Animal sexual behaviour
This article is about the sexual behaviour of non-human animals.
monogamy
polyandry
polygamy
promiscuity
sex apparently due to duress or coercion and
situational sexual behaviour)
non-reproductively motivated
interspecific sexuality
sex with dead animals
homosexual sexual behaviour
bisexual
copulation
oestrus
competition
masturbate
use objects as tools
"mating system"
Monogamy
long-lasting pairs and cooperate in raising offspring.
These pairs may last for a lifetime, such as in
pigeons,
or it may occasionally change from one mating season to another, such as in
emperor penguins.
tournament species
sexual dimorphism
extra-pair partners. This includes previous examples, such as
swans
extra-pair sexual activities
lead to offspring.
Social monogamy refers to a male and female's social living
arrangement (e.g., shared use of a territory, behaviour indicative of a
social pair, and/or proximity between a male and female) without
inferring any sexual interactions or reproductive patterns. In humans,
social monogamy takes the form of monogamous marriage. Sexual monogamy
is defined as an exclusive sexual relationship between a female and a
male based on observations of sexual interactions. Finally, the term
genetic monogamy is used when DNA analyses can confirm that a
female-male pair reproduce exclusively with each other. A combination of
terms indicates examples where levels of relationships coincide, e.g.,
sociosexual and sociogenetic monogamy describe corresponding social and
sexual, and social and genetic monogamous relationships, respectively.[15]
Social monogamy is relatively rare in the animal kingdom.
- Over 90% of avian species are socially
monogamous.
- Only 3% of mammalian species are
socially monogamous, although up to 15% of primate species are.
- Social monogamy has also been observed in
reptiles, fish, and
insects.
Sexual monogamy is also rare among animals
- While over 90% of
birds are socially monogamous, "on average, 30% or more of the baby
birds in any nest [are] sired by someone other than the resident male.
Patricia Adair Gowaty has estimated that, out of 180 different species of socially monogamous songbirds, only 10% are sexually monogamous.
Polygyny
Polygyny occurs when one male gets exclusive mating rights with multiple females. In some species, notably those with
harem-like structures, only one of a few males in a group of females will mate. Technically,
polygyny
in sociobiology and zoology is defined as a system in which a male has a
relationship with more than one female, but the females are
predominantly bonded to a single male. Should the active male be driven
out, killed, or otherwise removed from the group, in a number of species
the new male will ensure that breeding resources are not wasted on
another male's young.
[19] The new male may achieve this in many different ways, including:
Von Haartman specifically described the mating behaviour of the
European pied flycatcher as successive polygyny.
[20]
Within this system, the males leave their home territory once their
primary female lays her first egg. Males then create a second territory,
presumably in order to attract a secondary female to breed. Even when
they succeed at acquiring a second mate, the males typically return to
the first female to exclusively provide for her and her offspring.
[21]
Polygynous mating structures are estimated to occur in up to 90% of mammal species.
[22]
As polygyny is the most common form of polygamy among vertebrates
(including humans, to some extent), it has been studied far more
extensively than polyandry or polygynandry.
Polyandry
Polyandry occurs when one female gets exclusive mating rights with multiple males. In some species, such as
redlip blennies, both
polygyny and
polyandry are observed.
[23]
The males in some deep sea
anglerfishes are much smaller than the females. When they find a female they bite into her skin, releasing an
enzyme that digests the skin of their mouth and her body and fusing the pair down to the blood-vessel level. The male then slowly
atrophies, losing first his digestive organs, then his brain, heart, and eyes, ending as nothing more than a pair of
gonads, which release
sperm in response to
hormones in the female's bloodstream indicating
egg release. This extreme
sexual dimorphism ensures that, when the female is ready to spawn, she has a mate immediately available.
[24] A single anglerfish female can "mate" with many males in this manner.
Polygynandry
Polygynandry
occurs when multiple males mate indiscriminately with multiple females.
The numbers of males and females need not be equal, and in vertebrate
species studied so far, there are usually fewer males. Two examples of
systems in primates are promiscuous mating
chimpanzees and
bonobos.
These species live in social groups consisting of several males and
several females. Each female copulates with many males, and vice versa.
In bonobos, the amount of promiscuity is particularly striking because
bonobos use sex to alleviate social conflict as well as to reproduce.
This mutual promiscuity is the approach most commonly used by spawning
animals, and is perhaps the "original fish mating system."
[4]:161 Common examples are
forage fish, such as
herrings, which form huge mating
shoals in shallow water. The water becomes milky with sperm and the bottom is draped with millions of fertilised eggs.
[4]:161
Polygamy
The term
polygamy
is an umbrella term used to refer generally to non-monogamous matings.
As such, polygamous relationships can be polygynous, polyandrous or
polygynandrous. In a small number of species, individuals can display
either polygamous or monogamous behaviour depending on environmental
conditions. An example is the social wasp
Apoica flavissima.
[citation needed]
In some species, polygyny and polyandry is displayed by both sexes in
the population. Polygamy in both sexes has been observed in
red flour beetle (
Tribolium castaneum).
A
tournament species is one in which "mating tends to be highly polygamous and involves high levels of male-male aggression and competition."
[25] Tournament behaviour often correlates with high levels of
sexual dimorphism, examples of species including
chimpanzees and
baboons. Most polygamous species present high levels of tournament behaviour, with a notable exception being
bonobos.
