compatible types fuse to form aeciospores that infect grasses, completing the heteroecious cycle and enabling epidemics. Ecological implications of fungal dioecy extend to symbiotic interactions, particularly in mycorrhizal associations. The black , an ectomycorrhizal ascomycete, features two whose spatial segregation in soils limits compatible pairings, affecting colonization of host roots and productivity; this separation influences nutrient exchange and plant growth in Mediterranean ecosystems.

Evolutionary Mechanisms

Genetic and Chromosomal Basis

Dioecy, the condition of separate sexes in organisms, is often underpinned by specialized that determine male and female development. In many animals, including mammals, the XY/XX system prevails, where males are heterogametic (XY) and females homogametic (XX), with the carrying male-determining factors. This system is also observed in certain dioecious , such as (Carica papaya), where the nascent XY chromosomes control sex, with females as XX and males as XY. In contrast, birds and some insects like employ the ZW/ZZ system, where females are heterogametic (ZW) and males homogametic (ZZ), with the Z chromosome dosage influencing sex differentiation. Dosage compensation mechanisms have evolved to balance between sexes and chromosomes; in animals with XY systems, this often involves upregulation of the single X in males, while in like , adjusts expression from the sex chromosomes to prevent imbalances. Key genes play pivotal roles in sex determination across kingdoms. In animals, the DMRT1 gene, located on the sex chromosomes in some species, is essential for testis development and male gonad differentiation, acting as a conserved regulator from fish to mammals. In plants, cytoplasmic male sterility (CMS) arises from mitochondrial genes that disrupt pollen production, contributing to the genetic basis of dioecy by creating male-sterile individuals that can evolve into female plants when nuclear restorer genes are absent. In fungi, mating-type (MAT) loci function analogously to sex chromosomes, encoding transcriptional regulators that dictate compatibility and sexual identity, with bipolar or tetrapolar systems suppressing recombination to maintain distinct mating types. Environmental factors can modulate genetic sex determination, particularly through temperature-sensitive genes in reptiles, where specific alleles interact with incubation temperature to influence fate, blending with environmental cues in dioecious . In plants, epigenetic regulation, including and modifications, fine-tunes sex determination by silencing or activating key genes, allowing reversible shifts in sexual expression under stress or developmental cues. The evolution of sex chromosomes frequently involves recombination suppression, where reduced crossing-over between the proto-X and proto-Y (or Z and W) leads to genetic differentiation and accumulation of sex-specific genes. This process creates evolutionary strata, with older regions showing greater divergence due to prolonged lack of recombination, as seen in both and systems. Such suppression is crucial for linking sex-determining loci with sexually antagonistic alleles, driving the progression toward fully differentiated sex chromosomes. Recent genomic studies have further illuminated these mechanisms; for example, dioecy in the genus originated approximately 2.8–3.8 million years ago through young XY sex chromosomes, while research in plants has identified regulatory genes like LcTGA10 involved in following whole-genome duplications.

Pathways to Dioecy

Dioecy frequently evolves from hermaphroditism through an intermediate gynodioecious stage, where s conferring sterility produce individuals alongside hermaphrodites. In this pathway, a recessive male-sterility first spreads if it provides a transmission advantage through increased fertility, provided selfing rates are low enough to favor . Subsequent invasion by a female-sterility in the hermaphrodites then establishes separate sexes, as modeled in systems like the plant genus . This stepwise process has been documented as a common route in angiosperms, where over 6% of species exhibit dioecy derived from such transitions. An alternative pathway originates from monoecy, where individuals bear both male and female reproductive organs in separate structures. Here, selection for sexual specialization—such as reduced overlap in organ production—can lead to the fixation of modifiers that eliminate one sex function at the individual level, resulting in dioecious populations. This route is prevalent in families like Cucurbitaceae, where monoecious ancestors gave rise to dioecious species through gradual shifts in sex allocation. Examples include the transition in figs (Ficus spp.), where spatial separation of unisexual flowers on the same plant evolves into distinct male and female individuals in related lineages. Across kingdoms, dioecy shows convergent evolutionary patterns from hermaphroditic or isogamous ancestors. In animals, transitions often occur in lineages like fishes and mollusks, where hermaphroditic progenitors lose self-fertilization capabilities under selection for , leading to (dioecy). Fungi exhibit analogous shifts from homothallic (self-fertile) to heterothallic () mating types, resembling dioecy, through the expansion of non-recombining regions around mating loci from isogamous origins. Plants parallel these patterns during the angiosperm radiation, with dioecy emerging repeatedly from cosexual ancestors via similar genetic mechanisms. Theoretical models, particularly those developed by Charlesworth and colleagues, elucidate these pathways under Fisherian sex ratio selection, predicting a stable 1:1 sex ratio in dioecious populations. These models demonstrate that invades hermaphroditic populations when female fertility exceeds twice that of hermaphrodites, compensating for the loss of male function, while monoecy-to-dioecy transitions depend on and trade-offs. Such frameworks highlight the role of genetic modifiers in driving the evolution toward separate sexes across diverse taxa.

