Meeting Abstract

P3.52  Saturday, Jan. 5  Advantages of limb use underwater in the salamander Ambystoma tigrinum CREER, R.M.*; ASHLEY-ROSS, M.A.; Wake Forest University rossma@wfu.edu

The evolution of the tetrapod limb is commonly considered to have occurred for the purpose of terrestrial locomotion. However, fossil evidence indicates that the evolution of limbs occurred well before invasion of the land. One hypothesis to explain the utility of limbs for aquatic motion is that they assist in navigating obstacle-strewn shallow water environments. We tested this hypothesis in salamanders, the closest living analog to the postural condition of primitive tetrapods. We videotaped adult tiger salamanders (Ambystoma tigrinum) traveling through an underwater obstacle course made of acrylic pegs screwed into a Plexiglas sheet, and recorded the fastest transit time for each of five individuals. To test the contribution of axial versus limb propulsion, we tested the salamanders in three conditions: (1) with both sets of limbs unrestrained [control condition], (2) with a tight-fitting elastic tube around the body such that it restricted the use of the forelimbs, and (3) with a tight-fitting elastic tube around the body that restrained both forelimbs and hindlimbs. The transit time of salamanders with their forelimbs bound was approximately 100% longer than the control. Salamanders with both forelimbs and hindlimbs restrained took approximately 400% more time than the control. This result supports the hypothesis that limbs are of great utility in moving through complex three-dimensional underwater habitats.