From uni- to multimodal signaling: towards an integrative view on anuran communication

Undeniably, acoustic signals are the predominant mode of communication in frogs and toads. Acoustically active species are found throughout the vast diversity of anuran families. However, additional or alternative signal modalities have gained increasing attention. In several anurans seismic, visual and chemical communication has convergently evolved due to ecological constraints such as noisy environments. The emphasis of a visual cue, such as the inevitably moving vocal sac of acoustically advertising males, is facilitated by conspicuously coloured throats. Striking visual signals independent of vocalizations are limb movements with the dynamic display of bright colours. In some multimodal anuran communication systems the acoustic component acts as an alert signal, which alters the receiver attention to the following visual display. Recent findings of colourful glands on vocal sacs, producing volatile species-specific scent bouquets suggest the integration of acoustic, visual and chemical cues in species recognition and mate choice. The combination of signal components allows for a broadened display repertoire in challenging environmental conditions. Thus, frogs and toads may possess more complex communications skills than science previously has given them credit for.