Ventilatory Activity in Amphiuma tridactylum and Siren lacertina (Amphibia, Caudata)

Siren lacertina obtains 75% of its oxygen and eliminates 60% of its carbon dioxide via the lungs (Guimond and Hutchison, 1973a), and Amphiuma tridactylum obtains 56% of its oxygen and releases 23% of its carbon dioxide aerially (Guimond and Hutchison, 1974). Siren can utilize up to 26%, and Amphiuma up to 50%, of the inspired oxygen (Guimond and Hutchison, 1973a; Toews, 1973), the most efficient oxygen utilization in amphibian lungs studied. (Guimond and Hutchison, 1974). These two aquatic genera have the smallest total surface area of respiratory capillaries per g found in amphibians (Czopek, 1962b), and lowest metabolic rate at comparable temperatures of all amphibians studies (Whitford, 1973; Guimond and Hutchison, 1976). These respiratory adaptations enable Siren and Amphiuma to survive in hypoxic, hypercarbic shallow and warm water which would be inhospitable to other amphibians