Ecological and Adaptive Aspects

Advantages of Dioecy

Dioecy promotes by enforcing obligate between individuals of opposite sexes, thereby reducing homozygosity and the expression of deleterious recessive alleles in offspring. This mechanism enhances within populations, which confers adaptive advantages in heterogeneous or fluctuating environments by increasing the potential for to act on beneficial variants. In , studies of species like those in the genus demonstrate that dioecious lineages maintain higher nucleotide diversity compared to cosexual relatives, supporting more efficient purifying selection against harmful mutations and positive selection for adaptive traits. Similarly, in fungi with multiple analogous to dioecy, this system maximizes compatibility and opportunities, minimizing self-fertilization and boosting essential for resilience against pathogens and environmental stresses. Resource allocation in dioecious organisms allows for sex-specific specialization, where males focus resources on production and dispersal—such as in or in fungi—while females invest in or development and provisioning. This division optimizes reproductive efficiency; for instance, male often exhibit traits like greater height or lighter foliage to facilitate wind or insect-mediated dispersal, outperforming hermaphrodites that must balance both functions. In dioecious fungi, distinct enable specialized hyphal interactions during mating, streamlining and processes without the costs of dual reproductive structures. Such adaptations reduce trade-offs in use, leading to higher overall fitness in sex-specific roles, as evidenced by differential growth responses to in species like Salix where males prioritize for over carbon for . Sexual selection in dioecious systems fosters dimorphism that enhances mate competition and attraction, particularly in males, driving evolutionary innovations in reproductive traits. In plants, this manifests as brighter or more elaborate male flowers to attract pollinators, increasing male reproductive success through pollen export, as seen in species like Silene latifolia where male inflorescences are larger and more conspicuous than female ones. Fungal mating types similarly support selection for compatibility loci that improve fusion efficiency, indirectly promoting diversity in spore dispersal mechanisms. These dimorphisms not only boost individual fitness but also contribute to population-level stability via frequency-dependent selection, which maintains balanced sex ratios near 1:1, ensuring reproductive assurance across generations. At the level, dioecy correlates with elevated rates in certain contexts, such as young successional tropical forests where dioecious are overrepresented during early phases. The impact on diversification and rates is debated: some phylogenetic analyses suggest higher rates in dioecious clades due to increased facilitating , while others find lower or no consistent effect compared to nondioecious relatives. In fungi, multiple enhance propagule compatibility in sparse populations, aiding range expansion in disturbed ecosystems like microbiomes. This advantage supports long-term persistence, with frequency-dependent dynamics stabilizing sex ratios and preventing fixation of suboptimal alleles.

Disadvantages and Trade-offs

Dioecious organisms encounter significant challenges in mate location due to the spatial separation of individuals, which elevates search costs for or gametes and often results in or limitation, especially in low-density populations. In , this separation means females rely entirely on external vectors to receive from distant males, leading to reduced and set when male individuals are scarce or unevenly distributed. For instance, studies on the dioecious Ficus hispida demonstrate that female declines markedly with decreasing male density, as efficiency drops in sparse settings. Biased sex ratios further compound these issues; while male-biased ratios predominate in many natural populations and under stress, female-biased ratios can occur in specific cases (e.g., certain species under warming), intensifying mate-finding difficulties and heighten risks by limiting production. Seed dispersal in dioecious presents another key , as only females bear , resulting in narrower seed shadows and increased offspring clumping compared to cosexual systems where all individuals contribute to dispersal. This demographic constraint—halving the number of seed producers—amplifies local resource competition among seedlings and reduces colonization potential, particularly for with heavy, immobile that depend on limited vectors. In fragmented or sparse habitats, such limitations make populations vulnerable to if one sex becomes rare, as isolated females cannot sustain without nearby males for . Empirical models of dioecious populations, such as those in tropical forests, show that even with compensatory higher seed output per female, overall dispersal efficiency suffers, leading to heightened sensitivity to habitat loss. From an evolutionary perspective, dioecy exhibits instability, with elevated reversion rates to hermaphroditism in self-compatible lineages or small populations where the costs of separation—such as chronic mate scarcity—outweigh benefits. in the Caenorhabditis reveals that dioecy can dissolve rapidly under intense mate limitation and competition, favoring hermaphroditic mutants that ensure reproductive assurance. In , similar dynamics occur, as leaky sex expression in dioecious species often precedes full reversion, particularly in isolated or declining populations. These reversals underscore the fragility of dioecy in fluctuating environments. Empirical evidence highlights broader trade-offs, including mixed findings on speciation rates in dioecious clades relative to hermaphroditic sisters, with some analyses indicating reduced suggesting an evolutionary "dead end" in many lineages, though more recent studies show no consistent pattern. In resource-poor environments, such as arid or fragmented habitats, these disadvantages intensify, as sex-specific resource demands and spatial segregation exacerbate biases and limit adaptive potential under stress like . For example, modeling of dioecious responses to warming predicts amplified risks due to skewed ratios and impaired in nutrient-limited settings.

