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

Summary

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.