Huang Pengzhen, Fang Gu, Teichroeb Julie A, Zhang Endi, Chen Min
School of Life Sciences, East China Normal University, Shanghai, China.
Yangtze Delta Estuarine Wetland Ecosystem Observation and Research Station, Ministry of Education & Shanghai Science and Technology Committee, Shanghai, China.
Am J Primatol. 2023 Nov;85(11):e23550. doi: 10.1002/ajp.23550. Epub 2023 Sep 10.
Same-sex mounting behavior has been documented across primate species and several biological functions, that are often difficult to differentiate, have been proposed. Postmounting affiliative behaviors (e.g., embracing and grooming) have been partly overlooked and their performance may more clearly reveal the function of same-sex mounts for different age-sex classes. Here, considering postmounting grooming behaviors (PMG), we tested the affiliation hypothesis for same-sex mounts in an all-male unit (AMU) of captive golden snub-nosed monkeys (Rhinopithecus roxellana) (n = 7-8) and the needing to learn hypothesis in the juveniles of the AMU (n = 4) and the juvenile male from the neighboring one-male unit in Shanghai Wild Animal Park, China from November 2014 to June 2015. A total of 1986 same-sex mounts were recorded from the AMU individuals and the juvenile of the neighboring one-male unit. We found that neither dyadic proximity-based association nor grooming-based affiliation predicted the occurrence of mounts in the AMU, and PMG was more likely to occur in nontense than tense social contexts, providing no support for the affiliation hypothesis. Although dyadic grooming-based affiliation predicted the occurrence of PMG, it exerted no influence on the occurrence of mounts, which was necessary to support the hypothesis. However, consistent with the needing to learn hypothesis, from ages two to four, juveniles' mounting duration increased and they performed pelvic thrusting during mounting more and more often as they grew older. Reciprocated series mounts were much more common among juveniles than other mounting dyads, providing learning opportunities for both participants. The mounter was more likely to groom the mountee at the end of a mount among juveniles than other mounting dyads, suggesting that juvenile mounters may profit from mounting and groom mountees in return for providing them with opportunities to learn copulatory skills. A hypothesis that merits further investigation.
在灵长类物种中，同性爬跨行为已有记录，并且有人提出了几种常常难以区分的生物学功能。爬跨后的亲和行为（如拥抱和梳理毛发）在一定程度上被忽视了，其表现可能更清楚地揭示了同性爬跨对不同年龄 - 性别的功能。在此，考虑到爬跨后的梳理毛发行为（PMG），我们在2014年11月至2015年6月期间，对圈养的川金丝猴（Rhinopithecus roxellana）全雄单元（AMU）（n = 7 - 8）中的同性爬跨行为进行了亲和假设测试，并对AMU中的幼年个体（n = 4）以及来自中国上海野生动物园相邻单雄单元的幼年雄性个体进行了学习需求假设测试。从AMU个体和相邻单雄单元的幼年个体中总共记录到1986次同性爬跨行为。我们发现，基于二元接近度的关联和基于梳理毛发的亲和关系都无法预测AMU中爬跨行为的发生，并且PMG在非紧张的社会环境中比紧张的社会环境中更有可能发生，这并不支持亲和假设。尽管基于二元梳理毛发的亲和关系可以预测PMG的发生，但它对爬跨行为的发生没有影响，而这是支持该假设所必需的。然而，与学习需求假设一致，从两岁到四岁，幼年个体的爬跨持续时间增加，并且随着年龄的增长，它们在爬跨过程中进行骨盆推顶的频率越来越高。相互的系列爬跨在幼年个体中比其他爬跨二元组更为常见，为双方参与者提供了学习机会。在幼年个体中，爬跨者在爬跨结束时比其他爬跨二元组更有可能梳理被爬跨者，这表明幼年爬跨者可能从爬跨中受益，并通过梳理被爬跨者来回报为它们提供学习交配技能的机会。这是一个值得进一步研究的假设。
