Fantoni Federico, Maglieri Veronica, Giusti Nicolò, Scopa Chiara, Pallante Virginia, Loprete Antonio Lorenzo, Palagi Elisabetta
Department of Biology, Unit of Ethology, University of Pisa, Pisa, Italy.
Department of Neurosciences, University of Parma, Parma, Italy.
Am J Primatol. 2025 Jan;87(1):e23697. doi: 10.1002/ajp.23697. Epub 2024 Nov 17.
Facial communication regulates many aspects of social life in human and nonhuman primates. Empirically identifying distinct facial expressions and their underlying functions can help illuminate the evolution of species' communicative complexity. We focused on bared-teeth faces (BTFs), a highly versatile facial expression in the tolerant macaque Macaca tonkeana. By employing a diverse array of techniques (MaqFACS, unsupervised cluster analysis, Levenshtein distance, NetFACS), we quantitatively discriminated two distinct BTFs: bared-teeth (BT) and open mouth bared-teeth (OMBT), and evaluated their distribution across peaceful, playful, and agonistic contexts. Neither BT nor OMBT were context-specific, although BT frequently occurred during peaceful interactions and with low levels of stereotypy. OMBT was highly stereotyped during play, a context involving strong unpredictability. The presence of tongue-protrusion during OMBT was exclusive to peaceful contexts whereas the presence of glabella-lowering during BT and OMBT was specific to agonistic contexts. Hence, BT and OMBT per se are not context-specific, but their contextual relevance hinges on the inclusion of specific key elements. Moving forward, concurrent analyses of stereotypy and specificity should extend beyond our study to encompass other primate and non-primate species, facilitating direct comparisons and revealing how communicative and social complexity coevolve.
面部交流调节着人类和非人类灵长类动物社会生活的许多方面。通过实证识别不同的面部表情及其潜在功能，有助于阐明物种交流复杂性的演变。我们聚焦于露齿表情（BTF），这是宽容的汤基猕猴（Macaca tonkeana）中一种高度通用的面部表情。通过运用多种技术（猕猴面部动作编码系统、无监督聚类分析、莱文斯坦距离、网络面部动作编码系统），我们定量区分了两种不同的露齿表情：露齿（BT）和张嘴露齿（OMBT），并评估了它们在和平、嬉戏和争斗情境中的分布情况。尽管BT在和平互动中频繁出现且刻板程度较低，但BT和OMBT都不是特定情境专属的。OMBT在嬉戏过程中高度刻板，而嬉戏是一种具有强烈不可预测性的情境。OMBT过程中伸舌仅出现在和平情境中，而BT和OMBT过程中皱眉仅出现在争斗情境中。因此，BT和OMBT本身并非特定情境专属，但它们与情境的相关性取决于特定关键元素的包含情况。展望未来，对刻板性和特异性的并行分析应超越我们的研究范围，涵盖其他灵长类和非灵长类物种，以便进行直接比较并揭示交流和社会复杂性如何共同进化。
