HORNER, A.M.*; JAYNE, B.C.; University of Cincinnati; University of Cincinnati: The effects of viscosity on the axial motor pattern of the lungfish ( Protopterus annectens) during lateral undulatory swimming

Individual organisms often must move in different environments. For example, an amphibious animal living in either an estuarine or ephemeral freshwater ecosystem encounters a variety of environmental conditions, including water, land, and mud. Although recent studies have compared arboreal, terrestrial, and aquatic locomotion, few studies have examined locomotion in transition between these environments. Both external and internal mechanical factors are widely recognized as important for understanding mechanisms of propagating waves during undulatory swimming, but few studies of swimming have manipulated extrinsic factors. The African lungfish (Dipnoi: Protopterus annectens) is an ideal model to study locomotion in variable environments because this species occurs in areas prone to seasonal drought, and constructs burrows in mud for breeding and estivation. Thus, variable viscosity is ecologically relevant for this species, and can provide biomechanical insight. To test the effects of viscosity on the kinematics and motor pattern during lungfish swimming, we used a non-toxic PHPA polymer in aqueous solution to obtain viscosities of 1, 10, 100, and 1,000 centi-Stokes. With increased viscosity the disparity between the speed of swimming and speed of EMG wave propagation increased considerably. Consequently, the distance traveled per tail beat cycle from lowest to highest viscosity decreased tenfold. We found that the amplitude and longitudinal extent of muscle activity increased significantly with increased viscosity, although axial motor pattern did not deviate from a posteriorly propagated wave, and remained alternating between left and right sides.