METABOLIC DEPRESSION DURING ESTIVATION IN THE AUSTRALIAN FROGS, NEOBATRACHUS AND CYCLORANA

The standard metabolic rate (SMR) of a number of species of Western Australian frogs is similar to that predicted for other anuran amphibians. The metabolic rate during activity is elevated 10-20 times above SMR, in close agreement with other studies of the energetics of amphibian activity. Species of two genera, Neobatrachus and Cyclorana, readily enter aestivation, which involves cessation of activity, formation of an epidermal cocoon, and depression of metabolic rate below SMR. The magnitude of metabolic depression varies between species from 70 to 80% (i.e. aestivation metabolic rate is 20-30% of SMR). The variation in magnitude of metabolic depression most likely reflects, in part, the difficulty of distinguishing the early stages of aestivation from the normal resting state. Both standard and aestivating metabolic rate are strongly mass-dependent, but the magnitude of metabolic depression is remarkably consistent in a number of different genera of frogs, salamanders and fish. The metabolic rate of aestivating amphibians is similar to that predicted for a unicellular organism of equivalent body mass, but is substantially lower than the metabolic rate of aestivating mammals.