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Tonkean macaques chimpanzees

Sensory Exploitation Hypothesisi
Zinner, van Schaik, Nunn and Kappeler (2004) proposed that an altered version of Holland and Rice’s (1998) chase-away model to explain the function of sexual swellings. The chase-away model is governed on the idea of ‘sensory exploitation’, in which traits evolve to greatly stimulate the perceivers’ sensory system. Resultantly, these traits serve to manipulate a perceiver’s behaviour in the signaller’s favour. In the specific case of sexual swellings, it is Zimmer and colleagues suggestion that a male’s inherent preference for large swellings as a fertility signals is exploited to combat a male’s resistance to mate. Therefore, the small sexual swellings are thought to have become exaggerated as a form of antagonistic coevolution.

Support for this hypothesis comes from Anderson and Bielert (1994). Upon investigating different species of macaque, the researchers demonstrated an association between fertility and the size of an individual's sexual swelling. Specifically, females of low fertility, such as adolescents, exhibited substantially larger swellings than adults of a higher fertility level. Research remains fairly consistent across animal species. For instance, Hausfater’s (1975) research revealed that female yellow baboons (Papio cynocephalus) who struggle to conceive were, on average, those that displayed the most prominent sexual swellings. In contrast, Clutton-Brock and Harvey (1976) and later Pagel (1994) were critical of the sensory exploitation theory. They upheld the belief that, if female sexual swellings were not honest signals of a female’s fertility, males would have evolved to identify difference’s in female quality or to have equal preference over females with different swelling sizes.

Many Males Hypothesis
According to Hrdy’s (1977) ‘many male’ hypothesis, the function of sexual swellings is to increase a female’s opportunity to mate with several different males within and across cycles .This is because of a male’s attraction to the sexual swellings. By mating with multiple males, male parental certainty may be diluted. Resultantly, there may be a decreased the risk of infanticide to their future offspring. Males who have mated with the female during her conceptive cycle, may be more motivated to deter infanticidal males because they have an illusion that they are the father of the child. Indeed, promiscuous mating reduces the likelihood of successful infanticide.

Dixson and Mundy (1994) stated that sexual swellings function in cryptic female choice; the differential selection of gametes within the female reproductive tract. They found that the sexual swelling of chimpanzees makes it more difficult for males to deposit sperm near the cervix, and that males differ in their ability to do this. Therefore, the increased female promiscuity, caused by the sexual swellings, is likely to result in the female being inseminated by the male that is most successful in sperm competition. 137.205.238.79 (talk) 17:45, 26 February 2016 (UTC)

Redo
According to Hrdy's (1977) ‘many-males’ hypothesis, sexual swellings enable a female to attract multiple different as mating partners. By mating with several males across their menstrual cycle, a female can diminish a males’ parental certainly. This is because of a male’s attraction to the sexual swellings. In turn, this parental uncertainty is proposed to lead to two contrasting outcomes: it may increase the total amount of parental care that their offspring receives, whilst also reducing the possibility that a female’s offspring suffers infanticide. In support of Hrdy’s second conjecture, is the work of White, Balko and Fox’s (1993). Whilst studying the mating behaviour of captive ruffled lemurs (varecia variegate variegate) the authors discovered that the male ruffled lemurs were less likely to kill infants that they believed themselves to have sired.

To successfully ensure paternal confusion, Hrdy predicted that ovulation must be randomly distributed across the term where the sexual swelling is of maximum tumescence. This would ensure that males were unable to use the swelling as a signal of female fertility, and maintain the potential for paternal uncertainty to arise. Gordon, Gust, Busse and Wilson (1991) provide convincing evidence for this prediction. They noted that female sooty mangabey (cercocebus toquatus atys) produced sexual swellings both when they were fertile and with child. However, in 26-35 species of anthropoid primates sexual swellings are only observed during the most fertile period of a female’s menstrual cycle. This latter evidence diminishes the validity of the many-males hypothesis.

Additional criticism of the many-males hypothesis stems from a female's ability to attract multiple males on the basis of proceptivity alone without expresses any conspicuous visual cues that educate males of their mating probabilities. Specifically, female patas monkeys, grey langurs and retail monkeys evidence high sufficiency in attracting, and subsequently mating with, several males without exhibiting sexual swellings.

