KIDD, C.*; BRAINERD, E.L.: Abdominal pressure during high speed locomotion in the Texas spiny lizard, Sceloporus olivaceus
In this study we measured pressure in the abdominal cavity of Sceloporus olivaceus at rest and during high speed locomotion on a trackway. During trackway locomotion, abdominal pressure fluctuates rapidly around mean pressure and appears to be correlated with footfalls. Preliminary results from two individuals indicate that mean abdominal pressure increases during burst locomotion. Mean abdominal pressure during locomotion increased above mean resting pressure by 3.6 � 2.3 cmH2O (0.36 � 0.23 kPa) in one individual and by 3.5 � 1.9 cmH2O (0.35�0.19 kPa) in a second individual (mean � s.d.). Paired t-tests (paired pre-exercise and running pressures) showed that these increases were statistically significant in both individuals (p<0.0005). It is likely that these increased abdominal pressures are transmitted to the thoracic region since lizards lack a diaphragm and the lungs and other internal organs are contained within a single cavity. Previous work has shown that lung ventilation decreases dramatically in lizards sprinting on trackways, and the proposed explanation is for this decrease is a mechanical constraint on hypaxial muscles (Carrier, D. R. 1987. Exp. Biol. 47: 33-42). We propose that increased abdominal, and therefore thoracic, pressures may be an additional constraint on ventilation during sprinting in lizards. Supported by a Beckman Foundation Undergraduate Research Scholarship to C.K. and a National Science Foundation grant, IBN-9875245 to E.L.B.