ETNIER, S.A.*; DEAROLF, J.L.; MCLELLAN, W.A.; PABST, D.A.: Postural control of lateral flexibility in neonatal dolphins (Tursiops truncatus)

En utero, fetal bottlenose dolphins (Tursiops truncatus) are bent laterally such that the tail flukes and throat are juxtaposed. Dolphins begin swimming immediately after birth, yet the dorsoventral oscillations required to swim may be compromised by the lateral flexibility required by the fetus. We hypothesize that neonates actively limit these deformations by contracting laterally placed axial muscles. If these muscles provide postural control in the neonate, we predict that the lateral muscles have a high percentage of slow twitch fibers and a relatively large cross-sectional area. To test this hypothesis, we measured myosin ATPase activity in neonatal (N=4) and adult (N=4) intertransversarius caudae dorsalis (ICD) muscles. Neonates had 57% slow twitch fibers in the ICD, compared to 39% in adults and only 38% in other neonatal locomotor muscles (Dearolf et al. 2000). We measured the cross-sectional area of the ICD (at the anus) relative to the total cross-sectional area of locomotor muscles in an adult and neonatal dolphin. In the neonate, the ICD occupied 18% of the total cross-sectional area of locomotor muscle, compared to only 10% in the adult. These results suggest that the ICD is “primed” to act as an important postural muscle in neonatal dolphins, both with respect to its contractile properties and its potential force production. Additionally, the development of the ICD, which differs dramatically from that of other neonatal locomotor muscles, suggests that its function may be superceded by other morphological structures, such as connective tissue, later in development. Supported by NIH and NMFS.