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A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to
animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
, the term describes which males and females mate under which circumstances. Recognised systems include
monogamy Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
,
polygamy Crimes Polygamy (from Late Greek (') "state of marriage to many spouses") is the practice of marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this polygyny. When a woman is marr ...
(which includes
polygyny Polygyny (; from Neoclassical Greek πολυγυνία (); ) is the most common and accepted form of polygamy around the world, entailing the marriage of a man with several women. Incidence Polygyny is more widespread in Africa than in any ...
,
polyandry Polyandry (; ) is a form of polygamy in which a woman takes two or more husbands at the same time. Polyandry is contrasted with polygyny, involving one male and two or more females. If a marriage involves a plural number of "husbands and wives" ...
, and
polygynandry Polygynandry is a mating system in which both males and females have multiple mating partners during a breeding season. In sexually reproducing diploid animals, different mating strategies are employed by males and females, because the cost of gam ...
), and
promiscuity Promiscuity is the practice of engaging in sexual activity frequently with different partners or being indiscriminate in the choice of sexual partners. The term can carry a moral judgment. A common example of behavior viewed as promiscuous by ma ...
, all of which lead to different
mate choice Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choic ...
outcomes and thus these systems affect how
sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (in ...
works in the species which practice them. In plants, the term refers to the degree and circumstances 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 can be a usefu ...
. In human
sociobiology Sociobiology is a field of biology that aims to examine and explain social behavior in terms of evolution. It draws from disciplines including psychology, ethology, anthropology, evolution, zoology, archaeology, and population genetics. Within ...
, the terms have been extended to encompass the formation of relationships such as
marriage Marriage, also called matrimony or wedlock, is a culturally and often legally recognized union between people called spouses. It establishes rights and obligations between them, as well as between them and their children, and between ...
.


In plants

The primary mating systems in plants are
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 can be a usefu ...
(cross-fertilisation),
autogamy Autogamy, or self-fertilization, refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species o ...
(self-fertilisation) and
apomixis In botany, apomixis is asexual reproduction without fertilization. Its etymology is Greek for "away from" + "mixing". This definition notably does not mention meiosis. Thus "normal asexual reproduction" of plants, such as propagation from cuttin ...
(asexual reproduction without fertilization, but only when arising by modification of sexual function). Mixed mating systems, in which plants use two or even all three mating systems, are not uncommon. A number of models have been used to describe the parameters of plant mating systems. The basic model is the mixed mating model, which is based on the assumption that every fertilisation is either self-fertilisation or completely random cross-fertilisation. More complex models relax this assumption; for example, the
effective selfing model The effective selfing model is a mathematical model that describes the mating system of a plant population in terms of the degree of self-fertilisation present. Overview It was developed in the 1980s by Kermit Ritland, as an alternative to th ...
recognises that mating may be more common between pairs of closely related plants than between pairs of distantly related plants.