References

  1. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dioecy
  2. https://pmc.ncbi.nlm.nih.gov/articles/PMC3278288/
  3. https://pmc.ncbi.nlm.nih.gov/articles/PMC4204665/
  4. https://pubmed.ncbi.nlm.nih.gov/28311318/
  5. https://pmc.ncbi.nlm.nih.gov/articles/PMC5551102/
  6. https://www.pnas.org/doi/10.1073/pnas.1203495109
  7. https://www.dictionary.com/browse/dioecious
  8. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.13696
  9. https://pubmed.ncbi.nlm.nih.gov/19683010/
  10. https://www.annualreviews.org/doi/pdf/10.1146/annurev.es.11.110180.000311
  11. https://pmc.ncbi.nlm.nih.gov/articles/PMC2729626/
  12. https://bsapubs.onlinelibrary.wiley.com/doi/10.3732/ajb.1400196
  13. https://academic.oup.com/book/41106/chapter/350407725
  14. https://pmc.ncbi.nlm.nih.gov/articles/PMC8617835/
  15. https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001899
  16. https://bmcecolevol.biomedcentral.com/articles/10.1186/s12862-017-1071-3
  17. https://link.springer.com/article/10.1007/s10228-020-00754-6
  18. https://www.nature.com/articles/s41598-021-90691-9
  19. https://wires.onlinelibrary.wiley.com/doi/full/10.1002/wsbm.1636
  20. https://pmc.ncbi.nlm.nih.gov/articles/PMC8391622/
  21. https://www.ncbi.nlm.nih.gov/books/NBK9967/
  22. https://pubmed.ncbi.nlm.nih.gov/21281451/
  23. https://pubmed.ncbi.nlm.nih.gov/24316144/
  24. https://www.researchgate.net/publication/289866390_Reproductive_Biology_of_Elasmobranchs
  25. https://www.nature.com/articles/srep35461
  26. https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2020.00101/full
  27. https://www.journals.uchicago.edu/doi/10.1086/729063
  28. https://pmc.ncbi.nlm.nih.gov/articles/PMC9572608/
  29. https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/j.1537-2197.1995.tb11504.x
  30. https://www.sciencedirect.com/science/article/abs/pii/S1439179117304498
  31. https://www.zoology.ubc.ca/~otto/Reprints/Vamosi2003.pdf
  32. https://bsapubs.onlinelibrary.wiley.com/doi/10.2307/2446396
  33. https://www.publish.csiro.au/bt/fulltext/BT21112
  34. https://nsojournals.onlinelibrary.wiley.com/doi/10.1111/oik.08651
  35. https://pmc.ncbi.nlm.nih.gov/articles/PMC2504832/
  36. https://pubmed.ncbi.nlm.nih.gov/14635916/
  37. https://www.cell.com/current-biology/pdf/S0960-9822%2809%2900620-4.pdf
  38. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1420-9101.2009.01813.x
  39. https://www.nature.com/articles/s41437-024-00729-7
  40. https://pmc.ncbi.nlm.nih.gov/articles/PMC3639211/
  41. https://pmc.ncbi.nlm.nih.gov/articles/PMC1450409/
  42. https://www.annualreviews.org/doi/10.1146/annurev-ecolsys-112414-054215
  43. https://scholarship.miami.edu/view/pdfCoverPage?instCode=01UOML_INST&filePid=13355529960002976&download=true
  44. https://www.nature.com/articles/hdy201367
  45. https://www.embopress.org/doi/10.1002/j.1460-2075.1995.tb00211.x
  46. https://pmc.ncbi.nlm.nih.gov/articles/PMC98906/
  47. https://journals.uchicago.edu/doi/pdfplus/10.1086/282031
  48. https://pmc.ncbi.nlm.nih.gov/articles/PMC5467461/
  49. https://pmc.ncbi.nlm.nih.gov/articles/PMC1456265/
  50. https://pubmed.ncbi.nlm.nih.gov/2227416/
  51. https://pubmed.ncbi.nlm.nih.gov/9819054/
