Data from: Sexual segregation in Indo-Pacific bottlenose dolphins is driven by female avoidance of males

Sexual segregation is widespread in mammals, although the proximate causes are poorly understood in monomorphic species. Indo-Pacific bottlenose dolphins (Tursiops aduncus), which exhibit a high degree of fission-fusion dynamics, offer a useful lens to examine the ecological and social drivers of sexual segregation. While ecological hypotheses suggest that sexual segregation is a by-product of sex-specific ecological preferences (e.g. related to habitat, foraging, or predator avoidance), the social hypothesis proffers that segregation results from same-sex preferences (e.g. due to cooperative benefits) and/or opposite-sex avoidance (e.g. due to competitive or exploitative interactions). Indo-Pacific bottlenose dolphin females range from nearly solitary to highly sociable. Males associate in alliances that cooperate to sequester individual females and exclude competing males. Given evidence for allied sexual coercion, our primary hypothesis was that sexual segregation is driven by female avoidance of aggressive males. However, given robust evidence for sex-biased foraging tactics, ecological factors likely also contribute. Using the Sexual Segregation and Aggregation Statistic with 17,468 sighting records spanning 31 years, we found strong sexual segregation. Unique to our work, we analyzed the direction of joins and leaves between males and females from focal observations (N=10,715 fission-fusion events, 87 females, 111 males) to determine which sex drives sexual segregation. Females drove segregation by rarely joining and often leaving males. Although ecological factors likely reinforce sexual segregation, social factors predominate. This study demonstrates a sex-bias in fission-fusion dynamics in a socially complex wild mammal population and offers strong empirical support to the social hypothesis of sexual segregation.性隔离在哺乳动物中广泛存在，然而两性同型物种（monomorphic species）的性隔离近因仍未得到充分解析。印太瓶鼻海豚（Tursiops aduncus）展现出高度复杂的裂变-融合动态（fission-fusion dynamics），为探究性隔离的生态与社会驱动因素提供了绝佳研究视角。生态假说认为，性隔离是性别特异性生态偏好的副产品（例如与栖息地选择、觅食行为或反捕食策略相关）；而社会假说则提出，性隔离源于同性偏好（例如源于合作收益）和/或异性回避（例如源于竞争性或剥削性互动）。印太瓶鼻海豚的雌性个体活动模式从近乎独居到高度社交化不等；雄性则结成联盟，通过合作扣押单个雌性并排斥其他竞争雄性。鉴于存在联盟性性胁迫（allied sexual coercion）的相关证据，我们的核心假说为：性隔离由雌性回避具有攻击性的雄性所驱动。然而，鉴于已有充分证据表明存在性别偏向性觅食策略，生态因素同样可能参与其中。我们借助性隔离与聚集统计量（Sexual Segregation and Aggregation Statistic），对跨越31年的17468条目击记录进行分析，结果发现了显著的性隔离现象。本研究的独特之处在于，通过焦点观察法（共记录到10715次裂变-融合事件，涉及87头雌性个体与111头雄性个体），我们分析了雌雄个体间的加入与离开方向，以明确哪一性别主导了性隔离。研究结果显示，雌性通过极少加入雄性群体、频繁离开雄性群体的行为主导了性隔离。尽管生态因素可能会强化性隔离，但社会因素仍占据主导地位。本研究揭示了具有复杂社会结构的野生哺乳动物种群中，裂变-融合动态存在性别偏向性，并为性隔离的社会假说提供了强有力的实证支持。