Modeling the evolution of visual sexual signaling, receptivity, and sexual signal reliability among female primates

Communication between individuals of a species happens in myriad ways, especially among primates. Not only are verbal cues important, visual and behavioral cues can be just as important as well. Two non-verbal characteristics of the estrous period in many primate species are visual signs of ovulation and sexual receptivity. Visual signs of ovulation take the form of bright colorations and/or sexual swellings around the female's genital region on/around her time of ovulation. Different primate species also have varying lengths of receptivity, that is, willingness of a female to accept a male and permit copulation. In some species, this length of receptivity is equal to the length of time the female has visual ovulation signs present, while in other species such lengths can be much shorter or longer. Species will also vary in the amount of reliability in such signals, i.e. how closely do a female's visible ovulation signs and period of receptivity line up with her period of fertility? In this dissertation, I use mathematical modeling techniques to help answer each of these research questions relating to the evolution of primate non-verbal sexual communication. In Chapter 1, I show how certain ecological factors, such as increased group size and/or the presence of infanticide, can increase visual ovulation signaling among female primates. In Chapter 2, I show female continuous receptivity and concealed ovulation to be correlated, and how only in groups with visible ovulation signs present would one expect to find a relatively short length of time when the female will be receptive to mating. In Chapter 3, I investigate the evolution of sexual signal reliability, evaluating under what conditions will a female's visual sexual signaling line up perfectly (or not) with her peak time of fertility. Finally, in Chapter 4, I outline a future, related biological problem (the evolution of long-term pair-bonding) which could be addressed with many of the same mathematical methods/models used in the earlier chapters. Together, the results presented in this dissertation use mathematics to give new insight into primate evolution and help to resolve old mysteries surrounding primate non-verbal sexual communication.