Meeting Abstract

9.1  Thursday, Jan. 3  Examining the role of the amphibian and crocodilian “diaphragm” in aquatic locomotion URIONA, TJ*; FARMER, CG; Univ. of Utah, Salt Lake City; Univ. of Utah, Salt Lake City uriona@biology.utah.edu

The convergent evolution of a crocodilian and an amphibian diaphragm suggests this muscle complex has an adaptive function in an aquatic environment. In both groups the muscle anchors the lungs to the pelvic girdle. In crocodilians contraction of the muscle is known to cause the lung-liver complex to move caudad, and the morphology of the amphibian system suggests a similar translation will occur in this lineage also. Although most studies have focused on the role of the diaphragmatic muscle in assisting ventilation, inspiration in crocodilians and exhalation in amphibians, a caudal movement of the lung will change the relationship between the center of mass and the center of buoyancy and therefore this muscle may be used to control pitch. We investigated this possibility using electromyography in conjunction with an inclinometer. In both juvenile American alligators and in Xenopus we observed activity of the muscle coincident with head-down dives. In contrast to prior studies, we saw no activity in the amphibian diaphragm with ventilation. Furthermore, transection of the crocodilian diaphragm did not reduce vital capacity unless the respiratory system was taxed by the ingestion of a large meal. These data suggest the muscle complex serves aquatic locomotion in both crocodilians and Xenopus and that further research is requisite to fully understand the respiratory function of the muscles. The convergent evolution of such a strikingly similar morphology in these highly aquatic frogs and in semiaquatic crocodilians supports the hypothesis that a major selective pressure for the evolution of this system was aquatic locomotion.