Close bonds and social rank similarities favor non‐random mating in captive stump‐tailed macaques (Macaca arctoides)

Abstract

AbstractAssortative mating is non‐random mating by the mutual choice of phenotypes or behavioral types. In polygynandrous species, competition for mating by social rank can lead to assortative mating. However, although not an individual trait, social bonds also influence mating opportunities resembling assortative mating. Stump‐tailed macaques form long‐term close bonds and organize in a linear dominance–subordination hierarchy. Therefore, we studied whether the strength of the social bond and rank closeness influenced mating decisions and increased mating opportunities, particularly for low‐ and middle‐ranking animals. Firstly, we observed whether females directed proceptive behavior to close‐bonded or adjacent rank males. Secondly, we measured whether successful copulations were related to the strength of social bonds and close ranking. Thirdly, to ensure that copulations owed mainly to the aforementioned factors, we also evaluated whether sexual coercion was unrelated to social bonds and rank similarities. Finally, we assessed whether close bonds mediated agonistic support to females. The study subjects were 12 adult female and 11 male captive stump‐tailed macaques. We monitored daily females' reproductive status by vaginal cytology. Sexual behavior was recorded by all occurrences sampling and scan sampling to collect the agonistic and affiliative instances required to calculate social ranks, social bond strength, and agonistic support. The results indicated that the probability of females displaying proceptivity increased during the follicular phase toward close‐bonded and high‐ranking males. Copulation chances increased with male–female social bonds and rank closeness. Forced copulation decreased in close‐bonded individuals, while agonistic support increased in close‐ranking strong‐bonded animals. In conclusion, close social bonds and similar social rank result in non‐random mating in stump‐tailed macaques.