Influence of Body Size and Temperature on the Critical Oxygen Tension of Some Plethodontid Salamanders

Abstract

The critical O2 tension [Pc] was measured in lungless salamanders (Desmognathus quadramaculatus, D. monticola, D. fuscus fuscus, D. fuscus auriculatus) by placing the animals in closed respirometers in air and allowing them to deplete the O2 within the system. Metabolic rate was measured during the run and the PO2 at each measurement was calculated. Experiments were conducted at 15, 22.5 and 30.degree. C. Values of Pc ranged from 17-119 mm Hg. The level of Pc depended on the weight-specific surface area (and therefore, size) of the animal, the metabolic rate and the temperature. The transport capacity (slope of the regression of metabolic rate on PO2, at tensions below Pc) decreased with increasing sizes of the animals. The lower limit of O2 regulation (or Pc) was more sensitive to changes in metabolic rate in large animals than in small ones. Since respiratory limitations are more severe in large salamanders than in small animals, and at high environmental temperatures, these limitations may be the primary factor leading to the latitudinal and altitudinal size clines observed in plethodontids.