Our dataset allows for more precise predictions about muscle co-activation and synergies and has important implications for muscle activity and stimulation experiments.We also demonstrate how the syrinx can be stabilized during song to reduce mechanical noise and, as such, enhance repetitive execution of stereotypic motor patterns.In addition, we identify a cartilaginous structure suited to play a crucial role in the uncoupling of sound frequency and amplitude control, which permits a novel explanation of the evolutionary success of songbirds.
For over 200 years, morphologists and systematists have used the cross-species diversity of syringeal anatomy to classify avian taxa.The syrinx of the more than 4,000 songbird (Aves: Passeriformes: Passeri) species exhibits substantial anatomical variation [ (Vieillot, 1817), Passeriformes: Estrildidae).Because no apparent asymmetries were observed in the number of bones comprising the syringeal skeleton (N = 17), we consider the structure symmetrical in our description.The zebra finch syringeal skeleton is clearly sexually dimorphic, with the male syrinx being larger and more robust (Figures Ossified structural elements of the male and female zebra finch syrinx.However, how neural impulses are translated into the precise motor behavior of the complex vocal organ (syrinx) to create song is poorly understood.
First and foremost, we lack a detailed understanding of syringeal morphology.We created a morphome of the syrinx by annotating structures in this dataset based on the μCT scans with complementary guidance by high-field MRI, conventional histology and micro-dissection (see Methods).We will present this dataset starting with the ossified skeleton of the syrinx, subsequently adding on the other tissues, such as cartilage, sound-producing labia and finally muscles.These efforts will be aided by interactive 3D models as a tool to improve understanding of syringeal morphology and function as well as the dissemination of complicated biological structures [) contain motoneurons that connect with three major muscle systems: the respiratory system, including air sacs, modulated by intercostal and abdominal muscles; the syringeal musculature; and the suprasyringeal vocal tract, including trachea, larynx, oropharyngeal space and beak, modulated mainly by laryngeal, hyoid and orofacial muscles (Figure ).We constructed a 3D dataset of the syrinx with a 5-μm isotropic voxel resolution based on high-resolution μCT scans.(C) Virtual sagittal section through a 3D MRI dataset showing that the syrinx is located at the bifurcation of the trachea into the bilateral primary bronchi, close to the heart (red shaded outline) and lungs (green shaded outline). Without staining of soft tissues, only ossified tissue is clearly visible in μCT scans.