Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA.
Department of Anatomical Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY, USA.
Nature. 2024 Jun;630(8017):671-676. doi: 10.1038/s41586-024-07485-y. Epub 2024 Jun 12.
The subpectoral diverticulum (SPD) is an extension of the respiratory system in birds that is located between the primary muscles responsible for flapping the wing. Here we survey the pulmonary apparatus in 68 avian species, and show that the SPD was present in virtually all of the soaring taxa investigated but absent in non-soarers. We find that this structure evolved independently with soaring flight at least seven times, which indicates that the diverticulum might have a functional and adaptive relationship with this flight style. Using the soaring hawks Buteo jamaicensis and Buteo swainsoni as models, we show that the SPD is not integral for ventilation, that an inflated SPD can increase the moment arm of cranial parts of the pectoralis, and that pectoralis muscle fascicles are significantly shorter in soaring hawks than in non-soaring birds. This coupling of an SPD-mediated increase in pectoralis leverage with force-specialized muscle architecture produces a pneumatic system that is adapted for the isometric contractile conditions expected in soaring flight. The discovery of a mechanical role for the respiratory system in avian locomotion underscores the functional complexity and heterogeneity of this organ system, and suggests that pulmonary diverticula are likely to have other undiscovered secondary functions. These data provide a mechanistic explanation for the repeated appearance of the SPD in soaring lineages and show that the respiratory system can be co-opted to provide biomechanical solutions to the challenges of flight and thereby influence the evolution of avian volancy.
胸肋憩室(SPD)是鸟类呼吸系统的一种延伸,位于负责拍打翅膀的主要肌肉之间。在这里,我们调查了 68 种鸟类的肺部器官,结果表明,SPD 几乎存在于所有研究的翱翔类群中,但不存在于非翱翔类群中。我们发现,这种结构至少独立进化了七次,与翱翔飞行有关,这表明憩室可能与这种飞行方式具有功能和适应性的关系。我们以翱翔的鹰 Buteo jamaicensis 和 Buteo swainsoni 为模型,表明 SPD 不是通气的必要结构,充气的 SPD 可以增加胸大肌颅部的力臂,并且翱翔鹰的胸大肌肌束比非翱翔鸟类明显更短。这种与 SPD 介导的胸大肌杠杆作用增加相耦合的力专业化肌肉结构,产生了一种气动系统,适应于在翱翔飞行中预期的等长收缩条件。呼吸系统在鸟类运动中的机械作用的发现,强调了这个器官系统的功能复杂性和异质性,并表明肺憩室可能具有其他未被发现的次要功能。这些数据为 SPD 在翱翔谱系中反复出现提供了一个机械解释,并表明呼吸系统可以被用来为飞行的挑战提供生物力学解决方案,从而影响鸟类飞行的进化。