Parental investment and reproductive success
Female and male sexual behaviour differ in many species. Often, males
are more active in initiating mating, and bear the more conspicuous
sexual ornamentation like antlers and colourful plumage. This is a
result of
anisogamy, where
sperm are smaller and much less costly (energetically) to produce than
eggs.
This difference in physiological cost means that males are more limited
by the number of mates they can secure, while females are limited by
the quality of genes of her mates, a phenomenon known as
Bateman's principle.
[26] Many females also have extra reproductive burdens in that
parental care often falls mainly, or exclusively, on them. Thus, females are more limited in their potential
reproductive success.
[27] In species where males take on more of the reproductive costs, such as
sea horses and
jacanas, the role is reversed, and the females are larger, more aggressive and more brightly coloured than the males.
In hermaphroditic animals, the costs of parental care can be evenly distributed between the sexes, e.g.
earthworms. In some species of
planarians, sexual behaviour takes the form of
penis fencing.
In this form of copulation, the individual that first penetrates the
other with the penis, forces the other to be female, thus carrying the
majority of the cost of reproduction.
[28] Post mating,
banana slugs will some times gnaw off their partners penis as an act of
sperm competition.
[29] In the
grey slug,
the sharing of cost leads to a spectacular display, where the mates
suspend themselves high above the ground from a slime thread, ensuring
none of them can refrain from taking on the cost of egg-bearer.
[30]
Seasonality
Many animal species have specific mating (or breeding) periods e.g. (
seasonal breeding) so that offspring are born or hatch at an optimal time. In marine species with limited mobility and
external fertilisation like
corals,
sea urchins and
clams, the timing of the common spawning is the only externally visible form of sexual behaviour. In areas with continuously high
primary production,
some species have a series of breeding seasons throughout the year.
This is the case with most primates (who are primarily tropical and
subtropical animals). Some animals (
opportunistic breeders) breed dependent upon other conditions in their environment aside from time of year.
Mammals
Mating
seasons are often associated with changes to herd or group structure,
and behavioural changes, including territorialism amongst individuals.
These may be annual (e.g.
wolves), biannual (e.g.
dogs)
or more frequently (e.g. horses). During these periods, females of most
mammalian species are more mentally and physically receptive to sexual
advances, a period scientifically described as
estrous but commonly described as being "in season" or "in heat". Sexual behaviour may occur outside estrus,
[31] and such acts as do occur are not necessarily harmful.
[32]
Some mammals (e.g. domestic cats, rabbits and camilidae) are termed
"induced ovulators".
For these species, the female ovulates due to an external stimulus
during, or just prior, to mating, rather than ovulating cyclically or
spontaneously. Stimuli causing induced ovulation include the sexual
behaviour of coitus, sperm and pheromones. Domestic cats have
penile spines. Upon withdrawal of a
cat's penis, the spines rake the walls of the female's
vagina, which may cause ovulation.
[33][34]
Amphibians
For
many amphibians, an annual breeding cycle applies, typically regulated
by ambient temperature, precipitation, availability of surface water and
food supply. This breeding season is accentuated in temperate regions,
in boreal climate the breeding season is typically concentrated to a few
short days in the spring.
Fish
Like many
coral reef dwellers, the
clownfish
spawn around the time of the full moon in the wild. In a group of
clownfish, there is a strict dominance hierarchy. The largest and most
aggressive female is found at the top. Only two clownfish, a male and a
female, in a group reproduce through external fertilisation. Clownfish
are sequential hermaphrodites, meaning that they develop into males
first, and when they mature, they become females. If the female
clownfish is removed from the group, such as by death, one of the
largest and most dominant males will become a female. The remaining
males will move up a rank in the hierarchy.
Motivation
Various
neurohormones stimulate sexual wanting in animals. In general, studies have suggested that
dopamine is involved in sexual incentive motivation,
oxytocin and
melanocortins in sexual attraction, and
noradrenaline in sexual arousal.
[35] Vasopressin is also involved in the sexual behaviour of some animals.
[36]
Neurohormones in the mating systems of voles
The mating system of
prairie voles is
monogamous; after mating, they form a lifelong bond. In contrast,
montane voles have a
polygamous
mating style. When montane voles mate, they form no attachments and
separate after copulation. Studies on the brains of these two species
have found that it is two neurohormones and their respective receptors
that are responsible for these differences in mating strategies. Male
prairie voles release vasopressin after copulation prairie vole and
attachment to the female then develops. Female prairie voles release
oxytocin after reproducing and an attachment to her partner also
develops. Neither male nor female montane voles have such a high
quantity of oxytocin and vasopressin when they mate. Even when injected
with these neurohormones, the mating system does not change. In
contrast, if prairie voles are injected with the neurohormones, they may
form a lifelong attachment, even if they have not mated. The reason for
this is that prairie voles have more oxytocin and vasopressin receptors
than do montane voles, and are therefore far more receptive to the two
neurohormones. It is not the quantity of the hormone that determines the
mating system and bond-formation, rather, it is number of neurohormone
receptors.
[36]
Oxytocin and rat sexual behaviour
Mother rats experience a
postparum estrus
which makes them highly motivated to mate. However, they also have a
strong motivation to protect their newly born pups. As a consequence,
the mother rat solicits males to the nest but simultaneously becomes
aggressive towards them to protect her young. If the mother rat is given
injections of an oxytocin
receptor antagonist, they no longer experience these maternal motivations.
