Androdioecy is a reproductive system characterized by the coexistence of males and hermaphrodites. Androdioecy is rare in comparison with the other major reproductive systems: dioecy, gynodioecy and hermaphroditism. [1] In animals, androdioecy has been considered a stepping stone in the transition from dioecy to hermaphroditism, and vice versa. [2]
Androdioecy is sometimes referred to as a mixed breeding system with trioecy and gynodioecy. [3] It is a dimorphic sexual system in plants comparable with gynodioecy and dioecy. [4]
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. [5] [6] Particularly, males and hermaphrodites have to have the same fitness, in other words 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. [7] [8]
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.[ citation needed ]
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. Hermaphrodites may be beneficial in colonizing new habitats, because a single hermaphrodite can generate many other individuals. [9]
In the well-studied roundworm Caenorhabditis elegans , males are very rare and only occur in populations that are in bad condition or stressed. [10] In Caenorhabditis elegans androdioecy is thought to have evolved from dioecy, through a trioecous intermediate. [11]
In barnacles, androdioecy evolved from hermaphroditism. [3] Many plants self-fertilize, and males may be sustained in a population when inbreeding depression is severe because males guarantee outcrossing.[ citation needed ]
The most common form of androdioecy in animals involves hermaphrodites that can reproduce by autogamy or allogamy through ovum with males. However, this type does not involve outcrossing with sperm. This type of androdioecy generally occurs in predominantly gonochoric taxonomy groups. [12] : 21
One type of androdioecy contains outcrossing hermaphrodites which is present in some angiosperms. [12] : 21
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. [12] : 21
Despite their unlikely evolution, 115 androdioecious animal and about 50 androdioecious plant species are known. [2] [13] These species include
Rhabditidae (Order Rhabditida)
Diplogastridae (Order Rhabditida)
Steinernematidae (Order Rhabditida)
Allanotnematidae (Order Rhabditida)
In biology, gonochorism is a sexual system where there are only two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric.
Dioecy is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly or indirectly. 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.
Caenorhabditis is a genus of nematodes which live in bacteria-rich environments like compost piles, decaying dead animals and rotting fruit. The name comes from Greek: caeno- ; rhabditis = rod-like. In 1900, Maupas initially named the species Rhabditis elegans, Osche placed it in the subgenus Caenorhabditis in 1952, and in 1955, Dougherty raised Caenorhabditis to the status of genus.
A hermaphrodite is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are of different sexes, either male or female but not both, are gonochoric, which is the opposite of hermaphroditic.
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 and dioecy.
Eulimnadia texana, the Texas clam shrimp or desert shrimp, is a species belonging to the Limnadiidae family.
Diplogastridae, formerly Diplogasteridae, are a family of nematodes (roundworms) known from a wide range of habitats, often in commensal or parasitic associations with insects.
Pristionchus is a genus of nematodes (roundworms) in the family Diplogastridae that currently includes more than 50 described species. They are known mainly as non-parasitic associates of insects, especially beetles, while others have been reported from soil, organic matter, or rotting wood. The genus includes P. pacificus, a satellite model organism to the well-studied nematode Caenorhabditis elegans.
Pristionchus maxplancki is a species of diplogastrid nematodes (roundworms).
Sudhausia is a genus of nematodes (roundworms) of the family Diplogastridae. They live in association with dung beetles and are primarily known from Africa. Species of Sudhausia show a suite of biological features that, together, are unusual for nematodes and animals in general: hermaphrodites, which are females in form, mature to produce offspring before they are adults and thus even capable of mating, and their eggs grow in size during development. Hermaphrodites are also always live-bearing, which is unusual for nematodes under non-stressful conditions. The genus is named in honor of Walter Sudhaus, a German nematologist.
Levipalatum texanum is a free-living nematode (roundworm) in the family Diplogastridae. The species is androdioecious, consisting of self-fertile hermaphrodites which are morphologically females, and males. It is known from the south-eastern United States and has been found to live in association with scarab beetles, although it has also been baited from soil. Nematodes of this species can be cultured on bacterium Escherichia coli in the laboratory, and they are presumed to also feed on microorganisms in the wild. Levipalatum is a monotypic genus.
Caenorhabditis tropicalis is a species of Caenorhabditis nematodes, belonging to the Elegans super-group and Elegans group within the genus. It is a close relative of C. wallacei.C. tropicalis is collected frequently in tropical South America, Caribbean islands, and various islands in the Indian and Pacific Oceans from rotting fruit, flowers and stems. C. tropicalis was referred to as “C. sp. 11” prior to 2014.
Oscheius is a genus of nematode.
Myolaimidae is a family of nematodes in the order Rhabditida. It consists of two genera, Myolaimus and Deleyia.
Allodiplogaster sudhausi is a free-living nematode species in the Diplogastridae family. It was described in 2008 as Koerneria sudhausi, before being moved to the genus Allodiplogaster in 2014. A. sudhausi is omnivorous. It predates on other nematodes, but can be cultured on Escherichia coli OP50 bacterium on agar.
A sexual system is a pattern of sex allocation or a distribution of male and female function across organisms in a species. Terms like reproductive system and mating system have also been used as synonyms.
Steinernema hermaphroditum is a species of nematodes in the Steinernematidae family.
Salvatoria clavata is a species of Annelida in the family Syllidae.The species is similar to Brania pusilla but is a bit longer measuring in about 2mm to 3mm, individuals in this species can even grow to 10 mm. They have parental care. It has an acrosome shaped like a beaker.
Rhabdias ranae is a species of nematode. The species has been described as androdioecious.