Data from: Differences in combinatorial calls among the 3 elephant species cannot be explained by phylogeny

Understanding why related species combine calls in different ways could provide insight into the selection pressures on the evolution of combinatorial communication. African savannah elephants (Loxodonta africana), African forest elephants (Loxodonta cyclotis), and Asian elephants (Elephas maximus) all combine broadband calls (roars, barks, and cries) and low-frequency calls (rumbles) into single utterances known as "combination calls." We investigated whether the structure of such calls differs among species and whether any differences are better explained by phylogenetic relationships or by socio-ecological factors. Here, we demonstrate for the first time that the species differ significantly in the frequency with which they produce different call combinations using data from multiple study sites. E. maximus and L. africana mostly produced roar-rumble combinations, while L. cyclotis produced a more even distribution of roar-rumble, rumble-roar and rumble-roar-rumble combinations. There were also significant differences in favored structure among populations of the same species. Moreover, certain call orders were disproportionately likely to be given in particular behavioral contexts. In L. africana, rumble-roar-rumble combinations were significantly more likely than expected by chance to be produced by individuals separated from the group. In E. maximus, there was a marginally non-significant trend for rumble-roar-rumbles to be given more often than expected by chance in response to a disturbance. Site-specific socio-ecological conditions appear more influential for call combination structure than phylogenetic history.

探明近缘物种以不同方式组合发声的缘由，可为理解组合式通信演化所受的选择压力提供重要洞见。非洲草原象（Loxodonta africana）、非洲森林象（Loxodonta cyclotis）与亚洲象（Elephas maximus）均会将宽频发声（咆哮、吠叫与哭喊）与低频发声（隆隆声）整合为单一发声单元，此类单元被称为“组合鸣叫”。本研究旨在探究这类组合鸣叫的结构在不同物种间是否存在差异，以及此类差异更适合用系统发育关系还是社会生态因素来解释。本研究首次基于多个研究地点的观测数据，证明不同物种在产生各类发声组合的频率上存在显著差异。亚洲象与非洲草原象多产生咆哮-隆隆声组合，而非洲森林象的咆哮-隆隆声、隆隆声-咆哮声以及隆隆声-咆哮声-隆隆声组合的分布则更为均衡。同一物种的不同种群间，其偏好的发声组合结构也存在显著差异。此外，特定的发声序列在特定的行为情境中出现的比例远超随机预期。在非洲草原象中，脱离群体的个体产生隆隆声-咆哮声-隆隆声组合的概率显著高于随机预期。在亚洲象中，当受到干扰时，个体发出隆隆声-咆哮声-隆隆声组合的频率虽高于随机预期，但未达到显著水平，仅呈现出微弱的趋势。相较于系统发育历史，特定生境的社会生态条件对发声组合结构的影响更为显著。