A Comparison of the Water-Balance Response in Five Species of Plethodontid Salamanders

Abstract

The aquatic species Desmognathus quadramaculatus did not respond to either arginine vasopressin (AVP) or a salt load, and its rate of hydration following dehydration was lower than that of any of four terrestrial species of plethodontid salamanders also studied. Plethodon hoffmani and P. punctatus took up water most rapidly after dehydration, AVP, or a salt load and therefore appear to be better adapted physiologically to a dry environment than are P. cinereus and P. glutinosus. These physiological adaptations may partially account for the distributional relationships of these two pairs of contiguously allopatric terrestrial species. Urine production was least in D. quadramaculatus and greatest in P. hofmani and P. punctatus. Arginine vasopressin significantly reduced the amount of urine that accumulates in the bladder in P. punctatus, P. hoffmani, and P. glutinosus. Emptying the bladder of P. glutinosus every 30 min did not diminish the AVP response, suggesting that in this species the kidney rather than the bladder is a target organ for AVP. We conclude that there is a considerable range in the water-balance responses in the five species of plethodontid salamanders studied here and that the different responses can be correlated with the moisture conditions of the habitat. In contrast to terrestrial anurans, whose high rates of water uptake are due to high skin permeability, the rapid uptake of water reported here and elsewhere for urodeles appears to be a consequence of their relatively larger surface area.