A hermaphrodite () is a sexually reproducing organism that produces both male and female .
The individuals of many taxonomic groups of , primarily invertebrates, are hermaphrodites, capable of producing viable gametes of both . In the great majority of tunicata, , and , hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the female or male. Hermaphroditism is also found in some fish species, but is rare in other vertebrate groups. Most hermaphroditic species exhibit some degree of self-fertilization. The distribution of self-fertilization rates among animals is similar to that of plants, suggesting that similar pressures are operating to direct the evolution of selfing in animals and plants.
A rough estimate of the number of hermaphroditic animal species is 65,000, about 5% of all animal species, or 33% excluding insects. Insects are almost exclusively gonochoric.
About 94% of flowering plant species are either hermaphroditic (all flowers produce both male and female gametes) or Monoecy, where both male and female flowers occur on the same plant. There are also mixed breeding systems, in both plants and animals, where hermaphrodite individuals coexist with males (called androdioecy) or with females (called gynodioecy), or all three exist in the same species (called trioecy). Sometimes, both male and hermaphrodite flowers occur on the same plant (Andromonoecious) or both female and hermaphrodite flowers occur on the same plant (Gynomonoecious).
Hermaphrodism is not to be confused with ovotesticular syndrome in mammals, which is a separate and unrelated phenomenon. While people with the condition were previously called " true hermaphrodites" in medical literature, this usage is now considered to be outdated as of 2006 and misleading,
Etymology
The term hermaphrodite derives from the , from ,
which derives from
Hermaphroditus (Ἑρμαφρόδιτος), the son of
Hermes and
Aphrodite in
Greek mythology. According to
Ovid, he fused with the
nymph Salmacis resulting in one individual possessing physical traits of male and female sexes.
According to the earlier
Diodorus Siculus, he was born with a physical body combining male and female sexes.
The word
hermaphrodite entered the
English lexicon as early as the late fourteenth century.
Animals
Sequential hermaphrodites
Sequential hermaphrodites (
dichogamy) occur in
species in which the individual first develops as one sex, but can later change into the opposite sex.
(Definitions differ on whether sequential hermaphroditism encompasses serial hermaphroditism; for authors who exclude serial hermaphroditism, a sequential hermaphrodite is also stipulated to only change sex once.
) This contrasts with simultaneous hermaphrodites, in which an individual possesses fully functional male and female genitalia. Sequential hermaphroditism is common in fish (particularly
teleost fish) and many
gastropods (such as the common slipper shell). Sequential hermaphroditism can best be understood in terms of behavioral ecology and evolutionary life history theory, as described in the size-advantage mode
first proposed by Michael T. Ghiselin
which states that if an individual of a certain sex could significantly increase its reproductive success after reaching a certain size, it would be to their advantage to switch to that sex.
Sequential hermaphrodites can be divided into three broad categories:
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Protandry: Where an organism develops as a male, and then changes sex to a female.
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Example: The clownfish (genus Amphiprion) are colorful reef fish found living in symbiosis with . Generally one anemone contains a 'harem', consisting of a large female, a smaller reproductive male, and even smaller non-reproductive males. If the female is removed, the reproductive male will change sex and the largest of the non-reproductive males will mature and become reproductive. It has been shown that fishing pressure can change when the switch from male to female occurs, since fishermen usually prefer to catch the larger fish. The populations are generally changing sex at a smaller size, due to natural selection.
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Protogyny: Where the organism develops as a female, and then changes sex to a male.
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Example: (Family Labridae) are a group of reef fish in which protogyny is common. Wrasses also have an uncommon life history strategy, which is termed diandry (literally, two males). In these species, two male morphs exists: an initial phase male and a terminal phase male. Initial phase males do not look like males and spawn in groups with females. They are not territorial. They are, perhaps, female mimics (which is why they are found swimming in group with females). Terminal phase males are territorial and have a distinctively bright coloration.