In animals

The following are some of the mating systems generally recognized in animals: *
Monogamy Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
: One male and one female have an exclusive mating relationship. The term "
pair bond In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of offspring and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is freque ...
ing" often implies this. This is associated with one-male, one-female group compositions. There are two types of monogamy: type 1, which is facultative, and type 2, which is obligate. Facultative monogamy occurs when there are very low densities in a species. This means that mating occurs with only a single member of the opposite sex because males and females are very far apart. When a female needs aid from conspecifics in order to have a litter this is obligate monogamy. However, with this, the habitat carrying capacity is small so it means only one female can breed within the habitat. *
Polygamy Crimes Polygamy (from Late Greek (') "state of marriage to many spouses") is the practice of marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this polygyny. When a woman is marr ...
: Three types are recognized: **
Polygyny Polygyny (; from Neoclassical Greek πολυγυνία (); ) is the most common and accepted form of polygamy around the world, entailing the marriage of a man with several women. Incidence Polygyny is more widespread in Africa than in any ...
(the most common polygamous mating system in
vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...
so far studied): One male has an exclusive relationship with two or more females. This is associated with one-male, multi-female group compositions. Many perennial ''
Vespula squamosa ''Vespula squamosa'', the southern yellowjacket, is a social wasp. This species can be identified by its distinctive black and yellow patterning and orange queen. These yellowjackets are typically found in eastern North America, and its territ ...
'' (southern yellowjacket) colonies are polygynous. Different types of polygyny exist, such as lek polygyny and resource defense polygyny. Grayling butterflies (''
Hipparchia semele The grayling or rock grayling (''Hipparchia semele'') is a species in the brush-footed butterfly family Nymphalidae. Although found all over Europe, the grayling mostly inhabits coastal areas, with inland populations declining significantly in re ...
'') engage in resource defense polygyny, where females choose a territorial male based on the best oviposition site. Although most animals opt for only one of these strategies, some exhibit hybrid strategies, such as the bee species, ''
Xylocopa micans ''Xylocopa micans'', also known as the southern carpenter bee, is a species of bee within ''Xylocopa'', the genus of carpenter bees. The southern carpenter bee can be found mainly in the coastal and gulf regions of the southeastern United State ...
''. **
Polyandry Polyandry (; ) is a form of polygamy in which a woman takes two or more husbands at the same time. Polyandry is contrasted with polygyny, involving one male and two or more females. If a marriage involves a plural number of "husbands and wives" ...
: One female has an exclusive relationship with two or more males. This is very rare and is associated with multi-male, multi-female group compositions. Genetic polyandry is found some insect species such as ''Apis mellifera'' (the Western Honey Bee), in which a virgin queen will mate with multiple drones during her nuptial flight whereas each drone will die immediately upon mating once. The queen will then store the sperm collected from these multiple matings in her spermatheca to use to fertilize eggs throughout the course of her entire reproductive life. **
Polygynandry Polygynandry is a mating system in which both males and females have multiple mating partners during a breeding season. In sexually reproducing diploid animals, different mating strategies are employed by males and females, because the cost of gam ...
: Polygynandry is a slight variation of this, where two or more males have an exclusive relationship with two or more females; the numbers of males and females do not have to be equal, and in vertebrate species studied so far, the number of males is usually less. This is associated with multi-male, multi-female group compositions. *
Promiscuity Promiscuity is the practice of engaging in sexual activity frequently with different partners or being indiscriminate in the choice of sexual partners. The term can carry a moral judgment. A common example of behavior viewed as promiscuous by ma ...
: A member of one sex within the social group mates with any member of the opposite sex. This is associated with multi-male, multi-female group compositions. These mating relationships may or may not be associated with social relationships, in which the sexual partners stay together to become parenting partners. As the alternative term "pair bonding" implies, this is usual in monogamy. In many polyandrous systems, the males and the female stay together to rear the young. In polygynous systems where the number of females paired with each male is low and the male will often stay with one female to help rear the young, while the other females rear their young on their own. In polygynandry, each of the males may assist one female; if all adults help rear all the young, the system is more usually called " communal breeding". In highly polygynous systems, and in promiscuous systems, paternal care of young is rare, or there may be no parental care at all. These descriptions are idealized, and the social partnerships are often easier to observe than the mating relationships. In particular: *the relationships are rarely exclusive for all individuals in a species.
DNA fingerprinting DNA profiling (also called DNA fingerprinting) is the process of determining an individual's DNA characteristics. DNA analysis intended to identify a species, rather than an individual, is called DNA barcoding. DNA profiling is a forensic t ...
studies have shown that even in pair-bonding, matings outside the pair (
extra-pair copulation Extra-pair copulation (EPC) is a mating behaviour in monogamous species. Monogamy is the practice of having only one sexual partner at any one time, forming a long-term bond and combining efforts to raise offspring together; mating outside this pai ...
s) occur with fair frequency, and a significant minority of offspring result from them. However, the offspring that are a result of extra-pair copulations usually exhibit more advantageous genes. These genes can be associated with improvements in appearance, mating, and the functioning of internal body systems. *some species show different mating systems in different circumstances, for example in different parts of their geographical range, or under different conditions of food availability *mixtures of the simple systems described above may occur.
Sexual conflict Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between m ...
occurs between individuals of different sexes that have separate or conflicting requirements for optimal mating success. This conflict may lead to competitive adaptations and co-adaptations of one or both of the sexes to maintain mating processes that are beneficial to that sex.
Intralocus sexual conflict Intralocus sexual conflict is a type of sexual conflict that occurs when a genetic locus harbours alleles which have opposing effects on the fitness of each sex, such that one allele improves the fitness of males (at the expense of females), while ...
and interlocus sexual conflict describe the genetic influence behind sexual conflict, and are presently recognized as the most basic forms of sexual conflict.


