MATERIALS AND METHODS
Study sites and subjects We conducted the study at Dalongtan (31°29’N, 110°18’E; elevation: 2200 m) in Shennongjia National Park, central China. The study population is free-ranging, but partly provisioned. Reserve staff began provisioning the monkeys in 2006 for the purpose of ecotourism (Yu et al. 2013; Zhang et al. 2019). Food was provided two to three times per day and included lichen, pine seeds, apples, carrots, oranges, and peaches; the monkeys were provisioned at different feeding sites/platforms. When not provisioned, the monkeys ranged across an area with a radius of ~ 1 km. Provisioning likely affected the monkeys’ social behavior and daily activities, especially early in the process. However, they soon became habituated to humans, and instead of fleeing, the monkeys started to ignore the presence of researchers and reserve staff most of the time. Therefore, observations were made on a daily basis at distances between 5 and 50 m (Xiang et al. 2019). All adult members were individually identifiable based on a unique set of physical features, such as body size, pelage color, evidence of injuries or scars, the shape and size of a female’s nipples, and the shapes of granulomatous flanges which are present of fleshy nodules on both sides of the upper lip in adult males (Yu et al. 2013). The size of the focal band has increased from ~30 individuals comprising three OMUs and an associated AMU (five adult individuals) in January 2006 to > 90 individuals in five OMUs and one AMU (> seven adult males) in December 2019.
Data collectionWe collected data on a daily basis at distances 5 - 50 m from 0800 to 1800 in winter-spring or 0700-1900 in summer-autumn between January 2006 and March 2020. All instances of births, abortions, copulations and male takeovers were observed using ad libitum sampling. However, once a male takeover event had taken place, male attacks on pregnant females, infants and mothers with infants, afanticide afanticide events were observed in a focal animal sampling. This focal animal sampling extended to the end of the mating (potential conception) season (late November) of the year of the takeover (Yao et al. 2016). All events were recorded via continuous all-occurrence sampling once an event began (Xiang et al. 2019). The final replacement of the previous male was decided to have occurred when the previous male left the original unit and joined the AMU or when copulations between the new male and the females were observed without disturbance by the previous male. A successful infanticide attempt was defined to have occurred when the infant was killed by the male during the first set of attack, otherwise aggressive bouts towards the infant were scored as unsuccessful infanticide attempts.
For the paternity analysis, hairs with intact roots were collected from all infants born during the study period, their mothers, and from all reproductively mature adult males in the focal band (Guo et al. 2015). Hair samples of adult individuals were obtained by plucking them directly by hand (with gloves) while samples of young infants – who were difficult to approach – were obtained by using a pole with glue on its end which was brought in contact with the back of the target individuals (Guo et al. 2015). Paternity exclusion was established using sixteen different microsatellite loci (D13S321, D10S1432, D1S533, D14S306, D6S493, D7S817, D10S676, D1S1656, D1S1665, D7S1826, D7S2204, D6S1056, D2S442, D5S1457, D6S474, D10S611) [for details on the DNA protocols see Xiang et al. (2014) and Yang et al. (2014)]. The reliability of our genotyping results from hair samples was confirmed by comparing allele patterns with matched blood samples of five captive individuals: the agreement was 99.1%. Paternity for the 99 offspring born into the band from 2007 to 2018 was determined with the software CERVUS3.0 (Kalinowsk et al. 2007) with confidence levels of >80% (relaxed confidence) and > 95% (strict confidence). These inferences matched exclusion standards, and in all cases in which paternity was assigned to an extra-unit male the male residing within the social unit during the conception was excluded at two or more loci. The relatedness of female dyads in study population was divided into three categories: all ”mother-daughter” dyads and six full ”sister-sister” dyads were determined by observing infants born into OMUs since 2006, and five half ”sister-sister” dyads were identified based on the genetic data.
Data analysis Extra-unit copulations and extra-unit paternity were judged to have occurred if the mate or the farther resided in a different social unit. A chi-square test was used to identify whether (i) any extra-unit copulations primarily occurred between females and established males residing in one-male units or males residing in the all-male unit, and (ii) frequencies of extra-unit copulation of those female involved in male replacement are higher than those not involved. A Z score test was used to identify (i) if fetal or infant death rates following male replacement are higher than other circumstances, (ii) if pregnant females tend to terminate their pregnancies following male replacement. A two-sample independent t -test was used to establish whether there were significant differences (i) size of OMU (members except the infant) between OMUs in which infants were attacked or killed by males versus those in which infants did not suffer attacks, if (ii) between females’ birth interval and males’ tenure, and (iii) in the tenures between the tolerance male and aggressive male.