[37]
Prolactin influences social bonding in rats.
[37]
Oxytocin and primate sexual behaviour
Oxytocin plays a similar role in non-human primates as it does in humans.
Grooming, sex, and cuddling frequencies correlate positively with
levels of oxytocin. As the level of oxytocin increases so does sexual
motivation. While oxytocin plays a major role in parent child
relationships, it is also found to play a role in adult sexual
relationships. Its secretion affects the nature of the relationship or
if there will even be a relationship at all.
[citation needed]
Studies have shown that oxytocin is higher in monkeys in lifelong
monogamous relationships compared to monkeys which are single.
Furthermore, the oxytocin levels of the couples correlate positively;
when the oxytocin secretion of one increases the other one also
increases. Higher levels of oxytocin are related to monkeys expressing
more behaviours such as cuddling, grooming and sex, while lower levels
of oxytocin reduce motivation for these activities.
[citation needed]
Research on oxytocin's role in the animal brain suggests that it
plays less of a role in behaviours of love and affection than previously
believed. "When oxytocin was first discovered in 1909, it was thought
mostly to influence a mother’s labour contractions and milk let-down.
Then, in the 1990s, research with prairie voles found that giving them a
dose of oxytocin resulted in the formation of a bond with their future
mate (Azar, 40)." Oxytocin has since been treated by the media as the
sole player in the "love and mating game" in mammals. This view,
however, is proving to be false as, "most hormones don’t influence
behaviour directly. Rather, they affect thinking and emotions in
variable ways (Azar, 40)." There is much more involved in sexual
behaviour in the mammalian animal than oxytocin and vasopressin can
explain.
[38][39][40][41][42][43][44]
Pleasure
It
is often assumed that animals do not have sex for pleasure, or
alternatively that humans, pigs (and perhaps dolphins and one or two
species of primate) are the only species that do. This is sometimes
stated as "animals mate only for reproduction". This view is considered a
misconception by some scholars.
[45][46] Jonathan Balcombe
argues that the prevalence of non-reproductive sexual behaviour in
certain species suggests that sexual stimulation is pleasurable. He also
points to the presence of the
clitoris in some female mammals, and evidence for female orgasm in primates.
[47] On the other hand, it is impossible to know the subjective feelings of animals,
[35] and the notion that
non-human animals experience emotions similar to humans is a contentious subject.
[48][49][50][51]
A 2006
Danish Animal Ethics Council report,
[52]
which examined current knowledge of animal sexuality in the context of
legal queries concerning sexual acts by humans, has the following
comments, primarily related to domestically common animals:
Even though the evolution-related purpose of mating can be said to be
reproduction, it is not actually the creating of offspring which
originally causes them to mate. It is probable that they mate because
they are motivated for the actual copulation, and because this is
connected with a positive experience. It is therefore reasonable to
assume that there is some form of pleasure or satisfaction connected
with the act. This assumption is confirmed by the behaviour of males,
who in the case of many species are prepared to work to get access to
female animals, especially if the female animal is in oestrus, and males
who for breeding purposes are used to having sperm collected become very eager, when the equipment they associate with the collection is taken out.[53]
There is nothing in female mammals' anatomy or physiology that contradicts that stimulation of the sexual organs
and mating is able to be a positive experience. For instance, the
clitoris acts in the same way as with women, and scientific studies have
shown that the success of reproduction is improved by stimulation of
clitoris on (among other species) cows and mares in connection with
insemination, because it improves the transportation of the sperm due to
contractions of the inner genitalia. This probably also concerns female
animals of other animal species, and contractions in the inner genitals
are seen e.g. also during orgasm for women. It is therefore reasonable
to assume that sexual intercourse may be linked with a positive
experience for female animals.[54]
Koinophilia
Koinophilia is the love of the "normal" or phenotypically common (from the Greek,
koinos, meaning "the usual" or "common").
[55]
The term was introduced to scientific literature in 1990, and refers to
the tendency of animals seeking a mate to prefer that mate not to have
any unusual, peculiar or deviant features.
[55] Similarly, animals preferentially choose mates with low
fluctuating asymmetry.
[56]
However, animal sexual ornaments can evolve through runaway selection,
which is driven by (usually female) selection for non-standard traits.
[57]
Interpretation bias
The field of study of sexuality in non-human species was a long-standing
taboo.
[58] In the past, researchers sometimes failed to observe, mis-categorising and mis-described sexual behaviour which
did not meet their preconceptions.
In earlier periods, bias tended to support what would now be described
as conservative sexual mores. An example of overlooking behaviour
relates to descriptions of
giraffe mating:
When nine out of ten pairings occur between males, "[e]very male that sniffed a female was reported as sex, while anal intercourse with orgasm between males was only [categorized as] 'revolving around' dominance, competition or greetings."[58]
In the 21st century, liberal social or sexual views are often
projected upon animal subjects of research. Popular discussions of
bonobos are a frequently cited example. Current research frequently
expresses views such as that of the
Natural History Museum at the University of Oslo, which in 2006 held an exhibition on animal sexuality:
Many researchers have described homosexuality as something altogether
different from sex. They must realise that animals can have sex with
who they will, when they will and without consideration to a
researcher's ethical principles.[58]
Other animal activities may be misinterpreted due to the frequency
and context in which animals perform the behaviour. For example,
domestic ruminants display behaviours such as mounting and head-butting.
