Meeting Abstract

14.3  Jan. 4  The value of the crocodilian left aorta to digestion FARMER, CG; URIONA, TJ*; STEENBLINK, M; OLSEN, D; SANDERS, K; Univ. of Utah, Salt Lake City; Utah Artificial Heart Institute, Salt Lake City; Health Sciences Center, Salt Lake City uriona@biology.utah.edu

The crocodilian circulatory system has intrigued biologists for over 160 years but the functional significance of their four-chambered heart, which separates venous and arterial blood, and the retention of dual aortic arches, which enables venous blood to be shunted around the lungs, remains a mystery. This anatomy is widely believed to be adaptive, in part because of the control crocodilians have over blood flow through the left aorta. Crocodilians are the only vertebrate known to have an active internal heart valve that controls flow through the left aorta. Although many hypotheses have been put forward about the importance of this system to the wellbeing of the animals, they remain untested. Here we show the left aorta serves digestion by enabling venous blood to be sent to the stomach. In a group of juvenile American alligators we surgically removed the left aorta, resulting in a circulatory system that mimics that found birds and mammals, while another group underwent surgery without removal of the left aorta. Removal of the left aorta significantly slowed the rate of gastric acid secretion and rates of digestion of bone. Rapid rates of acid secretion may be particularly important to ectothermic reptiles because gastric acid secretion is highly sensitive to body temperature, yet competition for basking sites can limit the time small, lesser status animals can achieve their preferred body temperature and thus effectively secrete acid. In contrast, the warm and stable body temperatures of birds and mammals allow acid to be continuously secreted as necessary, albeit at a lower rate, eliminating the need for a conduit of venous blood to the stomach. Thus the retention of the dual aortic arches in crocodilians for digestive purposes does not support the hypothesis of an endothermic crocodilian ancestry.