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.

性别隔离（Sexual segregation）在哺乳动物中广泛存在，但单态性物种（monomorphic species）的性别隔离近因（proximate causes）仍未得到充分阐释。印太瓶鼻海豚（Indo-Pacific bottlenose dolphin, Tursiops aduncus）具有高度发达的裂变-融合动态（fission-fusion dynamics），是探究性别隔离的生态与社会驱动因素的理想研究模型。生态假说（ecological hypotheses）提出，性别隔离是性别特异性生态偏好的副产物，例如与栖息地选择、觅食行为或反捕食策略相关的偏好；而社会假说（social hypothesis）则认为，性别隔离源于同性社交偏好（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从近乎独居到高度社交化的状态跨度极大，雄性则结成联盟，通过合作扣留单个雌性并排斥其他竞争雄性。鉴于存在结盟性性胁迫（allied sexual coercion）的相关证据，我们的核心假说为：性别隔离由雌性对具有攻击性的雄性的回避所驱动；不过，鉴于已有大量关于性别偏向性觅食策略（sex-biased foraging tactics）的可靠证据，生态因素可能也起到了一定作用。本研究使用性别隔离与聚集统计量（Sexual Segregation and Aggregation Statistic），基于跨越31年的17468条目击记录，检测到了显著的性别隔离现象。本研究的独特之处在于，通过焦点观察（focal observations）分析了雌雄个体间的加入与离开方向（共10715次裂变-融合事件，涉及87只雌性、111只雄性），以明确哪一性别主导了性别隔离。结果显示，雌性通过极少加入雄性群体、频繁离开雄性群体来主导性别隔离。尽管生态因素可能强化了性别隔离，但社会因素占据主导地位。本研究证实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，并为性别隔离的社会假说提供了强有力的实证支持。