Kinship influences sperm whale social organization within, but generally not among, social units

Sperm whales have a multi-level social structure based upon long-term, cooperative social units. What role kinship plays in structuring this society is poorly understood. We combined extensive association data (518 days, during 2005-2016) and genetic data (18 microsatellites and 346bp mtDNA control region sequences) for 65 individuals from 12 social units from the Eastern Caribbean to examine patterns of kinship and social behaviour. Social units were clearly matrilineally-based, evidenced by greater relatedness within social units (mean r=0.14) than between them (mean r=0.00) and uniform mtDNA haplotypes within social units. Additionally, most individuals (82.5%) had a first-degree relative in their social unit, while we found no first-degree relatives between social units. Generally and within social units, individuals associated more with their closer relatives(matrix correlations: 0.18-0.25). However, excepting a highly-related pair of social units that merged over the study period, associations between social units were not correlated with kinship (p>0.1). These results are the first to robustly demonstrate kinship’s contribution to social unit composition and association preferences, though they also reveal variability in association preferences that is unexplained by kinship. Comparisons with other matrilineal species highlight the range of possible matrilineal societies, and how they can vary between and even within species.

抹香鲸拥有基于长期合作社会单元的多层级社会结构。目前学界对亲缘关系在该社会结构构建中所发挥的作用仍知之甚少。本研究整合了2005至2016年间累计518天的大量关联观测数据，以及来自东加勒比海12个社会单元的65头个体的遗传数据（包含18个微卫星位点与346bp的线粒体DNA控制区序列），以此探究亲缘关系与社会行为的模式。研究结果明确显示，社会单元以母系为核心构建：社会单元内部的亲缘系数（平均r=0.14）显著高于单元间（平均r=0.00），且同一社会单元内的线粒体DNA单倍型保持一致。此外，绝大多数个体（82.5%）在所属社会单元内拥有一级亲属，而不同社会单元之间未发现任何一级亲属关系。整体而言及在社会单元内部，个体与亲缘关系更近的同类互动频率更高（矩阵相关系数范围：0.18~0.25）。但值得注意的是，除了研究期间发生融合的一对高亲缘度社会单元之外，不同社会单元之间的关联模式与亲缘关系并无显著相关性（p>0.1）。本研究结果首次有力证实了亲缘关系对社会单元构成与社交偏好的塑造作用，同时也揭示了部分无法由亲缘关系解释的社交偏好差异。通过与其他母系社会物种的对比，本研究凸显了母系社会的多样形态，以及这类社会结构在物种间甚至物种内的变异模式。