The primary function of the cardiovascular system is to provide adequate oxygen and nutrients to the tissues, while ensuring the removal of carbon dioxide and other metabolic waste products. In vertebrates this goal is achieved through circulatory and cardiac designs that are often represented as an evolutionary progression from the two-chambered heart of fish to the completely divided four-chambered heart of birds and mammals. The completely divided four-chambered heart has evolved at least twice in vertebrates, once in the lineage that gave rise to mammals and once in ancestral archosaurs, the ancient group of reptiles that gave rise to modern birds and crocodiles. In crocodilians, the heart is four-chambered, just like birds and mammals, but retains two aortae (vessels that transport blood to the body). The left aorta arises from the right ventricle, alongside the pulmonary artery and consequently this anatomical arrangement results in the potential for oxygen poor blood to bypass the lungs and recirculate to the body. This type of blood flow is termed a right-to-left (R-L) cardiac shunt. This unique circulatory feature of crocodilians has been known for over 170 years and is often assumed to provide important physiological benefits. However few, if any, of these benefits have been experimentally verified. Here the PI will investigate the functional consequences of R-L cardiac shunting in the American alligator, Alligator mississippiensis, and in the broad-nose caiman, Caiman latirostris. The physiological functions of R-L cardiac shunting will be determined following surgical modification of the heart. The surgical procedure removes the left aorta and permanently eliminates the capacity for R-L cardiac shunt. In one set of experiments the hearts of hatchling alligators will be surgically modified and raised under controlled environmental conditions in the vivarium facilities at UC Irvine. In a second set of experiments, the hearts of hatchling caimans will be modified and the animals raised in semi-natural outdoor facilities in Rio Claro, Brazil. Animals will be measured periodically and at the end of a 12-18 month growth period a variety of physiological functions will be assessed. A third series of experiments will determine the physiological functions of R-L cardiac shunting in older animals. In these experiments, both alligators and caimans will be collected from the field, the hearts surgically modified and the effects of eliminating R-L cardiac shunt on a variety of physiological functions will be determined. The proposed research will form an integrated picture of the interactive functioning of the cardiovascular system and more importantly will addresses a notable and unanswered question in comparative biology vertebrate-what is the physiological function of R-L cardiac shunting in crocodilians? In addition to the specific scientific goals, the proposed research will directly contribute to the training of individuals in how to investigate and integrate complex biological systems. The project will provide undergraduates, graduates and postdoctoral fellows, a framework within which to think in terms of biological diversity, evaluate and consider environmental influences, and place research results within developmental and/or evolutionary trajectories. The integrative nature of the proposed research and the resulting training of students and postgraduate researchers will, in general, make a positive and lasting contribution to the health and strength of physiological sciences- a health and strength that is required to insure significant advances in the physiological sciences during the 21st century.
