The ability to imitate sounds depends on a process called vocal production learning, a rare evolutionary trait. In addition to the few mammalian groups that possess this ability, vocal production learning has evolved independently in three avian clades: songbirds, parrots, and hummingbirds. Although the anatomy and mechanisms of sound production in songbirds are well understood, little is known about the hummingbird’s vocal anatomy. We use high-resolution micro-computed tomography (μCT) and microdissection to reveal the three-dimensional structure of the syrinx, the vocal organ of the black jacobin (Florisuga fusca), a phylogenetically basal hummingbird species. We identify three features of the black jacobin’s syrinx: (i) a shift in the position of the syrinx to the outside of the thoracic cavity and the related loss of the sterno-tracheal muscle, (ii) complex intrinsic musculature, oriented dorso-ventrally, and (iii) ossicles embedded in the medial vibratory membranes. The extra-thoracic placement of the black jacobin’s syrinx and the dorso-ventrally oriented musculature likely aid to uncoupling syrinx movements from extensive flight-related thorax constraints. The syrinx morphology further allows for vibratory decoupling, precise control of complex acoustic parameters, and a large motor redundancy that may be key biomechanical factors leading to acoustic complexity and thus facilitating the occurrence of vocal production learning.

中文翻译：

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蜂鸟syrinx词组：黑色雅各宾声器官的详细三维描述

模仿声音的能力取决于称为声音产生学习的过程，这是一种罕见的进化特征。除了具有这种能力的少数哺乳动物群体以外，声乐生产学习已经在三个鸟类进化枝中独立发展：鸣鸟，鹦鹉和蜂鸟。尽管人们对鸣鸟的解剖结构和声音产生的机理已广为人知，但对蜂鸟的声带解剖知之甚少。我们使用高分辨率显微计算机断层扫描（μCT）和显微解剖技术来揭示syrinx的三维结构，该系统是系统发育的基础蜂鸟物种黑雅各布（Florisuga fusca）的发声器官。我们确定了黑色雅各宾氏syrinx的三个特征：（i）syrinx的位置向胸腔外部的偏移以及胸骨气管肌肉的相关损失，（ii）复杂的固有肌肉组织，背腹方向，和（iii）嵌入在内侧振动膜中的小骨。黑色雅各宾氏脊柱的胸外位置和背-腹侧的肌肉组织可能有助于使脊柱运动脱离与飞行相关的广泛胸腔约束。syrinx形态进一步实现了振动解耦，复杂声学参数的精确控制以及较大的电机冗余度，这可能是导致声学复杂性的关键生物力学因素，从而有利于发声学习。黑色雅各宾氏脊柱的胸外位置和背-腹侧的肌肉组织可能有助于使脊柱运动脱离与飞行相关的广泛胸腔约束。syrinx形态进一步实现了振动解耦，复杂声学参数的精确控制以及较大的电机冗余度，这可能是导致声学复杂性的关键生物力学因素，从而有利于发声学习。黑色雅各宾氏脊柱的胸外位置和背-腹侧的肌肉组织可能有助于使脊柱运动脱离与飞行相关的广泛胸腔约束。syrinx形态进一步实现了振动解耦，复杂声学参数的精确控制以及较大的电机冗余度，这可能是导致声学复杂性的关键生物力学因素，从而有利于发声学习。