This often occurs when the animals are establishing dominance
relationships and are not necessarily sexually motivated. Careful
analysis must be made to interpret what animal motivations are being
expressed by those behaviours.
[59]
Types of sexual behaviour
Reproductive sexual behaviour
Cuckoldry
Small male
bluegill sunfishes
cuckold large males by adopting
sneaker strategies.
Alternate male strategies which allow small males to engage in
cuckoldry can develop in species such as fish where
spawning is dominated by large and aggressive males. Cuckoldry is a variant of
polyandry, and can occur with
sneak spawners. A sneak spawner is a male that rushes in to join the spawning rush of a spawning pair.
[60] A spawning rush occurs when a fish makes a burst of speed, usually on a near vertical incline, releasing
gametes at the apex, followed by a rapid return to the lake or sea floor or fish aggregation.
[61] Sneaking males do not take part in courtship. In salmon and trout, for example,
jack males
are common. These are small silvery males that migrate upstream along
with the standard, large, hook-nosed males and that spawn by sneaking
into
redds to release sperm simultaneously with a mated pair. This behaviour is an
evolutionarily stable strategy for reproduction, because it is favoured by natural selection just like the "standard" strategy of large males.
[62]
Hermaphroditism
Female
groupers change their sex to male if no male is available.
Hermaphroditism
occurs when a given individual in a species possesses both male and
female reproductive organs, or can alternate between possessing first
one, and then the other. Hermaphroditism is common in invertebrates but
rare in vertebrates. It can be contrasted with
gonochorism,
where each individual in a species is either male or female, and
remains that way throughout their lives. Most fish are gonochorists, but
hermaphroditism is known to occur in 14 families of
teleost fishes.
[63]
Usually hermaphrodites are
sequential, meaning they can
switch sex, usually from female to male (
protogyny).
This can happen if a dominant male is removed from a group of females.
The largest female in the harem can switch sex over a few days and
replace the dominant male.
[63] This is found amongst
coral reef fishes such as
groupers,
parrotfishes and
wrasses. It is less common for a male to switch to a female (
protandry).
[4]:162 As an example, most
wrasses are
protogynous hermaphrodites within a haremic mating system.
[64][65] Hermaphroditism allows for complex mating systems. Wrasses exhibit three different mating systems: polygynous,
lek-like, and promiscuous mating systems.
[66]
Sexual cannibalism
Araneus diadematus – cannibalistic mating behaviour
Sexual cannibalism is a behaviour in which a female animal kills and
consumes the male before, during, or after copulation. Sexual
cannibalism confers fitness advantages to both the male and female.
[citation needed] Sexual cannibalism is common among insects, arachnids
[67] and
amphipods.
[67] There is also evidence of sexual cannibalism in
gastropods and
copepods.
[68]
Sexual coercion
During mating, the male
muscovy duck typically immobilises the female.
Sex in a forceful or apparently coercive context has been documented in a variety of species. In some
herbivorous herd species, or species where males and females are very different in size, the male
dominates sexually by force and size.
[citation needed]
Some species of birds appear to combine sexual intercourse with apparent violent assault; these include
ducks,
[69][70] and
geese.
[citation needed] Female
white-fronted bee-eaters
are subjected to forced copulations. When females emerge from their
nest burrows, males sometimes force them to the ground and mate with
them. Such forced copulations are made preferentially on females who are
laying and who may therefore lay eggs fertilised by the male.
[71]
In the
Acilius genus of
water beetles, an "
evolutionary arms race"
between the two sexes means that there is no courtship system for these
beetles. Their mating behaviours include males holding females
underwater till exhausted, and allowing only occasional access to the
surface to breathe for up to six hours (to prevent them breeding with
other males), and females which have a variety of body shapings (to
prevent males from gaining a grip).
[72]
It has been reported that young male elephants in South Africa sexually coerced and killed rhinoceroses.
[73]
This interpretation of the elephants' behaviour was disputed by one of
the original study's authors, who said there was "nothing sexual about
these attacks".
[74]
Parthenogenesis
Parthenogenesis
is a form of asexual reproduction in which growth and development of
embryos occur without fertilisation. Technically, parthenogenesis it is
not a behaviour, however, sexual behaviours may be involved.
Whip-tailed lizard
females have the ability to reproduce through parthenogenesis and as
such males are rare and sexual breeding non-standard. Females engage in
"pseudocopulation"
[75] to stimulate
ovulation,
with their behaviour following their hormonal cycles; during low levels
of oestrogen, these (female) lizards engage in "masculine" sexual
roles. Those animals with currently high oestrogen levels assume
"feminine" sexual roles. Lizards that perform the courtship ritual have
greater fecundity than those kept in isolation due to an increase in
hormones triggered by the sexual behaviours. So, even though asexual
whiptail lizards populations lack males, sexual stimuli still increase
reproductive success. From an
evolutionary
standpoint these females are passing their full genetic code to all of
their offspring rather than the 50% of genes that would be passed in
sexual reproduction.
[citation needed]
It is rare to find true parthenogenesis in fishes, where females
produce female offspring with no input from males. All-female species
include the Texas
silverside,
Menidia clarkhubbsi[76] as well as a complex of Mexican
mollies.
[4]:162
Parthenogenesis has been recorded in 70 vertebrate species
[77] including
hammerhead sharks,
[78] blacktip sharks,
[79] amphibians
[80][81] and crayfish.
