FIGURE 2 in The use of bioacoustics in anuran taxonomy: theory, terminology, methods and recommendations for best practice

FIGURE 2. Vocal sac variation in anurans. Except for Ceratophrys cranwelli (emitting a warning call with open mouth) and the pictured specimens of Hyperolius (emitting advertisement calls with aggressive components in male-male combat) all pictured specimens are emitting advertisement calls. Phrynobatrachus alleni is suspected to use its yellow vocal sac for visual signalling, and a visual function is also probable for the bright white vocal sacs of the two Guibemantis species, and of other frogs. All hyperoliids (such as Hyperolius viridiflavus shown here) have gular glands on the vocal sac that might have a visual function, in addition to probably producing pheromones (Starnberger et al. 2013). Note that the distinction between vocal sac types is not always clear; for instance, the vocal sacs of Rana temporaria and Boophis tsilomaro can be considered as partially paired subgular and partially paired lateral. All photos by the authors except Trachycephalus typhonius and Pseudopaludicola jaredi (by Daniel Loebmann).