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.