In humans

Compared to other
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...
s, where a species usually has a single mating system, humans display great variety. Humans also differ by having formal
marriage Marriage, also called matrimony or wedlock, is a culturally and often legally recognized union between people called spouses. It establishes rights and obligations between them, as well as between them and their children, and between ...
s which in some cultures involve negotiation and arrangement between elder relatives. Regarding sexual dimorphism (see the section about animals above), humans are in the intermediate group with moderate sex differences in body size but with relatively large testes, indicating relatively frequent sperm competition in socially monogamous and polygynous human societies. One estimate is that 83% of human societies are polygynous, 0.05% are polyandrous, and the rest are monogamous. Even the last group may at least in part be genetically polygynous.The Oxford Handbook of Evolutionary Psychology, Edited by Robin Dunbar and Louise Barret, Oxford University Press, 2007, Chapter 30 Ecological and socio-cultural impacts on mating and marriage systems by Bobbi S. Low From an evolutionary standpoint, females are more prone to practice
monogamy Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
because their reproductive success is based on the resources they are able to acquire through reproduction rather than the quantity of offspring they produce. However, males are more likely to practice
polygamy Crimes Polygamy (from Late Greek (') "state of marriage to many spouses") is the practice of marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this polygyny. When a woman is marr ...
because their reproductive success is based on the amount of offspring they produce, rather than any kind of benefit from parental investment. Polygyny is associated with an increased sharing of subsistence provided by women. This is consistent with the theory that if women raise the children alone, men can concentrate on the mating effort. Polygyny is also associated with greater environmental variability in the form of variability of
rainfall Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
. This may increase the differences in the resources available to men. An important association is that polygyny is associated with a higher
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...
load in an area which may make having good genes in a male increasingly important. A high pathogen load also decreases the relative importance of sororal polygyny which may be because it becomes increasingly important to have genetic variability in the offspring (See
Major histocompatibility complex and sexual selection The major histocompatibility complex in sexual selection concerns how major histocompatibility complex (MHC) molecules allow for immune system surveillance of the population of protein molecules in a host's cells. In 1976, Yamazaki et al. demonstr ...
). Virtually all the terms used to describe animal mating systems were adopted from
social anthropology Social anthropology is the study of patterns of behaviour in human societies and cultures. It is the dominant constituent of anthropology throughout the United Kingdom and much of Europe, where it is distinguished from cultural anthropology. In ...
, where they had been devised to describe systems of
marriage Marriage, also called matrimony or wedlock, is a culturally and often legally recognized union between people called spouses. It establishes rights and obligations between them, as well as between them and their children, and between ...
. This shows that human sexual behavior is unusually flexible since, in most animal species, one mating system dominates. While there are close analogies between animal mating systems and human marriage institutions, these analogies should not be pressed too far, because in human societies, marriages typically have to be recognized by the entire social group in some way, and there is no equivalent process in animal societies. The temptation to draw conclusions about what is "natural" for human sexual behavior from observations of animal mating systems should be resisted: a socio-biologist observing the kinds of behavior shown by humans in any other species would conclude that all known mating systems were natural for that species, depending on the circumstances or on individual differences. As culture increasingly affects human mating choices, ascertaining what is the 'natural' mating system of the human animal from a zoological perspective becomes increasingly difficult. Some clues can be taken from human anatomy, which is essentially unchanged from the prehistoric past: *humans have a large relative size of testes to body mass in comparison to most primates; *humans have a large ejaculate volume and sperm count in comparison to other primates; *as compared to most primates, humans spend more time in copulation; *as compared to most primates, humans
copulate Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...
with greater frequency; *the outward signs of
estrus The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous ...
in women (i.e. higher body temperature, breast swelling, sugar cravings, etc.), are often perceived to be less obvious in comparison to the outward signs of ovulation in most other mammals; *for most mammals, the estrous cycle and its outward signs bring on mating activity; the majority of female-initiated matings in humans coincides with estrus, but humans copulate throughout the reproductive cycle; *after ejaculation/orgasm in males and females, humans release a hormone that has a sedative effect; Some have suggested that these anatomical factors signify some degree of sperm competition, though as levels of genetic and societal promiscuity are highly varied across cultures, this evidence is far from conclusive.