Social Passport Hypothesis
The time surrounding a female chimpanzee’s first sexual swelling corresponds with their initial exploration of different territories and ultimately their permanent emigration away from their native group. The conspicuous sexual swelling may therefore act as a ‘social passport’ that advertises sexual receptivity during this transitional period between communities. Principally, the swelling acts to transform male aggression into sexual urges. Resultantly, the female gains acceptance from males’ living within the new social group; reducing the likelihood that they’ll be attacked by the males themselves increasing the chance that the male will protect them from hostile resident females. The latter is needed because, although the immigrant females are generally accepted by males, resident females are aggressive towards young immigrants. For instance, infanticide victims are most likely to be infants that were sired outside of the female attacker’s community or the children of mother's who had immigrated into the community before the offspring had been conceived. This relatively safe passage between different communities allows adolescent females to investigate the local competitors and resources of different territories before they decide where to re-settle and breed.

A female chimpanzee’s first sexual swelling occurs near the time when they first begin to explore different territories. This is a potentially dangerous period prior to a female’s permanent emigration away from their native social group. Based in this observation, sexual swellings are believed to act as a ‘social passport’ that advertises sexual receptivity during this transitional period between communities. The hypothesis proposes that the swelling transforms the aggression that males in the new social group may show to the female into sexual urges. . This is thought to gain the female acceptance from males living within the new social group. In turn, this male acceptance reduces the likelihood that the female will be attacked by the males themselves and increases the likelihood that the males will protect them from hostile resident females. . Under the social passport hypothesis, sexual swellings therefore allow a relatively safe passage between different communities allows adolescent females to investigate the local competitors and resources of different territories before they decide where to re-settle and breed permanently.

Version from Wiki:

The time surrounding a female chimpanzee’s first sexual swelling corresponds with their initial exploration of different territories and ultimately their permanent emigration away from their native group. Therefore, the conspicuous sexual swelling are believed to act as a ‘social passport’ that advertises sexual receptivity during this transitional period between communities. For instance, the swelling may act to transform male aggression into sexual urges and consequently gains the female acceptance from males living within the new social group. This acceptance reduces the likelihood that they will be attacked by the males themselves and increasing the likelihood that the male will protect them from hostile resident females. The latter is needed because, although the immigrant females are generally accepted by males, resident females are aggressive towards young immigrants. For instance, infanticide victims are most likely to be infants that were sired outside of the female attacker’s community, or the children of mother's who had immigrated into the community before the offspring had been conceived. This relatively safe passage between different communities allows adolescent females to investigate the local competitors and resources of different territories before they decide where to re-settle and breed.

Young females who already had an infant within a new community may also benefit from sexual swellings as a ‘social passport’. Specifically, for gaining male support during female-female interactions ; the young females may require help from males during conflicts with more dominant, higher-ranking females, over resources.

Under the social passport hypothesis, young females who have safely integrated within the new community still benefit from sexual swellings. Specifically, young females are believed to require the support of males that they have acquired when integrating into the new group during conflicts with females of a higher social rank or when protecting their infants from fights with the children of these higher-ranking females. Therefore, sexual swellings act as a social passport that eases female-female interactions.

Physical Features of Sexual Swellings
New Edit: The size of sexual swellings not only varies within each cycle, but can also vary in size across female cycles and across species. Specifically, the maximal swelling size increases from cycle to cycle for individual female chimpanzees and baboons. Additionally, the duration of maximal sexual swellings size varies considerably between species. Baboons for instance, have a maximal swelling that lasts for approximately 15.1 days, whilst the duration of maximal swelling lasts for 10.9 days in chimpanzees.

Old Edit: Sexual swellings are water-filled edemas of mainly the external or internal genitalia of females (D). However, the swellings can extend further to the skin of the circumanal, subcausal and paracallosal regions. Small sexual swellings are characterised by a moderate size and pinkness of the genitalia. The small swellings are found in Old and New World monkeys, in prosimians and in gibbons. In contrast, the prevalence of exaggerated sexual swellings ismainly restricted to Old Word primate species. For instance, they occur in all species of Cercocebus, Mandrillus, Theropithecus, Papio and Pan, and in most macaques, colobines and guenons.

