Gas Exchange in Spadefoot Toads Beneath the Ground
Seymour RS. 1973. Gas Exchange in Spadefoot Toads Beneath the Ground. Copeia. 1973(3):452-460
Oxygen concentrations in the air adjacent to buried spadefoot toads (Scaphiopus) in the field were close to atmospheric levels throughout the year. The measurements were confirmed by calculations based on the physical nature of field soils and the rate of oxygen consumption by soil microorganisms. Oxygen dissociation curves of whole blood of S. couchii and S. hammondii were shifted to the right in summer, probably representing an adaptation to high levels of activity. Whereas oxygen loading was largely unaffected by the shift, unloading was facilitated in the tissues. Hemoglobin concentration and hematocrit remained constant throughout the year in S. couchii, S. hammondii and S. bombifrons under field conditions. Increased blood viscosity at lower winter temperatures probably does not alter rates of gas exchange in dormant toads. Decreases in heart rate of dormant spadefoots reflected low metabolic rate. During burrowing, heart rates were similar to those of resting toads. Although the rate of lung ventilation decreased when S. couchii and S. hammondii were burrowing, the rate of pulmonary gas exchange was not reduced significantly. No ventilation movements occurred during undisturbed dormancy of S. couchii indicating that, under the experimental conditions, gas exchange occurred through the skin. However, buildup of shed skin around dormant toads in the field may necessitate pulmonary gas exchange.