![]() ![]() 4 Receptivity, even when the female is most fertile, is not a passive action. However, it can be seen by the female shifting to a specific stance allowing for penile insertion or ejaculation (depending on the species), remaining stationary in that position, etc. Receptivity is harder to measure in the field since it requires a male approaching and wanting to mate. 2 (See p.133 of Dixson (2012) for a more complete list of proceptive behaviors in female primates 3.) 4 Proceptivity instead gets measured via female behaviors: counts of affiliative behaviors (e.g., a female moving to sit near a male or to stay in his vicinity), more direct sexual solicitation (e.g., a female presenting her hindquarters to a male or making species-specific vocalizations, facial expressions, and/or gestures like lip-smacking in baboons or head-bobbing in rhesus monkeys), investigation of the male’s anogenital region, female grooming of the male, etc. Hence, attractivity can be thought of as the value to a male of a female being a sexual stimulus, and typically gets measured for primates in the field via male behaviors: frequency of approaches by males to a female, frequency of attempts by males to mount a female, etc. Finally, receptivity is the willingness of a female to accept a male and allow copulation/intravaginal ejaculation with him to occur 3. Proceptivity refers to behavioral cues displayed by females in order to initiate and/or maintain sexual interactions with males. Concealed ovulation, also of much interest, is the lack of any such visual signs around a female’s time of ovulation. around the female’s genital region, that are used to signal probable times of ovulation. Although the focus of this paper is on female sexual receptivity, much of the work surrounding the estrus cycles of female mammals has instead been in relation to sexual attractivity, that is non-behavioral cues, such as sexual swellings, bright colorations, etc. In general, there are three main characteristics used to describe the changes through which female mammals go when they are in estrus: sexual attractivity, proceptivity, and receptivity 2. Not only is this topic of interest among primatologists, it may help to give insight into why human females are continuously receptive to mating. As early as 1900, scientists were interested in when and why females were willing to receive male mates, noting that in most species there was a “special period of sexual desire.and only at that time, the female is willing to receive the male 1.” Despite recurring interest in this topic throughout the past century, there is still relatively limited research on primate sexual receptivity. The unique behavioral changes associated with the estrus cycle of female mammals have been researched for over a century. Overall, our work offers a theoretical framework for understanding the evolution and diversity of mating traits in female primates. Similar effects can also be achieved by increasing the non-genetic benefits provided by males. ![]() Our model predicts that increasing the impacts of infanticide will increase the length of the female receptive period, emphasizing the possible importance of paternity confusion. We find that both continuous receptivity and very short lengths of receptivity are able to evolve. We investigate how various factors, including having ovulation signs present versus concealed ovulation, female physiological costs, and group size, each influence the length of females’ receptive periods. Why is there such prominent variation in sexual receptivity length among primate species? Here we examine the evolutionary trade-offs associated with sexual receptivity length using mathematical modeling. Some primate species are like humans, sexually receptive to mating throughout their entire estrus cycle, while other species are the opposite, receptive for mere hours out of their several-week cycles. While there has been limited research on sexual receptivity in primates, this has been one recurring topic of interest. There has been much interest in the evolutionary forces responsible for, and underlying the diversity in, female primate reproductive cycles. ![]()
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