Meeting Abstract
32.2 Friday, Jan. 4 Forelimb muscle activity in swimming sliders and sea turtles: are muscle activation patterns conserved? RIVERA, A.R.V.*; WYNEKEN, J.; BLOB, R.W.; Clemson Univ; Florida Atlantic Univ; Clemson Univ arivera@clemson.edu
Tetrapod limbs have been modified numerous times through evolution to yield a diverse array of forms. New locomotor behaviors might arise through evolutionary changes in anatomy, changes in activation of muscles producing limb motion, or a combination of both. Turtles provide an excellent model to test for such changes because they display diverse locomotor styles and morphologies. Most freshwater turtles swim via asynchronous anteroposterior forelimb rowing, but sea turtles swim via synchronous dorsoventral flapping of forelimbs modified as flippers. Muscular arrangements differ between these groups, but comparisons of their forelimb motor patterns have not been performed. We compare high-speed video and electromyographic (EMG) data from the derived, flipper-shaped forelimbs of loggerhead sea turtles (Caretta caretta) to the generalized forelimbs of swimming red-eared sliders (Trachemys scripta). Limb cycles were defined as a recovery phase (sea turtles: abduction, sliders: protraction) followed by a thrust phase (sea turtles: adduction, sliders: retraction). Although relative durations of these phases differ slightly between the species (recovery phase = 44% cycle duration in sliders, 50% in sea turtles), aspects of their motor patterns are similar relative to landmark kinematic events. For example, latissimus dorsi (humeral abductor and protractor) becomes active shortly before the start of protraction and remains active until about 10% before maximal humerus protraction and elevation in both species. Muscle activation patterns were found to be similar for some muscles, but different for others. These data indicate the potential for conservation of motor patterns in the evolution of turtle limb function despite dramatic evolutionary changes in anatomical structure.
