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The mating and signalling system of the socially-tolerant crested macaque.

James Higham, Michael Heistermann, Carina Saggau, Muhammad Agil, Dyah Perwitasari Farajallah, Antje Engelhardt

The social and mating systems of primates are connected, as both derive from key elements of the environment. The macaques show great variability in both, and more socially tolerant species have more despotic mating systems, with marked sexual dimorphism and male reproductive skew. Further, mating systems determine signaling systems, with the presence of female signals of fertility such as sexual swellings dependent on factors such as mating seasonality. We tested the links between social, mating and signaling systems in the most socially-tolerant of all macaques, the crested macaque. We present data on 31 ovarian cycles from 19 females studied at Tangkoko, Sulawesi. We collected female fecal samples from which we timed ovulation, detailed observations of males and females, and calibrated images of sexual swellings. We show that female estrus periods are asynchronous, and that mating skew is marked and steep, with dominant males monopolizing a high proportion of consortships and matings. We also show that both female behavior and swelling size are reliable signals of the fertile phase, making the crested macaque very clear signalers of this compared to other tested species. We argue that this is consistent with a species where males engage in contest competition for dominance rank, in which rank is surrogate for male competitiveness, such that it is in female interest to increase paternity concentration and assurance in the most dominant males. We conclude that macaque social, mating and signaling systems are all related and describe the key ecological processes that give rise to these connections.