Genetic causes and effects

Monogamy has evolved multiple times in animals, with homologous brain structures predicting the mating and parental strategies used by them. These homologous structures were brought about by similar mechanisms. Even though there have been many different evolutionary pathways to get to monogamy, all the studied organisms express their genes very similarly in the fore and midbrain, implying a universal mechanism for the evolution of monogamy in vertebrates. While genetics is not the exclusive cause of mating systems within animals, it is influential in many animals, particularly
rodents Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...
, which have been the most heavily researched. Certain rodents’ mating systems—monogamous, polygynous, or socially monogamous with frequent promiscuity—are correlated with suggested evolutionary
phylogenies A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...
, where rodents more closely related genetically are more likely to use a similar mating system, suggesting an evolutionary basis. These differences in mating strategy can be traced back to a few significant
alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...
that affect behaviors that are heavily influential on mating system, such as the alleles responsible for the level of parental care, how animals choose their partner(s), and sexual competitiveness, among others, which are all at least partially influenced by genetics. While these genes may not perfectly correlate with the mating system that animals use, genetics is one factor that may lead to a species or population reproducing using one mating system over another, or even potentially multiple at different locations or points in time. Mating systems can also have large impacts on the genetics of a population, strongly affecting natural selection and speciation. In
plover Plovers ( , ) are a widely distributed group of wading birds belonging to the subfamily Charadriinae. Description There are about 66 species in the subfamily, most of them called "plover" or "dotterel". The closely related lapwing subf ...
populations, polygamous species tend to speciate more slowly than monogamous species do. This is likely because polygamous animals tend to move larger distances to find mates, contributing to a high level of
gene flow In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...
, which can genetically homogenize many nearby subpopulations. Monogamous animals, on the other hand, tend to stay closer to their starting location, not dispersing as much. Because monogamous animals don’t migrate as far, monogamous populations which are geographically closer together tend to reproductively isolate from each other more easily, and thus each subpopulation is more likely to diversify or speciate from the other nearby populations as compared to polygamous populations. In polygamous species, however, the male partner in polygynous species and female partner in polyandrous species often tend to spread further to look for mates, potentially to find more or better mates. The increased level of movement among populations leads to increased gene flow between populations, effectively making geographically distinct populations into genetically similar ones via interbreeding. This has been observed in some species of rodents, where generally promiscuous species were quickly differentiated into monogamous and polygamous
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
by a prominent introduction of monogamous behaviors in some populations of that species, showing the swift evolutionary effects different mating systems can have. Specifically, monogamous populations speciated up to 4.8 times faster and had lower extinction rates than non monogamous populations. Another way that monogamy has the potential to cause increased speciation is because individuals are more selective with partners and competition, causing different nearby populations of the same species to stop interbreeding as much, leading to speciation down the road. Another potential effect of polyandry in particular is increasing the quality of offspring and reducing the probability of reproductive failure. There are many possible reasons for this, one of the possibilities being that there is greater genetic variation in families because most offspring in a family will have either a different mother or father. This reduces the potential harm done by inbreeding, as siblings will be less closely related and more genetically diverse. Additionally, because of the increased genetic diversity among generations, the levels of
reproductive fitness Fitness (often denoted w or ω in population genetics models) is the quantitative representation of individual reproductive success. It is also equal to the average contribution to the gene pool of the next generation, made by the same individua ...
are also more variable, and so it is easier to select for positive traits more quickly, as the difference in fitness between members of the same generation would be greater. When many males are actively mating, polyandry can decrease the risk of extinction as well, as it can increase the
effective population size The effective population size (''N'e'') is a number that, in some simplified scenarios, corresponds to the number of breeding individuals in the population. More generally, ''N'e'' is the number of individuals that an idealised population w ...
. Increased effective population sizes are more stable and less prone to accumulating deleterious mutations due to genetic drift.


