Androdioecy is a

reproductive system The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are al ...

characterized by the coexistence of

males Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilisation. A male organism cannot reproduce sexually without access to ...

and

hermaphrodites A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

. Androdioecy is rare in comparison with the other major reproductive systems:

dioecy Dioecy ( ; ; adj. dioecious, ) 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 ...

gynodioecy Gynodioecy is a rare breeding system that is found in certain flowering plant species in which female and hermaphroditic plants coexist within a population. Gynodioecy is the evolutionary intermediate between hermaphroditism (exhibiting both f ...

and

hermaphroditism A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

. In animals, androdioecy has been considered a stepping stone in the transition from dioecy to hermaphroditism, and vice versa. Androdioecy,

trioecy Trioecy , also spelled triecy, is a sexual system characterized by the coexistence of males, females, and hermaphrodites. It has been found in both plants and animals. Like androdioecy and gynodioecy, trioecy is a mixed mating systems. Term ...

and

are sometimes referred to as a mixed mating systems. Androdioecy is a dimorphic sexual system in plants comparable with

and

Evolution of androdioecy

The fitness requirements for androdioecy to arise and sustain itself are theoretically so improbable that it was long considered that such systems do not exist. Particularly, males and hermaphrodites have to have the same fitness, in other words produce the same number of offspring, in order to be maintained. However, males only have offspring by fertilizing eggs or ovules of hermaphrodites, while hermaphrodites have offspring both through fertilizing eggs or ovules of other hermaphrodites and their own ovules. This means that all else being equal, males have to fertilize twice as many eggs or ovules as hermaphrodites to make up for the lack of female reproduction. Androdioecy can evolve either from hermaphroditic ancestors through the invasion of males or from dioecious ancestors through the invasion of hermaphrodites. The ancestral state is important because conditions under which androdioecy can evolve differ significantly.

Androdioecy with dioecious ancestry

In roundworms, clam shrimp, tadpole shrimp and cancrid shrimps, androdioecy has evolved from dioecy. In these systems, hermaphrodites can only fertilize their own eggs (self-fertilize) and do not mate with other hermaphrodites. Males are the only means of

outcrossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing in animals Out ...

. Hermaphrodites may be beneficial in colonizing new habitats, because a single hermaphrodite can generate many other individuals. In the well-studied

roundworm The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (hel ...

Caenorhabditis elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a Hybrid word, blend of the Greek ''caeno-'' (recent), ''r ...

'', males are very rare and only occur in populations that are in bad condition or stressed. In ''Caenorhabditis elegans'' androdioecy is thought to have evolved from dioecy, through a trioecous intermediate.

Androdioecy with hermaphroditic ancestry

In barnacles, androdioecy evolved from hermaphroditism. Many plants self-fertilize, and males may be sustained in a population when

inbreeding depression Inbreeding depression is the reduced biological fitness caused by loss of genetic diversity as a consequence of inbreeding, the breeding of individuals closely related genetically. This loss of genetic diversity results from small population siz ...

is severe because males guarantee outcrossing.

Types of androdioecy

The most common form of androdioecy in animals involves hermaphrodites that can reproduce by

autogamy Autogamy or self-fertilization refers to the Cell fusion, fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a Reproduction, reproductive mechanism employed by many flowering pl ...

allogamy Allogamy or cross-fertilization is the fertilization of an ovum from one individual with the spermatozoa of another. By contrast, autogamy is the term used for self-fertilization. In humans, the fertilization event is an instance of allogamy. Self-f ...

through ovum with males. However, this type does not involve outcrossing with sperm. This type of androdioecy generally occurs in predominantly gonochoric taxonomy groups. One type of androdioecy contains outcrossing hermaphrodites which is present in some

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit. T ...

. Another type of androdioecy has males and simultaneous hermaphrodites in a population due to developmental or conditional sex allocation. Like in some fish species small individuals are hermaphrodites and under circumstances of high density, large individuals become male.

