The Biomechanics of Tiger Salamander (Ambystoma tigrinum) Underwater Walking on Smooth and Rough Substrates

In nature, salamanders adapted to terrestrial and aquatic environments as well as varying substrate conditions in their habitats. Discovering more about the effects of substrate types on the kinematic measurements of underwater walking can offer us with more information regarding biological principles and limb evolution. A previous study conducted on the same salamander subjects led us to believe that a rough substrate such as gravel will provide the salamander with better traction and grip to thrust forward for walking underwater compared to a smooth substrate. Therefore, a rougher substrate is expected to have resulting kinematics that will differ significantly from underwater walking on a smooth surface. This project studied the biomechanics of underwater walking of the model organism, Tiger Salamander (Ambystoma tigrinum). The goal of the experiment was to analyze and collect data on the general locomotion and kinematic measurements while the salamander walked while submerged underwater. In order to obtain the information, two synchronized GoPros were used to film high speed videos of the strides of the salamanders at a lateral and dorsal viewpoint. Their unrestricted, voluntary strides were captured on both smooth and rough surfaces that provide a different expanse of traction. After filming was completed, each video was trimmed and compressed using VirtualDub. Then, the MATLAB digitizing module DLTdv5 was used to track multiple anatomical points among each salamander’s body. For each frame the x and y coordinate of five landmark anatomical features were tracked for both the horizontal and vertical video. The y coordinate of the dorsal perspective provided the estimated “z” coordinate for a more accurate analysis of any existing angled strides. Based on the 2-D trends of the digitized points, a custom MATLAB code was produced in order to extract information about their overall gait cycle and therefore the individual strides. This research will help us better piece together the evolutionary changes from underwater to terrestrial locomotion and understand how these fundamental biomechanical principles apply to other organisms. The average salamander stride duration, duty factor, stride length, stride velocity, minimum foot velocity, maximum foot velocity, foot slip distance, minimum potential kinetic and potential energy, and maximum potential and kinetic energy were used as kinetic markers to compare the effects of substrate type on the kinematics of underwater walking. After statistical analysis it was determined that there were significant differences existing between two salamanders on gravel and sand substrate for the following variables: minimum kinetic energy, average velocity, average velocity in body lengths, stride duration, and stride length in body lengths. For the very first time the change in potential and kinetic energy throughout a stride of a salamander while underwater walking was able to be calculated. This current study presented statistical evidence which confirmed that the kinematics of underwater walking of a salamander differs to some degree between smooth and rough substrates