Short Communication: Allometry of Lung Volume During Voluntary Submergence in the Saltwater Crocodile Crocodylus Porosus

During submergence, the volume of gas stored in the lungs of a reptilian diver functions not only as an O₂ store and CO₂ sink (Lenfant, Johansen, Petersen & Schmidt-Nielsen, 1970; Burggren & Shelton, 1979; Seymour, 1982) but can also be adjusted to achieve the desired buoyant state. Lung volume during voluntary submergence will often be a compromise between these two basic functions and should also increase with body mass. The relationship between submergence lung volume and body mass will depend on how tissue density and specific gravity selected by a submerged animal vary with body mass. Previous studies have determined the relationship between lung volume and body mass in reptiles from maximally inflated lungs of dead specimens and have calculated an interspecific scaling factor of 0·75 (Tenney & Tenney, 1970; Wood & Lenfant, 1976). This suggested that the lung volume of a reptile may scale in accordance with mass-specific aerobic metabolism which also has a scaling factor close to 0·75 (Tenney & Tenney, 1970). Although equations generated from interspecific data from maximally inflated lungs are useful for describing certain morphological characteristics of reptilian lungs (Perry, 1983), they are probably inappropriate for determining the lung volume selected by a conscious, undisturbed reptile while voluntarily submerged.