Meeting Abstract

P2.68  Sunday, Jan. 5 15:30  Evolutionary linkage of heart and lung development in lungless salamanders LEWIS, ZR*; HANKEN, J; Harvard University, Cambridge, MA; Harvard University, Cambridge, MA zlewis@oeb.harvard.edu

Separation of oxygenated from deoxygenated blood in the heart is a critical component of pulmonary respiration in tetrapods that facilitates their terrestrial existence. In mammals, the closure of the foramen ovale and the complete separation of left and right atria yield efficient dual circulatory pathways. In amphibians, an atrial septum forms embryonically to separate pulmonary and systemic blood flows. Whether the lungless salamanders (family Plethodontidae) possess an atrial septum as adults is a contentious topic; authors have stated opposing claims for over 100 years. The atrial septum presumably would have little function in lungless salamanders due to the absence of pulmonary return. Here, we use µ-CT imaging to examine atrial septum development of both lungless salamanders and salamanders with lungs. We show that lungless salamanders fail to develop atrial septa. In mammals, the lungs induce formation of the atrial septum by secreting morphogens to neighboring mesenchyme. We hypothesize that atrial septum loss in lungless salamanders is a direct result of evolutionary loss of this signal, and present evidence that administration of exogenous morphogens results in partial restoration of atrial septa. Hearts and lungs are a genetically and evolutionarily interconnected module, whose morphology and physiological function are dictated by developmental signals. Atrial septum loss in plethodontids is likely a direct consequence of lunglessness.