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It has long been established that one of the driving factors underlying changes in female socio-sexual behaviour across the ovarian cycle is variation in the hormones oestrogen and progesterone. However, the effect that the social environment, and specifically con-specific bystanders, exerts on social relationships is far less clear. Here we explore the modulating effects of infant bystanders on relationships between female ovarian cycling and socio-sexual behaviour in free-ranging rhesus macaques during the 6-month mating season on Cayo Santiago, Puerto Rico. We used non-invasive hormone assessment to time ovulation in females, and analysed measures of social and sexual behaviour with respect to a 2-day ovulation window. Rates of copulation and ejaculation varied relative to ovulation, with female-male sexual interactions peaking around ovulation. Moreover, the presence of an infant bystander affected these rates, with fewer sexual interactions occurring for a given day with respect to ovulation when infant bystanders were more frequently in close proximity to the female. Other bystander categories (adult females, adult males, and adult female & infant groupings) did not have the same effect on female mating behaviour. These results suggest that mother-offspring conflict might manifest not only as direct interactions between mother and infant (e.g., weaning or carrying conflict), but also through indirect interactions. [ABSTRACT FROM AUTHOR]

This paper reports the results of an eight-year study of seasonal reproduction in the free-ranging colony of rhesus monkeys on Cayo Santiago, Puerto Rico. There was a significant correlation between the start of the annual spring rainy season and the estimated median conception date (r = .94, p < .001) and median birth date (r = .94, p < .001). Conceptions followed the commencement of spring rains by 70 days. Significant and negative correlations were found between the number of days from the start of the rains to the first conception (r = −.93, p < 0.01) and median conceptions (r = −.91, p < .01). When spring rains were delayed, the interval- between the onset of rains and conceptions decreased linearly. The median birth date for the Cayo Santiago population was accurately predicted for 1984 using two methods. When results from Cayo Santiago were applied retrospectively to data from the colony of rhesus monkeys near La Parguera, Puerto Rico, it explained the three-month difference in seasonality of reproduction between the two populations located at the same latitude (18°N). Photoperiod, as a function of latitude, appears to set the temporal limits of seasonal reproduction in rhesus macaques, while the onset of spring rains regulates reproductive activity within that range, at least in the Cayo Santiago population. The biological channel through which the effect is mediated has not been identified. [ABSTRACT FROM AUTHOR]