Androdioecious species

Despite their unlikely evolution, 115 androdioecious animal and about 50 androdioecious plant species are known. These species include

Anthozoa Anthozoa is one of the three subphyla of Cnidaria, along with Medusozoa and Endocnidozoa. It includes Sessility (motility), sessile marine invertebrates and invertebrates of brackish water, such as sea anemones, Scleractinia, stony corals, soft c ...
(Corals)

*'' Goniastra australensis'' *'' Stylophora pistillata''

Nematoda The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitism, parasitic. Parasitic ...
(Roundworms)

Rhabditidae The Rhabditidae are a family of nematodes which includes the model organism A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in t ...

(Order

Rhabditida Rhabditida is an order of free-living, parasitic and microbivorous nematodes living in soil. The Cephalobidae, Panagrolaimidae, Steinernematidae, and Strongyloididae seem to be closer to the Tylenchia, regardless of whether these are merg ...

) *'' Caenorhabditis briggsae'' *''

'' *'' Caenorhabditis sp. 11'' *'' Oscheius myriophila'' *'' Oscheius dolchura'' *'' Oscheius tipulae'' *'' Oscheius guentheri'' *'' Rhabditis rainai'' *'' Rhabditis sp. (AF5)'' *'' Rhabdias nigrovenosum'' *'' Rhabdias rubrovenosa'' *'' Rhabdias ranae'' *'' Entomelas entomelas'' Diplogastridae (Order Rhabditida) *'' Allodiplogaster sudhausi'' *'' Diplogasteroides magnus'' *'' Levipalatum texanum'' *'' Pristionchus boliviae'' *'' Pristionchus fissidentatus'' *'' Pristionchus maupasi'' *'' Pristionchus mayeri'' *'' Pristionchus pacificus'' *'' Pristionchus triformis'' *'' Sudhausia aristotokia'' *'' Sudhausia crassa'' Steinernematidae (Order Rhabditida) *'' Steinernema hermaphroditum'' Allanotnematidae (Order Rhabditida) *'' Allantonema mirabile'' *'' Bradynema rigidum''

Dorylaimida Dorylaimida (dorylaims) is a diverse order of nematodes with both soil and freshwater species. Taxonomy History The order originated with the description of '' Dorylaimus stagnalis'' by Dujardin in 1845, and in 1876 De MAn proposed the fam ...

*'' Dorylaimus liratus''

Nemertea Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of about 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. ...
(Ribbon worms)

*'' Prostoma eilhardi''

Arthropoda Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an exoskeleton with a cuticle made of chitin, often mineralised with calcium carbonate, a body with differentiated ( metameric) segments, and paired jointed appendages. ...

Clam shrimp Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classif ...

*''

Eulimnadia texana ''Eulimnadia texana'', the Texas clam shrimp or desert shrimp, is a species belonging to the Limnadiidae family. It is endemic to North America. It is an arid land specialist, living for many years as a cyst and bursting into life at the arriva ...

'' *'' Eulimnadia africana'' *'' Eulimnadia agassizii'' *'' Eulimnadia antlei'' *'' Eulimnadia braueriana'' *'' Eulimnadia brasiliensis'' *'' Eulimnadia colombiensis'' *'' Eulimnadia cylondrova'' *'' Eulimnadia dahli'' *''

Eulimnadia diversa ''Eulimnadia'' is a genus of branchiopods in the family Limnadiidae. There are about 13 described species in ''Eulimnadia''. Species * '' Eulimnadia agassizii'' Packard, 1874 * '' Eulimnadia antillarum'' (Baird, 1852) * '' Eulimnadia antlei'' M ...

'' *'' Eulimnadia feriensis'' *'' Eulimnadia follisimilis'' *''

Eulimnadia thompsoni ''Eulimnadia'' is a genus of branchiopods in the family Limnadiidae. There are about 13 described species in ''Eulimnadia''. Species * '' Eulimnadia agassizii'' Packard, 1874 * '' Eulimnadia antillarum'' (Baird, 1852) * '' Eulimnadia antlei'' ...

