Abstract
Resources critical for successful breeding are typically partition in
nature. To increase reproductive fitness, females may associate with
males who provide access to high quality resources while mating other
males with good or compatible genes. Gibbons have traditionally been
described as living in small monogamous groups and the sole resident
adult male is assumed to sire all of the group’s offspring. Based on 16
years of field observations and microsatellite analyses, we describe the
social system and reproductive strategies of a population of Nomascus
concolor in the Wuliang Mountains, China. From 2003 to 2018, each of our
three study groups consisted one resident male and two breeding females
across 98.4% of observation months. Resident males spent 2.3 - 5.6%
time (N = 7 pairs) within 1 m of both females in their group, comparable
to monogamous gibbon groups. Weakened bond strength predicted
male/female replacement in two groups. However, microsatellite analyses
revealed that the rate of extra-group paternity (EGP) was 40.0% (N =
15), considerably greater than reported for monogamous gibbon species (0
- 10%). Females engaged in EGP to increase offspring heterozygosity.
Resident males seem unable to monopolize the mating activities of
females, floater males had reproductive success (N = 2). Our findings
indicate that in crested gibbons the social system is distinct from the
breeding system. Our study also highlights again that long-term
continuous field work and non-invasive genetic analysis are essential
for understanding breeding systems of long-lived mammals.