[82][83]
Unisexuality
Unisexuality occurs when a species is all-male or all-female. Unisexuality occurs in some fish species, and can take complex forms.
Squalius alburnoides,
a minnow found in several river basins in Portugal and Spain, appears
to be an all-male species. The existence of this species illustrates the
potential complexity of mating systems in fish. The species originated
as a hybrid between two species, and is
diploid, but not hermaphroditic. It can have
triploid and
tetraploid forms, including all-female forms that reproduce mainly through
hybridogenesis.
[84]
Others
- Interbreeding: Hybrid
offspring can result from the mating of two organisms of distinct but
closely related parent species, although the resulting offspring is not
always fertile. According to Alfred Kinsey, genetic studies on wild animal populations have shown a "large number" of inter-species hybrids.[85]
- Prostitution: There are reports that animals occasionally engage in prostitution.
A small number of pair-bonded females within a group of penguins took
nesting material (stones) after copulating with a non-partner male. The
researcher stated "I was watching opportunistically, so I can't give an
exact figure of how common it really is."[86]
It has been reported that "bartering of meat for sex ... forms part of
the social fabric of a troop of wild chimps living in the Tai National
Park in the Cote d'Ivoire."[87]
- Pavlovian conditioning: The sexualisation of objects or locations is recognised in the animal breeding world. For example, male animals may become sexually aroused
upon visiting a location where they have been allowed to have sex
before, or upon seeing a stimulus previously associated with sexual
activity such as an artificial vagina.[53]
Sexual preferences for certain cues can be artificially induced in rats
by pairing scents or objects with their early sexual experiences.[88] The primary motivation of this behaviour is Pavlovian conditioning, and the association is due to a conditioned response (or association) formed with a distinctive "reward".[88]
- Viewing images: A study using four adult male rhesus macaques (Macaca mulatta) showed that male rhesus macaques will give up a highly valued item, juice, to see images of the faces or perineum of high-status females.[89] Encouraging captive pandas to mate is problematic. Showing young male pandas "panda pornography"
is credited with a recent population boom among pandas in captivity in
China. One researcher attributed the success to the sounds on the
recordings.[90]
- Copulatory wounding and Traumatic Insemination: Injury to a
partner’s genital tract during mating occurs in at least 40 taxa,
ranging from fruit flies to humans. However, it often goes unnoticed due
to its cryptic nature and because of internal wounds not visible
outside.[91]
Non-reproductive sexual behaviour
There is a range of behaviours that animals perform which appear to
be sexually motivated but which can not result in reproduction. These
include:
- Masturbation: Some species, both male and female, masturbate, both when partners are available and otherwise.[92][93]
- Oral sex: Several species engage in both autofellatio and oral sex. This has been documented in brown bears,[94] Tibetan macaques,[95] wolves,[96] goats, primates, hyenas,[97] bats,[98] cape ground squirrels[99] and sheep. In the greater short-nosed fruit bat,
copulation by males is dorsoventral and the females lick the shaft or
the base of the male's penis, but not the glans which has already
penetrated the vagina. While the females do this, the penis is not
withdrawn and research has shown a positive relationship between length
of the time that the penis is licked and the duration of copulation.
Post copulation genital grooming has also been observed.[100]
- Homosexuality:
Same-sex sexual behaviour occurs in a range of species, especially in
social species, particularly in marine birds and mammals, monkeys, and
the great apes. As of 1999, the scientific literature contained reports of homosexual behaviour in at least 471 wild species.[101] Organisers of the Against Nature? exhibit stated that "homosexuality has been observed among 1,500 species, and that in 500 of those it is well documented."[102]
- Genital-genital rubbing:
This is sexual activity in which one animal rubs his or her genitals
against the genitals of another animal. This is stated to be the
"bonobo's most typical sexual pattern, undocumented in any other
primate".[104][105]
- Inter-species mating: Some animals opportunistically mate with individuals of another species.[106]
- Sex involving juveniles: Male stoats (Mustela erminea) will sometimes mate with infant females of their species.[107] This is a natural part of their reproductive biology – they have a delayed gestation period, so these females give birth the following year when they are fully grown. Juvenile male chimpanzees have been recorded mounting and copulating with immature chimps. Infants in bonobo societies are often involved in sexual behaviour.[108]
- Necrophilia:
This describes when an animal engages in a sexual act with a dead
animal. It has been observed in mammals, birds, reptiles and frogs.[109]
- Bisexuality: This describes when an animal shows sexual behaviour towards both males and females.
- Extended female sexuality: This is when females mate with males outside of their conceptive period.[110]
Seahorse
Seahorses,
once considered to be monogamous species with pairs mating for life,
were described in a 2007 study as "promiscuous, flighty, and more than a
little bit gay".
[111] Scientists at 15
aquaria
studied 90 seahorses of three species. Of 3,168 sexual encounters, 37%
were same-sex acts. Flirting was common (up to 25 potential partners a
day of both sexes); only one species (the British spiny seahorse)
included faithful representatives, and for these 5 of 17 were faithful,
12 were not. Bisexual behaviour was widespread and considered "both a
great surprise and a shock", with big-bellied seahorses of both sexes
not showing partner preference. 1,986 contacts were male-female, 836
were female-female and 346 were male-male.