'' *'' Eulimnadia sp. A'' *'' Eulimnadia sp. B'' *'' Eulimnadia sp. C'' Tadpole shrimp *'' Triops cancriformis'' *'' Triops newberryi'' *''

Triops longicaudatus ''Triops longicaudatus'' (commonly called American tadpole shrimp or longtail tadpole shrimp) is a freshwater crustacean of the order Notostraca, resembling a miniature horseshoe crab. It is characterized by an elongated, segmented body, a flatt ...

Barnacles Barnacles are arthropods of the subclass Cirripedia in the subphylum Crustacea. They are related to crabs and lobsters, with similar nauplius larvae. Barnacles are exclusively marine invertebrates; many species live in shallow and tidal water ...

*'' Paralepas klepalae'' *'' Paralepas xenophorae'' *'' Koleolepas avis'' *'' Koleolepas tinkeri'' *'' Ibla quadrivalvis'' *'' Ibla cumingii'' *'' Ibla idiotica'' *'' Ibla segmentata'' *'' Calantica studeri'' *'' Calantica siemensi'' *'' Calantica spinosa'' *'' Calantica villosa'' *'' Arcoscalpellum sp.'' *'' Euscalpellum squamuliferum'' *'' Scalpellum peronii'' *'' Scalpellum scalpellum'' *'' Scalpellum vulgare'' *'' Scillaelepas arnaudi'' *'' Scillaelepas bocquetae'' *'' Scillaelepas calyculacilla'' *'' Scillaelepas falcate'' *'' Scillaelepas fosteri'' *'' Smilium hastatum'' *'' Smilium peronii'' *'' Chelonibia patula'' *'' Chelonibia testudinaria'' *'' Bathylasma alearum'' *'' Bathylasma corolliforme'' *'' Conopea galeata'' *'' Conopea calceola'' *'' Conopea merrilli'' *'' Solidobalanus masignotus'' *'' Tetrapachylasma trigonum'' *'' Megalasma striatum'' *'' Octolasmis warwickii''

Lysmata ''Lysmata'' is a genus of shrimp in the infraorder Caridea, the caridean shrimp. The genus belongs to the family Lysmatidae. ''Lysmata'' are popular ornamental shrimp in the marine aquarium trade for their bright color patterns, interesting beha ...

*''

Lysmata wurdemanni ''Lysmata wurdemanni'' is a species of saltwater Caridea, shrimp in the family Lysmatidae, historically referred to as the Peppermint shrimp, peppermint shrimp in the marine aquarium trade. However, taxonomic revisions based on genetic and morph ...

'' *''

Lysmata amboinensis ''Lysmata amboinensis'' is an omnivore, omnivorous Caridea, shrimp species known by several common names including the Pacific cleaner shrimp. It is considered a cleaner shrimp as eating parasites and dead tissue from fish makes up a large part o ...

'' *'' Lysmata californica'' *'' Lysmata bahia'' *'' Lysmata intermedia'' *''

Lysmata grabhami ''Lysmata grabhami'' is a species of saltwater shrimp in the family Hippolytidae. It was first described by Gordon in 1935. It occurs in the tropical and subtropical Atlantic Ocean and is a cleaner shrimp, operating a cleaning station to which f ...

'' *'' Lysmata seticaudata'' *'' Lysmata nilita'' *'' Lysmata hochi'' *'' Lysmata nayaritensis'' *'' Lysmata rafa'' *'' Lysmata boggessi'' *'' Lysmata ankeri'' *''

Lysmata pederseni ''Lysmata pederseni'' is a species of saltwater shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – ty ...

'' *''

Lysmata debelius ''Lysmata debelius'' is a species of cleaner shrimp indigenous to the Indo-Pacific. It is popular in the aquarium trade, where it is known as the fire shrimp, blood shrimp or scarlet cleaner shrimp. Taxonomy ''Lysmata debelius'' was species desc ...

'' *'' Lysmata galapaguensis'' *'' Lysmata cf. trisetacea''

Insects Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...

