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Abstract：
Here we show for the first time that the plasticity in morphology and duration of yawning in Macaca tonkeana can be associated with different functional contexts. Macaca tonkeana is classified as a tolerant macaque species characterized by social interactions minimally constrained by dominance rank or kinship. Tonkean macaques, as other egalitarian species, rely on a complex facial communicative system. We found that the degree of mouth opening (ranging from covered to uncovered tooth yawns) and the duration of yawning were not strictly dependent. The shortest uncovered tooth yawns were associated with an intense locomotor/physical activity and peaked immediately after stressful social events thus indicating an increase in arousal. In contrast, longer yawns, independently from teeth exposure, were primarily associated with a relaxed state of the subject. In conclusion, our study suggests that to explore the potential different functions of yawning, it is necessary to focus on the variability of its expression both in terms of morphology and duration, because not all yawns tell the same story.
摘要：
在这里，我们首次表明，猕猴在形态上的可塑性和打哈欠的持续时间可以与不同的功能环境相关。猕猴被归类为一种宽容的猕猴，其特征是社会互动受到优势等级或亲属关系的最小限制。通经猕猴,和其他平等物种一样，依赖于复杂的面部交流系统。我们发现，张口的程度（从覆盖到未覆盖的牙齿打哈欠）和打哈欠的持续时间并不严格取决于。最短的未覆盖牙齿打哈欠与强烈的运动/身体活动有关，并在紧张的社交事件后立即达到顶峰，因此表明唤醒增加。相比之下,更长的哈欠，独立于牙齿暴露，主要与受试者的放松状态有关。总之,我们的研究表明，为了探索打哈欠的潜在不同功能，有必要关注其在形态和持续时间方面的表达变异性，因为不是所有的哈欠都讲同样的故事。