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Bidirectional sex changers: Where an organism has female and male reproductive organs, but may act either as a female or as a male during different stages in life.
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Example: Lythrypnus dalli (Family Lythrypnus) are a group of coral reef fish in which bidirectional sex change occurs. Once a social hierarchy is established a fish changes sex according to its social status, regardless of the initial sex, based on a simple principle: if the fish expresses subordinate behavior then it changes its sex to female, and if the fish expresses dominant or non-dominant superior behavior then it changes its sex to male.
Dichogamy can have both conservation-related implications for humans, as mentioned above, as well as economic implications. For instance,
are favoured fish for eating in many Asian countries and are often
aquacultured. Since the adults take several years to change from female to male, the
broodstock are extremely valuable individuals.
Simultaneous hermaphrodites
Simultaneous hermaphrodites (or homogamous hermaphrodites) are individuals in which both male and female sexual organs are present and functional at the same time.
Self-fertilization often occurs.
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Pulmonate and land are perhaps the best-known kinds of simultaneous hermaphrodites, and are the most widespread of terrestrial animals possessing this sexual polymorphism. Sexual material is exchanged between both animals via , and is then stored in the spermatheca. After exchange of Spermatozoon, both animals will lay fertilized eggs after a period of gestation. The eggs will proceed to hatch after a development period. Snails typically reproduce from early spring through late autumn.
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are an example of a hermaphroditic gastropod. Mating with a partner is more desirable biologically than self-fertilization, as the genetic material of the resultant offspring is varied, but if mating with a partner is not possible, self-fertilization is practiced. The male sexual organ of an adult banana slug is quite large in proportion to its size, as well as compared to the female organ. It is possible for banana slugs, while mating, to become stuck together. If a substantial amount of wiggling fails to separate them, the male organ will be bitten off (using the slug's radula), see apophallation. If a banana slug has lost its male sexual organ, it can still mate as a female, making hermaphroditism a valuable adaptation.
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The species of colourful sea slugs Goniobranchus reticulatus is hermaphroditic, with both male and female organs active at the same time during copulation. After mating, the external portion of the penis detaches, but is able to regrow within 24 hours.
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are another example of a simultaneous hermaphrodite. Although they possess ovaries and testes, they have a protective mechanism against self-fertilization. Sexual reproduction occurs when two worms meet and exchange , copulating on damp nights during warm seasons.
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The free-living hermaphroditic nematode Caenorhabditis elegans reproduces primarily by self-fertilization, but infrequent out-crossing events occur at a rate of approximately 1%.
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Hamlets do not practice self-fertilization, but a pair will mate multiple times over several nights, taking turns between which one acts as the male and which acts as the female.
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The mangrove killifish ( Mangrove rivulus) are simultaneous hermaphrodites, producing both eggs and sperm and routinely reproducing by self-fertilization. Each individual normally fertilizes itself when an egg and sperm produced by an internal organ unite inside the fish's body.
Pseudohermaphroditism
When
were first scientifically observed by explorers, they were thought to be hermaphrodites. Early observations of wild spotted hyenas led researchers to believe that all spotted hyenas, male or female, were born with what looked to be a penis. A female spotted hyena's apparent penis is in fact an enlarged clitoris, which contains an external birth canal.
It can be difficult to determine the sex of spotted hyenas until
sexual maturity, when they may become pregnant. When a female spotted hyena gives birth, she passes the cub through the cervix internally, but then passes it out through the elongated clitoris.
Plants
The term
hermaphrodite is used in
botany to describe, for example, a perfect
flower that has both
stamen (male, pollen-producing) and
(female, ovule-producing) parts. The overwhelming majority of flowering plant species are hermaphroditic.
Monoecy
Flowering plant species with separate, imperfect, male and female flowers on the same individual are called monoecious. Monoecy only occurs in about 7% of flowering plant species.
Monoecious plants are often referred to as hermaphroditic because they produce both male and female gametes. However, the individual flowers are not hermaphroditic if they only produce gametes of one sex.