  52. https://academic.oup.com/gbe/article/16/5/evae094/7659907
  53. https://www.ars.usda.gov/ARSUserFiles/50620500/Publications/JAK/rust_fungi.pdf
  54. https://www.researchgate.net/publication/259566343_Impact_of_the_competition_between_mating_types_on_the_cultivation_of_Tuber_melanosporum_Romeo_and_Juliet_and_the_matter_of_space_and_time
  55. https://pmc.ncbi.nlm.nih.gov/articles/PMC4381524/
  56. https://pubmed.ncbi.nlm.nih.gov/17675857/
  57. https://www.nature.com/scitable/topicpage/genetic-mechanisms-of-sex-determination-314/
  58. https://pmc.ncbi.nlm.nih.gov/articles/PMC8935305/
  59. https://academic.oup.com/gbe/article-abstract/9/9/2461/4092962
  60. https://elifesciences.org/articles/89284
  61. https://www.tandfonline.com/doi/full/10.1080/07352689.2017.1327762
  62. https://pmc.ncbi.nlm.nih.gov/articles/PMC12327351/
  63. https://pmc.ncbi.nlm.nih.gov/articles/PMC5489005/
  64. https://pmc.ncbi.nlm.nih.gov/articles/PMC8273503/
  65. https://pmc.ncbi.nlm.nih.gov/articles/PMC3670740/
  66. https://pmc.ncbi.nlm.nih.gov/articles/PMC7947811/
  67. https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.16276
  68. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12072860/
  69. https://www.journals.uchicago.edu/doi/abs/10.1086/283342
  70. https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2010.03609.x
  71. https://pmc.ncbi.nlm.nih.gov/articles/PMC2940314/
  72. https://link.springer.com/chapter/10.1007/978-3-662-03908-3_2
  73. https://www.annualreviews.org/doi/10.1146/annurev-arplant-042817-040615
  74. https://academic.oup.com/mbe/article/38/3/805/5905496
  75. https://pmc.ncbi.nlm.nih.gov/articles/PMC7947750/
  76. https://royalsocietypublishing.org/doi/10.1098/rstb.2015.0531
  77. https://onlinelibrary.wiley.com/doi/10.1111/jeb.12017
  78. https://pmc.ncbi.nlm.nih.gov/articles/PMC5681607/
  79. https://www.sciencedirect.com/science/article/pii/S0960982210017033
  80. https://bmcecolevol.biomedcentral.com/articles/10.1186/1471-2148-9-190
  81. https://royalsocietypublishing.org/doi/10.1098/rstb.2010.0002
  82. https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.12393
  83. https://onlinelibrary.wiley.com/doi/10.1111/jeb.12385
  84. https://bmcbiol.biomedcentral.com/articles/10.1186/1741-7007-9-56
  85. https://www.jstor.org/stable/25704652
  86. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0081140
  87. https://www.scienceopen.com/document_file/29a021d5-8ef7-4aaa-b6eb-ff542931170a/PubMedCentral/29a021d5-8ef7-4aaa-b6eb-ff542931170a.pdf
  88. https://www.pnas.org/doi/10.1073/pnas.2422162122
  89. https://www.sciencedirect.com/science/article/abs/pii/S0098847214002214
  90. https://academic.oup.com/evolut/article/55/5/880/6757785
  91. https://www.sciencedirect.com/science/article/pii/S0960982220318807
  92. https://onlinelibrary.wiley.com/doi/10.1111/ele.13207
  93. https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.1277
  94. https://www.journals.uchicago.edu/doi/abs/10.1086/303389
  95. https://www.researchgate.net/publication/267287047_Climate_change_perils_for_dioecious_plant_species
  96. https://bg.copernicus.org/articles/21/2133/2024/
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