*'' Icerya bimaculata'' *''

Icerya purchasi ''Icerya purchasi'' (common name: cottony cushion scale) is a scale insect that feeds on more than 80 families of woody plants, most notably on ''Citrus'' and ''Pittosporum''. Originally described in 1878 from specimens collected in New Zealand a ...

'' *'' Crypticerya zeteki''

Annelida The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to variou ...
(Ringed worms)

*'' Salvatoria clavata'' *'' Ophryotrocha gracilis'' *'' Ophryotrocha hartmanni'' *'' Ophryotrocha diadema'' *'' Ophryotrocha bacci'' *'' Ophryotrocha maculata'' *'' Ophryotrocha socialis''

Chordata A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (Apomorphy and synapomorphy, synapomorphies) th ...

*''

Kryptolebias marmoratus The mangrove rivulus or mangrove killifish, ''Kryptolebias marmoratus'' ( syn. ''Rivulus marmoratus''), is a species of killifish in the family Rivulidae. It lives in brackish and marine waters (less frequently in fresh water) along the coasts ...

'' *'' Serranus fasciatus'' *'' Serranus baldwini''

Angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit. T ...
(Flowering plants)

*Some '' Acer'' (maple) species *''

Castilla elastica ''Castilla elastica'', the Panama rubber tree, is a tree native to the tropical areas of Mexico, Central America, and northern South America. It was the principal source of latex among the Mesoamerican peoples in pre-Columbian times. The latex g ...

'' *'' Culcita macrocarpa'' *'' Datisca cannabina'' (false hemp) *'' Datisca glomerata'' (Durango root) *'' Fraxinus lanuginosa'' (Japanese ash) *''

Fraxinus ornus ''Fraxinus ornus'', the manna ash or South European flowering ash, is a species of ''Fraxinus'' native to Southern Europe and Southwestern Asia, from Spain and Italy north to Austria and the Czech Republic, and east through the Balkans, Turkey, a ...

'' *'' Fuchsia microphylla'' *''

Gagea serotina ''Gagea serotina'', synonym ''Lloydia serotina'', is an Arctic–alpine flowering plant of the lily family. It is widespread across the mountainous parts of western North America, from Alaska to New Mexico, and in Europe is found in the Alps, t ...

'' *'' Mercurialis annua'' (Annual mercury) *'' Neobuxbaumia mezcalaensis'' *'' Nephelium lappaceum'' (Rambutan) *'' Panax trifolius'' (

Ginseng Ginseng () is the root of plants in the genus ''Panax'', such as South China ginseng (''Panax notoginseng, P. notoginseng''), Korean ginseng (''Panax ginseng, P. ginseng''), and American ginseng (''American ginseng, P. quinquefol ...

) *'' Oxalis suksdorfii'' *'' Phillyrea angustifolia'' *'' Phillyrea latifolia'' *'' Ricinocarpos pinifolius'' *'' Sagittaria lancifolia'' (sub-androdioecy) *'' Saxifraga cernua'' *'' Schizopepon bryoniaefolius'' *'' Spinifex littoreus'' *''

Ulmus minor ''Ulmus minor'' Mill., the field elm, is by far the most polymorphic of the European species, although its taxonomy remains a matter of contention. Its natural range is predominantly south European, extending to Asia Minor and Iran; its norther ...

References

External links

* *{{cite journal , last1 = Pennisi , first1 = Elizabeth , author-link = Elizabeth Pennisi , s2cid = 84857451 , year = 2006, title = Sex and the Single Killifish , url = http://www3.uakron.edu/biology/science06.pdf , journal = Science , volume = 313 , issue = 5792, page = 2006 , doi = 10.1126/science.313.5792.1381 , pmid = 16959986 , access-date = 2008-01-25 , archive-url = https://web.archive.org/web/20081001223411/http://www3.uakron.edu/biology/science06.pdf , archive-date = 2008-10-01 , url-status = dead *Diana Wolf
'Breeding systems: Evolution of androdioecy'
Sex Mating systems Sexual system