The Effects of Dissolved O₂ and CO₂ on Metabolism and Gas-Exchange Partitioning in Aquatic Salamanders

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Abstract
Pseudobranchus striatus, a completely aquatic species which typically inhabits pond waters with low O2 and high CO2 concentrations, exhibited a decrease in metabolic rate in the presence of high environmental CO2 tensions. Aerial O2 uptake expressed as a percentage of total O2 consumption increased slightly with increased CO2 concentrations at O2 tensions below 100 mm Hg. Of the 3 species observed, this species showed the lowest metabolic rate and the highest degree of CO2 tolerance. In Taricha torosa, a partially aquatic species which inhabits waters with high O2 and low CO2 concentrations during its aquatic phase, standard metabolic rate increased as CO2 tensions increased. Percent aerial O2 uptake was positively correlated with increased PCO2 [CO2 tension] at O2 tensions above 120 mm Hg. This species showed the highest metabolic rate and the lowest degree of CO2 tolerance. In Diemictylus viridescens, a species which is morphologically and ecologically intermediate between the other 2, standard metabolic rate decreased and percent aerial O2 uptake increased in response to increased PCO2 over all O2 tensions. As the degree of terrestriality increased among these amphibian species: metabolic rate increased; ability to obtain O2 from water decreased; tolerance to dissolved CO2 decreased and CO2 tensions became more important in stimulating aerial respiration within the ranges of PO2 [O2 tension] normally encountered.