Meeting Abstract

35.1  Sunday, Jan. 5 08:00  Unidirectional airflow in varanids and the evolution of pulmonary airflow patterns in Diapsida SCHACHNER, ER*; CIERI, RL; BUTLER, JP; FARMER, CG; University of Utah; University of Utah; Havard School of Public Health; Harvard Medical School; University of Utah eschachner@gmail.com

Historically the highly specialized avian lung has been considered unique due to the decoupling of the ventilatory pump and gas exchanging regions, as well as the presence of unidirectional flow through the bronchial tree. These traits are usually associated with their active, volant lifestyle and endothermic metabolism; however, the recent discovery of unidirectional airflow in the lungs of crocodilians suggests that these assumptions are false. Here we demonstrate region-specific patterns of unidirectional airflow in the lungs of three species of Varanus: in vivo data from Varanus exanthematicus, and ex vivo data from V. albigularis and V. niloticus. Pulmonary anatomy was studied using computed tomography of multiple individuals of each taxon, and 3D surface models of the bronchial tree were created in Avizo 7.1. Two distinct regions of unidirectional flow were identified within the varanid lung: intrabronchial flow in a cranial bronchus and interbronchial flow in the more caudal lateral bronchi. As in birds and crocodilians, flow patterns throughout the varanid lung appear to arise from aerodynamic valves as there are no anatomical structures (i.e., flaps or sphincters) maintaining or inducing flow. These data suggest that unidirectional flow is homologous in Archosauria and Varanoidea, and as a result the origin of unidirectional flow is likely far older than the Triassic split between crocodilians and birds. These results also indicate that this trait evolved completely independently from high aerobic activity metabolism or endothermy.