Metabolism, gas exchange, and acid-base balance of giant salamanders
Version of Record online: 13 DEC 2011
© 2011 The Author. Biological Reviews © 2011 Cambridge Philosophical Society
Volume 87, Issue 3, pages 583–601, August 2012
How to Cite
Ultsch, G. R. (2012), Metabolism, gas exchange, and acid-base balance of giant salamanders. Biological Reviews, 87: 583–601. doi: 10.1111/j.1469-185X.2011.00211.x
- Issue online: 4 JUL 2012
- Version of Record online: 13 DEC 2011
- (Received 6 May 2011; revised 7 November 2011; accepted 11 November 2011)
- gas exchange in salamanders;
- acid-base balance in salamanders;
- giant salamanders;
- evolution of air-breathing
The giant salamanders are aquatic and paedomorphic urodeles including the genera Andrias and Cryptobranchus (Cryptobranchidae), Amphiuma (Amphiumidae), Siren (Sirenidae), and Necturus (Proteidae, of which only N. maculosus is considered ‘a giant'). Species in the genera Cryptobranchus and Necturus are considered aquatic salamanders well adapted for breathing water, poorly adapted for breathing air, and with limited abilities to compensate acid-base disturbances. As such, they are water-breathing animals with a somewhat fish-like respiratory and acid-base physiology, whose habitat selection is limited to waters that do not typically become hypoxic or hypercarbic (although this assertion has been questioned for N. maculosus). Siren and Amphiuma species, by contrast, are dependent upon air-breathing, have excellent lungs, inefficient (Siren) or no (Amphiuma) gills, and are obligate air-breathers with an acid-base status more similar to that of terrestrial tetrapods. As such, they can be considered to be air-breathing animals that live in water. Their response to the aquatic hypercarbia that they often encounter is to maintain intracellular pH (pHi) and abandon extracellular pH regulation, a process that has been referred to as preferential pHi regulation.
The acid-base status of some present-day tropical air-breathing fishes, and of Siren and Amphiuma, suggests that the acid-base transition from a low PCO2-low  system typical of water-breathing fishes to the high PCO2-high  systems of terrestrial tetrapods may have been completed before emergence onto land, and likely occurred in habitats that were typically both hypoxic and hypercarbic.