[111]
Bonobo
The
bonobo, which has a
matriarchal society,
is a fully bisexual species –
both males and females engage in sexual behaviour with the same and
the opposite sex, with females being particularly noted for engaging in
sexual behaviour with each other and at up to 75% of sexual activity
being nonreproductive. Primatologist Frans de Waal believes that bonobos
use sexual activity to resolve conflict between individuals.
[112] Sexual activity occurs between almost all ages and sexes of bonobo societies.
[113]
Dolphin
Male
bottlenose dolphins
have been observed working in pairs to follow or restrict the movement
of a female for weeks at a time, waiting for her to become sexually
receptive. The same pairs have also been observed engaging in
intense sexual play with each other. Janet Mann, a professor of biology and psychology at Georgetown University, argues
[114] that the common same-sex behaviour among male
dolphin
calves is about bond formation and benefits the species evolutionarily.
They cite studies that have shown the dolphins later in life are
bisexual and the male bonds forged from homosexuality work for
protection as well as locating females with which to reproduce. In 1991,
an English man was prosecuted for allegedly having sexual contact with a
dolphin.
[115]
The man was found not guilty after it was revealed at trial that the
dolphin was known to tow bathers through the water by hooking his penis
around them.
[115]
Hyena
The female
spotted hyena has
a unique urinary-genital system, closely resembling the penis of the male, called a
pseudo-penis.
The family structure is matriarchal and dominance relationships with
strong sexual elements are routinely observed between related females.
They are notable for using visible sexual arousal as a sign of
submission but not dominance in males as well as females (females have a
sizable erectile
clitoris).
[116] It is speculated that to facilitate this, their
sympathetic and
parasympathetic nervous systems may be partially reversed in respect to their reproductive organs.
[117]
Mating behaviour
Vertebrates
Mammals
Mammals mate by vaginal copulation. To achieve this, the male usually mounts the female from behind.
[118] The female may exhibit
lordosis
in which she arches her back ventrally to facilitate entry of the
penis. Amongst the land mammals, other than humans, only bonobos mate in
a face-to-face position,
[119][better source needed] although ventro-ventral copulation has also been observed in
Rhabdomys.[120] Some sea mammals copulate in a belly-to-belly position.
[121][122] Some
camelids mate in a lying-down position.
[123] In most mammals ejaculation occurs after multiple intromissions,
[124] but in most ruminant species, a single
pelvic thrust occurs during copulation.
[125][126]
Invertebrates
Invertebrates are often
hermaphrodites. Some hermaphroditic
land snails
begin mating with an elaborate tactile courting ritual. The two snails
circle around each other for up to six hours, touching with their
tentacles, and biting lips and the area of the genital pore, which shows
some preliminary signs of the eversion of the penis. As the snails
approach mating, hydraulic pressure builds up in the blood sinus
surrounding an organ housing a sharpened dart. The dart is made of
calcium carbonate or
chitin, and is called a
love dart.
Each snail manoeuvres to get its genital pore in the best position,
close to the other snail's body. Then, when the body of one snail
touches the other snail's genital pore, it triggers the firing of the
love dart.
[127]
After the snails have fired their darts, they copulate and exchange
sperm as a separate part of the mating progression. The love darts are
covered with a mucus that contains a
hormone-like substance that facilitates the survival of the sperm.
[128][129]
Penis fencing is a mating behaviour engaged in by certain species of
flatworm, such as
Pseudobiceros bedfordi. Species which engage in the practice are hermaphroditic, possessing both eggs and sperm-producing testes.
[130]
The species "fence" using two-headed dagger-like penises which are
pointed, and white in colour. One organism inseminates the other. The
sperm is absorbed through pores in the skin, causing fertilisation.
Corals can be both
gonochoristic (unisexual) and
hermaphroditic,
each of which can reproduce sexually and asexually. Reproduction also
allows corals to settle new areas. Corals predominantly reproduce
sexually. 25% of
hermatypic corals (stony corals) form single sex (
gonochoristic) colonies, while the rest are
hermaphroditic.
[131] About 75% of all hermatypic corals "broadcast spawn" by releasing
gametes –
eggs and
sperm – into the water to spread offspring. The gametes fuse during fertilisation to form a microscopic
larva called a
planula, typically pink and elliptical in shape.
[132] Synchronous spawning is very typical on the coral reef and often, even when multiple
species
are present, all corals spawn on the same night. This synchrony is
essential so that male and female gametes can meet. Corals must rely on
environmental cues, varying from species to species, to determine the
proper time to release gametes into the water. The cues involve lunar
changes, sunset time, and possibly chemical signalling.
[131] Synchronous spawning may form hybrids and is perhaps involved in coral
speciation.
[133]
Butterflies spend much time searching for mates. When the male spots a mate, he will fly closer and release
pheromones. He then performs a special
courtship dance
to attract the female. If the female appreciates the dancing she may
join him. Then they join their bodies together end to end at their
abdomens. Here, the male passes the sperm to the female's egg-laying tube, which will soon be fertilised by the sperm.
[134] The male often dies shortly after mating.
Many animals make
plugs of mucus to seal the female's
orifice
after mating. Normally such plugs are secreted by the male, to block
subsequent partners. In spiders the female can assist the process.
[135]
Spider sex is unusual in that males transfer their sperm to the female
on small limbs called pedipalps. They use these to pick their sperm up
from their genitals and insert it into the female's sexual orifice,
rather than copulating directly.
