Several studies have documented the importance of social bonding for the enhancement of individual fitness. However, little is known about how social relationships develop through ontogeny, and whether their development follows the same trajectory in males and females. Here we analyzed affiliative interactions (proximity, social grooming, play) combined with demographic and genetic data in semi-free-ranging rhesus macaques (Macaca mulatta) on Cayo Santiago over their first 4 yr of life (from birth to sexual maturation) to understand how these interactions change through development in both sexes. Generalized linear mixed models revealed that social behaviors mostly followed different developmental trajectories in males and females and were highly dependent on the social context. In particular, sex differences in social behavior varied through development depending on the partner’s sex and age. Females engaged in more social interactions than males, especially with other females, and were more involved in grooming around the time of maturation. In contrast, males interacted more with males and age peers, especially around maturation. Sex differences in social behavior varied through development, but also depended on rank, partner’s rank, and kin line, although not consistently. High-ranking individuals, especially older females, were generally preferred as social partners. Moreover, both male and female individuals interacted mostly with maternal kin, although males also preferred paternal kin over nonkin. Importantly, most developmental changes in sociality happened when individuals were ca. 2 yr old, suggesting that this might be a milestone in the development of sociality in rhesus macaques. The only notable exception to this pattern was play, which was more pronounced in males from the beginning of their lives. We propose that play might serve as a trigger of sex differences in social behavior, with sex differences emerging early in development and increasing through time as males and females gradually grow into their adult social roles.

中文翻译：

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恒河猴（Macaca mulatta）社会关系发展的性别差异


一些研究已经证明了社会联系对于增强个人健康的重要性。然而，人们对社会关系如何通过个体发育发展以及男性和女性的发展是否遵循相同的轨迹知之甚少。在这里，我们分析了圣地亚哥岛半散养恒河猴（Macaca mulatta）生命前 4 年（从出生到性成熟）的亲和互动（接近、社交梳理、玩耍）以及人口统计和遗传数据，以了解这些相互作用如何随着两性的发展而变化。广义线性混合模型表明，男性和女性的社会行为大多遵循不同的发展轨迹，并且高度依赖于社会背景。特别是，社会行为中的性别差异在发展过程中随伴侣的性别和年龄而变化。雌性比雄性参与更多的社会互动，尤其是与其他雌性的互动，并且在成熟时更多地参与梳理毛发。相比之下，男性与男性和同龄人的互动更多，尤其是在成熟时期。社会行为中的性别差异随着发展而变化，但也取决于等级、伴侣的等级和亲属关系，尽管不一致。高层人士，尤其是老年女性，通常更受青睐作为社会伙伴。此外，男性和女性个体都主要与母系亲属互动，尽管男性也更喜欢父系亲属而不是非亲属。重要的是，大多数社会性的发展变化发生在个体大约在成年时期。 2岁，表明这可能是恒河猴社会性发展的一个里程碑。 这种模式唯一值得注意的例外是玩耍，这在男性中从一开始就更加明显。我们认为，玩耍可能是社会行为中性别差异的触发因素，性别差异在发育早期就出现，并随着男性和女性逐渐成长为成年社会角色而不断增加。