Comparisons of paternity success for resident and non-resident males and their influences on paternal sibling cohorts in Japanese macaques on Shodoshima Island

In group-living mammals, reproductive success can be attributed to both resident and non-resident males. However, the reproductive success of non-resident males has rarely been investigated at an individual level. As male reproductive success is highly skewed towards specific males, often the most dominant males, the percentage of similar-aged paternal siblings within groups is expected to increase. However, the extent to which each male contributes to the production of cohorts of paternal siblings remains unclear. Here we examined the paternity of 46 offspring born over five consecutive years in a group of Japanese macaques Macaca fuscata on Shodoshima Island. We quantitatively assessed paternity success for males, including both resident and non-resident males, and the percentages of paternal sibling dyads in the same age cohorts produced by those males. Non-resident males sired neither higher nor lower percentage of offspring compared to resident males, indicating that various males, including non-resident males, usually partake in the within-group breeding of macaque groups. These are possibly because female preference of mating partners can change over time. Subadult males had a lower percentage of paternity success, which may be because females may not prefer the physically immature subadult males. Various males, including non-resident males, contributed to the creation of paternal sibling in the same age cohort. The overall results suggest that not only resident but also non-resident males play an important role in shaping within-group kin structures. Future studies are required to examine how paternal siblings interact with each other.