Center for the Evolutionary Origins of Human Behavior, Kyoto University, Inuyama, Aichi, Japan.
College of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga, Japan.
Sci Rep. 2024 Feb 13;14(1):3631. doi: 10.1038/s41598-024-54172-z.
Primates have varied vocal repertoires to communicate with conspecifics and sometimes other species. The larynx has a central role in vocal source generation, where a pair of vocal folds vibrates to modify the air flow. Here, we show that Madagascan lemurs have a unique additional pair of folds in the vestibular region, parallel to the vocal folds. The additional fold has a rigid body of a vocal muscle branch and it is covered by a stratified squamous epithelium, equal to those of the vocal fold. Such anatomical features support the hypothesis that it also vibrates in a manner like the vibrations that occur in the vocal folds. To examine the acoustic function of the two pairs of folds, we made a silicone compound model to demonstrate that they can simultaneously vibrate to lower the fundamental frequency and increase vocal efficiency. Similar acoustic effects are achieved using different features of the larynx for the other primates, e.g., by vibrating multiple sets of ventricular folds in several species and further by an evolutionary modification of enlarged larynx in howler monkeys. Our multidisciplinary approaches found that these functions were acquired through a unique evolutionary adaptation of the twin vocal folds in Madagascan lemurs.
灵长类动物拥有多样化的发声器官，可以与同种动物甚至其他物种进行交流。声带在声源生成中起着核心作用，它由一对声带振动来调节气流。我们发现马达加斯加狐猴的前庭区域还有一对平行于声带的额外褶皱。额外褶皱有一个由声带肌肉分支组成的刚性体，表面覆盖着与声带相同的复层扁平上皮。这种解剖学特征支持了这样一种假设，即它也以类似于声带振动的方式振动。为了研究这两对褶皱的声学功能，我们制作了一个硅树脂复合模型，证明它们可以同时振动，从而降低基频并提高发声效率。其他灵长类动物也通过不同的喉部特征来实现类似的声学效果，例如通过在多个物种中振动多组室带，或者通过吼猴的喉部进化放大来实现。我们的多学科方法发现，这些功能是通过马达加斯加狐猴的一对孪生声带的独特进化适应获得的。
