Swimming in Constricting (Elaphe g. guttata) and Nonconstricting (Nerodia fasciata pictiventris) Colubrid Snakes

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Abstract
The axial skeleton, musculature and the waveform during swimming were examined for Nerodia f. piciventris, a nonconstricting colubrid, and Elaphe g. guttata, a constricting colubrid. Both species possess qualitatively similar configurations of the segments of 3 major epaxial muscles (M. semispinalisspinalis, M. longissimus dorsi and M. iliocostalis). Segmental lengths of these three muscles of Elaphe are slightly less than or equal to those of Nerodia, whereas Elaphe has 50% more total vertebrae than Nerodia. Between the 2 species examined, no differences were found in waveform or maximum swimming velocity, whereas there were slight differences in the relation between relative swimming velocity and the frequency of wave propagation. For both species the amplitude and wavelength of the lateral undulations increased from anterior to posterior. Within each species, relative amplitude and relative wavelength tended to decrease slightly as swimming speed or snake size increased. For Nerodia the maximum absolute swimming velocity scaled with total snake length to the 0.6 power. For all snakes stability in the transverse plane increased with increased swimming speed. Snakes and angulliform fish exhibited similar burst swimming velocities and a similar relationship between frequency of undulation and relative forward velocity.