CAREER: Lung Ventilation in Lizards and the Evolution of Amniote Respiratory Mechanisms

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The proposed career plan integrates research on the anatomy and physiology of vertebrate respiration with the development of two new, inquiry-based courses in vertebrate anatomy and comparative physiology. These courses will depart from the traditional lecture-and-exam format of most college courses, and will instead emphasize the development of students' research-related intellectual skills. The research component of the proposed career plan focuses on the evolution of breathing mechanisms (lung ventilation) in vertebrate animals. The PIs current understanding of the evolution of lung ventilation is wholly inadequate. The PIs know that the primitive condition is to use a mouth pump (buccal pump) to force air into the lungs under positive pressure (as seen in frogs and lungfish) and that the derived condition (as seen in reptiles, birds and mammals) is to rotate the ribs and suck air down into the lungs (aspiration breathing). The PIs currently have little information, however, on how or why this dramatic transition from buccal pumping to aspiration breathing occurred. Physiological traits, such as breathing mechanisms, generally cannot be inferred from fossilized bones; therefore, we must rely on living animals that exhibit intermediate states between different mechanisms. Unfortunately for studies of lung ventilation, researchers have generally assumed that no living animals exhibit an intermediate state. The PIs have recently discovered, however, that some lizards utilize both a buccal pump and an aspiration pump during exercise. The breathing mechanism of lizards may therefore be a "living fossil" of an intermediate mechanism between pure buccal pumping and pure aspiration breathing. The proposed research incorporates comprehensive anatomical and physiological studies of lung ventilation in a wide range of lizard species, with the goal of using this living fossil model to understand the dramatic evolutionary transition that occurred between buccal pump and aspiration breathing in vertebrate animals.