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 O uptake among them by measuring theVO while submerged and determining the responses to progressive hypoxia at 10-240 mmHg at 20° C. Both species ofAmphiuma were metabolic O conformers over the entire range ofPO. About half ofSiren lacertina were conformers over this range, and half were regulators with an average critical O 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 O conductance", defined asΔVO/ΔPO(µl O · g · h · mmHg) in the range of metabolic O 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 O loss through the skin, or in facilitating its uptake, as correlated with the O tensions normally prevailing in the environment of each species.