Abstract

For animals that tend to remain with their natal group rather than individually disperse, group sizes may become too large to benefit individual fitness. In such cases, group splitting (or fission) allows philopatric animals to form more optimal group sizes without sacrificing all familiar social relationships. Although permanent group splitting is observed in many mammals, it occurs relatively infrequently. Here, we use combined generalized modeling and machine learning approaches to provide a comprehensive examination of group splitting in a population of killer whales (Orcinus orca) that occurred over three decades. Fission occurred both along and across maternal lines, where animals dispersed in parallel with their closest maternal kin. Group splitting was more common: (1) in larger natal groups, (2) when the common maternal ancestor was no longer alive, and (3) among groups with greater substructuring. The death of a matriarch did not appear to immediately trigger splitting. Our data suggest intragroup competition for food, leadership experience and kinship are important factors that influence group splitting in this population. Our approach provides a foundation for future studies to examine the dynamics and consequences of matrilineal fission in killer whales and other taxa.

Significance statement

Group living among mammals often involves long-term social affiliation, strengthened by kinship and cooperative behaviours. As such, changes in group membership may have significant consequences for individuals’ fitness and a population’s genetic structure. Permanent group splitting is a complex and relatively rare phenomenon that has yet to be examined in detail in killer whales. In the context of a growing population, in which offspring of both sexes remain with their mothers for life, we provide the first in-depth examination of group splitting in killer whales, where splitting occurs both along and across maternal lines. We also undertake the first comprehensive assessment of how killer whale intragroup cohesion is influenced by both external and internal factors, including group structure, population and group demography, and resource abundance.

中文翻译：

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家庭之争：永久群分裂成高度灭绝的哺乳动物，虎鲸（Orcinus orca）

摘要

对于倾向于保留其出生组而不是单独分散的动物，组的大小可能会变得太大而无助于个体适应。在这种情况下，群体分裂（或裂变）使慈善动物可以在不牺牲所有熟悉的社会关系的情况下形成更理想的群体规模。尽管在许多哺乳动物中均观察到永久性基团分裂，但这种分裂很少发生。在这里，我们使用广义建模与机器学习相结合的方法，对虎鲸（Orcinus orca）发生了三十多年。裂变沿母体线发生和发生在母体线之间，其中动物与其最接近的母体血统平行地分散。群体分裂更为普遍：（1）在较大的新生儿组中；（2）当共同的祖先不再活着时；（3）在子结构较大的组中。女家长的死似乎没有立即引发分裂。我们的数据表明，群体内部的食物竞争，领导经验和亲属关系是影响该群体中群体分裂的重要因素。我们的方法为将来研究虎鲸和其他类群中母系裂变的动力学和后果提供了基础。

重要性声明

哺乳动物之间的群体生活通常涉及长期的社会联系，并通过亲属关系和合作行为得到加强。因此，团体成员资格的改变可能对个人的健康状况和人群的遗传结构产生重大影响。永久性群体分裂是一种复杂且相对罕见的现象，尚未在虎鲸中进行详细研究。在人口不断增长的情况下，男女双方的后代仍与母亲同伴一生，我们首次对虎鲸的群体分裂进行了深入的研究，其中分裂发生在母系之间或跨母系。我们还进行了首次综合评估，以了解虎鲸组内凝聚力如何受外部和内部因素（包括群体结构，人口和群体人口统计学，