[135]
On the 14 occasions a sexual plug was made, the female produced it
without assistance from the male. On ten of these occasions the male's
pedipalps then seemed to get stuck while he was transferring the sperm
(which is rarely the case in other species of spider), and he had great
difficulty freeing himself. In two of those ten instances, he was eaten
as a result.
[135]
Genetic evidence of interspecies sexual activity
Research into
human evolution confirms that, in some cases, interspecies sexual activity may have been responsible for the evolution of new species (
speciation). Analysis of animal
genes found evidence that after
humans had diverged from other
apes, interspecies mating nonetheless occurred regularly enough to change certain genes in the new
gene pool.
[136] Researchers found that the
X chromosomes of humans and chimps may have
diverged
around 1.2 million years after the other chromosomes. One possible
explanation is that modern humans emerged from a hybrid of human and
chimp populations.
[137]
A 2012 study questioned this explanation, concluding that "there is no
strong reason to involve complicated factors in explaining the autosomal
data".
[138]
Inbreeding avoidance
When close relatives mate, progeny may exhibit the detrimental effects of
inbreeding depression. Inbreeding depression is predominantly caused by the
homozygous expression of recessive deleterious alleles.
[139] Over time, inbreeding depression may lead to the evolution of
inbreeding avoidance
behaviour. Several examples of animal behaviour that reduce mating of
close relatives and inbreeding depression are described next.
Reproductively active female
naked mole-rats tend to associate with unfamiliar males (usually non-kin), whereas reproductively inactive females do not discriminate.
[140] The preference of reproductively active females for unfamiliar males is interpreted as an adaptation for avoiding inbreeding.
When mice inbreed with close relatives in their natural habitat, there is a significant detrimental effect on progeny survival.
[141] In the house mouse, the
major urinary protein (MUP) gene cluster provides a highly polymorphic scent signal of genetic identity that appears to underlie
kin recognition and
inbreeding avoidance. Thus there are fewer matings between mice sharing MUP
haplotypes than would be expected if there were random mating.
[142]
Meerkat females appear to be able to discriminate the odour of their kin from the odour of their non-kin.
[143]
Kin recognition is a useful ability that facilitates both cooperation
among relatives and the avoidance of inbreeding. When mating does occur
between meerkat relatives, it often results in
inbreeding depression.
Inbreeding depression was evident for a variety of traits: pup mass at
emergence from the natal burrow, hind-foot length, growth until
independence and juvenile survival.
[144]
The
grey-sided vole (
Myodes rufocanus) exhibits male-biased dispersal as a means of avoiding incestuous matings.
[145]
Among those matings that do involve inbreeding the number of weaned
juveniles in litters is significantly smaller than that from non-inbred
litters indicating inbreeding depression.
In natural populations of the bird
Parus major (great tit),
inbreeding is likely avoided by dispersal of individuals from their
birthplace, which reduces the chance of mating with a close relative.
[146]
Toads display
breeding site fidelity, as do many
amphibians. Individuals that return to natal ponds to breed will likely encounter
siblings as potential mates. Although
incest is possible,
Bufo americanus
siblings rarely mate. These toads likely recognise and actively avoid
close kins as mates. Advertisement vocalisations by males appear to
serve as cues by which females recognise their kin.
[147]
See also
La sexualité animale est diverse et dépend des espèces. Certaines pratiques peuvent être rapprochées de pratiques humaines.
Une définition complexe
La notion de sexualité chez les animaux diffère de celle qu'on applique généralement aux humains. Ainsi, le
Trésor de la Langue Française définit ainsi la « sexualité » chez les animaux :
« Ensemble des mécanismes physiologiques qui concourent au rapprochement des sexes et à la reproduction de l'espèce1. »
Alors que chez l'être humain cela désigne :
« Ensemble des tendances et des activités qui, à travers le
rapprochement des corps, l'union des sexes (généralement accompagnés
d'un échange psycho-affectif), recherchent le plaisir charnel,
l'accomplissement global de la personnalité1. »
Cette notion, très psychologique, est donc difficile à appliquer
telle quelle aux animaux, et la sexualité se cantonne donc le plus
souvent dans le règne animal à la somme des comportements sexuels
observables, sans dimension psychologique ou ontologique. Il en va de
même de la sexualité prise au sens d'« orientation sexuelle »
2,
qui est une définition éminemment subjective et existentialiste,
notamment dans sa dimension exclusive : par exemple, si on observe des
comportements homosexuels chez de nombreux vertébrés, l'« homosexualité » au sens d'attirance sexuelle
exclusivement tournée vers des individus de même sexe n'a jamais été observé dans la nature
[réf. nécessaire].
Rites nuptiaux
De nombreux animaux ont des rituels de
parade nuptiale
ayant surtout pour fonction de démontrer la capacité des partenaires à
engendrer une progéniture saine et robuste et/ou à s'en occuper
convenablement.
Ainsi, chez les
macaques à longue queue (
Macaca fascicularis),
le mâle approche la femelle en commençant par l'épouiller et lui
nettoyer le pelage. Selon une étude publiée en décembre 2007 dans la
revue
Animal Behavior, réalisée entre 2003 et 2005 par Michael
Gumert, un spécialiste du comportement animal de l'université
technologique Nanyang de Singapour, portant sur cinquante groupes de
macaques à longue queue et 243 séances d'épouillage et réalisée dans le
Parc national de Tanjung Puting à Kalimantan Tengah en Indonésie, on a
constaté une augmentation de l'activité sexuelle après un épouillage, le
nombre de rapports sexuels des femelles passant de 1,5 par heure en
temps normal à 3,5. La durée du soin peut aller de quelques secondes à
une demi-heure voire plus, et elle augmente si le mâle a un statut
inférieur ou si le nombre de femelles est restreint
3.