65% of
gymnosperm species are dioecious, but
Pinophyta are almost all monoecious.
Some plants can change their sex throughout their lifetime, a phenomenon called sequential hermaphroditism.
Andromonoecy
In
Andromonoecy species, the plants produce perfect (hermaphrodite) flowers and separate fertile male flowers that are sterile as female.
Andromonoecy occurs in about 4000 species of flowering plants (2% of flowering plants).
Gynomonoecy
In
Gynomonoecy species, the plants produce hermaphrodite flowers and separate male-sterile pistillate flowers.
One example is the meadow saxifrage,
Saxifraga granulata.
Charles Darwin gave several other examples in his 1877 book "The Different Forms of Flowers on Plants of the Same Species".
About 57% of moss species and 68% of liverworts are Dioicy, meaning that their gametophytes produce either male or female gametes, but not both.
Sequential hermaphroditism is common in and some vascular plants.
Use regarding humans
of a person displaying ambiguous genitalia, one of a nine-part series. The series may be the earliest medical photographic documentation of an intersex person.
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Historically, the term hermaphrodite was used in law to refer to people whose sex was in doubt. The 12th-century Decretum Gratiani states that "Whether an hermaphrodite may witness a testament, depends on which sex prevails" ("Hermafroditus an ad testamentum adhiberi possit, qualitas sexus incalescentis ostendit.").[Decretum Gratiani, C. 4, q. 2 et 3, c. 3]
Alexander ab Alexandro (1461–1523) stated, using the term hermaphrodite, that the people who bore the sexes of both man and woman were regarded by the Athenians and the Romans as monsters, and thrown into the sea at Athens and into the Tiber at Rome.
During the Victorian era, medical authors attempted to ascertain whether or not humans could be hermaphrodites, adopting a precise biological definition to the term.
The term "intersex" described a wide variety of combinations of what are ambiguous biological characteristics. Intersex biology may include, for example, ambiguous-looking external genitalia, that include mixed XX and XY chromosome pairs (46XX/46XY, 46XX/47XXY or 45X/XY mosaic). Clinically, medicine currently uses the terminology "disorders of sex development"
Intersex civil society organizations, and many human rights institutions,
In some cases, variations in sex characteristics are caused by unusual levels of sex hormones, which may be the result of an atypical set of sex chromosomes. One common cause of variations in sex characteristics traits is the crossing over of the testis-determining factor (SRY) from the Y chromosome to the X chromosome during meiosis. The SRY is then activated in only certain areas, causing development of testes in some areas by beginning a series of events starting with the upregulation of the transcription factor (SOX9), and in other areas not being active (causing the growth of ovarian tissues). Thus, testicular and ovarian tissues will both be present in the same individual.
Fetuses were previously thought to be phenotypically female before the sexual differentiation stage;
Evolution
The evolution of
anisogamy may have contributed to the evolution of simultaneous hermaphroditism and sequential hermaphroditism,
it remains unclear if the evolution of anisogamy first led to hermaphroditism or
gonochorism.
A 2023 study argued that hermaphroditism can evolve directly from Mating type under certain circumstances, such as if the fertilization is well organized and the average size of groups is small.
In animals
Joan Roughgarden and Priya Iyer argued that the last
common ancestor for animals was hermaphroditic and that transitions from hermaphroditism to gonochorism were more numerous than the reverse. Other scientists have criticized this argument; saying it’s based on
paraphyletic Spiralia, assignments of sexual modes for the
phylum level than the species level, and methods exclusively based on maximum parsimony.
Hermaphroditism is polyphyletic in where it evolved from gonochorism
In plants
It is widely accepted that the first
were outcrossing hermaphrodites.
In flowering plants, hermaphroditism is ancestral to dioecy.
Hermaphroditism in plants may promote self fertilization in pioneer populations.
See also
Further reading
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Discovery Health Channel, (2007) "I Am My Own Twin"
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, reprinted in:
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External links
