Call acoustics reflect body size across four clades of anurans

An inverse relationship between body size and advertisement call frequency has been found in several frog species. However, the generalizability of this relationship across different clades and across a large distribution of species remains underexplored. We investigated this relationship in a large sample of 136 species belonging to four clades of anurans (Bufo, Hylina, Leptodactylus and Rana) using semi-automatic, high-throughput analysis software. We employed two measures of call frequency: fundamental frequency (F0) and dominant frequency (DF). The slope of the relationship between male snout-vent length (SVL) and frequency did not differ significantly among the four clades. However, Rana call at a significantly lower frequency relative to size than the other clades, and Bufo call at a significantly higher frequency relative to size than Leptodactylus. Because the relationship between F0 and body size may be more straightforwardly explained by biomechanical constraints, we confirmed that a similar inverse relationship was observed between F0 and SVL. Finally, spectral flatness, an indicator of the tonality of the vocalizations, was found to be inversely correlated with SVL, contradicting an oft-cited prediction that larger animals should have rougher voices. Our results confirm a tight and widespread link between body size and call frequency in anurans, and suggest that laryngeal allometry and vocal fold dimensions in particular are responsible.