Chez les
manchots Adélie, les femelles chapardent à leurs partenaires des galets qu'elles utilisent pour améliorer le confort de leur nid
4.
Les dons nuptiaux, accordés par les mâles aux femelles et visant à
enrichir les apports nutritionnels de ces dernières, sont fréquents chez
les insectes et les araignées
5,6,7.
Critères définissant la culture chez l'animal
La culture est un ensemble de
savoirs
et de pratiques (règles sociales, utilisation d'outils, apprentissages
sociaux…) qui, au sein d'un groupe donné, se partagent et se
transmettent socialement et non par
héritage génétique.
« L'exemple le plus célèbre de culture animale est le lavage de patates douces chez le macaque japonais. »
« Si une pareille variante comportementale se généralise au sein du groupe, si elle se transmet par tradition
d'une génération à l'autre et si le groupe se dote ainsi d'une
particularité acquise qui lui est propre, alors on est fondé de parler
de culture au sens large8. »
Homosexualité et bisexualité animales
La
sexualité animale ne se limite pas à des rapports monosexuels ou
hétérosexuels
à intention reproductive. Ainsi, les comportements sexuels animaliers
peuvent avoir différents objets et revêtir de multiples formes. Les
spécialistes ont noté divers comportements analogues aux comportements
humains non reproductifs tels qu'
homosexualité,
bisexualité ou
masturbation9.
L'
homosexualité au sens large (ou comportementaliste) se définit par des rapports sexuels et/ou amoureux entre individus de même sexe
10.
Dans son livre
Biological Exuberance: Animal Homosexuality and Natural Diversity paru en 1999, le chercheur
Bruce Bagemihl
affirme que des comportements homosexuels animaux ont été observés chez
près de 450 espèces animales (essentiellement des espèces qui ont peu
de
dimorphisme sexuel),
dans chaque grande zone géographique et chaque groupe animal, et qu'ils
peuvent être séparés en 5 groupes distincts : parade amoureuse,
affection, relation sexuelle, vie en couple et comportement parental
11. Les organisateurs de l'exposition
Against Nature?
affirmaient que des comportements homosexuels étaient retrouvés chez la
plupart des groupes de vertébrés, mais aussi parmi les insectes, les
araignées, les crustacés, les octopodes et les vers parasites, le
phénomène étant reporté chez près de 1500 espèces animales et bien
documenté chez 500 d'entre elles
12.
Pour le professeur
Thierry Lodé, de l'université de Rennes 1
13,
« toutes les conduites sexuelles existent dans la nature » bien que les comportements exclusifs restent plutôt rares, l'
évolution privilégiant toujours la reproduction. Toutefois, des chercheurs
14,15,16
pensent que le qualificatif d'homosexualité ne peut pas être appliqué
au règne animal car bien que le comportement homoérotique occasionnel
soit présent chez certains, l'homosexualité au sens humain contemporain
d'« attirance sexuelle exclusivement dirigée vers des partenaires de
même sexe au détriment de la reproduction sexuée » n'est presque jamais
observée, et ne constitue en aucun cas un acte « conscient ».
Masturbation animale
La
masturbation
au sens large est une pratique sexuelle consistant à stimuler les
parties génitales dans le but d'obtenir ou de donner du plaisir ; cette
pratique a été observée chez de nombreuses espèces, sauvages comme
domestiques.
Ces observations indiquent, selon les militants pro-masturbation, que
cette pratique est totalement naturelle (bien que certains opposants à
la masturbation contestent ces preuves). Le sujet est donc très
controversé.
[réf. nécessaire]
Autres comportements sexuels
- Des comportements sexuels entre adultes et petits ont été observés chez certaines espèces animales, comme les singes bonobos.
- Une jeune otarie de Kerguelen mâle a tenté de s'accoupler avec un manchot royal (dans les Île Marion). Le manchot s'en est sorti sans dommages ; les experts en éthologie recherchent encore la raison d'un tel comportement17.
Comportements sexuels culturels chez l'animal
Un exemple de comportement sexuel de l'ordre du culturel serait chez le bonobo l'utilisation d'objet pour la
masturbation18.
Voir aussi
Bibliographie et vidéographie
- (en) Anders Agmo Functional and dysfunctional sexual behavior [archive] Elsevier 2007
- (en) Bruce Bagemihl, Biological Exuberance: Animal Homosexuality and Natural Diversity, Stonewall Inn Editions, 1999. ISBN 0-312-25377-X
- (en) John Roughgarden, Evolution's Rainbow : Diversity, Gender, and Sexuality in Nature and People, éd. University Press, 2004
- (fr) Thierry Lodé, La guerre des sexes chez les animaux, Odile Jacob, 2006. (ISBN 2-7381-1901-8)
- Documentaire Homosexualité animale (épisode de la série Animaux trop Humains [archive]), réalisé par Bertrand Loyer, Jessica Menendez et Stéphane Alexandresco, 2006. Distributeur : Off the Fence, Saint Thomas Productions.
Articles connexes
Liens externes