Several characteristics have been identified as being correlates of sexual swellings in primates. Exaggerated sexual swellings are commonly found in primates which live in large social groups with multiple males. It’s noted that those species with such swellings have a higher average of males per group than those without; over twice as many, and of the ‘Old World’ primate species which have multi-male social systems 71% show exaggerated swellings. Additionally, primates with sexual swellings have been shown to demonstrate non-seasonal breeding patterns, longer mating periods and longer ovulation cycles. Of the 23 species which are both non-seasonal breeders, and live in multi-male societies, 91% have sexual swellings. Peak swelling is likely to coincide with the highest potential of ovulation but this is not a perfect association. For example, research on West African Chimpanzees showed that the higher probabilities of ovulation tended to be within 7 to 9 days of the onset of maximum swelling of sexual skin.

Exaggerated sexual swellings also increase gradually in size throughout the female’s cycle beginning after menstruation,. For example, research on baboons showed that after 14 days of gradual increase swellings peaked for 2 days before reducing. These cyclic changes in appearance of the sexual skin reflect changes of ovarian hormones (oestrogen and progestogen) during the female menstrual cycle. Specifically, the increase in sexual swelling size during the follicular phase is correlated with an increase in oestrogen levels, and the decrease in swelling size during the luteal phase is associated with rising in progesterone levels. In support of this idea, shown in ovariectomized chimpanzees, swelling can be induced by estrogen and inhibited by progesterone. .

The maximal size of an individual's swelling is likely to coincide with the highest potential of ovulation but this is not a perfect association. For example, research on West African Chimpanzees showed that the higher probabilities of ovulation tended to be within 7 to 9 days of the onset of maximum swelling of sexual skin. . Additionally, a study into wild white-handed gibbons showed that maximum swelling size and ovulation overlapped closely in 80% of menstrual cycles.

The size of sexual swellings not only varied within each cycle, but also can vary in size within an individual across cycles. Specifically, Deschner, Heistermann and Boesch (2004) noted that maximal swelling size increases from cycle to cycle within one individual chimpanzee. Such inter-individual differences have also been discovered whilst investigating baboons. The duration of maximal sexual swellings size also varies considerably between species. baboons for instance, have a maximal swelling that lasts for approximately 15.1 days, whilst the duration of maximal swelling lasts for 10.9 days in chimpanzees.

Like size, firmness varies considerably across the cycle. For instance, in chimpanzees, the state of maximum firmness correlates with the period of maximum tumescence.

137.205.238.79 (talk) 18:07, 26 February 2016 (UTC)

Lead
Sexual swellings are enlarged areas of the perineal skin occurring in some female primates that vary in size over the course of the menstrual cycle. Females use the exaggerated swellings to compete for access to males, and to advertise variation in female fitness.

Sexual swellings are enlarged areas of the perineal skin occurring in some female primates that vary in size and firmness over the course of the menstrual cycle. Thought to be an honest signal of fertility, males primates are attracted to these swellings and resultantly prefer, and compete for, females with the largest swellings.

Though the prevalence of sexual swellings is certain, their function remains unknown. . Over the last 50 years, eight principle explanations have been proposed; each claiming to account for the function of exaggerated swellings. Alone, however, no single hypothesis is believed to account for the function of sexual swellings; a combination of these theories may be more appropriate. In line with this ideal, the most recent account regarding sexual swellings’ function combines several existing theories in the attempt to prodive a more comprehensive account of sexual swellings.

Studies of chimpanzees and Barbary macaques suggest that sexual swellings serve as honest advertising of female fertility. This encourages males to copulate when the probability of conception is highest. Larger sexual swellings in female baboons, for example, signal greater reproductive value. Male baboons, as a result, are seen to prefer females with these larger sexual swellings, as sexual swelling size is related to an earlier age of sexual maturation, as well as with both increased numbers of offspring and improved survival rates. It is, therefore, likely that mating with these females will increase their chances of producing surviving offspring. Through advertising their quality, females can mate with high quality males who are capable of defending their offspring from other males, and those who can offer greater material benefits. Psuncv (talk) 13:46, 26 March 2016 (UTC)

Male Services
The male services hypothesis is praised for its ability to account for the evidence that swellings do not always precisely indicate ovulation; the lack of precision is likely to extend the duration of mate guarding and consortship behaviours outlined by the hypothesis. Some of the hypotheses predictions are not met, however. For instance, despite the benefits of a reduction in harassment from subordinate males when with dominant males, it has been observed that females do not always choose to mate with these stronger and more dominant mates.

cut offs
Exaggerated sexual swellings can be observed during the periovulatory phase of a female mammals’ sexual cycle.