Energetic efficiency of vocalization by the frog Physalaemus pustulosus

Abstract

Male Physalaemus pustulosus consume, on average, 1.2 μl of oxygen in the production of a single call, which is equivalent to an energy input per call of 0.024 J. The total power of complex cells, which can have a varying number of components, ranged from 0.36 to 0.46 mW. The total acoustic energy contained in these complex calls ranged from 0.12 to 0.30 mJ. The energetic efficiency of the vocalization ranged from 0.5 to 1.2%, which is similar to the range estimated for some other animals. The low energetic efficiency of vocalization by these frogs is due, in part, to the fact that the wavelengths of the call are too long, relative to the size of the frog, to be radiated efficiently. Although shorter wavelengths (higher frequencies) are radiated by the frog at relatively greater intensities, longer wavelengths (lower frequencies) attenuate less rapidly in the environment. It is suggested that selection generated by the acoustics of the environment favours calls with lower frequencies, but the morphology of the animal sets a lower limit to which frequencies can evolve.