Contribution of gular pumping to lung ventilation in monitor lizards

A controversial hypothesis has proposed that Lizards are subject to a speed dependent axial constraint that prevents effective Lung ventilation during moderate- and high-speed Locomotion. This hypothesis has been challenged b y results demonstrating that monitor lizards (genus Varanus) experience no axial constraint. Evidence presented here shows that, during locomotion, va ranids use a positive pressure gular pump to assist Lung ventilation. Disab ling the gular pump reveals that the axial constraint is present in varanid s but it is masked by gular pumping under normal conditions. These findings support the prediction that the axial constraint may be found in other tet rapods that breathe by costal aspiration and locomote with a lateral undula tory gait.