In microorganisms


Bacteria

Mating in
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
involves transfer of DNA from one cell to another and incorporation of the transferred DNA into the recipient bacteria's
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...
by
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
. Transfer of DNA between bacterial cells can occur in three main ways. First, a bacterium can take up
exogenous DNA Exogenous DNA is DNA originating outside the organism of concern or study. Exogenous DNA can be found naturally in the form of partially degraded fragments left over from dead cells. These DNA fragments may then become integrated into the chromos ...
released into the intervening medium from another bacterium by a process called transformation. DNA can also be transferred from one bacterium to another by the process of transduction, which is mediated by an infecting virus (bacteriophage). The third method of DNA transfer is ''conjugation'', in which a
plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...
mediates transfer through direct cell contact between cells. Transformation, unlike transduction or conjugation, depends on numerous bacterial gene products that specifically interact to perform this complex process, and thus transformation is clearly a bacterial
adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
for DNA transfer. In order for a bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state termed natural competence. In ''
Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillus ...
'' about 40 genes are required for the development of competence and DNA uptake. The length of DNA transferred during ''B. subtilis'' transformation can be as much as a third and up to the whole chromosome. Transformation appears to be common among bacterial species, and at least 60 species are known to have the natural ability to become competent for transformation. The development of competence in nature is usually associated with stressful environmental conditions, and seems to be an adaptation for facilitating repair of DNA damage in recipient cells.


Archaea

In several species of
archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...
, mating is mediated by formation of cellular aggregates. ''
Halobacterium ''Halobacterium'' (common abbreviation ''Hbt.'') is a genus in the family Halobacteriaceae. The genus ''Halobacterium'' ("salt" or "ocean bacterium") consists of several species of Archaea with an aerobic metabolism which requires an environmen ...
volcanii'', an extreme
halophilic The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...
archaeon, forms cytoplasmic bridges between cells that appear to be used for transfer of DNA from one cell to another in either direction. When the
hyperthermophilic A hyperthermophile is an organism that thrives in extremely hot environments—from 60 °C (140 °F) upwards. An optimal temperature for the existence of hyperthermophiles is often above 80 °C (176 °F). Hyperthermophiles are often within the doma ...
archaea ''
Sulfolobus solfataricus ''Saccharolobus solfataricus'' is a species of thermophilic archaeon. It was transferred from the genus ''Sulfolobus'' to the new genus ''Saccharolobus'' with the description of Saccharolobus caldissimus in 2018. It was first isolated and disco ...
'' and '' Sulfolobus acidocaldarius'' are exposed to the DNA damaging agents UV irradiation,
bleomycin -13- (1''H''-imidazol-5-yl)methyl9-hydroxy-5- 1''R'')-1-hydroxyethyl8,10-dimethyl-4,7,12,15-tetraoxo-3,6,11,14-tetraazapentadec-1-yl}-2,4'-bi-1,3-thiazol-4-yl)carbonyl]amino}propyl)(dimethyl)sulfonium , chemical_formula = , C=55 , H=84 , N=1 ...
or Mitomycins, mitomycin C, species-specific cellular aggregation is induced. Aggregation in ''S. solfataricus'' could not be induced by other physical stressors, such as pH or temperature shift, suggesting that aggregation is induced specifically by DNA damage. Ajon et al. showed that UV-induced cellular aggregation mediates chromosomal marker exchange with high frequency in ''S. acidocaldarius''. Recombination rates exceeded those of uninduced cultures by up to three orders of magnitude. Frols et al. and Ajon et al. hypothesized that cellular aggregation enhances species-specific DNA transfer between ''Sulfolobus'' cells in order to provide increased repair of damaged DNA by means of
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
. This response appears to be a primitive form of sexual interaction similar to the more well-studied bacterial transformation systems that are also associated with species specific DNA transfer between cells leading to homologous recombinational repair of DNA damage.


