Metabolic oxygen regulation and conformity during submergence in the salamandersSiren lacertina, Amphiuma means, andAmphiuma tridactylum, and a comparison with other giant salamanders.

The giant salamanders of North America include 4 genera, all of which are aquatic. We have compared the efficacy of aquatic O2 uptake among them by measuring theVO2 while submerged and determining the responses to progressive hypoxia at 10-240 mmHg at 20° C. Both species ofAmphiuma were metabolic O2 conformers over the entire range ofPO2. About half ofSiren lacertina were conformers over this range, and half were regulators with an average critical O2 tension of 92 mmHg. There were no short-term changes (days) in the response ofSiren to progressive hypoxia, but one animal switched from conformation to regulation after 4-5 months. Neither genus is considered to have an exceptionally low metabolic rate. The "whole-body O2 conductance", defined asΔVO2/ΔPO2(µl O2 · g-1 · h-1 · mmHg-1) in the range of metabolic O2 conformity, was least in the species most dependent upon air-breathing and most likely to be found in hypoxic waters (e.g., 0.076 forAmphiuma), and greatest in those that airbreathe less frequently and/or are found in relatively normoxic waters (e.g., 0.429 forNecturus). These conductances are considered to be adaptive in terms of preventing O2 loss through the skin, or in facilitating its uptake, as correlated with the O2 tensions normally prevailing in the environment of each species.