Meeting Abstract

16.2  Thursday, Jan. 3  Removal of cardiac shunt impairs growth in the American alligator EME, J.; GWALTHNEY, J.; OWERKOWICZ, T.; BLANK, J.M.; HICKS, J.W.*; UC Irvine; UC Irvine; UC Irvine; UC Irvine; UC Irvine jhicks@uci.edu

Reptilian cardiac shunting is hypothesized to have adaptive importance in various physiological functions, e.g., inducing hypometabolism, metering lung oxygen during diving, aiding recovery from metabolic acidosis and/or facilitating digestion. However, to demonstrate the adaptive significance, elimination of cardiac shunt must be shown to reduce fitness. Among reptiles, crocodilians possess a unique cardiac anatomy (fully-divided ventricle with two aortae) that allows for surgical elimination of right-to-left cardiac shunt. We altered the outflow tract of hatchling alligators by occluding the left aorta proximal and distal to the Foramen of Panizza. The surgical and sham-operated groups (n=36 each) were subsequently split into three exercise regimes: run, swim and sedentary (n=24 each). Run and swim groups were exercised to exhaustion on a treadmill or in a swim flume every other day for 15 months and growth was monitored. Loss of cardiac shunt significantly reduced the mass of alligators. In addition, running and swimming significantly constrained growth relative to sedentary animals, and both exercise modes reduced the difference in growth between alligators with and without shunting ability. We suggest that cardiac shunting has adaptive significance to crocodilians, by maintaining increased growth and allowing animals to achieve sexually reproductive size more rapidly. Supported by NSF IOB 04445680 to JWH.