Protists

Protists are a large group of diverse
eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
s, mainly unicellular animals and plants, that do not form tissues. Eukaryotes emerged in evolution more than 1.5 billion years ago. The earliest eukaryotes were likely protists. Mating and
sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...
are widespread among extant eukaryotes. Based on a phylogenetic analysis, Dacks and Roger proposed that facultative sex was present in the common ancestor of all eukaryotes. However, to many biologists it seemed unlikely until recently, that mating and sex could be a primordial and fundamental characteristic of eukaryotes. A principal reason for this view was that mating and sex appeared to be lacking in certain
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...
ic protists whose ancestors branched off early from the eukaryotic family tree. However, several of these protists are now known to be capable of, or to recently have had, the capability for
meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...
and hence mating. To cite one example, the common intestinal parasite ''
Giardia intestinalis ''Giardia duodenalis'', also known as ''Giardia intestinalis'' and ''Giardia lamblia'', is a flagellated parasitic microorganism of the genus ''Giardia'' that colonizes the small intestine, causing a diarrheal condition known as giardiasis. The ...
'' was once considered to be a descendant of a protist lineage that predated the emergence of meiosis and sex. However, ''G. intestinalis'' was recently found to have a core set of genes that function in meiosis and that are widely present among sexual eukaryotes. These results suggested that ''G. intestinalis'' is capable of meiosis and thus mating and sexual reproduction. Furthermore, direct evidence for meiotic recombination, indicative of mating and sexual reproduction, was also found in ''G. intestinalis''. Other protists for which evidence of mating and sexual reproduction has recently been described are parasitic protozoa of the genus ''
Leishmania ''Leishmania'' is a parasitic protozoan, a single-celled organism of the genus '' Leishmania'' that are responsible for the disease leishmaniasis. They are spread by sandflies of the genus ''Phlebotomus'' in the Old World, and of the genus ' ...
'', ''
Trichomonas vaginalis ''Trichomonas vaginalis'' is an anaerobic, flagellated protozoan parasite and the causative agent of a sexually transmitted disease called trichomoniasis. It is the most common pathogenic protozoan that infects humans in industrialized countri ...
'', and
acanthamoeba ''Acanthamoeba'' is a genus of amoebae that are commonly recovered from soil, fresh water, and other habitats. ''Acanthamoeba'' has two evolutive forms, the metabolically active trophozoite and a dormant, stress-resistant cyst. Trophozoites are ...
. Protists generally reproduce asexually under favorable environmental conditions, but tend to reproduce sexually under stressful conditions, such as starvation or heat shock.


Viruses

Both animal viruses and bacterial viruses (
bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bac ...
) are able to undergo mating. When a cell is mixedly infected by two genetically marked viruses, recombinant virus progeny are often observed indicating that mating interaction had occurred at the DNA level. Another manifestation of mating between viral genomes is multiplicity reactivation (MR). MR is the process by which at least two virus genomes, each containing inactivating genome damage, interact with each other in an infected cell to form viable progeny viruses. The genes required for MR in bacteriophage T4 are largely the same as the genes required for allelic recombination. Examples of MR in animal viruses are described in the articles ''
Herpes simplex virus Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), also known by their taxonomical names '' Human alphaherpesvirus 1'' and ''Human alphaherpesvirus 2'', are two members of the human ''Herpesviridae'' family, a set of viruses that produce viral in ...
'', ''
Influenza A virus '' A virus'' (''IAV'') causes influenza in birds and some mammals, and is the only species of the genus ''Alphainfluenzavirus'' of the virus family ''Orthomyxoviridae''. Strains of all subtypes of influenza A virus have been isolated from wild ...
'', ''
Adenoviridae Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from thei ...
'', ''
Simian virus 40 SV40 is an abbreviation for simian vacuolating virus 40 or simian virus 40, a polyomavirus that is found in both monkeys and humans. Like other polyomaviruses, SV40 is a DNA virus that has the potential to cause tumors in animals, but most ofte ...
'', '' Vaccinia virus'', and ''
Reoviridae ''Reoviridae'' is a family of double-stranded RNA viruses. Member viruses have a wide host range, including vertebrates, invertebrates, plants, protists and fungi. They lack lipid envelopes and package their segmented genome within multi-layere ...
''.


In arthropods


Fruit flies

Fruit flies like '' A. suspensa'' have demonstrated polygamy. The males often attract females through marking where they will perch and release air-borne pheromones from the tip of their abdomen to mark and defend individual leaves.


See also

*
Heterosexuality Heterosexuality is romantic attraction, sexual attraction or sexual behavior between people of the opposite sex or gender. As a sexual orientation, heterosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" ...
*
Assortative mating Assortative mating (also referred to as positive assortative mating or homogamy) is a mating pattern and a form of sexual selection in which individuals with similar phenotypes or genotypes mate with one another more frequently than would be ...
*
r/K selection theory In ecology, ''r''/''K'' selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of indivi ...
*
Monocotyledon reproduction The monocots (or Monocotyledons) are one of the two major groups of flowering plants (or Angiosperms), the other being the dicots (or dicotyledons). In order to reproduce they utilize various strategies such as employing forms of asexual reproducti ...
*
Sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...


References


Further reading

* {{Animal sexual behavior Ecology Ethology Fertility Sexual selection Sociobiology Heterosexuality