Riede Tobias, Li Zhiheng, Tokuda Isao T, Farmer Colleen G
Department of Physiology, Midwestern University, Glendale, AZ 85308, USA
Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712, USA.
J Exp Biol. 2015 Apr;218(Pt 7):991-8. doi: 10.1242/jeb.117101. Epub 2015 Feb 5.
Sauropsid vocalization is mediated by the syrinx in birds and the larynx in extant reptiles; but whereas avian vocal production has received much attention, the vocal mechanism of basal reptilians is poorly understood. The American alligator (Alligator mississippiensis) displays a large vocal repertoire during mating and in parent-offspring interactions. Although vocal outputs of these behaviors have received some attention, the underlying mechanism of sound production remains speculative. Here, we investigate the laryngeal anatomy of juvenile and adult animals by macroscopic and histological methods. Observations of the cartilaginous framework and associated muscles largely corroborate earlier findings, but one muscle, the cricoarytenoideus, exhibits a heretofore unknown extrinsic insertion that has important implications for effective regulation of vocal fold length and tension. Histological investigation of the larynx revealed a layered vocal fold morphology. The thick lamina propria consists of non-homogenous extracellular matrix containing collagen fibers that are tightly packed below the epithelium but loosely organized deep inside the vocal fold. We found few elastic fibers but comparatively high proportions of hyaluronan. Similar organizational complexity is also seen in mammalian vocal folds and the labia of the avian syrinx: convergent morphologies that suggest analogous mechanisms for sound production. In tensile tests, alligator vocal folds demonstrated a linear stress-strain behavior in the low strain region and nonlinear stress responses at strains larger than 15%, which is similar to mammalian vocal fold tissue. We have integrated morphological and physiological data in a two-mass vocal fold model, providing a systematic description of the possible acoustic space that could be available to an alligator larynx. Mapping actual call production onto possible acoustic space validates the model's predictions.
蜥形纲动物的发声是由鸟类的鸣管和现存爬行动物的喉部介导的；然而，尽管鸟类的发声产生受到了很多关注，但基础爬行动物的发声机制却知之甚少。美国短吻鳄（密西西比鳄）在交配和亲子互动过程中展现出丰富的发声 repertoire。尽管这些行为的发声输出受到了一些关注，但发声产生的潜在机制仍属推测。在这里，我们通过宏观和组织学方法研究幼年和成年动物的喉部解剖结构。对软骨框架和相关肌肉的观察在很大程度上证实了早期的发现，但有一块肌肉，即环杓肌，表现出一种迄今未知的外部附着，这对有效调节声带长度和张力具有重要意义。喉部的组织学研究揭示了一种分层的声带形态。厚厚的固有层由非均质的细胞外基质组成，其中含有胶原纤维，这些纤维在上皮下方紧密排列，但在声带内部深处组织松散。我们发现弹性纤维很少，但透明质酸的比例相对较高。在哺乳动物的声带和鸟类鸣管的唇中也观察到了类似的组织复杂性：趋同的形态表明存在类似的发声机制。在拉伸试验中，短吻鳄的声带在低应变区域表现出线性应力 - 应变行为，在应变大于 15% 时表现出非线性应力响应，这与哺乳动物的声带组织相似。我们将形态学和生理学数据整合到一个双质量声带模型中，系统地描述了短吻鳄喉部可能的声学空间。将实际的叫声产生映射到可能的声学空间上验证了该模型的预测。
